10-Q

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

 _____________________________________________

FORM 10-Q

 ____________________________________________

(Mark One)
☒	QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended September 30, 2020

OR

☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from                      to                     

Commission file number 001-35714

_____________________________________________ 

MPLX LP

(Exact name of registrant as specified in its charter)

 _____________________________________________

	Delaware	27-0005456
(State or other jurisdiction of incorporation or organization)		(I.R.S. Employer Identification No.)

200 E. Hardin Street,	Findlay,	Ohio	45840
(Address of principal executive offices)			(Zip code)

(419) 421-2414

(Registrant’s telephone number, including area code)

 _____________________________________________

Securities Registered pursuant to Section 12(b) of the Act
Title of each class	Trading symbol(s)	Name of each exchange on which registered
Common Units Representing Limited Partnership Interests	MPLX	New York Stock Exchange

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes  x     No  ¨

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files.) Yes  x    No  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer	x	Accelerated filer	☐
Non-accelerated filer	☐	Smaller reporting company	☐
		Emerging growth company	☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ¨

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act) Yes  ☐    No  x

MPLX LP had 1,040,169,324 common units outstanding at October 29, 2020.

Table of Contents

	Page
PART I – FINANCIAL INFORMATION
Item 1.   Financial Statements:
Consolidated Statements of Income (Unaudited)	3
Consolidated Statements of Comprehensive Income (Unaudited)	4
Consolidated Balance Sheets (Unaudited)	5
Consolidated Statements of Cash Flows (Unaudited)	6
Consolidated Statements of Equity (Unaudited)	7
Notes to Consolidated Financial Statements (Unaudited)	9
Item 2.   Management’s Discussion and Analysis of Financial Condition and Results of Operations	39
Item 3.   Quantitative and Qualitative Disclosures about Market Risk	66
Item 4.   Controls and Procedures	67
PART II – OTHER INFORMATION
Item 1.    Legal Proceedings	67
Item 1A. Risk Factors	68
Item 2.    Unregistered Sales of Equity Securities	68
Item 6.    Exhibits	69
Signatures	71

Unless the context otherwise requires, references in this report to “MPLX LP,” “MPLX,” “the Partnership,” “we,” “our,” “us,” or like terms refer to MPLX LP and its subsidiaries. Additionally, throughout this Quarterly Report on Form 10-Q, we have used terms in our discussion of the business and operating results that have been defined in our Glossary of Terms.

1

Glossary of Terms

The abbreviations, acronyms and industry technology used in this report are defined as follows.

ASC	Accounting Standards Codification
ASU	Accounting Standards Update
ATM Program	An at-the-market program for the issuance of common units
Barrel	One stock tank barrel, or 42 United States gallons of liquid volume, used in reference to crude oil or other liquid hydrocarbons
Bcf/d	One billion cubic feet per day
Btu	One British thermal unit, an energy measurement
Condensate	A natural gas liquid with a low vapor pressure mainly composed of propane, butane, pentane and heavier hydrocarbon fractions
DCF (a non-GAAP financial measure)	Distributable Cash Flow
EBITDA (a non-GAAP financial measure)	Earnings Before Interest, Taxes, Depreciation and Amortization
FASB	Financial Accounting Standards Board
GAAP	Accounting principles generally accepted in the United States of America
LIBOR	London Interbank Offered Rate
mbpd	Thousand barrels per day
Merger	MPLX acquisition by merger of Andeavor Logistics LP (“ANDX”) on July 30, 2019
MMBtu	One million British thermal units, an energy measurement
MMcf/d	One million cubic feet of natural gas per day
NGL	Natural gas liquids, such as ethane, propane, butanes and natural gasoline
NYSE	New York Stock Exchange
Predecessor	The related assets, liabilities and results of operations of ANDX prior to the date of the Merger, July 30, 2019, effective October 1, 2018
Realized derivative gain/loss	The gain or loss recognized when a derivative matures or is settled
SEC	United States Securities and Exchange Commission
SMR	Steam methane reformer, operated by a third party and located at the Javelina gas processing and fractionation complex in Corpus Christi, Texas
Unrealized derivative gain/loss	The gain or loss recognized on a derivative due to changes in fair value prior to the instrument maturing or settling
VIE	Variable interest entity
Wholesale Exchange	The transfer to MPC of the Western wholesale distribution business, which MPLX acquired as a result of its acquisition of ANDX on July 31, 2020.

2

Part I—Financial Information

Item 1. Financial Statements

MPLX LP

Consolidated Statements of Income (Unaudited)

	Three Months Ended   September 30,				Nine Months Ended   September 30,
(In millions, except per unit data)	2020		2019		2020			2019
Revenues and other income:
Service revenue	$	604	$	632	$	1,779		$	1,865
Service revenue - related parties	909		899		2,694			2,549
Service revenue - product related	41		26		102			86
Rental income	102		99		296			291
Rental income - related parties	241		293		712			904
Product sales	165		171		454			576
Product sales - related parties	37		32		100			109
Income/(loss) from equity method investments(1)	83		95		(1,012		)	255
Other income	2		2		5			6
Other income - related parties	63		31		190			84
Total revenues and other income	2,247		2,280		5,320			6,725
Costs and expenses:
Cost of revenues (excludes items below)	323		407		1,006			1,099
Purchased product costs	152		129		374			489
Rental cost of sales	33		37		101			103
Rental cost of sales - related parties	32		45		119			124
Purchases - related parties	297		303		853			894
Depreciation and amortization	346		302		992			916
Impairment expense	—		—		2,165			—
General and administrative expenses	96		102		289			293
Restructuring expenses	36		—		36			—
Other taxes	33		29		94			84
Total costs and expenses	1,348		1,354		6,029			4,002
Income/(loss) from operations	899		926		(709		)	2,723
Related party interest and other financial costs	—		5		4			8
Interest expense (net of amounts capitalized of $8 million, $13 million, $31 million and $36 million, respectively)	207		212		624			640
Other financial costs	17		16		49			38
Income/(loss) before income taxes	675		693		(1,386		)	2,037
Provision for income taxes	1		4		1			2
Net income/(loss)	674		689		(1,387		)	2,035
Less: Net income attributable to noncontrolling interests	9		8		24			20
Less: Net income attributable to Predecessor	—		52		—			401
Net income/(loss) attributable to MPLX LP	665		629		(1,411		)	1,614
Less: Series A preferred unit distributions	20		20		61			61
Less: Series B preferred unit distributions	10		7		31			7
Limited partners’ interest in net income/(loss) attributable to MPLX LP	$	635	$	602	$	(1,503	)	$	1,546
Per Unit Data (See Note 6)
Net income/(loss) attributable to MPLX LP per limited partner unit:
Common - basic	$	0.61	$	0.61	$	(1.43	)	$	1.78
Common - diluted	$	0.61	$	0.61	$	(1.43	)	$	1.78
Weighted average limited partner units outstanding:
Common - basic	1,046		974		1,054			855
Common - diluted	1,047		975		1,054			855

(1) The nine months ended September 30, 2020 includes $1,264 million of impairment expense. See Note 4.

The accompanying notes are an integral part of these consolidated financial statements.

3

MPLX LP

Consolidated Statements of Comprehensive Income (Unaudited)

	Three Months Ended   September 30,				Nine Months Ended   September 30,
(In millions)	2020		2019		2020			2019
Net income/(loss)	$	674	$	689	$	(1,387	)	$	2,035
Other comprehensive income/(loss), net of tax:
Remeasurements of pension and other postretirement benefits related to equity method investments, net of tax	—		—		(1		)	1
Comprehensive income/(loss)	674		689		(1,388		)	2,036
Less comprehensive income attributable to:
Noncontrolling interests	9		8		24			20
Income attributable to Predecessor	—		52		—			401
Comprehensive income/(loss) attributable to MPLX LP	$	665	$	629	$	(1,412	)	$	1,615

The accompanying notes are an integral part of these consolidated financial statements.

4

MPLX LP

Consolidated Balance Sheets (Unaudited)

 

(In millions)	September 30, 2020			December 31, 2019
Assets
Current assets:
Cash and cash equivalents	$	28		$	15
Receivables, net	477			593
Current assets - related parties	591			656
Inventories	117			110
Other current assets	59			110
Total current assets	1,272			1,484
Equity method investments	4,081			5,275
Property, plant and equipment, net	21,615			22,145
Intangibles, net	991			1,270
Goodwill	7,657			9,536
Right of use assets, net	323			365
Noncurrent assets - related parties	675			303
Other noncurrent assets	48			52
Total assets	36,662			40,430
Liabilities
Current liabilities:
Accounts payable	140			242
Accrued liabilities	169			187
Current liabilities - related parties	364			1,008
Accrued property, plant and equipment	121			283
Long-term debt due within one year	307			9
Accrued interest payable	207			210
Operating lease liabilities	65			66
Other current liabilities	158			127
Total current liabilities	1,531			2,132
Long-term deferred revenue	291			217
Long-term liabilities - related parties	281			290
Long-term debt	20,042			19,704
Deferred income taxes	12			12
Long-term operating lease liabilities	258			302
Deferred credits and other liabilities	184			192
Total liabilities	22,599			22,849
Commitments and contingencies (see Note 21)
Series A preferred units	968			968
Equity
Common unitholders - public (393 million and 392 million units issued and outstanding)	9,436			10,800
Common unitholder - MPC (647 million and 666 million units issued and outstanding)	2,827			4,968
Series B preferred units (.6 million and .6 million units issued and outstanding)	601			611
Accumulated other comprehensive loss	(16		)	(15		)
Total MPLX LP partners’ capital	12,848			16,364
Noncontrolling interests	247			249
Total equity	13,095			16,613
Total liabilities, preferred units and equity	$	36,662		$	40,430

The accompanying notes are an integral part of these consolidated financial statements.

5

MPLX LP

Consolidated Statements of Cash Flows (Unaudited)

	Nine Months Ended   September 30,
(In millions)	2020			2019
Increase/(decrease) in cash, cash equivalents and restricted cash
Operating activities:
Net (loss)/income	$	(1,387	)	$	2,035
Adjustments to reconcile net income/(loss) to net cash provided by operating activities:
Amortization of deferred financing costs	44			29
Depreciation and amortization	992			916
Impairment expense	2,165			—
Deferred income taxes	(1		)	1
Asset retirement expenditures	—			(1		)
Loss/(gain) on disposal of assets	1			(3		)
Loss/(income) from equity method investments(1)	1,012			(255		)
Distributions from unconsolidated affiliates	350			379
Changes in:
Current receivables	69			38
Inventories	(8		)	(3		)
Fair value of derivatives	1			(4		)
Current accounts payable and accrued liabilities	(27		)	(81		)
Current assets/current liabilities - related parties	36			(148		)
Right of use assets/operating lease liabilities	(2		)	6
Deferred revenue	85			58
All other, net	6			23
Net cash provided by operating activities	3,336			2,990
Investing activities:
Additions to property, plant and equipment	(982		)	(1,720		)
Acquisitions, net of cash acquired	—			6
Disposal of assets	54			14
Investments in unconsolidated affiliates	(244		)	(494		)
Distributions from unconsolidated affiliates - return of capital	112			2
All other, net	—			3
Net cash used in investing activities	(1,060		)	(2,189		)
Financing activities:
Long-term debt - borrowings	5,990			8,674
- repayments	(5,372		)	(7,423		)
Related party debt - borrowings	4,870			7,708
- repayments	(5,464		)	(7,583		)
Debt issuance costs	(23		)	(20		)
Distributions to noncontrolling interests	(26		)	(20		)
Distributions to Series A preferred unitholders	(61		)	(61		)
Distributions to Series B preferred unitholders	(41		)	(21		)
Distributions to unitholders and general partner	(2,162		)	(1,731		)
Distributions to common and Series B preferred unitholders from Predecessor	—			(502		)
Contributions from MPC	34			52
Contributions from noncontrolling interests	—			94
All other, net	(8		)	(12		)
Net cash used in financing activities	(2,263		)	(845		)
Net increase/(decrease) in cash, cash equivalents and restricted cash	13			(44		)
Cash, cash equivalents and restricted cash at beginning of period	15			85
Cash, cash equivalents and restricted cash at end of period	$	28		$	41

(1) The 2020 period includes $1,264 million of impairment expense. See Note 4.

The accompanying notes are an integral part of these consolidated financial statements.

6

MPLX LP Consolidated Statements of Equity (Unaudited)
	Partnership
(In millions)	Common Unit-holders Public			Common Unit-holder MPC			Series B Preferred Unit-holders			Accumulated Other Comprehensive Loss			Non-controlling Interests			Equity of Predecessor			Total
Balance at December 31, 2018	$	8,336		$	(1,612	)	$	—		$	(16	)	$	156		$	10,867		$	17,731
Net income (excludes amounts attributable to preferred units)	176			307			—			—			6			180			669
Distributions to:
Unitholders	(188		)	(327		)	—			—			—			(261		)	(776		)
Noncontrolling interests	—			—			—			—			(6		)	—			(6		)
Contributions from:
MPC	—			—			—			—			—			15			15
Noncontrolling interests	—			—			—			—			94			—			94
Other	2			—			—			1			—			—			3
Balance at March 31, 2019	8,326			(1,632		)	—			(15		)	250			10,801			17,730
Net income (excludes amounts attributable to preferred units)	168			293			—			—			6			169			636
Distributions to:
Unitholders	(191		)	(332		)	—			—			—			(241		)	(764		)
Noncontrolling interests	—			—			—			—			(6		)	—			(6		)
Contributions from:
MPC	—			—			—			—			—			13			13
Other	2			—			—			—			—			—			2
Balance at June 30, 2019	8,305			(1,671		)	—			(15		)	250			10,742			17,611
Net income (excludes amounts attributable to Series A preferred units)	222			380			7			—			8			52			669
Allocation of MPC's net investment at acquisition	2,983			7,199			615			—			—			(10,797		)	—
Distributions to:
Unitholders	(262		)	(432		)	(21		)	—			—			—			(715		)
Noncontrolling interests	—			—			—			—			(8		)	—			(8		)
Contributions from:
MPC	—			292			—			—			—			3			295
Conversion of Series A preferred units	36			—			—			—			—			—			36
Other	5			(1		)	—			—			—			—			4
Balance at September 30, 2019	$	11,289		$	5,767		$	601		$	(15	)	$	250		$	—		$	17,892
The accompanying notes are an integral part of these consolidated financial statements.

7

MPLX LP Consolidated Statements of Equity (Unaudited)
	Partnership
(In millions)	Common Unit-holders Public			Common Unit-holder MPC			Series B Preferred Unit-holders			Accumulated Other Comprehensive Loss			Non-controlling Interests			Equity of Predecessor		Total
Balance at December 31, 2019	$	10,800		$	4,968		$	611		$	(15	)	$	249		$	—	$	16,613
Net (loss)/income (excludes amounts attributable to preferred units)	(1,022		)	(1,733		)	11			—			8			—		(2,736		)
Distributions to:
Unitholders	(271		)	(446		)	(21		)	—			—			—		(738		)
Noncontrolling interests	—			—			—			—			(9		)	—		(9		)
Contributions from:
MPC	—			225			—			—			—			—		225
Other	2			—			—			(1		)	—			—		1
Balance at March 31, 2020	9,509			3,014			601			(16		)	248			—		13,356
Net income (excludes amounts attributable to preferred units)	229			388			10			—			7			—		634
Distributions to:
Unitholders	(270		)	(458		)	—			—			—			—		(728		)
Noncontrolling interests	—			—			—			—			(8		)	—		(8		)
Contributions from:
MPC	—			6			—			—			—			—		6
Other	1			1			—			—			—			—		2
Balance at June 30, 2020	9,469			2,951			611			(16		)	247			—		13,262
Net income (excludes amounts attributable to preferred units)	236			399			10			—			9			—		654
Distributions to:
Unitholders	(271		)	(445		)	(20		)	—			—			—		(736		)
Noncontrolling interests	—			—			—			—			(9		)	—		(9		)
Contributions from:
MPC	—			13			—			—			—			—		13
Wholesale Exchange	—			(90		)	—			—			—			—		(90		)
Other	2			(1		)	—			—			—			—		1
Balance at September 30, 2020	$	9,436		$	2,827		$	601		$	(16	)	$	247		$	—	$	13,095

The accompanying notes are an integral part of these consolidated financial statements.

8

Notes to Consolidated Financial Statements (Unaudited)

1. Description of the Business and Basis of Presentation

Description of the Business – MPLX LP is a diversified, large-cap master limited partnership formed by Marathon Petroleum Corporation that owns and operates midstream energy infrastructure and logistics assets, and provides fuels distribution services. References in this report to “MPLX LP,” “MPLX,” “the Partnership,” “we,” “ours,” “us,” or like terms refer to MPLX LP and its subsidiaries. References to “MPC” refer collectively to Marathon Petroleum Corporation as our sponsor and its subsidiaries, other than the Partnership. We are engaged in the transportation, storage and distribution of crude oil, asphalt and refined petroleum products; the gathering, processing and transportation of natural gas; and the gathering, transportation, fractionation, storage and marketing of NGLs. MPLX’s principal executive office is located in Findlay, Ohio.

MPLX’s business consists of two segments based on the nature of services it offers: Logistics and Storage (“L&S”), which relates primarily to crude oil, asphalt and refined petroleum products; and Gathering and Processing (“G&P”), which relates primarily to natural gas and NGLs. See Note 9 for additional information regarding the operations and results of these segments.

On July 30, 2019, MPLX completed its acquisition by merger (the “Merger”) of Andeavor Logistics LP (“ANDX”). At the effective time of the Merger, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units. ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. See Note 3 for additional information regarding the Merger.

On July 31, 2020, MPLX completed the exchange of Western Refining Wholesale, LLC (WRW”) to Western Refining Southwest, Inc. (“WRSW”), a wholly owned subsidiary of MPC, in exchange for the redemption of 18,582,088 MPLX common units held by WRSW (the “Wholesale Exchange”). See Note 3 for additional information regarding the Wholesale Exchange. These financial statements include the results of WRSW through July 31, 2020.

Impairments – The outbreak of COVID-19 and its development into a pandemic in March 2020 resulted in significant economic disruption globally. Actions taken by various governmental authorities, individuals and companies around the world to prevent the spread of COVID-19 through social distancing have restricted travel, many business operations, public gatherings and the overall level of individual movement and in-person interaction across the globe. Although there have been some signs of economic improvement, these events significantly reduced global economic activity and resulted in a decline in the demand for the midstream services we provide beginning with the first quarter of 2020. Macroeconomic conditions and global geopolitical events have also resulted in significant price volatility related to those aforementioned products.

The overall deterioration in the economy and the environment in which MPLX and its customers operate, as well as a sustained decrease in unit price, were considered triggering events resulting in impairments of the carrying value of certain assets during the first quarter of 2020. We recognized impairments related to goodwill, certain equity method investments and certain long-lived assets (including intangibles), within our G&P segment. Many of our producer customers refined and updated production forecasts in response to the current environment, which impacted their current and expected future demand for our services, including the future utilization of our assets. Additionally, certain of our contracts have commodity price exposure, including NGL prices, which have experienced increased volatility as noted above. The table below provides information related to the impairments recognized during the first quarter of 2020 as well as the corresponding footnote where additional information can be found. No additional events or circumstances arose during the second or third quarters of 2020 which would indicate the need for any additional impairment beyond those recognized during the first quarter.

(In millions)	Impairment		Footnote Reference
Goodwill	$	1,814	12
Equity method investments	1,264		4
Intangibles, net	177		12
Property, plant and equipment, net	174		11
Total impairments	$	3,429

Basis of Presentation – The accompanying interim consolidated financial statements are unaudited; however, in the opinion of MPLX’s management, these statements reflect all adjustments necessary for a fair statement of the results for the periods reported. All such adjustments are of a normal, recurring nature unless otherwise disclosed. These interim consolidated financial statements, including the notes, have been prepared in accordance with the rules and regulations of the SEC

9

applicable to interim period financial statements and do not include all of the information and disclosures required by GAAP for complete financial statements. Certain amounts in prior years have been reclassified to conform to current year presentation.

These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the year ended December 31, 2019. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results to be expected for the full year.

In relation to the Merger described above and in Note 3, ANDX’s assets, liabilities and results of operations prior to the Merger are collectively included in what we refer to as the “Predecessor” from October 1, 2018, which was the date that MPC acquired Andeavor. MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s relationship with ANDX prior to the Merger. As an entity under common control with MPC, MPLX recorded the assets acquired and liabilities assumed on its consolidated balance sheets at MPC’s historical carrying value. For the acquiring entity, transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the accompanying financial statements and related notes of MPLX LP have been retrospectively adjusted to include the historical results of ANDX beginning October 1, 2018.

MPLX’s consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly owned consolidated subsidiaries, the interests owned by third parties have been recorded as “Noncontrolling interests” on the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. MPLX’s investments in which MPLX exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. MPLX’s investments in VIEs in which MPLX exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method.

In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule. Distributions, although earned, are not accrued until declared. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in Note 6.

2. Accounting Standards

Recently Adopted

ASU 2016-13, Credit Losses - Measurement of Credit Losses on Financial Instruments

Effective January 1, 2020, we adopted ASU 2016-13 using the modified retrospective transition method. This ASU requires entities to consider a broader range of information to estimate expected credit losses, which may result in earlier recognition of losses. The ASU requires the company to utilize an expected loss methodology in place of the incurred loss methodology for financial instruments, including trade receivables, and off-balance sheet credit exposures. Adoption of the standard did not have a material impact on our financial statements.

We are exposed to credit losses, primarily as a result of the midstream services that we provide. We assess each customer’s ability to pay through our credit review process, which considers various factors such as external credit ratings; a review of financial statements to determine liquidity, leverage, trends and business specific risks; market information; pay history and our business strategy. We monitor our ongoing credit exposure through timely review of customer payment activity. At September 30, 2020, we reported $477 million of accounts receivable, net of allowances of $4 million.

We also adopted the following ASUs during the first nine months of 2020, which did not have a material impact to our financial statements or financial statement disclosures:

ASU		Effective Date
2018-13	Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement	January 1, 2020
2020-04	Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting	April 1, 2020

10

3. Acquisitions and Dispositions

Wholesale Exchange

On July 31, 2020, MPLX entered into a Redemption Agreement (the “Redemption Agreement”) with WRSW, an Arizona corporation and wholly owned subsidiary of MPC, pursuant to which MPLX agreed to transfer to WRSW all of the outstanding membership interests in WRW in exchange for the redemption of MPLX common units held by WRSW. The transaction effects the transfer to MPC of the Western wholesale distribution business that MPLX acquired as a result of its acquisition of ANDX as described below. Per the terms of the Redemption Agreement, MPLX redeemed 18,582,088 common units (the “Redeemed Units”) held by WRSW on July 31, 2020. The number of Redeemed Units was calculated by dividing WRW’s aggregate valuation of $340 million by the simple average of the volume weighted average NYSE prices of an MPLX common unit for the ten trading days ending at market close on July 27, 2020. MPLX canceled the Redeemed Units immediately following the Wholesale Exchange. The carrying value of the net assets of WRW transferred to MPC was approximately $90 million as of July 31, 2020, resulting in $250 million being recorded to “Common Unit-holder MPC” within the Consolidated Statements of Equity, in addition to the fair value of the redeemed units. Included within the $90 million carrying value of the WRW net assets was approximately $65 million of goodwill.

Acquisition of Andeavor Logistics LP

On May 7, 2019, ANDX, Tesoro Logistics GP, LLC (then the general partner of ANDX (“TLGP”)), MPLX, MPLX GP LLC (the general partner of MPLX (“MPLX GP”)), and MPLX MAX LLC, a wholly owned subsidiary of MPLX (“Merger Sub”), entered into an Agreement and Plan of Merger (the “Merger Agreement”) that provided for, among other things, the merger of Merger Sub with and into ANDX. On July 30, 2019, the Merger was completed, and ANDX survived the Merger as a wholly owned subsidiary of MPLX. At the effective time of the Merger, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units. ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. See Note 7 for information on units issued in connection with the Merger.

Additionally, as a result of the Merger, each ANDX TexNew Mex Unit issued and outstanding immediately prior to the effective time of the Merger was converted into a right for WRSW, a wholly owned subsidiary of MPC, as the holder of all such units, to receive a unit representing a substantially equivalent limited partner interest in MPLX (the “MPLX TexNew Mex Units”). By virtue of the conversion, all ANDX TexNew Mex Units were cancelled and ceased to exist as of the effective time of the Merger. The MPLX TexNew Mex Units are a new class of units in MPLX substantially equivalent to the ANDX TexNew Mex Units, including substantially equivalent rights, powers, duties and obligations that the ANDX TexNew Mex Units had immediately prior to the closing of the Merger.

As a result of the Merger, the ANDX Special Limited Partner Interest outstanding immediately prior to the effective time of the Merger was converted into a right for WRSW, as the holder of all such interest, to receive a substantially equivalent special limited partner interest in MPLX (the “MPLX Special Limited Partner Interest”). By virtue of the conversion, the ANDX Special Limited Partner Interest was cancelled and ceased to exist as of the effective time of the Merger. For information on ANDX’s preferred units, please see Note 7.

The assets of ANDX consist of a network of owned and operated crude oil, refined product and natural gas pipelines; crude oil and water gathering systems; refining logistics assets; terminals with crude oil and refined products storage capacity; rail facilities; marine terminals including storage; bulk petroleum distribution facilities; a trucking fleet; and natural gas processing and fractionation systems and complexes. The assets are located in the western and inland regions of the United States and complement MPLX’s existing business and assets.

MPC accounted for its October 1, 2018 acquisition of Andeavor (through which it acquired control of ANDX), using the acquisition method of accounting, which required Andeavor assets and liabilities to be recorded by MPC at the acquisition date fair value. The Merger was closed on July 30, 2019, and the results of ANDX have been incorporated into the results of MPLX as of October 1, 2018, which is the date that common control was established. As a result of MPC’s relationship with both MPLX and ANDX, the Merger has been treated as a common control transaction, which requires the recasting of MPLX’s historical results and the recognition of assets acquired and liabilities assumed using MPC’s historical carrying value. We recognized $14 million in acquisition costs during the first nine months of 2019 related to the Merger, which are reflected in general and administrative expenses. For the three and nine months ended September 30, 2019, we recognized $612 million and $1,789 million of revenues and other income, respectively, related to ANDX. For the three and nine months ended September 30, 2019 we recognized $191 million and $539 million, respectively, of net income related to ANDX.

11

4. Investments and Noncontrolling Interests

The following table presents MPLX’s equity method investments at the dates indicated:

	Ownership as of	Carrying value at
	September 30,	September 30,		December 31,
(In millions, except ownership percentages)	2020	2020		2019
L&S
MarEn Bakken Company LLC(1)	25%	$	469	$	481
Illinois Extension Pipeline Company, L.L.C.	35%	261		265
LOOP LLC	41%	249		238
Andeavor Logistics Rio Pipeline LLC(2)	67%	195		202
Minnesota Pipe Line Company, LLC	17%	189		190
Whistler Pipeline LLC(2)	38%	184		134
Explorer Pipeline Company	25%	78		83
W2W Holdings LLC(2)(3)	50%	77		—
Wink to Webster Pipeline LLC(2)(3)	15%	—		126
Other(2)		100		55
Total L&S		1,802		1,774
G&P
MarkWest Utica EMG, L.L.C.(2)	57%	720		1,984
Sherwood Midstream LLC(2)	50%	560		537
MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C.(2)	67%	307		302
Rendezvous Gas Services, L.L.C.(2)	78%	164		170
Sherwood Midstream Holdings LLC(2)	51%	151		157
Centrahoma Processing LLC	40%	147		153
Other(2)		230		198
Total G&P		2,279		3,501
Total		$	4,081	$	5,275

(1) The investment in MarEn Bakken Company LLC includes our 9.19 percent indirect interest in a joint venture (“Dakota Access”) that owns and operates the Dakota Access Pipeline and Energy Transfer Crude Oil Pipeline projects, collectively referred to as the Bakken Pipeline system or DAPL.    

(2) Investments deemed to be VIEs. Some investments included within “Other” have also been deemed to be VIEs.

(3) During the nine months ended September 30, 2020, we contributed our ownership in Wink to Webster Pipeline LLC to W2W Holdings LLC.

For those entities that have been deemed to be VIEs, neither MPLX nor any of its subsidiaries have been deemed to be the primary beneficiary due to voting rights on significant matters. While we have the ability to exercise influence through participation in the management committees which make all significant decisions, we have equal influence over each committee as a joint interest partner and all significant decisions require the consent of the other investors without regard to economic interest and as such we have determined that these entities should not be consolidated and apply the equity method of accounting with respect to our investments in each entity.

Sherwood Midstream has been deemed the primary beneficiary of Sherwood Midstream Holdings due to its controlling financial interest through its authority to manage the joint venture. As a result, Sherwood Midstream consolidates Sherwood Midstream Holdings. Therefore, MPLX also reports its portion of Sherwood Midstream Holdings’ net assets as a component of its investment in Sherwood Midstream. As of September 30, 2020, MPLX has a 24.51 percent indirect ownership interest in Sherwood Midstream Holdings through Sherwood Midstream.

MPLX’s maximum exposure to loss as a result of its involvement with equity method investments includes its equity investment, any additional capital contribution commitments and any operating expenses incurred by the subsidiary operator in excess of its compensation received for the performance of the operating services. MPLX did not provide any financial support to equity method investments that it was not contractually obligated to provide during the nine months ended September 30, 2020.

12

During the first quarter of 2020, we recorded an other than temporary impairment for three joint ventures in which we have an interest as discussed in Note 1. Impairment of these investments was $1,264 million, of which $1,251 million was related to MarkWest Utica EMG and its investment in Ohio Gathering Company, L.L.C. The fair value of the investments was determined based upon applying the discounted cash flow method, which is an income approach. The discounted cash flow fair value estimate is based on known or knowable information at the interim measurement date. The significant assumptions that were used to develop the estimate of the fair value under the discounted cash flow method include management’s best estimates of the expected future cash flows, including prices and volumes, the weighted average cost of capital and the long-term growth rate. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As such, the fair value of these equity method investments represents a Level 3 measurement. As a result, there can be no assurance that the estimates and assumptions made for purposes of the impairment test will prove to be an accurate prediction of the future. The impairment was recorded through “Income from equity method investments.” The impairments were largely due to a reduction in forecasted volumes gathered and processed by the systems operated by the joint ventures. There were no additional impairments recorded during the second or third quarters of 2020.

Summarized financial information for MPLX’s equity method investments for the nine months ended September 30, 2020 and 2019 is as follows:

	Nine Months Ended September 30, 2020
(In millions)	VIEs			Non-VIEs		Total
Revenues and other income	$	132		$	933	$	1,065
Costs and expenses	308			405		713
Income from operations	(176		)	528		352
Net income	(230		)	477		247
(Loss)/income from equity method investments(1)	$	(1,138	)	$	126	$	(1,012	)

(1) Includes the impact of any basis differential amortization or accretion in addition to the impairment of $1,264 million.

	Nine Months Ended September 30, 2019
(In millions)	VIEs		Non-VIEs		Total
Revenues and other income	$	479	$	1,116	$	1,595
Costs and expenses	251		434		685
Income from operations	228		682		910
Net income	192		605		797
Income from equity method investments(1)	$	89	$	166	$	255

(1) Includes the impact of any basis differential amortization or accretion.

Summarized balance sheet information for MPLX’s equity method investments as of September 30, 2020 and December 31, 2019 is as follows:

	September 30, 2020
(In millions)	VIEs		Non-VIEs		Total
Current assets	$	774	$	367	$	1,141
Noncurrent assets	6,398		5,024		11,422
Current liabilities	304		194		498
Noncurrent liabilities	$	1,611	$	857	$	2,468

	December 31, 2019
(In millions)	VIEs		Non-VIEs		Total
Current assets	$	534	$	330	$	864
Noncurrent assets	5,862		5,134		10,996
Current liabilities	192		245		437
Noncurrent liabilities	$	305	$	822	$	1,127

13

As of September 30, 2020, the underlying net assets of MPLX’s investees in the G&P segment exceeded the carrying value of its equity method investments by approximately $58 million. At December 31, 2019, the carrying value of MPLX’s equity method investments in the G&P segment exceeded the underlying net assets of its investees by approximately $1.0 billion. As of September 30, 2020 and December 31, 2019, the carrying value of MPLX’s equity method investments in the L&S segment exceeded the underlying net assets of its investees by $331 million and $329 million, respectively. At September 30, 2020 and December 31, 2019, the G&P basis difference was being amortized into net income over the remaining estimated useful lives of the underlying assets, except for $31 million and $498 million of excess related to goodwill, respectively. At September 30, 2020 and December 31, 2019, the L&S basis difference was being amortized into net income over the remaining estimated useful lives of the underlying assets, except for $167 million of excess related to goodwill.

5. Related Party Agreements and Transactions

MPLX engages in transactions with both MPC and certain of its equity method investments as part of its normal business; however, transactions with MPC make up the majority of MPLX’s related party transactions. Transactions with related parties are further described below.

MPLX has various long-term, fee-based commercial agreements with MPC. Under these agreements, MPLX provides transportation, terminal, fuels distribution, marketing, storage, management, operational and other services to MPC. MPC has committed to provide MPLX with minimum throughput volumes on crude oil and refined products and other fees for storage capacity; operating and management fees; as well as reimbursements for certain direct and indirect costs. MPC has also committed to provide a fixed fee for 100 percent of available capacity for boats, barges and third-party chartered equipment under the marine transportation service agreement. MPLX also has a keep-whole commodity agreement with MPC under which MPC pays us a processing fee for NGLs related to keep-whole agreements and delivers shrink gas to the producers on our behalf. We pay MPC a marketing fee in exchange for assuming the commodity risk. Additionally, MPLX has obligations to MPC for services provided to MPLX by MPC under omnibus and employee services-type agreements as well as other various agreements.

MPC has also been advancing certain strategic priorities to lay a foundation for long-term success, including plans to optimize its assets and structurally lower costs in 2021 and beyond, which included an involuntary workforce reduction plan. The workforce reduction plan, together with employee reductions resulting from MPC's indefinite idling of its Martinez, California and Gallup, New Mexico refineries, affected approximately 2,050 employees. All of the employees that conduct MPLX’s business are directly employed by affiliates of MPC, and certain of those employees were affected by MPC’s workforce reductions. During the third quarter of 2020, MPLX reimbursed MPC for $36 million related to severance and employee benefits related expenses that MPC recorded in connection with its workforce reductions. These costs are shown on the Consolidated Statements of Income as “Restructuring expenses.”

Related Party Loan

MPLX is party to a loan agreement with MPC Investment LLC (“MPC Investment”) (the “MPC Loan Agreement”). Under the terms of the agreement, MPC Investment makes a loan or loans to MPLX on a revolving basis as requested by MPLX and as agreed to by MPC Investment. In connection with the Merger, on July 31, 2019, MPLX and MPC Investment amended and restated the MPC Loan Agreement to increase the borrowing capacity under the MPC Loan Agreement to $1.5 billion in aggregate principal amount of all loans outstanding at any one time. The entire unpaid principal amount of the loan, together with all accrued and unpaid interest and other amounts (if any), shall become due and payable on July 31, 2024, provided that MPC Investment may demand payment of all or any portion of the outstanding principal amount of the loan, together with all accrued and unpaid interest and other amounts (if any), at any time prior to July 31, 2024. Borrowings under the MPC Loan Agreement prior to July 31, 2019 bore interest at LIBOR plus 1.50 percent while borrowings as of and after July 31, 2019 bear interest at LIBOR plus 1.25 percent or such lower rate as would be applicable to such loans under the MPLX Credit Agreement as discussed in Note 15. Activity on the MPC Loan Agreement was as follows:

(In millions)	Nine Months Ended September 30, 2020			Year Ended December 31, 2019
Borrowings	$	4,870		$	8,540
Average interest rate of borrowings	2.380		%	3.441		%
Repayments	$	5,464		$	7,946
Outstanding balance at end of period(1)	$	—		$	594

(1) Included in “Current liabilities - related parties” on the Consolidated Balance Sheets.

14

Prior to the Merger, ANDX was also party to a loan agreement with MPC (“ANDX-MPC Loan Agreement”). This facility was entered into on December 21, 2018, with a borrowing capacity of $500 million. In connection with the Merger, on July 31, 2019, MPLX repaid the entire outstanding balance and terminated the ANDX-MPC Loan Agreement. Activity on the ANDX-MPC Loan Agreement prior to the Merger was as follows:

(In millions)	Year Ended December 31, 2019
Borrowings	$	773
Average interest rate of borrowings	4.249		%
Repayments	$	773
Outstanding balance at end of period	$	—

Related Party Revenue

Related party sales to MPC consist of crude oil and refined products pipeline and trucking transportation services based on tariff/contracted rates; storage, terminal and fuels distribution services based on contracted rates; and marine transportation services. Related party sales to MPC also consist of revenue related to volume deficiency credits.

MPLX also has operating agreements with MPC under which it receives a fee for operating MPC’s retained pipeline assets and a fixed annual fee for providing oversight and management services required to run the marine business. MPLX also receives management fee revenue for engineering, construction and administrative services for operating certain of its equity method investments.

Revenue received from related parties included on the Consolidated Statements of Income was as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020		2019
Service revenues - related parties
MPC	$	908	$	899	$	2,692	$	2,549
Other	1		—		2		—
Total Service revenue - related parties	909		899		2,694		2,549
Rental income - related parties
MPC	241		293		712		904
Product sales - related parties(1)
MPC	37		32		100		109
Other income - related parties
MPC	48		14		144		34
Other	15		17		46		50
Total Other income - related parties	$	63	$	31	$	190	$	84

(1) There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For the three and nine months ended September 30, 2020, these sales totaled $107 million and $332 million, respectively. For the three and nine months ended September 30, 2019, these sales totaled $301 million and $819 million, respectively.

Related Party Expenses

MPC provides executive management services and certain general and administrative services to MPLX under the terms of our omnibus agreements (“Omnibus charges”). Omnibus charges included in “Rental cost of sales - related parties” primarily relate to services that support MPLX’s rental operations and maintenance of assets available for rent. Omnibus charges included in “Purchases - related parties” primarily relate to services that support MPLX’s operations and maintenance activities, as well as compensation expenses. Omnibus charges included in “General and administrative expenses” primarily relate to services that support MPLX’s executive management, accounting and human resources activities. MPLX also obtains employee services from MPC under employee services agreements (“ESA charges”). ESA charges for personnel directly involved in or supporting operations and maintenance activities related to rental services are classified as “Rental cost of sales - related parties.” ESA charges for personnel directly involved in or supporting operations and maintenance activities related to other services are classified as “Purchases - related parties.” ESA charges for personnel involved in executive management, accounting and

15

human resources activities are classified as “General and administrative expenses.” In addition to these agreements, MPLX purchases products from MPC, makes payments to MPC in its capacity as general contractor to MPLX, and has certain lease agreements with MPC.

Expenses incurred from MPC under the omnibus and employee services agreements as well as other purchases from MPC included on the Consolidated Statements of Income are as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020		2019
Rental cost of sales - related parties
MPC	$	32	$	45	$	119	$	124
Purchases - related parties
MPC	293		297		840		878
Other	4		6		13		16
Total Purchase - related parties	297		303		853		894
General and administrative expenses
MPC	63		59		195		174
Restructuring expenses
MPC	$	36	$	—	$	36	$	—

Some charges incurred under the omnibus and ESA agreements are related to engineering services and are associated with assets under construction. These charges are added to “Property, plant and equipment, net” on the Consolidated Balance Sheets. For the three and nine months ended September 30, 2020, these charges totaled $29 million and $80 million, respectively. For the three and nine months ended September 30, 2019, these charges totaled $48 million and $127 million, respectively.

Related Party Assets and Liabilities

Assets and liabilities with related parties appearing on the Consolidated Balance Sheets are detailed in the table below. This table identifies the various components of related party assets and liabilities, including those associated with leases (see Note 20 for additional information) and deferred revenue on minimum volume commitments. If MPC fails to meet its minimum committed volumes, MPC will pay MPLX a deficiency payment based on the terms of the agreement. The deficiency amounts are recorded as “Current liabilities - related parties.” In many cases, MPC may then apply the amount of any such deficiency payments as a credit for volumes in excess of its minimum volume commitment in future periods under the terms of the applicable agreements. MPLX recognizes related party revenues for the deficiency payments when credits are used for volumes in excess of minimum quarterly volume commitments, where it is probable the customer will not use the credit in future periods or upon the expiration of the credits. The use or expiration of the credits is a decrease in “Current liabilities - related parties.” In addition, capital projects MPLX is undertaking at the request of MPC are reimbursed in cash and recognized in income over the remaining term of the applicable agreements or in some cases as an equity contribution from its sponsor.

16

(In millions)	September 30, 2020		December 31, 2019
Current assets - related parties
Receivables - MPC	$	543	$	621
Receivables - Other	7		22
Prepaid - MPC	11		9
Other - MPC	1		—
Lease Receivables - MPC	29		4
Total	591		656
Noncurrent assets - related parties
Long-term receivables - MPC	32		21
Right of use assets - MPC	231		232
Long-term lease receivables - MPC	390		43
Unguaranteed residual asset - MPC	22		7
Total	675		303
Current liabilities - related parties
Payables - MPC	247		911
Payables - Other	42		37
Operating lease liabilities - MPC	1		1
Deferred revenue - Minimum volume deficiencies - MPC	54		42
Deferred revenue - Project reimbursements - MPC	19		16
Deferred revenue - Project reimbursements - Other	1		1
Total	364		1,008
Long-term liabilities - related parties
Long-term operating lease liabilities - MPC	230		230
Long-term deferred revenue - Project reimbursements - MPC	45		53
Long-term deferred revenue - Project reimbursements - Other	6		7
Total	$	281	$	290

Other Related Party Transactions

From time to time, MPLX may also sell to or purchase from related parties, assets and inventory at the lesser of average unit cost or net realizable value. Sales to and purchases from related parties were immaterial for the nine months ended September 30, 2020 and 2019, respectively.

6. Net Income/(Loss) Per Limited Partner Unit

Net income/(loss) per unit applicable to common units is computed by dividing net income/(loss) attributable to MPLX LP less income/(loss) allocated to participating securities by the weighted average number of common units outstanding.

Classes of participating securities for the three and nine months ended September 30, 2020 and 2019 include:

	Nine Months Ended September 30,
	2020	2019
Common Units	ü	ü
Equity-based compensation awards	ü	ü
Series A preferred units	ü	ü
Series B preferred units	ü	ü

17

For the three and nine months ended September 30, 2020 and 2019, MPLX had dilutive potential common units consisting of certain equity-based compensation awards. Potential common units omitted from the diluted earnings per unit calculation for the three and nine months ended September 30, 2020 and 2019 were less than 1 million.

	Three Months Ended September 30,						Nine Months Ended September 30,
(In millions)	2020			2019			2020			2019
Net income/(loss) attributable to MPLX LP	$	665		$	629		$	(1,411	)	$	1,614
Less: Distributions declared on Series A preferred units(1)	20			20			61			61
Distributions declared on Series B preferred units(1)	10			10			31			31
Limited partners’ distributions declared on MPLX common units (including common units of general partner)(1)(2)	715			704			2,158			1,919
Undistributed net loss attributable to MPLX LP	$	(80	)	$	(105	)	$	(3,661	)	$	(397	)

(1) See Note 7 for distribution information.

(2) The three and nine months ended September 30, 2019 amounts are net of $12.5 million and $25 million, respectively, of waived distributions with respect to units held by MPC and its affiliates.

	Three Months Ended September 30, 2020
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	715		$	20	$	10	$	745
Undistributed net loss attributable to MPLX LP	(80		)	—		—		(80		)
Net income attributable to MPLX LP(1)	$	635		$	20	$	10	$	665
Weighted average units outstanding:
Basic	1,046
Diluted	1,047
Net income attributable to MPLX LP per limited partner unit:
Basic	$	0.61
Diluted	$	0.61

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

18

	Three Months Ended September 30, 2019
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	704		$	20	$	10	$	734
Undistributed net loss attributable to MPLX LP	(105		)	—		—		(105		)
Net income attributable to MPLX LP(1)	$	599		$	20	$	10	$	629
Weighted average units outstanding:
Basic(2)	974
Diluted(2)	975
Net income attributable to MPLX LP per limited partner unit:
Basic	$	0.61
Diluted	$	0.61

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

(2) The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire three months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

	Nine Months Ended September 30, 2020
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	2,158		$	61	$	31	$	2,250
Undistributed net loss attributable to MPLX LP	(3,661		)	—		—		(3,661		)
Net (loss)/income attributable to MPLX LP(1)	$	(1,503	)	$	61	$	31	$	(1,411	)
Weighted average units outstanding:
Basic	1,054
Diluted	1,054
Net income attributable to MPLX LP per limited partner unit:
Basic	$	(1.43	)
Diluted	$	(1.43	)

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

19

	Nine Months Ended September 30, 2019
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	1,919		$	61	$	31	$	2,011
Undistributed net loss attributable to MPLX LP	(397		)	—		—		(397		)
Net income attributable to MPLX LP(1)	$	1,522		$	61	$	31	$	1,614
Weighted average units outstanding:
Basic(2)	855
Diluted(2)	855
Net income attributable to MPLX LP per limited partner unit:
Basic	$	1.78
Diluted	$	1.78

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

(2) The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire nine months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

7. Equity

The changes in the number of common units outstanding during the nine months ended September 30, 2020 are summarized below:

(In units)	Common
Balance at December 31, 2019	1,058,355,471
Unit-based compensation awards	395,091
Units redeemed in Wholesale Exchange	(18,582,088	)
Balance at September 30, 2020	1,040,168,474

Wholesale Exchange and Merger

In connection with the Wholesale Exchange as discussed in Note 3, 18,582,088 units were redeemed by MPC in exchange for all of the outstanding membership interests in WRW. These units were cancelled by MPLX immediately following the transaction.

In connection with the Merger and as discussed in Note 3, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units while ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. This resulted in the issuance of MPLX common units of approximately 102 million units to public unitholders and approximately 161 million units to MPC on July 30, 2019.

Series B Preferred Units

Prior to the Merger, ANDX had outstanding 600,000 units of 6.875 percent Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Units representing limited partner interests of ANDX at a price to the public of $1,000 per unit. Upon completion of the Merger, the ANDX preferred units converted to preferred units of MPLX representing substantially equivalent limited partnership interests in MPLX (the “Series B preferred units”). The Series B preferred units are pari passu with the Series A preferred units with respect to distribution rights and rights upon liquidation. Distributions on the Series B preferred units are payable semi-annually in arrears on the 15th day, or the first business day thereafter, of February and August of each year up to and including February 15, 2023. After February 15, 2023, the holders of Series B preferred units are entitled to receive cumulative, quarterly distributions payable in arrears on the 15th day of February, May, August and November of each year, or the first business day thereafter, based on a floating annual rate equal to the three-month LIBOR plus 4.652 percent.

20

The changes in the Series B preferred unit balance from December 31, 2019 through September 30, 2020 are summarized below. Series B preferred units are included in the Consolidated Balance Sheets and Consolidated Statements of Equity within “Equity of Predecessor” for the period prior to the Merger and within “Series B preferred units” for the period following the Merger.

(In millions)	Series B Preferred Units
Balance at December 31, 2019	$	611
Net income allocated	31
Distributions received by Series B preferred unitholders	(41		)
Balance at September 30, 2020	$	601

TexNew Mex Units - Prior to the Merger, MPC held 80,000 ANDX TexNew Mex units, representing all outstanding units. At the time of the Merger, each ANDX TexNew Mex unit was automatically converted into TexNew Mex units of MPLX with substantially the same rights and obligations as the ANDX TexNew Mex units. The TexNew Mex units represent the right to receive quarterly distribution payments in an amount calculated using the distributable cash flow generated by a particular portion of the TexNew Mex pipeline system, in excess of a base amount and adjusted for previously agreed upon stipulations and contingencies. Distributions earned by TexNew Mex units during the fourth quarter of 2019 and during the six months ended June 30, 2020 were immaterial. Distributions of $5 million were earned by TexNew Mex units during the three months ended September 30, 2020.

Cash distributions – In accordance with the MPLX partnership agreement, on October 27, 2020, MPLX declared a quarterly cash distribution for the third quarter of 2020, totaling $715 million, or $0.6875 per common unit. This rate will also be received by Series A preferred unitholders. These distributions will be paid on November 13, 2020 to common unitholders of record on November 6, 2020. Series B preferred unitholders are entitled to receive a fixed distribution of $68.75 per unit, per annum, payable semi-annually in arrears on February 15 and August 15, or the first business day thereafter, up to and including February 15, 2023. After February 15, 2023, the holders of Series B preferred units are entitled to receive cumulative, quarterly distributions payable in arrears on the 15th day of February, May, August and November of each year, or the first business day thereafter, based on a floating annual rate equal to the three-month LIBOR plus 4.652 percent, in each case assuming a distribution is declared by the Board of Directors. Accordingly, MPLX made a cash distribution payment totaling $21 million to Series B unitholders on August 17, 2020.

Quarterly distributions for 2020 and 2019 are summarized below:

(Per common unit)	2020		2019
March 31,	$	0.6875	$	0.6575
June 30,	0.6875		0.6675
September 30,	$	0.6875	$	0.6775

The allocation of total quarterly cash distributions to limited and preferred unitholders is as follows for the three and nine months ended September 30, 2020 and 2019. MPLX’s distributions are declared subsequent to quarter end; therefore, the following table represents total cash distributions applicable to the period in which the distributions were earned.

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020		2019
Common and preferred unit distributions:
Common unitholders, includes common units of general partner	$	715	$	704	$	2,158	$	1,919
Series A preferred unit distributions	20		20		61		61
Series B preferred unit distributions	10		10		31		31
Total cash distributions declared	$	745	$	734	$	2,250	$	2,011

The distribution on common units for the three and nine months ended September 30, 2019 includes the impact of the issuance of approximately 102 million units issued to public unitholders and approximately 161 million units issued to MPC in connection with the Merger. Due to the timing of the closing, distributions presented in the table above include second quarter

21

distributions for MPLX common units and Series B preferred units issued to former ANDX unitholders in connection with the Merger. The distributions on common units exclude $12.5 million of waived distributions for the three months ended September 30, 2019 and $25 million of waived distributions for the nine months ended September 30, 2019.

8. Series A Preferred Units

On May 13, 2016, MPLX LP issued approximately 30.8 million 6.5 percent Series A Convertible preferred units for a cash purchase price of $32.50 per unit. The Series A preferred units rank senior to all common units and pari passu with all Series B preferred units with respect to distributions and rights upon liquidation. The holders of the Series A preferred units are entitled to receive, when and if declared by the board, a quarterly distribution equal to the greater of $0.528125 per unit or the amount of distributions they would have received on an as converted basis. On October 27, 2020, MPLX declared a quarterly cash distribution of $0.6875 per common unit for the third quarter of 2020. Holders of the Series A preferred units will receive the common unit rate in lieu of the lower $0.528125 base amount.

The holders may convert their Series A preferred units into common units at any time, in full or in part, subject to minimum conversion amounts and conditions. After the fourth anniversary of the issuance date, MPLX may convert the Series A preferred units into common units at any time, in whole or in part, subject to certain minimum conversion amounts and conditions, if the closing price of MPLX common units is greater than $48.75 for the 20-day trading period immediately preceding the conversion notice date. The conversion rate for the Series A preferred units shall be the quotient of (a) the sum of (i) $32.50, plus (ii) any unpaid cash distributions on the applicable preferred unit, divided by (b) $32.50, subject to adjustment for unit distributions, unit splits and similar transactions. The holders of the Series A preferred units are entitled to vote on an as-converted basis with the common unitholders and have certain other class voting rights with respect to any amendment to the MPLX partnership agreement that would adversely affect any rights, preferences or privileges of the preferred units. In addition, upon certain events involving a change of control, the holders of preferred units may elect, among other potential elections, to convert their Series A preferred units to common units at the then change of control conversion rate.

Approximately 29.6 million Series A preferred units remaining outstanding as of September 30, 2020. The changes in the redeemable preferred balance from December 31, 2019 through September 30, 2020 are summarized below:

(In millions)	Redeemable Series A Preferred Units
Balance at December 31, 2019	$	968
Net income allocated	61
Distributions received by Series A preferred unitholders	(61		)
Balance at September 30, 2020	$	968

The Series A preferred units are considered redeemable securities under GAAP due to the existence of redemption provisions upon a deemed liquidation event which is outside MPLX’s control. Therefore, they are presented as temporary equity in the mezzanine section of the Consolidated Balance Sheets. The Series A preferred units have been recorded at their issuance date fair value, net of issuance costs. Income allocations increase the carrying value and declared distributions decrease the carrying value of the Series A preferred units. As the Series A preferred units are not currently redeemable and not probable of becoming redeemable, adjustment to the initial carrying amount is not necessary and would only be required if it becomes probable that the Series A preferred units would become redeemable.

9. Segment Information

MPLX’s chief operating decision maker is the chief executive officer (“CEO”) of its general partner. The CEO reviews MPLX’s discrete financial information, makes operating decisions, assesses financial performance and allocates resources on a type of service basis. MPLX has two reportable segments: L&S and G&P. Each of these segments is organized and managed based upon the nature of the products and services it offers.

• L&S – transports, stores, distributes and markets crude oil, asphalt, refined petroleum products and water. Also includes an inland marine business, terminals, rail facilities, storage caverns and refining logistics.

• G&P – gathers, processes and transports natural gas; and gathers, transports, fractionates, stores and markets NGLs.

Our CEO evaluates the performance of our segments using Segment Adjusted EBITDA. Amounts included in net income and excluded from Segment Adjusted EBITDA include: (i) depreciation and amortization; (ii) provision/(benefit) for income taxes; (iii) amortization of deferred financing costs; (iv) extinguishment of debt; (v) non-cash equity-based compensation; (vi)

22

impairment expense; (vii) net interest and other financial costs; (viii) income/(loss) from equity method investments; (ix) distributions and adjustments related to equity method investments; (x) unrealized derivative gains/(losses); (xi) acquisition costs; (xii) noncontrolling interest; and (xiii) other adjustments as deemed necessary. These items are either: (i) believed to be non-recurring in nature; (ii) not believed to be allocable or controlled by the segment; or (iii) are not tied to the operational performance of the segment.

The tables below present information about revenues and other income, capital expenditures and investments in unconsolidated affiliates as well as total assets for our reportable segments:

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020			2019
L&S
Service revenue	$	989	$	976	$	2,924		$	2,787
Rental income	249		304		737			935
Product related revenue	9		22		49			57
Income from equity method investments	36		60		126			159
Other income	51		17		154			45
Total segment revenues and other income(1)	1,334		1,379		3,990			3,983
Segment Adjusted EBITDA(2)	893		766		2,604			1,895
Restructuring expenses	27		—		27			—
Capital expenditures	118		272		410			700
Investments in unconsolidated affiliates	4		95		132			163
G&P
Service revenue	524		555		1,549			1,627
Rental income	94		88		271			260
Product related revenue	234		207		607			714
Income/(loss) from equity method investments	47		35		(1,138		)	96
Other income	14		16		41			45
Total segment revenues and other income(1)	913		901		1,330			2,742
Segment Adjusted EBITDA(2)	442		399		1,252			1,120
Restructuring expenses	9		—		9			—
Capital expenditures	131		321		375			953
Investments in unconsolidated affiliates	$	18	$	76	$	112		$	331

(1) Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $139 million and $443 million for the three and nine months ended September 30, 2020, respectively, and $182 million and $498 million for the three and nine months ended September 30, 2019, respectively. Third party revenues for the G&P segment were $858 million and $1,181 million for the three and nine months ended September 30, 2020, respectively, and $843 million and $2,581 million for the three and nine months ended September 30, 2019, respectively.

(2) See below for the reconciliation from Segment Adjusted EBITDA to net income.

(In millions)	September 30, 2020		December 31, 2019
Segment assets
Cash and cash equivalents	$	28	$	15
L&S	21,144		20,810
G&P	15,490		19,605
Total assets	$	36,662	$	40,430

23

The table below provides a reconciliation between net (loss)/income and Segment Adjusted EBITDA.

	Three Months Ended September 30,						Nine Months Ended September 30,
(In millions)	2020			2019			2020			2019
Reconciliation to Net income/(loss):
L&S Segment Adjusted EBITDA	$	893		$	766		$	2,604		$	1,895
G&P Segment Adjusted EBITDA	442			399			1,252			1,120
Total reportable segments	1,335			1,165			3,856			3,015
Depreciation and amortization(1)	(346		)	(302		)	(992		)	(916		)
Provision for income taxes	(1		)	(4		)	(1		)	(2		)
Amortization of deferred financing costs	(15		)	(10		)	(44		)	(29		)
Non-cash equity-based compensation	(4		)	(5		)	(12		)	(17		)
Impairment expense	—			—			(2,165		)	—
Net interest and other financial costs	(223		)	(223		)	(647		)	(657		)
Gain on extinguishment of debt	14			—			14			—
Income/(loss) from equity method investments	83			95			(1,012		)	255
Distributions/adjustments related to equity method investments	(130		)	(145		)	(369		)	(399		)
Unrealized derivative (losses)/gains(2)	(10		)	11			(1		)	7
Acquisition costs	—			(9		)	—			(14		)
Restructuring expenses	(36		)	—			(36		)	—
Other	(3		)	(1		)	(5		)	(1		)
Adjusted EBITDA attributable to noncontrolling interests	10			9			27			23
Adjusted EBITDA attributable to Predecessor(3)	—			108			—			770
Net income/(loss)	$	674		$	689		$	(1,387	)	$	2,035

(1) Depreciation and amortization attributable to L&S was $164 million and $440 million for the three and nine months ended September 30, 2020, respectively, and $113 million and $373 million for the three and nine months ended September 30, 2019, respectively. Depreciation and amortization attributable to G&P was $182 million and $552 million for the three and nine months ended September 30, 2020, respectively, and $189 million and $543 million for the three and nine months ended September 30, 2019, respectively.

(2) MPLX makes a distinction between realized and unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

(3) The adjusted EBITDA adjustments related to Predecessor are excluded from adjusted EBITDA attributable to MPLX LP prior to the Merger.

10. Inventories

Inventories consist of the following:

(In millions)	September 30, 2020		December 31, 2019
NGLs	$	3	$	5
Line fill	11		10
Spare parts, materials and supplies	103		95
Total inventories	$	117	$	110

24

11. Property, Plant and Equipment

Property, plant and equipment with associated accumulated depreciation is shown below:

(In millions)	Estimated Useful Lives	September 30, 2020		December 31, 2019
L&S
Pipelines	2-51 years	$	6,001	$	5,572
Refining Logistics	13-40 years	2,196		2,870
Terminals	4-40 years	1,534		1,109
Marine	15-20 years	961		906
Land, building and other	1-61 years	1,576		1,817
Construction-in progress		403		660
Total L&S property, plant and equipment		12,671		12,934
G&P
Gathering and transportation	5-40 years	7,413		7,159
Processing and fractionation	10-40 years	5,944		5,545
Land, building and other	3-40 years	509		484
Construction-in-progress		382		745
Total G&P property, plant and equipment		14,248		13,933
Total property, plant and equipment		26,919		26,867
Less accumulated depreciation(1)		5,304		4,722
Property, plant and equipment, net		$	21,615	$	22,145

(1) The September 30, 2020 balance includes property, plant and equipment impairment charges recorded during the first quarter of 2020 as discussed below.

Long-lived assets used in operations are assessed for impairment whenever changes in facts and circumstances indicate that the carrying value of the assets may not be recoverable based on the expected undiscounted future cash flow of an asset group. For purposes of impairment evaluation, long-lived assets must be grouped at the lowest level for which independent cash flows can be identified, which is at least at the segment level and in some cases for similar assets in the same geographic region where cash flows can be separately identified. If the sum of the undiscounted cash flows is less than the carrying value of an asset group, fair value is calculated, and the carrying value is written down if greater than the calculated fair value.

No impairment triggers were identified in the second or third quarters of 2020; however, during the first quarter of 2020, we did identify an impairment trigger relating to asset groups within our Western G&P reporting unit as a result of significant impacts to forecasted cash flows for these asset groups resulting from the first quarter events and circumstances as discussed in Note 1. The cash flows associated with these assets were significantly impacted by volume declines reflecting decreased forecasted producer customer production as a result of lower commodity prices. After assessing each asset group within the Western G&P reporting unit for impairment, only the East Texas G&P asset group had a carrying value in excess of the fair value of its underlying assets. As a result, an impairment of $174 million was recorded to “Impairment expense” on the Consolidated Statements of Income in the first quarter of 2020. Fair value of the assets was determined using a combination of an income and cost approach. The income approach utilized significant assumptions including management’s best estimates of the expected future cash flows, the estimated useful life of the asset group and discount rate. The cost approach utilized assumptions for the current replacement costs of similar assets adjusted for estimated depreciation and deterioration of the existing equipment and economic obsolescence. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of our impairment analysis will prove to be an accurate prediction of the future. The fair value measurements for the asset group fair values represent Level 3 measurements.

12. Goodwill and Intangibles

Goodwill

MPLX annually evaluates goodwill for impairment as of November 30, as well as whenever events or changes in circumstances indicate it is more likely than not that the fair value of a reporting unit with goodwill is less than its carrying amount.

25

There were no events or changes in circumstances noted in the second or third quarters of 2020 which would indicate it is more likely than not that the fair value of our reporting units with goodwill is less than their carrying amount. During the first quarter of 2020, we determined that an interim impairment analysis of the goodwill recorded was necessary based on consideration of a number of first quarter events and circumstances as discussed in Note 1. Our producer customers in our Eastern G&P region reduced production forecasts and drilling activity in response to the global economic downturn. Additionally, a decline in NGL prices impacted our future revenue forecast. After performing our evaluations related to the interim impairment of goodwill during the first quarter of 2020, we recorded an impairment of $1,814 million within the Eastern G&P reporting unit, which was recorded to “Impairment expense” on the Consolidated Statements of Income. The impairment was primarily driven by additional guidance related to the slowing of drilling activity, which has reduced production growth forecasts from our producer customers. This resulted in goodwill totaling approximately $7.7 billion as of March 31, 2020 within four reporting units. The fair value of the remaining reporting units with goodwill were in excess of their carrying value by percentages ranging from 8.5 percent to 270.0 percent. The reporting unit whose fair value exceeded its carrying amount by 8.5 percent, our Crude Gathering reporting unit, had goodwill totaling $1.1 billion at March 31, 2020. The operations which make up this reporting unit were acquired through the merger with ANDX. MPC accounted for its October 1, 2018 acquisition of Andeavor (through which it acquired control of ANDX), using the acquisition method of accounting, which required Andeavor assets and liabilities to be recorded by MPC at the acquisition date fair value. The Merger was closed on July 30, 2019 and has been treated as a common control transaction, which required the recognition of assets acquired and liabilities assumed using MPC’s historical carrying value. As such, given the short amount of time from when fair value was established to the date of the impairment test, the amount by which the fair value exceeded the carrying value within this reporting unit was not unexpected.

Our reporting units are one level below our operating segments and are determined based on the way in which segment management operates and reviews each operating segment. The fair value of our six reporting units was determined based on applying both a discounted cash flow or income approach as well as a market approach. The discounted cash flow fair value estimate is based on known or knowable information at the measurement date. The significant assumptions that were used to develop the estimates of the fair values under the discounted cash flow method included management’s best estimates of the expected future results and discount rate, which ranged from 9.5 percent to 11.5 percent. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of the interim goodwill impairment test will prove to be an accurate prediction of the future. The fair value measurements for the individual reporting units represent Level 3 measurements.

After performing our evaluations related to the impairment of goodwill during the fiscal year ending December 31, 2019, we recorded an impairment of $1,197 million within the Western G&P reporting unit. The remainder of the reporting units’ fair values were in excess of their carrying values. The impairment was primarily driven by updated guidance related to the slowing of drilling activity, which has reduced production growth forecasts from our producer customers. This resulted in goodwill totaling approximately $9.5 billion as of December 31, 2019, with all but one of our six reporting units having goodwill.

The changes in carrying amount of goodwill were as follows:

(In millions)	L&S			G&P			Total
Gross goodwill as of December 31, 2018	$	7,234		$	2,912		$	10,146
Accumulated impairment losses	—			(130		)	(130		)
Balance as of December 31, 2018	7,234			2,782			10,016
Impairment losses	—			(1,197		)	(1,197		)
Acquisitions	488			229			717
Balance as of December 31, 2019	7,722			1,814			9,536
Impairment losses	—			(1,814		)	(1,814		)
Wholesale Exchange (Note 3)	(65		)	—			(65		)
Balance as of September 30, 2020	7,657			—			7,657
Gross goodwill as of September 30, 2020	7,657			3,141			10,798
Accumulated impairment losses	—			(3,141		)	(3,141		)
Balance as of September 30, 2020	$	7,657		$	—		$	7,657

26

Intangible Assets

During the first quarter of 2020, we also determined that an impairment analysis of intangibles within our Western G&P reporting unit was necessary. See Note 11 for additional information regarding our assessment around the Western G&P reporting unit, and more specifically our East Texas G&P asset group. The fair value of the intangibles in our East Texas G&P asset group was determined based on applying the multi-period excess earnings method, which is an income approach. Key assumptions included management’s best estimates of the expected future cash flows from existing customers, customer attrition rates and the discount rate. After performing our evaluations related to the impairment of intangible assets associated with our East Texas G&P asset group during the first quarter of 2020, we recorded an impairment of $177 million to “Impairment expense” on the Consolidated Statements of Income related to our customer relationships.

MPLX’s remaining intangible assets are comprised of customer contracts and relationships. Gross intangible assets with accumulated amortization as of September 30, 2020 and December 31, 2019 is shown below:

		September 30, 2020							December 31, 2019
(In millions)	Useful Lives	Gross		Accumulated Amortization(1)(2)			Net		Gross		Accumulated Amortization			Net
L&S	6 - 8 years	$	283	$	(72	)	$	211	$	283	$	(45	)	$	238
G&P	6 - 25 years	1,288		(508		)	780		1,288		(256		)	1,032
		$	1,571	$	(580	)	$	991	$	1,571	$	(301	)	$	1,270

(1) Amortization expense attributable to the G&P and L&S segments for the nine months ended September 30, 2020 was $75 million and $27 million, respectively.

(2) Impairment charge of $177 million is included within the G&P accumulated amortization.

Estimated future amortization expense related to the intangible assets at September 30, 2020 is as follows:

(In millions)
2020	$	32
2021	128
2022	128
2023	128
2024	124
Thereafter	451
Total	$	991

13. Fair Value Measurements

Fair Values – Recurring

Fair value measurements and disclosures relate primarily to MPLX’s derivative positions as discussed in Note 14. The following table presents the financial instruments carried at fair value on a recurring basis as of September 30, 2020 and December 31, 2019 by fair value hierarchy level. MPLX has elected to offset the fair value amounts recognized for multiple derivative contracts executed with the same counterparty.

	September 30, 2020					December 31, 2019
(In millions)	Assets		Liabilities			Assets		Liabilities
Significant unobservable inputs (Level 3)
Embedded derivatives in commodity contracts	$	—	$	(61	)	$	—	$	(60	)
Total carrying value on Consolidated Balance Sheets	$	—	$	(61	)	$	—	$	(60	)

Level 3 instruments include all NGL transactions and embedded derivatives in commodity contracts. The embedded derivative liability relates to a natural gas purchase commitment embedded in a keep-whole processing agreement. The fair value calculation for these Level 3 instruments used significant unobservable inputs including: (1) NGL prices interpolated and extrapolated due to inactive markets ranging from $0.46 to $0.97 per gallon with a weighted average of $0.58 per gallon and

27

(2) the probability of renewal of 100 percent for the first five-year term and second five-year term of the gas purchase commitment and related keep-whole processing agreement, respectively. Increases or decreases in the fractionation spread result in an increase or decrease in the fair value of the embedded derivative liability, respectively. Beyond the embedded derivative discussed above, we had no outstanding commodity contracts as of September 30, 2020 or December 31, 2019.

Changes in Level 3 Fair Value Measurements

The following table is a reconciliation of the net beginning and ending balances recorded for net assets and liabilities classified as Level 3 in the fair value hierarchy.

	Three Months Ended September 30, 2020					Three Months Ended September 30, 2019
(In millions)	Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)			Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)
Fair value at beginning of period	$	—	$	(51	)	$	—	$	(65	)
Total (losses)/gains (realized and unrealized) included in earnings(1)	—		(12		)	—		9
Settlements	—		2			—		2
Fair value at end of period	—		(61		)	—		(54		)
The amount of total (losses)/gains for the period included in earnings attributable to the change in unrealized gains/(losses) relating to liabilities still held at end of period	$	—	$	(11	)	$	—	$	9

	Nine Months Ended September 30, 2020					Nine Months Ended September 30, 2019
(In millions)	Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)			Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)
Fair value at beginning of period	$	—	$	(60	)	$	—	$	(61	)
Total (losses)/gains (realized and unrealized) included in earnings(1)	—		(5		)	—		2
Settlements	—		4			—		5
Fair value at end of period	—		(61		)	—		(54		)
The amount of total (losses)/gains for the period included in earnings attributable to the change in unrealized gains/(losses) relating to liabilities still held at end of period	$	—	$	(2	)	$	—	$	5

(1) Gains and losses on commodity derivative contracts classified as Level 3 are recorded in “Product sales” on the Consolidated Statements of Income. Gains and losses on derivatives embedded in commodity contracts are recorded in “Purchased product costs” and “Cost of revenues” on the Consolidated Statements of Income.

Fair Values – Reported

MPLX’s primary financial instruments are cash and cash equivalents, receivables, receivables from related parties, lease receivables from related parties, accounts payable, payables to related parties and long-term debt. MPLX’s fair value assessment incorporates a variety of considerations, including (1) the duration of the instruments, (2) MPC’s investment-grade credit rating and (3) the historical incurrence of and expected future insignificance of bad debt expense, which includes an evaluation of counterparty credit risk. MPLX believes the carrying values of its current assets and liabilities approximate fair value. The recorded value of the amounts outstanding under the bank revolving credit facility, if any, approximates fair value due to the variable interest rate that approximates current market rates. Derivative instruments are recorded at fair value, based on available market information (see Note 14).

28

The fair value of MPLX’s long-term debt is estimated based on recent market non-binding indicative quotes. The fair value of the SMR liability is estimated using a discounted cash flow approach based on the contractual cash flows and MPLX’s unsecured borrowing rate. The long-term debt and SMR liability fair values are considered Level 3 measurements. The following table summarizes the fair value and carrying value of our debt, excluding finance leases, and SMR liability:

	September 30, 2020				December 31, 2019
(In millions)	Fair Value		Carrying Value		Fair Value		Carrying Value
Long-term debt (including amounts due within one year)	$	21,721	$	20,455	$	21,054	$	19,800
SMR liability	$	87	$	76	$	90	$	80

14. Derivative Financial Instruments

As of September 30, 2020, MPLX had no outstanding commodity contracts beyond the embedded derivative discussed below.

Embedded Derivative - MPLX has a natural gas purchase commitment embedded in a keep-whole processing agreement with a producer customer in the Southern Appalachian region expiring in December 2022. The customer has the unilateral option to extend the agreement for two consecutive five-year terms through December 2032. For accounting purposes, the natural gas purchase commitment and the term extending options have been aggregated into a single compound embedded derivative. The probability of the customer exercising its options is determined based on assumptions about the customer’s potential business strategy decision points that may exist at the time they would elect whether to renew the contract. The changes in fair value of this compound embedded derivative are based on the difference between the contractual and index pricing and the probability of the producer customer exercising its option to extend. The changes in fair value are recorded in earnings through “Purchased product costs” on the Consolidated Statements of Income. As of September 30, 2020 and December 31, 2019, the estimated fair value of this contract was a liability of $61 million and $60 million, respectively.

Certain derivative positions are subject to master netting agreements, therefore, MPLX has elected to offset derivative assets and liabilities that are legally permissible to be offset. As of September 30, 2020 and December 31, 2019, there were no derivative assets or liabilities that were offset on the Consolidated Balance Sheets. The impact of MPLX’s derivative instruments on its Consolidated Balance Sheets is summarized below:

(In millions)	September 30, 2020					December 31, 2019
Derivative contracts not designated as hedging instruments and their balance sheet location	Asset		Liability			Asset		Liability
Commodity contracts(1)
Other current assets / Other current liabilities	$	—	$	(4	)	$	—	$	(5	)
Other noncurrent assets / Deferred credits and other liabilities	—		(57		)	—		(55		)
Total	$	—	$	(61	)	$	—	$	(60	)

(1) Includes embedded derivatives in commodity contracts as discussed above.

For further information regarding the fair value measurement of derivative instruments, see Note 13. There were no material changes to MPLX’s policy regarding the accounting for Level 2 and Level 3 instruments as previously disclosed in MPLX’s Annual Report on Form 10-K for the year ended December 31, 2019. MPLX does not designate any of its commodity derivative positions as hedges for accounting purposes.

29

The impact of MPLX’s derivative contracts not designated as hedging instruments and the location of gains and losses recognized on the Consolidated Statements of Income is summarized below:

	Three Months Ended September 30,						Nine Months Ended September 30,
(In millions)	2020			2019			2020			2019
Purchased product costs
Realized (loss)/gain	$	(2	)	$	(2	)	$	(4	)	$	(5	)
Unrealized (loss)/gain	(10		)	11			(1		)	7
Purchased product costs derivative (loss)/gain	(12		)	9			(5		)	2
Total derivative (loss)/gain	$	(12	)	$	9		$	(5	)	$	2

15. Debt

MPLX’s outstanding borrowings consist of the following:

(In millions)	September 30, 2020			December 31, 2019
MPLX LP:
Bank revolving credit facility	$	95		$	—
Term loan facility	—			1,000
Floating rate senior notes	1,000			2,000
Fixed rate senior notes	19,506			16,887
Consolidated subsidiaries:
MarkWest	23			23
ANDX	121			190
Financing lease obligations(1)	12			19
Total	20,757			20,119
Unamortized debt issuance costs	(118		)	(106		)
Unamortized discount/premium	(290		)	(300		)
Amounts due within one year	(307		)	(9		)
Total long-term debt due after one year	$	20,042		$	19,704

(1)    See Note 20 for lease information.

Credit Agreement

Effective July 30, 2019, in connection with the closing of the Merger, MPLX amended and restated its revolving credit facility (as amended, the “MPLX Credit Agreement”) to, among other things, increase borrowing capacity to up to $3.5 billion and extend its term from July 2022 to July 2024. During the nine months ended September 30, 2020, MPLX borrowed $2.995 billion under the MPLX Credit Agreement, at an average interest rate of 1.510 percent, and repaid $2.9 billion. At September 30, 2020, MPLX had $95 million in outstanding borrowings and less than $1 million in letters of credit outstanding under the MPLX Credit Agreement, resulting in total availability of $3.405 billion, or 97.3 percent of the borrowing capacity.

Term Loan Agreement

On September 26, 2019, MPLX entered into a Term Loan Agreement which provides for a committed term loan facility for up to an aggregate of $1 billion. Borrowings under the Term Loan Agreement bear interest, at MPLX’s election, at either (i) the Adjusted LIBO Rate (as defined in the Term Loan Agreement) plus a margin ranging from 75.0 basis points to 100.0 basis points per annum, depending on MPLX’s credit ratings, or (ii) the Alternate Base Rate (as defined in the Term Loan Agreement). On August 18, 2020 MPLX fully repaid the $1.0 billion of outstanding borrowings on the Term Loan Agreement, which resulted in the recognition of $1 million of unamortized issuance costs, which is included on the Consolidated Statements of Income as “Other financial costs”.

30

Floating Rate Senior Notes

On September 9, 2019, MPLX issued $2.0 billion aggregate principal amount of floating rate senior notes in a public offering, consisting of $1.0 billion aggregate principal amount of notes due September 2021 and $1.0 billion aggregate principal amount of notes due September 2022 (collectively, the “Floating Rate Senior Notes”). The Floating Rate Senior Notes were offered at a price to the public of 100 percent of par. The Floating Rate Senior Notes are callable, in whole or in part, at par plus accrued and unpaid interest at any time on or after September 10, 2020. Interest on the Floating Rate Senior Notes is payable quarterly in March, June, September and December, commencing on December 9, 2019. The interest rate applicable to the floating rate senior notes due September 2021 is LIBOR plus 0.9 percent per annum. The interest rate applicable to the floating rate senior notes due September 2022 is LIBOR plus 1.1 percent per annum.

On September 14, 2020 MPLX redeemed, at par value, all of the $1.0 billion aggregate principal amount of notes due September 2021 which resulted in the recognition of $3 million of unamortized issuance costs, which is included on the Consolidated Statements of Income as “Other financial costs”.

Fixed Rate Senior Notes

MPLX’s senior notes, including those issued by consolidated subsidiaries, consist of various series of senior notes expiring between 2022 and 2058 with interest rates ranging from 1.750 percent to 6.250 percent. Interest on each series of notes is payable semi-annually in arrears on various dates depending on the series of the notes.

On August 18, 2020 MPLX issued $3 billion aggregate principal amount of senior notes in a public offering, consisting of $1.5 billion aggregate principal amount of 1.750 percent senior notes due March 2026 and $1.5 billion aggregate principal amount of 2.650 percent senior notes due August 2030 (collectively, the “August 2020 New Senior Notes”). The August 2020 New Senior Notes were offered at a price to the public of 99.785 percent and 99.913 percent of par, respectively. Interest on each series of notes in the August 2020 New Senior Notes is payable semi-annually in arrears, commencing on March 1, 2021 for the senior notes due March 2026 and commencing on February 15, 2021 for the senior notes due August 2030. The net proceeds were used to repay the $1.0 billion of outstanding borrowings under the MPLX Term Loan Agreement, to repay the $1.0 billion floating rate notes due September 2021 and to redeem all of the $450 million aggregate principal amount of 6.375 percent senior notes due May 2024, $69 million of which was issued by ANDX. These notes were redeemed at 103.2 percent of the aggregate principal amount, which resulted in a payment of $14 million related to the note premium offset by the immediate recognition of $18 million of unamortized debt premium/discount and issuance costs, both of which are included on the Consolidated Statements of Income as “Other financial costs.” Proceeds were also used to reduce amounts outstanding under the MPLX Credit Agreement at the time and will be used to redeem the $300 million aggregate principal amount of 6.250 percent senior notes due October 15, 2022, including approximately $34 million in aggregate principal amount of senior notes issued by ANDX, in October of 2020. The 6.250 percent senior notes are included on the Consolidated Balance Sheets as “Long-term debt due within one year” at September 30, 2020.

31

16. Revenue

Disaggregation of Revenue

The following tables represent a disaggregation of revenue for each reportable segment for the three and nine months ended September 30, 2020 and 2019:

	Three Months Ended September 30, 2020
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	87	$	517	$	604
Service revenue - related parties	902		7		909
Service revenue - product related	—		41		41
Product sales	7		158		165
Product sales - related parties	2		35		37
Total revenues from contracts with customers	$	998	$	758	1,756
Non-ASC 606 revenue(1)					491
Total revenues and other income					$	2,247

	Three Months Ended September 30, 2019
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	95	$	537	$	632
Service revenue - related parties	881		18		899
Service revenue - product related	—		26		26
Product sales	14		157		171
Product sales - related parties	8		24		32
Total revenues from contracts with customers	$	998	$	762	1,760
Non-ASC 606 revenue(1)					520
Total revenues and other income					$	2,280

	Nine Months Ended September 30, 2020
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	248	$	1,531	$	1,779
Service revenue - related parties	2,676		18		2,694
Service revenue - product related	—		102		102
Product sales	39		415		454
Product sales - related parties	10		90		100
Total revenues from contracts with customers	$	2,973	$	2,156	5,129
Non-ASC 606 loss(1)					191
Total revenues and other income					$	5,320

32

	Nine Months Ended September 30, 2019
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	260	$	1,605	$	1,865
Service revenue - related parties	2,527		22		2,549
Service revenue - product related	—		86		86
Product sales	40		536		576
Product sales - related parties	17		92		109
Total revenues from contracts with customers	$	2,844	$	2,341	5,185
Non-ASC 606 revenue(1)					1,540
Total revenues and other income					$	6,725

(1) Non-ASC 606 Revenue includes rental income, income/(loss) from equity method investments, derivative gains and losses, mark-to-market adjustments, and other income.

Contract Balances

Contract assets typically relate to aid in construction agreements where the revenue recognized and MPLX’s rights to consideration for work completed exceeds the amount billed to the customer or for deficiency payments associated with minimum volume commitments which have not been billed to customers. Contract assets are generally classified as current and included in “Other current assets” on the Consolidated Balance Sheets.

Contract liabilities, which we refer to as “Deferred revenue” and “Long-term deferred revenue,” typically relate to advance payments for aid in construction agreements and deferred customer credits associated with makeup rights and minimum volume commitments. Related to minimum volume commitments, breakage is estimated and recognized into service revenue in instances where it is probable the customer will not use the credit in future periods. We classify contract liabilities as current or long-term based on the timing of when we expect to recognize revenue.

“Receivables, net” primarily relate to our commodity sales. Portions of the “Receivables, net” balance are attributed to the sale of commodity product controlled by MPLX prior to sale while a significant portion of the balance relates to the sale of commodity product on behalf of our producer customers. Both types of transactions are commingled and excluded from the table below. MPLX remits the net sales price back to our producer customers upon completion of the sale. Each period end, certain amounts within accounts payable relate to our payments to producer customers. Such amounts are not deemed material at period end as a result of when we settle with each producer.

The tables below reflect the changes in our contract balances for the nine-month periods ended September 30, 2020 and 2019:

(In millions)	Balance at December 31, 2019(1)		Additions/ (Deletions)			Revenue Recognized(2)			Balance at September 30, 2020
Contract assets	$	39	$	(9	)	$	(1	)	$	29
Deferred revenue	23		16			(6		)	33
Deferred revenue - related parties	53		77			(60		)	70
Long-term deferred revenue	90		25			—			115
Long-term deferred revenue - related parties	$	55	$	(7	)	$	—		$	48

33

(In millions)	Balance at December 31, 2018(1)		Additions/ (Deletions)			Revenue Recognized(2)			Balance at September 30, 2019
Contract assets	$	36	$	(6	)	$	(2	)	$	28
Deferred revenue	13		11			(4		)	20
Deferred revenue - related parties	65		34			(50		)	49
Long-term deferred revenue	56		26			—			82
Long-term deferred revenue - related parties	$	52	$	5		$	—		$	57

(1) Balance represents ASC 606 portion of each respective line item.

(2) No significant revenue was recognized related to past performance obligations in the current periods.

Remaining Performance Obligations

The table below includes estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period.

As of September 30, 2020, the amounts allocated to contract assets and contract liabilities on the Consolidated Balance Sheets are $264 million and are reflected in the amounts below. This will be recognized as revenue as the obligations are satisfied, which is expected to occur over the next 30 years. Further, MPLX does not disclose variable consideration due to volume variability in the table below.

(In millions)
2020	$	461
2021	1,727
2022	1,701
2023	1,591
2024 and thereafter	5,869
Total revenue on remaining performance obligations(1),(2),(3)	$	11,349

(1) All fixed consideration from contracts with customers is included in the amounts presented above. Variable consideration that is constrained or not required to be estimated as it reflects our efforts to perform is excluded.

(2) Arrangements deemed implicit leases are included in “Rental income” and are excluded from this table.

(3) Only minimum volume commitments that are deemed fixed are included in the table above. MPLX has various minimum volume commitments in processing arrangements that vary based on the actual Btu content of the gas received. These amounts are deemed variable consideration and are excluded from the table above.

We do not disclose information on the future performance obligations for any contract with an original expected duration of

one year or less.

17. Supplemental Cash Flow Information

	Nine Months Ended September 30,
(In millions)	2020			2019
Net cash provided by operating activities included:
Interest paid (net of amounts capitalized)	$	631		$	648
Income taxes paid	1			—
Non-cash investing and financing activities:
Net transfers of property, plant and equipment (to)/from materials and supplies inventories	(1		)	1
Fair value of common units redeemed for Wholesale Exchange	$	340		$	—

34

The Consolidated Statements of Cash Flows exclude changes to the Consolidated Balance Sheets that did not affect cash. The following is the change of additions to property, plant and equipment related to capital accruals:

	Nine Months Ended September 30,
(In millions)	2020			2019
(Decrease)/increase in capital accruals	$	(197	)	$	(67	)

18. Accumulated Other Comprehensive Loss

MPLX LP records an accumulated other comprehensive loss on the Consolidated Balance Sheets relating to pension and other post-retirement benefits provided by LOOP LLC (“LOOP”) and Explorer Pipeline Company (“Explorer”) to their employees. MPLX LP is not a sponsor of these benefit plans.

The following table shows the changes in “Accumulated other comprehensive loss” by component during the period December 31, 2019 through September 30, 2020.

(In millions)	Pension Benefits			Other Post-Retirement Benefits			Total
Balance at December 31, 2019(1)	$	(14	)	$	(1	)	$	(15	)
Other comprehensive loss - remeasurements(2)	—			(1		)	(1		)
Balance at September 30, 2020(1)	$	(14	)	$	(2	)	$	(16	)

The following table shows the changes in “Accumulated other comprehensive loss” by component during the period December 31, 2018 through September 30, 2019.

(In millions)	Pension Benefits			Other Post-Retirement Benefits			Total
Balance at December 31, 2018(1)	$	(14	)	$	(2	)	$	(16	)
Other comprehensive income - remeasurements(2)	—			1			1
Balance at September 30, 2019(1)	$	(14	)	$	(1	)	$	(15	)

(1) These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on the Consolidated Statements of Income under the caption “Income/(loss) from equity method investments.”

(2) Components of other comprehensive income/loss - remeasurements relate to actuarial gains and losses as well as amortization of prior service costs. MPLX records an adjustment to “Comprehensive income” in accordance with its ownership interest in LOOP and Explorer.

19. Equity-Based Compensation

Phantom Units

The following is a summary of phantom unit award activity of MPLX LP common units for the nine months ended September 30, 2020:

	Number of Units		Weighted Average Fair Value
Outstanding at December 31, 2019	1,109,568		$	35.97
Granted	215,677		19.31
Settled	(558,398	)	37.73
Forfeited	(5,383	)	35.87
Outstanding at September 30, 2020	761,464		$	29.96

Performance Units – MPLX grants performance units to certain officers of the general partner and certain eligible MPC officers who make significant contributions to its business. These performance units pay out 75 percent in cash and 25 percent in MPLX LP common units and often contain both market and performance conditions based on various metrics. Market conditions are valued using a Monte Carlo valuation while performance conditions are reevaluated periodically and valued at the compensation cost associated with the performance outcome deemed most probable.

35

The performance units granted in 2020 are hybrid awards having a three-year performance period of January 1, 2020 through December 31, 2022. The payout of the award is dependent on two independent conditions, each constituting 50 percent of the overall target units granted. The awards have a performance condition based on MPLX LP’s distributable cash flow, and a market condition based on MPLX LP’s total unitholder return. The market condition was valued using a Monte Carlo valuation, resulting in a grant date fair value of $0.80 per unit for the 2020 equity-classified performance units. Grant date fair value of the performance condition is based on potential payouts per unit of up to $2.00 per unit. Compensation cost associated with the performance condition is based on the grant date fair value of the payout deemed most probable to occur and is adjusted as the expectation for payout changes.

During the first quarter of 2018, a performance award was granted; however, due to the nature of the award terms, the grant date for this award was not established until the first quarter of 2020 and we began recognizing units and expense related to this award at that time. The performance units granted in 2018 are hybrid awards having a three-year performance period of January 1, 2018 through December 31, 2020. The payout of the award is dependent on two independent conditions, each constituting 50 percent of the overall target units granted. The awards have a performance condition based on an average of MPLX LP’s distributable cash flow and a market condition based on MPLX LP’s total unitholder return. The market condition was valued using a Monte Carlo valuation, resulting in a grant date fair value of $0.45 per unit for the 2018 equity-classified performance units. Grant date fair value of the performance condition is based on potential payouts per unit of up to $2.00 per unit. Compensation cost associated with the performance condition is based on the grant date fair value of the payout deemed most probable to occur and is adjusted as the expectation for payout changes.

The following is a summary of the activity for performance unit awards to be settled in MPLX LP common units for the nine months ended September 30, 2020:

	Number of Units
Outstanding at December 31, 2019	2,157,347
Granted	2,147,211
Settled	(1,169,354	)
Forfeited	(31,668	)
Outstanding at September 30, 2020	3,103,536

20. Leases

During the first quarter of 2020, reimbursements for projects at certain MPLX refining logistics locations were agreed to between MPLX and MPC. These reimbursements relate to the storage services agreements between MPLX and MPC at these locations and required the embedded leases within these agreements to be reassessed under the leasing standard. As a result of the reassessment, one of our leases was reclassified from an operating lease to a sales-type lease. As a result, the underlying assets previously shown on the Consolidated Balance Sheets associated with the sales-type lease were derecognized and the net investment in the lease (i.e., the sum of the present value of the future lease payments and the unguaranteed residual value of the assets) was recorded as a lease receivable. See Note 5 for the location of lease receivables and unguaranteed residual assets on the Consolidated Balance Sheets. The difference between the net book value of the underlying assets and the net investment in the lease has been recorded as a Contribution from MPC in the Consolidated Statements of Equity given that the transaction related to refining logistics was a common control transaction. During the first quarter of 2020, MPLX derecognized approximately $171 million of property, plant and equipment, recorded a lease receivable of approximately $370 million, recorded an unguaranteed residual asset of approximately $10 million and a Contribution from MPC of $209 million.

36

Lease revenues included on the Consolidated Statements of Income were as follows:

	Three Months Ended September 30, 2020				Three Months Ended September 30, 2019
(In millions)	Related Party		Third Party		Related Party		Third Party
Operating leases:
Operating lease revenue(1)	$	208	$	70	$	248	$	63
Sales-type leases:
Profit/(loss) recognized at the commencement date	—		—		—		N/A
Interest income (Sales-type lease revenue- fixed minimum)	37		—		3		N/A
Interest income (Revenue from variable lease payments)	$	1	$	—	$	1	N/A

	Nine Months Ended September 30, 2020				Nine Months Ended September 30, 2019
(In millions)	Related Party		Third Party		Related Party		Third Party
Operating leases:
Operating lease revenue(1)	$	589	$	199	$	773	$	196
Sales-type leases:
Profit/(loss) recognized at the commencement date	—		—		—		N/A
Interest income (Sales-type lease revenue- fixed minimum)	113		—		3		N/A
Interest income (Revenue from variable lease payments)	$	1	$	—	$	1	N/A

(1) These amounts are presented net of executory costs.

See Note 5 for additional information on where related party lease assets are recorded in the Consolidated Balance Sheets. Third party lease assets are less than $1 million as of September 30, 2020 and are included within the “Receivables, net” and “Other noncurrent assets” captions within the Consolidated Balance Sheets.

The following is a schedule of future payments on the sales-type leases as of September 30, 2020:

(In millions)	Related Party
2020	$	39
2021	157
2022	157
2023	158
2024	158
2025 and thereafter	473
Total minimum future rentals	1,142
Less: present value discount	723
Lease receivable	$	419

21. Commitments and Contingencies

MPLX is the subject of, or a party to, a number of pending or threatened legal actions, contingencies and commitments involving a variety of matters, including laws and regulations relating to the environment. Some of these matters are discussed below. For matters for which MPLX has not recorded a liability, MPLX is unable to estimate a range of possible loss because

37

the issues involved have not been fully developed through pleadings, discovery or court proceedings. However, the ultimate resolution of some of these contingencies could, individually or in the aggregate, be material.

Environmental Matters – MPLX is subject to federal, state and local laws and regulations relating to the environment. These laws generally provide for control of pollutants released into the environment and require responsible parties to undertake remediation of hazardous waste disposal sites. Penalties may be imposed for non-compliance.

At September 30, 2020 and December 31, 2019, accrued liabilities for remediation totaled $18 million and $19 million, respectively. It is not presently possible to estimate the ultimate amount of all remediation costs that might be incurred or the penalties, if any, that may be imposed. At September 30, 2020 and December 31, 2019, there were no balances with MPC for indemnification of environmental costs.

MPLX is involved in environmental enforcement matters arising in the ordinary course of business. While the outcome and impact to MPLX cannot be predicted with certainty, management believes the resolution of these environmental matters will not, individually or collectively, have a material adverse effect on its consolidated results of operations, financial position or cash flows.

MPLX is also a party to a number of other lawsuits and other proceedings arising in the ordinary course of business. While the ultimate outcome and impact to MPLX cannot be predicted with certainty, management believes the resolution of these other lawsuits and proceedings will not, individually or collectively, have a material adverse effect on its consolidated financial position, results of operations or cash flows.

Guarantees – Over the years, MPLX has sold various assets in the normal course of its business. Certain of the related agreements contain performance and general guarantees, including guarantees regarding inaccuracies in representations, warranties, covenants and agreements, and environmental and general indemnifications that require MPLX to perform upon the occurrence of a triggering event or condition. These guarantees and indemnifications are part of the normal course of selling assets. MPLX is typically not able to calculate the maximum potential amount of future payments that could be made under such contractual provisions because of the variability inherent in the guarantees and indemnities. Most often, the nature of the guarantees and indemnities is such that there is no appropriate method for quantifying the exposure because the underlying triggering event has little or no past experience upon which a reasonable prediction of the outcome can be based.

In connection with our 9.19 percent indirect interest in a joint venture (“Dakota Access”) that owns and operates the Dakota Access Pipeline and Energy Transfer Crude Oil Pipeline projects, collectively referred to as the Bakken Pipeline system or DAPL, we have entered into a Contingent Equity Contribution Agreement whereby MPLX LP, along with the other joint venture owners in the Bakken Pipeline system, has agreed to make equity contributions to the joint venture upon certain events occurring to allow the entities that own and operate the Bakken Pipeline system to satisfy their senior note payment obligations. The senior notes were issued to repay amounts owed by the pipeline companies to fund the cost of construction of the Bakken Pipeline system.

In March 2020, the U.S. District Court for the District of Columbia (the “D.D.C.”) ordered the U.S. Army Corps of Engineers (“Army Corps”), which granted permits and an easement for the Bakken Pipeline system, to conduct a full environmental impact statement (“EIS”), and further requested briefing on whether an easement necessary for the operation of the Bakken Pipeline system should be vacated while the EIS is being prepared.

On July 6, 2020, the D.D.C. ordered vacatur of the easement to cross Lake Oahe during the pendency of an EIS and further ordered a shut down of the pipeline by August 5, 2020. The D.D.C. denied a motion to stay that order. Dakota Access and the Army Corps appealed the D.D.C.’s order to the U.S. Court of Appeals for the District of Columbia Circuit (the “Court of Appeals”). On July 14, 2020, the Court of Appeals issued an administrative stay while the court considered Dakota Access and the Army Corps’ emergency motion for stay pending appeal. On August 5, 2020, the Court of Appeals stayed the D.D.C.’s injunction that required the pipeline be shutdown and emptied of oil by August 5, 2020. The Court of Appeals denied a stay of the D.D.C.’s March order, which required the EIS, and further denied a stay of the D.D.C.’s July order, which vacated the easement. In the D.D.C., briefing is ongoing for a renewed request for an injunction, which is expected to be completed by the end of 2020. Oral argument on the merits of the case at the Court of Appeals occurred on November 4, 2020. The pipeline remains operational.

If the pipeline is temporarily shutdown pending completion of the EIS, MPLX would have to contribute its 9.19 percent pro rata share of funds required to pay interest accruing on the notes and any portion of the principal that matures while the pipeline is shutdown. MPLX also expects to contribute its 9.19 percent pro rata share of any costs to remediate any deficiencies to reinstate the permit and/or return the pipeline into operation. If the vacatur of the easement permit results in a permanent

38

shutdown of the pipeline, MPLX would have to contribute its 9.19 percent pro rata share of the cost to redeem the bonds (including the 1% redemption premium required pursuant to the indenture governing the notes) and any accrued and unpaid interest. As of September 30, 2020, our maximum potential undiscounted payments under the Contingent Equity Contribution Agreement were approximately $230 million.

Other Legal Proceedings – In early July, MPLX received a Notification of Trespass Determination from the Bureau of Indian Affairs (“BIA”) relating to a portion of the Tesoro High Plains Pipeline that crosses the Fort Berthold Reservation in North Dakota. The notification covered the rights of way for 23 tracts of land and demanded the immediate cessation of pipeline operations. The notification also assessed trespass damages of approximately $187 million. We appealed this determination, which triggered an automatic stay of the requested pipeline shutdown and payment. On October 29, the Assistant Secretary - Indian Affairs issued an order vacating the BIA’s trespass order and requiring the Regional Director for the BIA Great Plains Region to issue a new decision on or before December 15 covering all 34 tracts at issue.

We continue to work towards a settlement of this matter with holders of the property rights at issue. Management does not believe the ultimate resolution of this matter will have a material adverse effect on our consolidated financial position, results of operations, or cash flows.

Contractual Commitments and Contingencies – At September 30, 2020, MPLX’s contractual commitments to acquire property, plant and equipment totaled $181 million. These commitments were primarily related to G&P plant expansion, terminal and pipeline projects. In addition, from time to time and in the ordinary course of business, MPLX and its affiliates provide guarantees of MPLX’s subsidiaries payment and performance obligations in the G&P segment. Certain natural gas processing and gathering arrangements require MPLX to construct new natural gas processing plants, natural gas gathering pipelines and NGL pipelines and contain certain fees and charges if specified construction milestones are not achieved for reasons other than force majeure. In certain cases, certain producers may have the right to cancel the processing arrangements if there are significant delays that are not due to force majeure. As of September 30, 2020, management does not believe there are any indications that MPLX will not be able to meet the construction milestones, that force majeure does not apply or that such fees and charges will otherwise be triggered.

Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations

Management’s Discussion and Analysis of Financial Condition and Results of Operations should also be read in conjunction with the unaudited consolidated financial statements and accompanying footnotes included under Item 1. Financial Statements and in conjunction with our Annual Report on Form 10-K for the year ended December 31, 2019.

Disclosures Regarding Forward-Looking Statements

This Quarterly Report on Form 10-Q, particularly Management’s Discussion and Analysis of Financial Condition and Results of Operations and Quantitative and Qualitative Disclosures about Market Risk, includes forward-looking statements that are subject to risks, contingencies or uncertainties. You can identify forward-looking statements by words such as “anticipate,” “believe,” “commitment,” “could,” “design,” “estimate,” “expect,” “forecast,” “goal,” “guidance,” “imply,” “intend,” “may,” “objective,” “opportunity,” “outlook,” “plan,” “policy,” “position,” “potential,” “predict,” “priority,” “project,” “proposition,” “prospective,” “pursue,” “seek,” “should,” “strategy,” “target,” “will,” “would” or other similar expressions that convey the uncertainty of future events or outcomes.

Forward-looking statements include, among other things, statements regarding:

• future levels of revenues and other income, income from operations, net income attributable to MPLX LP, earnings per unit, Adjusted EBITDA or DCF (see the Non-GAAP Financial Information section below for the definitions of Adjusted EBITDA and DCF);

• future levels of capital, environmental or maintenance expenditures, general and administrative and other expenses;

• the success or timing of completion of ongoing or anticipated capital or maintenance projects;

• the amount and timing of future distributions; and

• the anticipated effects of actions of third parties such as competitors, activist investors or federal, foreign, state or local regulatory authorities or plaintiffs in litigation.

39

Our forward-looking statements are not guarantees of future performance and you should not rely unduly on them, as they involve risks, uncertainties and assumptions that we cannot predict. Material differences between actual results and any future performance suggested in our forward-looking statements could result from a variety of factors, including the following:

• the effects of the outbreak of COVID-19, including any related government policies and actions, and the adverse impact thereof on our business, financial condition, results of operations and cash flows, including our growth, operating costs, labor availability, logistical capabilities, customer demand for our services and industry demand generally, cash position, taxes, the price of our securities and trading markets with respect thereto, our ability to access capital markets, and the global economy and financial markets generally;

• the ability of Marathon Petroleum Corporation (“MPC”) to achieve its strategic objectives and the effects of those strategic decisions on us;

• the risk that anticipated opportunities and any other synergies from or benefits of the Andeavor Logistics LP (“ANDX”) acquisition may not be fully realized or may take longer to realize than expected, including whether the transaction will be accretive within the expected timeframe or at all;

• disruption from the ANDX acquisition making it more difficult to maintain relationships with customers, employees or suppliers;

• risks relating to any unforeseen liabilities of ANDX;

• further impairments;

• negative capital market conditions, including an increase of the current yield on common units;

• the ability to achieve strategic and financial objectives, including with respect to distribution coverage, future distribution levels, proposed projects and completed transactions;

• the success of MPC’s portfolio optimization, including the ability to complete any divestitures on commercially reasonable terms and/or within the expected timeframe, and the effects of any such divestitures on the business, financial condition, results of operations and cash flows;

• adverse changes in laws including with respect to tax and regulatory matters;

• the adequacy of capital resources and liquidity, including the availability of sufficient cash flow to pay distributions and access to debt on commercially reasonable terms, and the ability to successfully execute business plans, growth strategies and self-funding models;

• the timing and extent of changes in commodity prices and demand for crude oil, refined products, feedstocks or other hydrocarbon-based products;

• volatility in or degradation of market and industry conditions as a result of the COVID-19 pandemic, including any related policies and actions, other infectious disease outbreaks, natural hazards, extreme weather events, or otherwise;

• changes to the expected construction costs and timing of projects and planned investments, and the ability to obtain regulatory and other approvals with respect thereto;

• completion of midstream infrastructure by competitors;

• disruptions due to equipment interruption or failure, including electrical shortages and power grid failures;

• the suspension, reduction or termination of MPC’s obligations under MPLX’s commercial agreements;

• modifications to financial policies, capital budgets, and earnings and distributions;

• the ability to manage disruptions in credit markets or changes to credit ratings;

• compliance with federal and state environmental, economic, health and safety, energy and other policies and regulations or enforcement actions initiated thereunder;

• adverse results in litigation;

• the reliability of processing units and other equipment;

• the effect of restructuring or reorganization of business components;

• the potential effects of changes in tariff rates on our business, financial condition, results of operations and cash flows;

• foreign imports and exports of crude oil, refined products, natural gas and NGLs;

• changes in producer customers’ drilling plans or in volumes of throughput of crude oil, natural gas, NGLs, refined products or other hydrocarbon-based products;

• non-payment or non-performance by our producer and other customers;

• changes in the cost or availability of third-party vessels, pipelines, railcars and other means of transportation for crude oil, natural gas, NGLs, feedstocks and refined products;

40

• the price, availability and acceptance of alternative fuels and alternative-fuel vehicles and laws mandating such fuels or vehicles;

• actions taken by our competitors, including pricing adjustments and the expansion and retirement of pipeline capacity, processing, fractionation and treating facilities in response to market conditions;

• expectations regarding joint venture arrangements and other acquisitions or divestitures of assets;

• midstream and refining industry overcapacity or under capacity;

• accidents or other unscheduled shutdowns affecting our machinery, pipelines, processing, fractionation and treating facilities or equipment, or those of our suppliers or customers;

• acts of war, terrorism or civil unrest that could impair our ability to gather, process, fractionate or transport crude oil, natural gas, NGLs or refined products; and

• political pressure and influence of environmental groups upon policies and decisions related to the production, gathering, refining, processing, fractionation, transportation and marketing of crude oil or other feedstocks, refined products, natural gas, NGLs or other hydrocarbon-based products.

For additional risk factors affecting our business, see the risk factors described in our Annual Report on Form 10-K for the year ended December 31, 2019, as updated in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2020. We undertake no obligation to update any forward-looking statements except to the extent required by applicable law.

MPLX OVERVIEW

We are a diversified, large-cap MLP formed by MPC, that owns and operates midstream energy infrastructure and logistics assets, and provides fuels distribution services. We are engaged in the transportation, storage and distribution of crude oil and refined petroleum products; the gathering, processing and transportation of natural gas; and the gathering, transportation, fractionation, storage and marketing of NGLs. Our operations are conducted in our Logistics and Storage and Gathering and Processing segments.

SIGNIFICANT FINANCIAL AND OTHER HIGHLIGHTS

Significant financial highlights including revenues and other income, income from operations, net income, adjusted EBITDA attributable to MPLX and DCF attributable to GP and LP unitholders for the three months ended September 30, 2020 and September 30, 2019 are shown in the chart below. These results include the recast of ANDX financial information into MPLX’s financial information as a result of the Merger. See the Non-GAAP Financial Information section below for the definitions of Adjusted EBITDA and DCF and the Results of Operations section for further details regarding changes in these metrics.

(1) Q3 2019 includes Adjusted EBITDA attributable to Predecessor and portion of DCF adjustments attributable to Predecessor.

41

Other Highlights

RECENT DEVELOPMENTS

• On July 31, 2020, MPLX completed the exchange of Western Refining Wholesale, LLC to Western Refining Southwest, Inc. (“WRSW”), a wholly owned subsidiary of MPC, in exchange for the redemption of 18,582,088 MPLX common units held by WRSW, valued at $340 million.

• On August 18, 2020, MPLX issued $3 billion aggregate principal amount of new senior notes consisting of $1.5 billion aggregate principal amount of 1.750 percent senior notes due March 2026 and $1.5 billion aggregate principal amount of 2.650 percent senior notes due August 2030. The net proceeds were used to repay the $1.0 billion of outstanding borrowings under the MPLX Term Loan Agreement, to repay the $1.0 billion floating rate notes due September 2021, to redeem all of the $450 million aggregate principal amount of 6.375 percent senior notes due May 2024, to reduce amounts outstanding under the MPLX Credit Agreement at the time and to redeem the $300 million aggregate principal amount of 6.250 percent senior notes due October 15, 2022 (these notes were redeemed on October 15, 2020).

• On November 1, 2020, MPLX finalized the 2020 Terminal Services Agreement, which replaces and simplifies several existing terminal services agreements which were entered into by subsidiaries of Andeavor and Andeavor Logistics LP. The simplification is expected to have no economic impact to MPLX.

• On November 2, 2020, MPLX announced the board authorization of a unit repurchase program for the repurchase of up to $1 billion of MPLX’s outstanding common units held by the public. MPLX may utilize various methods to effect the repurchases, which could include open market repurchases, negotiated block transactions, tender offers, accelerated unit repurchases or open market solicitations for units, some of which may be effected through Rule 10b5-1 plans. The timing and amount of repurchases, if any, will depend upon several factors, including market and business conditions, and repurchases may be initiated, suspended or discontinued at any time. The repurchase authorization has no expiration date.

• Announced a third quarter distribution rate of $0.6875 per common unit.

CURRENT ECONOMIC ENVIRONMENT

The outbreak of COVID-19 and its development into a pandemic in March 2020 has resulted in significant economic disruption globally. Actions taken by various governmental authorities, individuals and companies around the world to prevent the spread of COVID-19 through social distancing have restricted travel, many business operations, public gatherings and the overall level of individual movement and in-person interaction across the globe. This has significantly reduced global economic activity and resulted in a decline in the demand for products for which we provide midstream services. Macroeconomic conditions and global geopolitical events have also resulted in significant price volatility related to those aforementioned products.

We are actively responding to the impacts that these matters are having on our business by:

• Canceling or delaying certain capital expenditures that we had expected to make in 2020

• Taking actions to reduce operating expenses across the business

• Continuing to evaluate and high-grade our capital portfolio

Many uncertainties remain with respect to COVID-19, including its resulting economic effects, and we are unable to predict the ultimate economic impacts from COVID-19 and how quickly national economies can recover once the pandemic ultimately subsides. However, the adverse impact will likely continue to have an impact on our business and our customers’ businesses. We believe we have proactively addressed many of the known impacts of COVID-19 to the extent possible and will strive to continue to do so, but there can be no guarantee the measures will be fully effective.

NON-GAAP FINANCIAL INFORMATION

Our management uses a variety of financial and operating metrics to analyze our performance. These metrics are significant factors in assessing our operating results and profitability and include the non-GAAP financial measures of Adjusted EBITDA and DCF. The amount of Adjusted EBITDA and DCF generated is considered by the board of directors of our general partner in approving MPLX’s cash distributions.

42

We define Adjusted EBITDA as net income adjusted for: (i) depreciation and amortization; (ii) provision/(benefit) for income taxes; (iii) amortization of deferred financing costs; (iv) extinguishment of debt; (v) non-cash equity-based compensation; (vi) impairment expense; (vii) net interest and other financial costs; (viii) income/(loss) from equity method investments; (ix) distributions and adjustments related to equity method investments; (x) unrealized derivative gains/(losses); (xi) acquisition costs; (xii) noncontrolling interest; and (xiii) other adjustments as deemed necessary. We also use DCF, which we define as Adjusted EBITDA adjusted for: (i) deferred revenue impacts; (ii) net interest and other financial costs; (iii) maintenance capital expenditures; (iv) equity method investment capital expenditures paid out; and (v) other adjustments as deemed necessary. MPLX makes a distinction between realized and unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

We believe that the presentation of Adjusted EBITDA and DCF provides useful information to investors in assessing our financial condition and results of operations. The GAAP measures most directly comparable to Adjusted EBITDA and DCF are net income and net cash provided by operating activities. Adjusted EBITDA and DCF should not be considered alternatives to GAAP net income or net cash provided by operating activities. Adjusted EBITDA and DCF have important limitations as analytical tools because they exclude some but not all items that affect net income and net cash provided by operating activities or any other measure of financial performance or liquidity presented in accordance with GAAP. Adjusted EBITDA and DCF should not be considered in isolation or as substitutes for analysis of our results as reported under GAAP. Additionally, because Adjusted EBITDA and DCF may be defined differently by other companies in our industry, our definitions of Adjusted EBITDA and DCF may not be comparable to similarly titled measures of other companies, thereby diminishing their utility. For a reconciliation of Adjusted EBITDA and DCF to their most directly comparable measures calculated and presented in accordance with GAAP, see Results of Operations.

Management also utilizes Segment Adjusted EBITDA in evaluating the financial performance of our segments. The use of this measure allows investors to understand how management evaluates financial performance to make operating decisions and allocate resources.

COMPARABILITY OF OUR FINANCIAL RESULTS

Our acquisitions have impacted comparability of our financial results (see Note 3 of the Notes to Consolidated Financial Statements).

RESULTS OF OPERATIONS

The following tables and discussion are a summary of our results of operations for the three and nine months ended September 30, 2020 and 2019, including a reconciliation of Adjusted EBITDA and DCF from “Net income” and “Net cash provided by operating activities,” the most directly comparable GAAP financial measures. Prior period financial information has been retrospectively adjusted for common control transactions.

43

	Three Months Ended September 30,							Nine Months Ended September 30,
(In millions)	2020		2019		Variance			2020			2019		Variance
Total revenues and other income(1)	$	2,247	$	2,280	$	(33	)	$	5,320		$	6,725	$	(1,405	)
Costs and expenses:
Cost of revenues (excludes items below)	323		407		(84		)	1,006			1,099		(93		)
Purchased product costs	152		129		23			374			489		(115		)
Rental cost of sales	33		37		(4		)	101			103		(2		)
Rental cost of sales - related parties	32		45		(13		)	119			124		(5		)
Purchases - related parties	297		303		(6		)	853			894		(41		)
Depreciation and amortization	346		302		44			992			916		76
Impairment expense	—		—		—			2,165			—		2,165
General and administrative expenses	96		102		(6		)	289			293		(4		)
Restructuring expenses	36		—		36			36			—		36
Other taxes	33		29		4			94			84		10
Total costs and expenses	1,348		1,354		(6		)	6,029			4,002		2,027
Income/(loss) from operations	899		926		(27		)	(709		)	2,723		(3,432		)
Related party interest and other financial costs	—		5		(5		)	4			8		(4		)
Interest expense, net of amounts capitalized	207		212		(5		)	624			640		(16		)
Other financial costs	17		16		1			49			38		11
Income/(loss) before income taxes	675		693		(18		)	(1,386		)	2,037		(3,423		)
Provision for income taxes	1		4		(3		)	1			2		(1		)
Net income/(loss)	674		689		(15		)	(1,387		)	2,035		(3,422		)
Less: Net income attributable to noncontrolling interests	9		8		1			24			20		4
Less: Net income attributable to Predecessor	—		52		(52		)	—			401		(401		)
Net income/(loss) attributable to MPLX LP	665		629		36			(1,411		)	1,614		(3,025		)
Adjusted EBITDA attributable to MPLX LP (excluding Predecessor results)(2)	1,335		1,165		170			3,856			3,015		841
Adjusted EBITDA attributable to MPLX LP (including Predecessor results)(3)	N/A		1,273		N/A			N/A			3,785		N/A
DCF attributable to GP and LP unitholders (including Predecessor results)(3)	$	1,032	$	997	$	35		$	3,075		$	2,963	$	112

(1) The nine months ended September 30, 2020 includes impairment expense of approximately $1.3 billion related to three equity method investments.

(2) Non-GAAP measure. See reconciliation below to the most directly comparable GAAP measures. Excludes adjusted EBITDA and DCF adjustments attributable to Predecessor.

(3) Non-GAAP measure. See reconciliation below to the most directly comparable GAAP measures. Includes adjusted EBITDA and DCF adjustments attributable to Predecessor.

44

	Three Months Ended September 30,									Nine Months Ended September 30,
(In millions)	2020			2019			Variance			2020			2019			Variance
Reconciliation of Adjusted EBITDA attributable to MPLX LP and DCF attributable to GP and LP unitholders from Net income:
Net income/(loss)	$	674		$	689		$	(15	)	$	(1,387	)	$	2,035		$	(3,422	)
Provision for income taxes	1			4			(3		)	1			2			(1		)
Amortization of deferred financing costs	15			10			5			44			29			15
Gain on extinguishment of debt	(14		)	—			(14		)	(14		)	—			(14		)
Net interest and other financial costs	223			223			—			647			657			(10		)
Income from operations	899			926			(27		)	(709		)	2,723			(3,432		)
Depreciation and amortization	346			302			44			992			916			76
Non-cash equity-based compensation	4			5			(1		)	12			17			(5		)
Impairment expense	—			—			—			2,165			—			2,165
(Income)/loss from equity method investments	(83		)	(95		)	12			1,012			(255		)	1,267
Distributions/adjustments related to equity method investments	130			145			(15		)	369			399			(30		)
Unrealized derivative losses/(gains)(1)	10			(11		)	21			1			(7		)	8
Restructuring expenses	36			—			36			36			—			36
Acquisition costs	—			9			(9		)	—			14			(14		)
Other	3			1			2			5			1			4
Adjusted EBITDA	1,345			1,282			63			3,883			3,808			75
Adjusted EBITDA attributable to noncontrolling interests	(10		)	(9		)	(1		)	(27		)	(23		)	(4		)
Adjusted EBITDA attributable to Predecessor(2)	—			(108		)	108			—			(770		)	770
Adjusted EBITDA attributable to MPLX LP(3)	1,335			1,165			170			3,856			3,015			841
Deferred revenue impacts	29			36			(7		)	92			67			25
Net interest and other financial costs	(223		)	(223		)	—			(647		)	(657		)	10
Maintenance capital expenditures	(41		)	(75		)	34			(108		)	(174		)	66
Maintenance capital expenditures reimbursements	11			18			(7		)	31			34			(3		)
Equity method investment capital expenditures paid out	(5		)	(8		)	3			(16		)	(16		)	—
Restructuring expenses	(36		)	—			(36		)	(36		)	—			(36		)
Other	(3		)	6			(9		)	—			16			(16		)
Portion of DCF adjustments attributable to Predecessor(2)	—			27			(27		)	—			159			(159		)
DCF	1,067			946			121			3,172			2,444			728
Preferred unit distributions	(35		)	(30		)	(5		)	(97		)	(92		)	(5		)
DCF attributable to GP and LP unitholders	1,032			916			116			3,075			2,352			723
Adjusted EBITDA attributable to Predecessor(2)	—			108			(108		)	—			770			(770		)
Portion of DCF adjustments attributable to Predecessor(2)	—			(27		)	27			—			(159		)	159
DCF attributable to GP and LP unitholders (including Predecessor results)	$	1,032		$	997		$	35		$	3,075		$	2,963		$	112

(1) MPLX makes a distinction between realized and unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

45

(2) The adjusted EBITDA and DCF adjustments related to Predecessor are excluded from adjusted EBITDA attributable to MPLX LP and DCF attributable to GP and LP unitholders prior to the acquisition date.

(3) For the three months ended September 30, 2020, the L&S and G&P segments made up $893 million and $442 million of Adjusted EBITDA attributable to MPLX LP, respectively. For the three months ended September 30, 2019, the L&S and G&P segments made up $766 million and $399 million of Adjusted EBITDA attributable to MPLX LP, respectively. For the nine months ended September 30, 2020, the L&S and G&P segments made up $2,604 million and $1,252 million of Adjusted EBITDA attributable to MPLX LP, respectively. For the nine months ended September 30, 2019, the L&S and G&P segments made up $1,895 million and $1,120 million of Adjusted EBITDA attributable to MPLX LP, respectively.

	Nine Months Ended September 30,
(In millions)	2020			2019			Variance
Reconciliation of Adjusted EBITDA attributable to MPLX LP and DCF attributable to GP and LP unitholders from Net cash provided by operating activities:
Net cash provided by operating activities	$	3,336		$	2,990		$	346
Changes in working capital items	(154		)	134			(288		)
All other, net	(6		)	(23		)	17
Non-cash equity-based compensation	12			17			(5		)
Net (loss)/gain on disposal of assets	(1		)	3			(4		)
Gain on extinguishment of debt	(14		)	—			(14		)
Net interest and other financial costs	647			657			(10		)
Current income taxes	2			1			1
Asset retirement expenditures	—			1			(1		)
Unrealized derivative (gains)/losses(1)	1			(7		)	8
Restructuring Expenses	36			—			36
Acquisition costs	—			14			(14		)
Other adjustments to equity method investment distributions	19			20			(1		)
Other	5			1			4
Adjusted EBITDA	3,883			3,808			75
Adjusted EBITDA attributable to noncontrolling interests	(27		)	(23		)	(4		)
Adjusted EBITDA attributable to Predecessor(2)	—			(770		)	770
Adjusted EBITDA attributable to MPLX LP(3)	3,856			3,015			841
Deferred revenue impacts	92			67			25
Net interest and other financial costs	(647		)	(657		)	10
Maintenance capital expenditures	(108		)	(174		)	66
Maintenance capital expenditures reimbursements	31			34			(3		)
Equity method investment capital expenditures paid out	(16		)	(16		)	—
Restructuring Expenses	(36		)	—			(36		)
Other	—			16			(16		)
Portion of DCF adjustments attributable to Predecessor(2)	—			159			(159		)
DCF	3,172			2,444			728
Preferred unit distributions	(97		)	(92		)	(5		)
DCF attributable to GP and LP unitholders	3,075			2,352			723
Adjusted EBITDA attributable to Predecessor(2)	—			770			(770		)
Portion of DCF adjustments attributable to Predecessor(2)	—			(159		)	159
DCF attributable to GP and LP unitholders (including Predecessor results)	$	3,075		$	2,963		$	112

(1) MPLX makes a distinction between realized and unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

(2) The adjusted EBITDA and DCF adjustments related to Predecessor are excluded from adjusted EBITDA attributable to MPLX LP and DCF attributable to GP and LP unitholders prior to the acquisition date.

(3) For the nine months ended September 30, 2020, the L&S and G&P segments made up $2,604 million and $1,252 million of Adjusted EBITDA attributable to MPLX LP, respectively. For the nine months ended September 30, 2019, the L&S and G&P segments made up $1,895 million and $1,120 million of Adjusted EBITDA attributable to MPLX LP, respectively.

46

Three months ended September 30, 2020 compared to three months ended September 30, 2019

Total revenues and other income decreased $33 million in the third quarter of 2020 compared to the same period of 2019. This decrease was primarily due to lower G&P fees from lower volumes in the Southwest and lower prices in the Bakken and Rockies. This was partially offset by higher G&P fees from higher volumes in the Rockies and higher prices in the Southwest, Marcellus and Southern Appalachia. There were also decreases due to the Wholesale Exchange and lower L&S pipeline, terminal and storage volumes, including decreased throughputs on our Explorer and Bakken pipeline equity method investments. These decreases were partially offset by favorable L&S rate impacts, increased volume deficiency payments and favorable impacts from increased marine equipment.

Cost of Revenues decreased $84 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to lower operating costs due to lower throughput, lower project-related spend, the Wholesale Exchange as well as other miscellaneous decreases.

Purchased product costs increased $23 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to an increase of $20 million related to unrealized derivative gains in the prior year compared to unrealized derivative losses in the current year and higher prices of $21 million in the Southwest, partially offset by lower volumes of $21 million in the Southwest.

Rental cost of sales - related parties decreased $13 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to lower operating costs due to reduced throughput as well as decreased project spend from overall cost reduction initiatives.

Purchases - related parties decreased $6 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to aligning various expenses as a result of the ANDX acquisition as well as the Wholesale Exchange.

Depreciation and amortization expense increased $44 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to write-offs of assets under construction of $27 million related to idled MPC refineries as well as property, plant and equipment placed in service in the fourth quarter of 2019 and the first nine months of 2020.

General and administrative expenses decreased $6 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to decreased employee costs from MPC as well as acquisition costs incurred in 2019.

Restructuring expenses increased $36 million in the third quarter of 2020 compared to the same period of 2019. This was due to cost cutting measures employed by MPC during the third quarter of 2020 which resulted in restructuring charges, some of which were allocated to MPLX based on impacted employees.

Net interest expense and other financial costs decreased $9 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to decreased interest on variable rate debt as a result of lower interest rates during the quarter, as well as from the repayment of debt with higher interest rates and the issuance of new senior notes at lower interest rates.

Nine months ended September 30, 2020 compared to nine months ended September 30, 2019

Total revenues and other income decreased $1,405 million in the first nine months of 2020 compared to the same period of 2019. This was primarily driven by our ownership in MarkWest Utica EMG, L.L.C. (“MarkWest Utica EMG”), our indirect ownership in Ohio Gathering Company, L.L.C. through our investment in MarkWest Utica EMG and our ownership in Uintah Basin Field Services, L.L.C., as we recognized impairments related to these investments in the first quarter of 2020 in the amount of $1,264 million. Also contributing to the decrease was lower fees from lower volumes in the Southwest and Rockies, and lower prices in all of the G&P regions partially offset by increased volumes in the Marcellus. There were also decreases due to lower L&S pipeline, terminal and storage volumes, including decreased throughputs on our Explorer and Bakken pipeline equity method investments which were offset by favorable L&S rate impacts, increased volume deficiency payments and favorable impacts from increased marine equipment.

Cost of Revenues decreased $93 million in the first nine months of 2020 compared to the same period of 2019, primarily due to lower project-related costs, which include repairs, maintenance and operating costs in the L&S and G&P segments, as well as from the Wholesale Exchange.

47

Purchased product costs decreased $115 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to lower prices of $73 million in the Southwest and Southern Appalachia and $52 million from lower volumes in the Southwest. This was offset by an increase of $8 million due to unrealized derivative gains in the prior year compared to unrealized derivative losses in the current year.

Purchases - related parties decreased $41 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to aligning various expenses as a result of the ANDX acquisition, lower product purchases from MPC attributable to the Wholesale Exchange, lower project spend and decreased other miscellaneous costs from MPC.

Depreciation and amortization expense increased $76 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to property, plant and equipment placed in service in the fourth quarter of 2019 and the first nine months of 2020 as well as write-offs of assets under construction of $27 million related to idled MPC refineries.

Impairment expense increased $2,165 million in the first nine months of 2020 compared to the same period of 2019. During the first quarter of 2020 we recorded impairment expense for goodwill, intangible assets and property, plant and equipment of $1,814 million, $177 million and $174 million, respectively. The impairment of goodwill related to our Eastern G&P reporting unit while the intangible asset and property, plant and equipment impairments relate to certain assets in our Southwest region. The impairments were primarily driven by the slowing of drilling activity, which has reduced production growth forecasts from our producer customers.

Restructuring expenses increased $36 million in the first nine months of 2020 compared to the same period of 2019. This was due to cost cutting measures employed by MPC during the third quarter of 2020 which resulted in restructuring charges, some of which were allocated to MPLX based on impacted employees.

Other taxes increased $10 million in the first nine months of 2020 compared to the same period of 2019 primarily due to refunds and credits related to prior periods.

Net interest expense and other financial costs decreased $9 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to decreased interest on variable rate debt as a result of lower interest rates during the year, as well as from the repayment of debt with higher interest rates and the issuance of new senior notes at lower interest rates.

SEGMENT RESULTS

We classify our business in the following reportable segments: L&S and G&P. Segment Adjusted EBITDA represents Adjusted EBITDA attributable to the reportable segments. Amounts included in net income and excluded from Segment Adjusted EBITDA include: (i) depreciation and amortization; (ii) provision/(benefit) for income taxes; (iii) amortization of deferred financing costs; (iv) extinguishment of debt; (v) non-cash equity-based compensation; (vi) impairment expense; (vii) net interest and other financial costs; (viii) income/(loss) from equity method investments; (ix) distributions and adjustments related to equity method investments; (x) unrealized derivative gains/(losses); (xi) acquisition costs; (xii) noncontrolling interests; and (xiii) other adjustments as deemed necessary. These items are either: (i) believed to be non-recurring in nature; (ii) not believed to be allocable or controlled by the segment; or (iii) not tied to the operational performance of the segment.

The tables below present information about Segment Adjusted EBITDA for the reported segments for the three and nine months ended September 30, 2020 and 2019. Prior period financial information has been retrospectively adjusted for common control transactions.

48

L&S Segment

(1) Includes adjusted EBITDA attributable to Predecessor.

	Three Months Ended September 30,									Nine Months Ended September 30,
(In millions)	2020			2019			Variance			2020			2019			Variance
Service revenue	$	989		$	976		$	13		$	2,924		$	2,787		$	137
Rental income	249			304			(55		)	737			935			(198		)
Product related revenue	9			22			(13		)	49			57			(8		)
Income from equity method investments	36			60			(24		)	126			159			(33		)
Other income	51			17			34			154			45			109
Total segment revenues and other income	1,334			1,379			(45		)	3,990			3,983			7
Cost of revenues	173			262			(89		)	601			707			(106		)
Purchases - related parties	219			216			3			629			633			(4		)
Depreciation and amortization	164			113			51			440			373			67
General and administrative expenses	55			59			(4		)	159			152			7
Restructuring expenses	27			—			27			27			—			27
Other taxes	19			16			3			53			43			10
Segment income from operations	677			713			(36		)	2,081			2,075			6
Depreciation and amortization	164			113			51			440			373			67
Income from equity method investments	(36		)	(60		)	24			(126		)	(159		)	33
Distributions/adjustments related to equity method investments	55			70			(15		)	169			184			(15		)
Restructuring expenses	27			—			27			27			—			27
Acquisition costs	—			9			(9		)	—			14			(14		)
Non-cash equity-based compensation	3			3			—			8			10			(2		)
Other	3			1			2			5			1			4
Adjusted EBITDA attributable to Predecessor	—			(83		)	83			—			(603		)	603
Segment adjusted EBITDA(1)	893			766			127			2,604			1,895			709
Capital expenditures	118			272			(154		)	410			700			(290		)
Investments in unconsolidated affiliates	$	4		$	95		$	(91	)	$	132		$	163		$	(31	)

(1) See the Reconciliation of Adjusted EBITDA attributable to MPLX LP and DCF attributable to GP and LP unitholders from Net income table for the reconciliation to the most directly comparable GAAP measure.

Three months ended September 30, 2020 compared to three months ended September 30, 2019

Service revenue increased $13 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to a $21 million increase due to the reclassification of lease income between service revenue, rental income and other income based on modifications to lease contracts, a $10 million increase from additional marine equipment, an increase in

49

volume deficiency payments, favorable price impacts and other miscellaneous items. These increases were partially offset by reduced pipeline and storage volumes and an $8 million decrease due to the Wholesale Exchange.

Rental income decreased $55 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to a decrease of $55 million due to the reclassification of lease income between service revenue, rental income and other income based on modifications to lease contracts.

Product related revenue decreased $13 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to the Wholesale Exchange.

Income from equity method investments decreased $24 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to decreased throughput on the Explorer and Bakken pipelines during 2020.

Other income increased $34 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to the reclassification of lease income between service revenue, rental income and other income based on modifications to lease contracts.

Cost of revenues decreased $89 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to lower operating costs due to lower throughput, lower project-related spend, the Wholesale Exchange as well as other miscellaneous expense decreases.

Depreciation and amortization increased $51 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to write-offs of assets under construction of $27 million related to idled MPC refineries as well as property, plant and equipment placed in service in the fourth quarter of 2019 and the first nine months of 2020.

Restructuring expenses increased $27 million in the third quarter of 2020 compared to the same period of 2019. This was due to cost cutting measures employed by MPC during the third quarter of 2020 which resulted in restructuring charges, some of which were allocated to MPLX based on impacted employees.

Nine months ended September 30, 2020 compared to nine months ended September 30, 2019

Service revenue increased $137 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to a $104 million increase due to the reclassification of lease income between service revenue, rental income and other income based on modifications to lease contracts and a $35 million increase from additional marine equipment. There were also increases related to volume deficiency payments and favorable price impacts partially offset by unfavorable volume impacts and an $8 million decrease due to the Wholesale Exchange.

Rental income decreased $198 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to a decrease of $214 million due to the reclassification of lease income between service revenue, rental income and other income based on modifications to lease contracts. The decrease was partially offset by increased terminal storage revenue as well as other miscellaneous increases.

Product related revenue decreased $8 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to the Wholesale Exchange.

Income from equity method investments decreased $33 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to decreased throughput on the Explorer and Bakken pipelines during 2020.

Other income increased $109 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to the reclassification of lease income between service revenue, rental income and other income based on modifications to lease contracts.

Cost of revenues decreased $106 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to lower operating costs due to lower throughput, lower project-related spend, a decrease of $7 million from the Wholesale Exchange as well as other miscellaneous expense decreases.

Depreciation and amortization increased $67 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to property, plant and equipment placed in service in the fourth quarter of 2019 and the first nine months of 2020 as well as write-offs of assets under construction of $27 million related to idled MPC refineries.

50

General and administrative expenses increased $7 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to increased employee costs from MPC, partially offset by a decrease due to transaction costs incurred in 2019 related to the ANDX acquisition.

Restructuring expenses increased $27 million in the first nine months of 2020 compared to the same period of 2019. This was due to cost cutting measures employed by MPC during the third quarter of 2020 which resulted in restructuring charges, some of which were allocated to MPLX based on impacted employees.

Other taxes increased $10 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to refunds and credits related to prior periods.

51

G&P Segment

(1) Includes adjusted EBITDA attributable to Predecessor.

	Three Months Ended September 30,									Nine Months Ended September 30,
(In millions)	2020			2019			Variance			2020			2019			Variance
Service revenue	$	524		$	555		$	(31	)	$	1,549		$	1,627		$	(78	)
Rental income	94			88			6			271			260			11
Product related revenue	234			207			27			607			714			(107		)
Income/(loss) from equity method investments	47			35			12			(1,138		)	96			(1,234		)
Other income	14			16			(2		)	41			45			(4		)
Total segment revenues and other income	913			901			12			1,330			2,742			(1,412		)
Cost of revenues	215			227			(12		)	625			619			6
Purchased product costs	152			129			23			374			489			(115		)
Purchases - related parties	78			87			(9		)	224			261			(37		)
Depreciation and amortization	182			189			(7		)	552			543			9
Impairment expense	—			—			—			2,165			—			2,165
General and administrative expenses	41			43			(2		)	130			141			(11		)
Restructuring expenses	9			—			9			9			—			9
Other taxes	14			13			1			41			41			—
Segment income/(loss) from operations	222			213			9			(2,790		)	648			(3,438		)
Depreciation and amortization	182			189			(7		)	552			543			9
Impairment expense	—			—			—			2,165			—			2,165
(Income)/loss from equity method investments	(47		)	(35		)	(12		)	1,138			(96		)	1,234
Distributions/adjustments related to equity method investments	75			75			—			200			215			(15		)
Restructuring expenses	9			—			9			9			—			9
Unrealized derivative losses/(gains)(1)	10			(11		)	21			1			(7		)	8
Non-cash equity-based compensation	1			2			(1		)	4			7			(3		)
Adjusted EBITDA attributable to Predecessor	—			(25		)	25			—			(167		)	167
Adjusted EBITDA attributable to noncontrolling interests	(10		)	(9		)	(1		)	(27		)	(23		)	(4		)
Segment Adjusted EBITDA(2)	442			399			43			1,252			1,120			132
Capital expenditures	131			321			(190		)	375			953			(578		)
Investments in unconsolidated affiliates	$	18		$	76		$	(58	)	$	112		$	331		$	(219	)

(1) MPLX makes a distinction between realized and unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

52

(2) See the Reconciliation of Adjusted EBITDA attributable to MPLX LP and DCF attributable to GP and LP unitholders from Net income table for the reconciliation to the most directly comparable GAAP measure.

Three months ended September 30, 2020 compared to three months ended September 30, 2019

Service revenue decreased $31 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to lower fees from lower volumes in the Southwest and Rockies of $22 million, a decrease from lower prices in the Bakken and Rockies of $6 million as well as other miscellaneous decreases.

Rental income increased $6 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to higher fees related to gathering contracts in the Marcellus.

Product related revenue increased $27 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to higher prices in the Southwest, Marcellus and Southern Appalachia of approximately $23 million and higher volumes in the Rockies of $21 million, partially offset by and lower volumes in the Southwest of $15 million and lower prices in the Rockies and Bakken of $11 million, as well as other miscellaneous increases.

Income from equity method investments increased $12 million in the third quarter of 2020 compared to the same period of 2019. This increase was due to lower basis differential amortization related to MarkWest Utica EMG as a result of impairments recorded in the first quarter of 2020 and an increase from the Sherwood Midstream LLC joint venture due to additional plants coming online during the second half of 2019.

Cost of revenues decreased $12 million in the third quarter of 2020 compared to the same period of 2019. This decrease is attributable to lower repairs, maintenance and operating costs in the Southwest and Marcellus.

Purchased product costs increased $23 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to an increase of $20 million related to unrealized derivative gains in the prior year compared to unrealized derivative losses in the current year and higher prices of $21 million in the Southwest, partially offset by lower volumes of $21 million in the Southwest.

Purchases - related parties decreased $9 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to aligning various expenses as a result of the ANDX acquisition.

Depreciation and amortization decreased $7 million in the third quarter of 2020 compared to the same period of 2019. This was primarily due to the impairment of intangible assets and property, plant and equipment during the first quarter of 2020 which has resulted in less depreciation expense in the current period when compared to prior periods.

Restructuring expenses increased $9 million in the third quarter of 2020 compared to the same period of 2019. This was due to cost cutting measures employed by MPC during the third quarter of 2020 which resulted in restructuring charges, some of which were allocated to MPLX based on impacted employees.

Nine months ended September 30, 2020 compared to nine months ended September 30, 2019

Service revenue decreased $78 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to lower fees from lower volumes in the Rockies and Southwest of $40 million as well as other miscellaneous decreases.

Rental income increased $11 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to higher fees related to gathering contracts in the Marcellus.

Product related revenue decreased $107 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to lower prices in all of the G&P regions of approximately $154 million and lower volumes of $42 million in the Southwest. This was partially offset by $42 million of volume increases in the Marcellus, Rockies and the Javelina plant in the Southwest (this plant experienced downtime for maintenance in 2019), as well as other miscellaneous increases.

Income from equity method investments decreased $1,234 million in the first nine months of 2020 compared to the same period of 2019. The large decrease was driven by our ownership in MarkWest Utica EMG, our indirect ownership in Ohio Gathering Company, L.L.C. through our investment in MarkWest Utica EMG and our ownership in Uintah Basin Field Services, L.L.C., as we recognized impairments related to these investments in the first quarter of 2020 in the amount of $1,264

53

million. This was partially offset by an increase in the Sherwood Midstream LLC joint venture due to additional plants coming online during the second half of 2019.

Cost of revenues increased $6 million in the first nine months of 2020 compared to the same period of 2019. The majority of the increase is attributable to aligning various expenses as a result of the ANDX acquisition offset by lower repairs, maintenance and operating costs in the Southwest, Southern Appalachia and Marcellus.

Purchased product costs decreased $115 million in the first nine months of 2020 compared to the same period of 2019. This was primarily due to lower prices of $73 million in the Southwest and Southern Appalachia and $52 million from lower volumes in the Southwest. This was offset by an increase of $8 million due to unrealized derivative gains in the prior year compared to unrealized derivative losses in the current year.

Purchases - related parties decreased $37 million in the first nine months of 2020 compared to the same period of 2019. This decrease is primarily attributable to aligning various expenses as a result of the ANDX acquisition.

Depreciation and amortization increased $9 million in the first nine months of 2020 compared to the same period of 2019 primarily due to property, plant and equipment placed in service in the fourth quarter of 2019 and the first nine months of 2020 partially offset by the impairment of intangible assets and property, plant and equipment during the first quarter of 2020 which has resulted in less depreciation expense in the current period when compared to prior periods.

Impairment expense increased $2,165 million in the first nine months of 2020 compared to the same period of 2019. During the first quarter of 2020 we recorded impairment expense for goodwill, intangible assets and property, plant and equipment of $1,814 million, $177 million and $174 million, respectively. The impairment of goodwill related to our Eastern G&P reporting unit while the intangible asset and property, plant and equipment impairments relate to certain assets in our Southwest region. The impairments were primarily driven by the slowing of drilling activity, which has reduced production growth forecasts from our producer customers.

General and administrative expenses decreased $11 million in the first nine months of 2020 compared to the same period of 2019 due to lower employee related costs.

Restructuring expenses increased $9 million in the first nine months of 2020 compared to the same period of 2019. This was due to cost cutting measures employed by MPC during the third quarter of 2020 which resulted in restructuring charges, some of which were allocated to MPLX based on impacted employees.

SEASONALITY

The volume of crude oil and refined products transported and stored utilizing our assets is directly affected by the level of supply and demand for crude oil and refined products in the markets served directly or indirectly by our assets. Many effects of seasonality on the L&S segment’s revenues are mitigated through the use of our fee-based transportation and storage services agreements with MPC that include minimum volume commitments.

Our G&P segment can be affected by seasonal fluctuations in the demand for natural gas and NGLs and the related fluctuations in commodity prices caused by various factors including variations in weather patterns from year to year. We are able to manage the seasonality impacts through the execution of our marketing strategy and via our storage capabilities. Overall, our exposure to seasonality fluctuations is minimal.

54

OPERATING DATA⁽¹⁾

	Three Months Ended   September 30,				Nine Months Ended   September 30,
	2020		2019		2020		2019
L&S
Pipeline throughput (mbpd)
Crude oil pipelines	3,077		3,367		3,007		3,240
Product pipelines	1,613		1,859		1,701		1,875
Total pipelines	4,690		5,226		4,708		5,115
Average tariff rates ($ per barrel)(2)
Crude oil pipelines	$	0.96	$	0.97	$	0.96	$	0.94
Product pipelines	0.85		0.77		0.82		0.73
Total pipelines	$	0.93	$	0.90	$	0.91	$	0.86
Terminal throughput (mbpd)	2,701		3,292		2,696		3,267
Marine Assets (number in operation)(3)
Barges	301		264		301		264
Towboats	23		23		23		23

55

	Three Months Ended   September 30, 2020		Three Months Ended   September 30, 2019
	MPLX LP(4)	MPLX LP Operated(5)	MPLX LP(4)	MPLX LP Operated(5)
G&P
Gathering Throughput (MMcf/d)
Marcellus Operations	1,312	1,312	1,271	1,271
Utica Operations	—	1,816	—	2,381
Southwest Operations	1,413	1,479	1,653	1,653
Bakken Operations	130	130	149	149
Rockies Operations	481	659	627	827
Total gathering throughput	3,336	5,396	3,700	6,281
Natural Gas Processed (MMcf/d)
Marcellus Operations	4,222	5,706	4,264	5,300
Utica Operations	—	530	—	866
Southwest Operations	1,377	1,439	1,667	1,667
Southern Appalachian Operations	227	227	254	254
Bakken Operations	129	129	149	149
Rockies Operations	481	481	568	568
Total natural gas processed	6,436	8,512	6,902	8,804
C2 + NGLs Fractionated (mbpd)
Marcellus Operations(6)	477	477	433	433
Utica Operations(6)	—	30	—	49
Southwest Operations	21	21	19	19
Southern Appalachian Operations(7)	11	11	13	13
Bakken Operations	25	25	29	29
Rockies Operations	3	3	4	4
Total C2 + NGLs fractionated(8)	537	567	498	547

56

	Nine Months Ended   September 30, 2020		Nine Months Ended   September 30, 2019
	MPLX LP(4)	MPLX LP Operated(5)	MPLX LP(4)	MPLX LP Operated(5)
G&P
Gathering Throughput (MMcf/d)
Marcellus Operations	1,372	1,372	1,273	1,273
Utica Operations	—	1,840	—	2,186
Southwest Operations	1,445	1,491	1,618	1,618
Bakken Operations	137	137	149	149
Rockies Operations	523	706	639	835
Total gathering throughput	3,477	5,546	3,679	6,061
Natural Gas Processed (MMcf/d)
Marcellus Operations	4,177	5,582	4,211	5,218
Utica Operations	—	587	—	835
Southwest Operations	1,479	1,543	1,608	1,608
Southern Appalachian Operations	231	231	244	244
Bakken Operations	137	137	149	149
Rockies Operations	512	512	575	575
Total natural gas processed	6,536	8,592	6,787	8,629
C2 + NGLs Fractionated (mbpd)
Marcellus Operations(6)	466	466	431	431
Utica Operations(6)	—	32	—	45
Southwest Operations	16	16	13	13
Southern Appalachian Operations(7)	12	12	12	12
Bakken Operations	25	25	22	22
Rockies Operations	4	4	4	4
Total C2 + NGLs fractionated(8)	523	555	482	527

	Three Months Ended   September 30,				Nine Months Ended   September 30,
	2020		2019		2020		2019
Pricing Information
Natural Gas NYMEX HH ($ per MMBtu)	$	2.13	$	2.33	$	1.92	$	2.57
C2 + NGL Pricing ($ per gallon)(9)	$	0.45	$	0.44	$	0.40	$	0.53

(1) Operating data is inclusive of operating data for ANDX.

(2) Average tariff rates calculated using pipeline transportation revenues divided by pipeline throughput barrels.

(3) Represents total at end of period.

(4) This column represents operating data for entities that have been consolidated into the MPLX financial statements.

(5) This column represents operating data for entities that have been consolidated into the MPLX financial statements as well as operating data for MPLX-operated equity method investments.

(6) Hopedale is jointly owned by Ohio Fractionation and MarkWest Utica EMG. Ohio Fractionation is a subsidiary of MarkWest Liberty Midstream. MarkWest Liberty Midstream and MarkWest Utica EMG are entities that operate in the Marcellus and Utica regions, respectively. Marcellus Operations includes Ohio Fractionation’s portion utilized of the jointly owned Hopedale Fractionation Complex. Utica Operations includes MarkWest Utica EMG’s portion utilized of the jointly owned Hopedale Fractionation Complex. Additionally, Sherwood Midstream has the right to fractionation revenue and the obligation to pay expenses related to 40 mbpd of capacity in the Hopedale 3 and Hopedale 4 fractionators.

(7) Includes NGLs fractionated for the Marcellus Operations and Utica Operations.

(8) Purity ethane makes up approximately 193 mbpd and 182 mbpd of total MPLX Operated, fractionated products for the three months ended September 30, 2020 and 2019, respectively, and approximately 192 mbpd and 189 mbpd of total fractionated products for the nine months ended September 30, 2020 and 2019, respectively. Purity ethane makes up approximately 188 mbpd and 172 mbpd of total MPLX LP consolidated, fractionated products for the three months ended September 30, 2020 and 2019, respectively, and approximately 186 mbpd and 179 mbpd of total fractionated products for the nine months ended September 30, 2020 and 2019, respectively.

(9) C2 + NGL pricing based on Mont Belvieu prices assuming an NGL barrel of approximately 35 percent ethane, 35 percent propane, six percent Iso-Butane, 12 percent normal butane and 12 percent natural gasoline.

57

LIQUIDITY AND CAPITAL RESOURCES

Cash Flows

Our cash and cash equivalents were $28 million at September 30, 2020 and $15 million at December 31, 2019. The change in cash, cash equivalents and restricted cash was due to the factors discussed below. Net cash provided by (used in) operating activities, investing activities and financing activities were as follows:

	Nine Months Ended September 30,
(In millions)	2020			2019
Net cash provided by (used in):
Operating activities	$	3,336		$	2,990
Investing activities	(1,060		)	(2,189		)
Financing activities	(2,263		)	(845		)
Total	$	13		$	(44	)

Net cash provided by operating activities increased $346 million in the first nine months of 2020 compared to the first nine months of 2019, primarily due net income adjusted for non-cash items.

Net cash used in investing activities decreased $1,129 million in the first nine months of 2020 compared to the first nine months of 2019, primarily due to decreased spending related to the capital budget, a return of capital from our investments in Wink to Webster and Whistler and decreased contributions to equity method investments.

Financing activities were a $2,263 million use of cash in the first nine months of 2020 compared to an $845 million use of cash in the first nine months of 2019. The primary reason for the increase in the use of cash was due to lower net borrowings in the current year for third party obligations as well as net repayments on the MPC Loan Agreement in the current year compared to net borrowing in the prior year.

Debt and Liquidity Overview

On August 18, 2020, MPLX issued $3 billion aggregate principal amount of new senior notes consisting of $1.5 billion aggregate principal amount of 1.750 percent senior notes due March 2026 and $1.5 billion aggregate principal amount of 2.650 percent senior notes due August 2030. The net proceeds were used to repay the $1.0 billion of outstanding borrowings under the MPLX Term Loan Agreement, to repay the $1.0 billion floating rate notes due September 2021, to redeem all of the $450 million aggregate principal amount of 6.375 percent senior notes due May 2024, to reduce amounts outstanding under the MPLX Credit Agreement at the time and to redeem the $300 million aggregate principal amount of 6.250 percent senior notes due October 15, 2022 (these notes were redeemed on October 15, 2020).

58

Our outstanding borrowings at September 30, 2020 consist of the following:

(In millions)	September 30, 2020			December 31, 2019
MPLX LP:
Bank revolving credit facility	$	95		$	—
Term loan facility	—			1,000
Floating rate senior notes	1,000			2,000
Fixed rate senior notes	19,506			16,887
Consolidated subsidiaries:
MarkWest	23			23
ANDX	121			190
Financing lease obligations	12			19
Total	20,757			20,119
Unamortized debt issuance costs	(118		)	(106		)
Unamortized discount/premium	(290		)	(300		)
Amounts due within one year	(307		)	(9		)
Total long-term debt due after one year	$	20,042		$	19,704

Our intention is to maintain an investment grade credit profile. As of September 30, 2020, the credit ratings on our senior unsecured debt were at or above investment grade level as follows:

Rating Agency	Rating
Moody’s	Baa2 (negative outlook)
Standard & Poor’s	BBB (negative outlook)
Fitch	BBB (negative outlook)

The ratings reflect the respective views of the rating agencies. Although it is our intention to maintain a credit profile that supports an investment grade rating, there is no assurance that these ratings will continue for any given period of time. The ratings may be revised or withdrawn entirely by the rating agencies if, in their respective judgments, circumstances so warrant.

The MPLX Credit Agreement and Term Loan Agreement contain certain representations and warranties, affirmative and restrictive covenants and events of default that we consider to be usual and customary for an agreement of this type. The financial covenant requires MPLX to maintain a ratio of Consolidated Total Debt as of the end of each fiscal quarter to Consolidated EBITDA (both as defined in the MPLX Credit Agreement) for the prior four fiscal quarters of no greater than 5.0 to 1.0 (or 5.5 to 1.0 during the six-month period following certain acquisitions). Consolidated EBITDA is subject to adjustments for certain acquisitions completed and capital projects undertaken during the relevant period. Other covenants restrict us and/or certain of our subsidiaries from incurring debt, creating liens on assets and entering into transactions with affiliates. As of September 30, 2020, we were in compliance with the covenants, including the financial covenant with a ratio of Consolidated Total Debt to Consolidated EBITDA of 3.9 to 1.0.

The agreements governing our debt obligations do not contain credit rating triggers that would result in the acceleration of interest, principal or other payments solely in the event that our credit ratings are downgraded. However, any downgrades in the credit ratings of our senior unsecured debt ratings to below investment grade ratings could, among other things, increase the applicable interest rates and other fees payable under the MPLX Credit Agreement and may limit our ability to obtain future financing, including refinancing existing indebtedness.

59

Our liquidity totaled $4.9 billion at September 30, 2020 consisting of:

	September 30, 2020
(In millions)	Total Capacity		Outstanding Borrowings			Available Capacity
Bank revolving credit facility due 2024(1)	$	3,500	$	(95	)	$	3,405
MPC Loan Agreement	1,500		—			1,500
Total liquidity	$	5,000	$	(95	)	4,905
Cash and cash equivalents						28
Total liquidity						$	4,933

(1) Outstanding borrowings include less than $1 million in letters of credit outstanding under this facility.

We expect our ongoing sources of liquidity to include cash generated from operations and borrowings under the MPC Loan Agreement, the MPLX Credit Agreement and access to capital markets. We believe that cash generated from these sources will be sufficient to meet our short-term and long-term funding requirements, including working capital requirements, capital expenditure requirements, contractual obligations, and quarterly cash distributions. MPC manages our cash and cash equivalents on our behalf directly with third-party institutions as part of the treasury services that it provides to us under our omnibus agreement. From time to time, we may also consider utilizing other sources of liquidity, including the formation of joint ventures or sales of non-strategic assets.

Equity and Preferred Units Overview

On July 31, 2020, MPLX completed the exchange of Western Refining Wholesale, LLC to Western Refining Southwest, Inc. (“WRSW”), a wholly owned subsidiary of MPC, in exchange for the redemption of 18,582,088 MPLX common units held by WRSW, valued at $340 million.

Common units

The table below summarizes the changes in the number of units outstanding through September 30, 2020:

(In units)
Balance at December 31, 2019	1,058,355,471
Unit-based compensation awards	395,091
Units redeemed in Wholesale Exchange	(18,582,088	)
Balance at September 30, 2020	1,040,168,474

ATM

MPLX expects the net proceeds, if any, from sales under our ATM Program will be used for general business purposes including repayment or refinancing of debt and funding for acquisitions, working capital requirements and capital expenditures. During the nine months ended September 30, 2020, we issued no common units under our ATM program. As of September 30, 2020, $1.7 billion of common units remain available for issuance through the ATM Program.

Distributions

We intend to pay a minimum quarterly distribution to the holders of our common units of $0.2625 per unit, or $1.05 per unit on an annualized basis, to the extent we have sufficient cash from our operations after the establishment of cash reserves and the payment of costs and expenses, including reimbursements of expenses to our general partner. The amount of distributions paid under our policy and the decision to make any distributions is determined by our general partner, taking into consideration the terms of our partnership agreement. Such minimum distribution would equate to $273 million per quarter, or $1,092 million per year, based on the number of common units outstanding at September 30, 2020. On October 27, 2020, we announced the board of directors of our general partner had declared a distribution of $0.6875 per unit that will be paid on November 13, 2020 to unitholders of record on November 6, 2020. This is consistent with the second quarter 2020 distribution of $0.6875 per unit and an increase of 1.5 percent over the third quarter 2019 distribution. This rate will also be received by Series A preferred unitholders. Although our partnership agreement requires that we distribute all of our available cash each quarter, we do not otherwise have a legal obligation to distribute any particular amount per common unit.

60

Series B preferred unitholders are entitled to receive a fixed distribution of $68.75 per unit, per annum, payable semi-annually in arrears on February 15 and August 15, or the first business day thereafter, up to and including February 15, 2023. After February 15, 2023, the holders of Series B preferred units are entitled to receive cumulative, quarterly distributions payable in arrears on the 15th day of February, May, August and November of each year, or the first business day thereafter, based on a floating annual rate equal to the three-month LIBOR plus 4.652 percent, in each case assuming a distribution is declared by the Board of Directors. Accordingly, a cash distribution payment totaling $21 million was paid to Series B unitholders on August 17, 2020.

TexNew Mex units are entitled to receive quarterly distribution payments in an amount calculated using the distributable cash flow generated by a particular portion of the TexNew Mex pipeline system, in excess of a base amount and adjusted for previously agreed upon stipulations and contingencies. Distributions earned by TexNew Mex units during the fourth quarter of 2019 and during the six months ended June 30, 2020 were immaterial. Distributions of $5 million were earned by TexNew Mex units during the three months ended September 30, 2020.

The allocation of total quarterly cash distributions is as follows for the three and nine months ended September 30, 2020 and 2019. MPLX’s distributions are declared subsequent to quarter end; therefore, the following table represents total cash distributions applicable to the period in which the distributions were earned.

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions, except per unit data)	2020		2019		2020		2019
Distribution declared:
Limited partner units - public	$	270	$	266	$	810	$	718
Limited partner units - MPC	445		438		1,348		1,201
Total LP distribution declared	715		704		2,158		1,919
Series A preferred units	20		20		61		61
Series B preferred units	10		10		31		31
Total distribution declared	745		734		2,250		2,011
Cash distributions declared per limited partner common unit	$	0.6875	$	0.6775	$	2.0625	$	2.0025

Capital Expenditures

Our operations are capital intensive, requiring investments to expand, upgrade, enhance or maintain existing operations and to meet environmental and operational regulations. Our capital requirements consist of maintenance capital expenditures and growth capital expenditures. Examples of maintenance capital expenditures are those made to replace partially or fully depreciated assets, to maintain the existing operating capacity of our assets and to extend their useful lives, or other capital expenditures that are incurred in maintaining existing system volumes and related cash flows. In contrast, growth capital expenditures are those incurred for capital improvements that we expect will increase our operating capacity to increase volumes gathered, processed, transported or fractionated, decrease operating expenses within our facilities or increase operating income over the long term. Examples of growth capital expenditures include the acquisition of equipment or the construction costs associated with new well connections, and the development of additional pipeline, processing or storage capacity. In general, growth capital includes costs that are expected to generate additional or new cash flow for MPLX.

61

Our capital expenditures are shown in the table below:

	Nine Months Ended September 30,
(In millions)	2020			2019
Capital expenditures:
Maintenance	$	108		$	174
Maintenance reimbursements	(31		)	(34		)
Growth	677			1,479
Growth reimbursements	(2		)	(17		)
Total capital expenditures	752			1,602
Less: (Decrease)/increase in capital accruals	(197		)	(67		)
Asset retirement expenditures	—			1
Additions to property, plant and equipment, net of reimbursements(1)	949			1,668
Investments in unconsolidated affiliates	244			494
Acquisitions	—			(6		)
Total capital expenditures and acquisitions	1,193			2,156
Less: Maintenance capital expenditures (including reimbursements)	77			140
Acquisitions	—			(6		)
Total growth capital expenditures(2)	$	1,116		$	2,022

(1) This amount is represented in the Consolidated Statements of Cash Flows as Additions to property, plant and equipment after excluding growth and maintenance reimbursements. Reimbursements are shown as Contributions from MPC within the Financing activities section of the Consolidated Statements of Cash Flows.

(2) Amount excludes contributions from noncontrolling interests of zero and $94 million for the nine months ended September 30, 2020 and 2019, respectively, as reflected in the financing section of our statement of cash flows. Also excludes a $69 million return of capital from our Wink to Webster Pipeline joint venture in the first quarter of 2020, a $41 million return of capital from our Whistler Pipeline joint venture in the second quarter of 2020 and a $2 million return of capital from our Rio Pipeline joint venture in the third quarter of 2020. These are reflected in the investing section of our statement of cash flows for the nine months ended September 30, 2020.

Contractual Cash Obligations

As of September 30, 2020, our contractual cash obligations included long-term debt, finance and operating lease obligations, purchase obligations for services and to acquire property, plant and equipment, and other liabilities. During the nine months ended September 30, 2020, our third-party long-term debt obligations increased by $645 million while obligations on our MPC Loan Agreement decreased by $594 million. In connection with the Wholesale Exchange, future purchase obligations decreased by approximately $7.2 billion. These commitments included fuel costs associated with the wholesale product supply agreement with MPC. There were no other material changes to these obligations outside the ordinary course of business since December 31, 2019.

Off-Balance Sheet Arrangements

Off-balance sheet arrangements comprise those arrangements that may potentially impact our liquidity, capital resources and results of operations, even though such arrangements are not recorded as liabilities under U.S. GAAP. Our off-balance sheet arrangements are limited to indemnities and guarantees that are described in Note 21. Although these arrangements serve a variety of our business purposes, we are not dependent on them to maintain our liquidity and capital resources, and we are not aware of any circumstances that are reasonably likely to cause the off-balance sheet arrangements to have a material adverse effect on our liquidity and capital resources.

TRANSACTIONS WITH RELATED PARTIES

At September 30, 2020, MPC owned our non-economic general partnership interest and held approximately 62 percent of our outstanding common units.

Excluding revenues attributable to volumes shipped by MPC under joint tariffs with third parties that are treated as third-party revenues for accounting purposes, MPC accounted for 55 percent and 54 percent of our total revenues and other income for the third quarter of 2020 and 2019, respectively. We provide crude oil and product pipeline transportation services based on regulated tariff rates and storage services and inland marine transportation based on contracted rates.

62

Of our total costs and expenses, MPC accounted for 31 percent and 30 percent for the third quarter of 2020 and 2019, respectively. MPC performed certain services for us related to information technology, engineering, legal, accounting, treasury, human resources and other administrative services.

For further discussion of agreements and activity with MPC and related parties see Item 1. Business in our Annual Report on Form 10-K for the year ended December 31, 2019 and Note 5 of the Notes to Consolidated Financial Statements in this report.

ENVIRONMENTAL MATTERS AND COMPLIANCE COSTS

We have incurred and may continue to incur substantial capital, operating and maintenance, and remediation expenditures as a result of environmental laws and regulations. If these expenditures, as with all costs, are not ultimately reflected in the prices of our products and services, our operating results will be adversely affected. We believe that substantially all of our competitors must comply with similar environmental laws and regulations. However, the specific impact on each competitor may vary depending on a number of factors, including, but not limited to, the age and location of its operating facilities.

As of September 30, 2020, there have been no significant changes to our environmental matters and compliance costs since our Annual Report on Form 10-K for the year ended December 31, 2019.

CRITICAL ACCOUNTING ESTIMATES

As of September 30, 2020, there have been no significant changes to our critical accounting estimates since our Annual Report on Form 10-K for the year ended December 31, 2019, except as noted below.

Impairment Assessments of Long-Lived Assets, Intangible Assets, Goodwill and Equity Method Investments

Fair value calculated for the purpose of testing our long-lived assets, intangible assets, goodwill and equity method investments for impairment is estimated using the expected present value of future cash flows method and comparative market prices when appropriate. Significant judgment is involved in performing these fair value estimates since the results are based on forecasted assumptions. Significant assumptions include:

• Future Operating Performance. Our estimates of future operating performance are based on our analysis of various supply and demand factors, which include, among other things, industry-wide capacity, our planned utilization rate, end-user demand, capital expenditures and economic conditions as well as commodity prices. Such estimates are consistent with those used in our planning and capital investment reviews.

• Future volumes. Our estimates of future throughput of crude oil, natural gas, NGL and refined product volumes are based on internal forecasts and depend, in part, on assumptions about our customers’ drilling activity which is inherently subjective and contingent upon a number of variable factors (including future or expected pricing considerations), many of which are difficult to forecast. Management considers these volume forecasts and other factors when developing our forecasted cash flows.

• Discount rate commensurate with the risks involved. We apply a discount rate to our cash flows based on a variety of factors, including market and economic conditions, operational risk, regulatory risk and political risk. This discount rate is also compared to recent observable market transactions, if possible. A higher discount rate decreases the net present value of cash flows.

• Future capital requirements. These are based on authorized spending and internal forecasts.

Assumptions about the effects of COVID-19 and the macroeconomic environment are inherently subjective and contingent upon the duration of the pandemic and its impact on the macroeconomic environment, which is difficult to forecast. We base our fair value estimates on projected financial information which we believe to be reasonable. However, actual results may differ from these projections.

The need to test for impairment can be based on several indicators, including a significant reduction in prices of or demand for commodities, a poor outlook for profitability, a significant reduction in pipeline throughput volumes, a significant reduction in natural gas or NGL volumes processed, other changes to contracts or changes in the regulatory environment in which the asset or equity method investment is located.

63

Long-lived assets used in operations are assessed for impairment whenever changes in facts and circumstances indicate that the carrying value of the assets may not be recoverable based on the expected undiscounted future cash flow of an asset group. For purposes of impairment evaluation, long-lived assets must be grouped at the lowest level for which independent cash flows can be identified, which is at least at the segment level and in some cases for similar assets in the same geographic region where cash flows can be separately identified. If the sum of the undiscounted cash flows is less than the carrying value of an asset group, fair value is calculated, and the carrying value is written down if greater than the calculated fair value.

No impairment triggers were identified in the second or third quarters of 2020, however, during the first quarter of 2020, we identified an impairment trigger relating to asset groups within our Western G&P reporting unit as a result of significant impacts to forecasted cash flows for these asset groups resulting from the first quarter events and circumstances as discussed in Note 1 of the Notes to Consolidated Financial Statements. The cash flows associated with these assets were significantly impacted by volume declines reflecting decreased forecasted producer customer production as a result of lower commodity prices. After assessing each asset group within the Western G&P reporting unit for impairment, only the East Texas G&P asset group had a carrying value in excess of the fair value of its underlying assets. As a result, an impairment of $174 million of property, plant and equipment and $177 million of intangibles was recorded to “Impairment expense” on the Consolidated Statements of Income for the first quarter of 2020. Fair value of our PP&E was determined using a combination of an income and cost approach. The income approach utilized significant assumptions including management’s best estimates of the expected future cash flows and the estimated useful life of the asset group. The cost approach utilized assumptions for the current replacement costs of similar assets adjusted for estimated depreciation and deterioration of the existing equipment and economic obsolescence. The fair value of the intangibles was determined based on applying the multi-period excess earnings method, which is an income approach. Key assumptions included management’s best estimates of the expected future cash flows from existing customers, customer attrition rates and the discount rate. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of our impairment analysis will prove to be an accurate prediction of the future. The fair value measurements for the asset group fair values represent Level 3 measurements.

Additionally, in order to strengthen the competitive position of MPC’s assets and in response to continued decreased demand for their products, on August 3, 2020, MPC announced their decision to indefinitely idle the Gallup and Martinez refineries and plans to evaluate possibilities to strategically reposition the Martinez refinery, including the potential conversion of the refinery into a renewable diesel facility. While no impairment was identified as a result of this announcement for MPLX, we will continue to monitor for both impairment and potential changes in useful lives of assets related to these refineries.

Unlike long-lived assets, goodwill must be tested for impairment at least annually, and between annual tests if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. Goodwill is tested for impairment at the reporting unit level. A goodwill impairment loss is measured as the amount by which a reporting unit’s carrying value exceeds its fair value, without exceeding the recorded amount of goodwill.

The “Current Economic Environment” section describes the effects that the outbreak of COVID-19 and its development into a pandemic and the decline in commodity prices have had on our business. Due to these developments in the first quarter of 2020, we performed impairment assessments as discussed further below.

Prior to performing our goodwill impairment assessment as of March 31, 2020, MPLX had goodwill totaling approximately $9,536 million. As part of that assessment, MPLX recorded approximately $1,814 million of impairment expense in the first quarter of 2020 related to our Eastern G&P reporting unit within the G&P operating segment, which brought the amount of goodwill recorded within this reporting unit to zero. The impairment was primarily driven by updated guidance related to the slowing of drilling activity which has reduced production growth forecasts from our producer customers. For the remaining reporting units with goodwill, we determined that no significant adjustments to the carrying value of goodwill were necessary. The interim impairment assessment resulted in the fair value of the reporting units exceeding their carrying value by percentages ranging from approximately 8.5 percent to 270.0 percent. The reporting unit whose fair value exceeded its carrying amount by 8.5 percent, our Crude Gathering reporting unit, had goodwill totaling $1.1 billion at March 31, 2020. The operations which make up this reporting unit were acquired through the merger with ANDX. MPC accounted for its October 1, 2018 acquisition of Andeavor (through which it acquired control of ANDX), using the acquisition method of accounting, which required Andeavor assets and liabilities to be recorded by MPC at the acquisition date fair value. The Merger was closed on July 30, 2019 and has been treated as a common control transaction, which required the recognition of assets acquired and liabilities assumed using MPC’s historical carrying value. As such, given the short amount of time from when fair value was established to the date of the impairment test, the amount by which the fair value exceeded the carrying value within this reporting unit is not unexpected. An increase of one percentage point to the discount rate used to estimate the fair value of this reporting unit would not have resulted in goodwill impairment as of March 31, 2020. No other reporting units had had fair values exceeding carrying values of less than 20 percent. There were no events or changes in circumstances noted in the second

64

or third quarters of 2020 which would indicate it is more likely than not that the fair value of our reporting units with goodwill is less than their carrying amount.

Significant assumptions used to estimate the reporting units’ fair value included estimates of future cash flows and market information for comparable assets. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of the impairment tests will prove to be an accurate prediction of the future. See Note 12 of the Notes to Consolidated Financial Statements for additional information relating to goodwill.

Equity method investments are assessed for impairment whenever factors indicate an other than temporary loss in value. Factors providing evidence of such a loss include the fair value of an investment that is less than its carrying value, absence of an ability to recover the carrying value or the investee’s inability to generate income sufficient to justify our carrying value. During the first quarter of 2020, we assessed certain of our equity method investments for impairment as a result of a number of first quarter events and circumstances as discussed in Note 1 of the Notes to Consolidated Financial Statements. As a result, we recorded an other than temporary impairment for three joint ventures in which we have an interest. Impairment of these investments was $1,264 million, of which $1,251 million was related to MarkWest Utica EMG, L.L.C. and its investment in Ohio Gathering Company, L.L.C. The fair value of the investments was determined based upon applying the discounted cash flow method, which is an income approach. The discounted cash flow fair value estimate is based on known or knowable information at the interim measurement date. The significant assumptions that were used to develop the estimate of the fair value under the discounted cash flow method include management’s best estimates of the expected future cash flows, including prices and volumes, the weighted average cost of capital and the long-term growth rate. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As such, the fair value of these equity method investments represents a Level 3 measurement. As a result, there can be no assurance that the estimates and assumptions made for purposes of the impairment test will prove to be an accurate prediction of the future. The impairment was recorded through “Income from equity method investments.” The impairments were largely due to a reduction in forecasted volumes gathered and processed by the systems operated by the joint ventures. At September 30, 2020 we had $4,081 million of equity method investments recorded on the Consolidated Balance Sheets.

An estimate of the sensitivity to net income resulting from impairment calculations is not practicable, given the numerous assumptions (e.g., pricing, volumes and discount rates) that can materially affect our estimates. That is, unfavorable adjustments to some of the above listed assumptions may be offset by favorable adjustments in other assumptions. See Note 4 of the Notes to Consolidated Financial Statements for additional information relating to equity method investments.

ACCOUNTING STANDARDS NOT YET ADOPTED

While new financial accounting pronouncements will be effective for our financial statements in the future, there are no standards that have not yet been adopted that are expected to have a material impact on our financial statements. Accounting standards are discussed in Note 2 of the Notes to Consolidated Financial Statements.

65

Item 3. Quantitative and Qualitative Disclosures about Market Risk

We are exposed to market risks related to the volatility of commodity prices. We employ various strategies, including the potential use of commodity derivative instruments, to economically hedge the risks related to these price fluctuations. We are also exposed to market risks related to changes in interest rates. As of September 30, 2020, we did not have any open financial derivative instruments to economically hedge the risks related to interest rate fluctuations or commodity derivative instruments to economically hedge the risks related to the volatility of commodity prices; however, we continually monitor the market and our exposure and may enter into these arrangements in the future. While there is a risk related to changes in fair value of derivative instruments we may enter into; such risk is mitigated by price or rate changes related to the underlying commodity or financial transaction.

Commodity Price Risk

The information about commodity price risk for the three and nine months ended September 30, 2020 does not differ materially from that discussed in Item 7A. Quantitative and Qualitative Disclosures about Market Risk of our Annual Report on Form 10-K for the year ended December 31, 2019.

Outstanding Derivative Contracts

We have a natural gas purchase commitment embedded in a keep-whole processing agreement with a producer customer in the Southern Appalachian region expiring in December 2022. The customer has the unilateral option to extend the agreement for two consecutive five-year terms through December 2032. For accounting purposes, the natural gas purchase commitment and the term extending options have been aggregated into a single compound embedded derivative. The probability of the customer exercising its options is determined based on assumptions about the customer’s potential business strategy decision points that may exist at the time they would elect whether to renew the contract. The changes in fair value of this compound embedded derivative are based on the difference between the contractual and index pricing and the probability of the producer customer exercising its option to extend. The changes in fair value are recorded in earnings through “Purchased product costs” on the Consolidated Statements of Income. As of September 30, 2020 and December 31, 2019, the estimated fair value of this contract was a liability of $61 million and $60 million, respectively.

Open Derivative Positions and Sensitivity Analysis

As of September 30, 2020, we have no open commodity derivative contracts. We evaluate our portfolio of commodity derivative instruments on an ongoing basis and add or revise strategies in anticipation of changes in market conditions and in risk profiles.

Interest Rate Risk

Sensitivity analysis of the effect of a hypothetical 100-basis-point change in interest rates on long-term debt, excluding finance leases, is provided in the following table. Fair value of cash and cash equivalents, receivables, accounts payable and accrued interest approximate carrying value and are relatively insensitive to changes in interest rates due to the short-term maturity of the instruments. Accordingly, these instruments are excluded from the table.

(In millions)	Fair value as of September 30, 2020(1)		Change in Fair Value(2)		Change in Income Before Income Taxes for the Nine Months Ended September 30, 2020(3)
Long-term debt (including amounts due within one year)
Fixed-rate	$	20,626	$	1,831	N/A
Variable-rate	$	1,095	$	19	$	24

(1) Fair value was based on market prices, where available, or current borrowing rates for financings with similar terms and maturities.

(2) Assumes a 100-basis-point decrease in the weighted average yield-to-maturity at September 30, 2020.

(3) Assumes a 100-basis-point change in interest rates. The change to net income was based on the weighted average balance of all outstanding variable-rate debt for the nine months ended September 30, 2020.

At September 30, 2020, our portfolio of long-term debt consisted of fixed-rate instruments and variable-rate instruments including our term loan, floating rate senior note and our revolving credit facility. The fair value of our fixed-rate debt is relatively sensitive to interest rate fluctuations. Our sensitivity to interest rate declines and corresponding increases in the fair

66

value of our debt portfolio unfavorably affects our results of operations and cash flows only when we elect to repurchase or otherwise retire fixed-rate debt at prices above carrying value. Interest rate fluctuations generally do not impact the fair value of borrowings under our bank revolving credit or term loan facilities, but may affect our results of operations and cash flows. As of September 30, 2020, we did not have any financial derivative instruments to hedge the risks related to interest rate fluctuations; however, we continually monitor the market and our exposure and may enter into these agreements in the future.

Item 4. Controls and Procedures

Disclosure Controls and Procedures

An evaluation of the effectiveness of the design and operation of our disclosure controls and procedures (as defined in Rules 13a-15(e) and 15d-15(e) under the Securities Exchange Act of 1934, as amended) was carried out under the supervision and with the participation of management, including the chief executive officer and chief financial officer of our general partner. Based upon that evaluation, the chief executive officer and chief financial officer of our general partner concluded that the design and operation of these disclosure controls and procedures were effective as of September 30, 2020, the end of the period covered by this report.

Changes in Internal Control Over Financial Reporting

During the quarter ended September 30, 2020, there were no changes in our internal control over financial reporting that have materially affected, or are reasonably likely to materially affect, our internal control over financial reporting.

Part II – Other Information

Item 1. Legal Proceedings

We are the subject of, or a party to, a number of pending or threatened legal actions, contingencies and commitments involving a variety of matters, including laws and regulations relating to the environment. Except as described below, there have been no material changes to the legal proceedings previously disclosed in our Annual Report on Form 10-K, as updated in our Quarterly Reports on Form 10-Q for the quarters ended March 31, 2020 and June 30, 2020.

Litigation

Dakota Access Pipeline

In connection with our 9.19 percent indirect interest in a joint venture (“Dakota Access”) that owns and operates the Dakota Access Pipeline and Energy Transfer Crude Oil Pipeline projects, collectively referred to as the Bakken Pipeline system or DAPL, we have entered into a Contingent Equity Contribution Agreement whereby MPLX LP, along with the other joint venture owners in the Bakken Pipeline system, has agreed to make equity contributions to the joint venture upon certain events occurring to allow the entities that own and operate the Bakken Pipeline system to satisfy their senior note payment obligations. The senior notes were issued to repay amounts owed by the pipeline companies to fund the cost of construction of the Bakken Pipeline system.

As previously disclosed in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2020, in March 2020, the U.S. District Court for the District of Columbia (the “D.D.C.”) ordered the U.S. Army Corps of Engineers (“Army Corps”), which granted permits and an easement for the Bakken Pipeline system, to conduct a full environmental impact statement (“EIS”), and further requested briefing on whether an easement necessary for the operation of the Bakken Pipeline system should be vacated while the EIS is being prepared.

On July 6, 2020, the D.D.C. ordered vacatur of the easement to cross Lake Oahe during the pendency of an EIS and further ordered a shut down of the pipeline by August 5, 2020. The D.D.C. denied a motion to stay that order. Dakota Access and the Army Corps appealed the D.D.C.’s order to the U.S. Court of Appeals for the District of Columbia Circuit (the “Court of Appeals”). On July 14, 2020, the Court of Appeals issued an administrative stay while the court considered Dakota Access and the Army Corps’ emergency motion for stay pending appeal. On August 5, 2020, the Court of Appeals stayed the D.D.C.’s injunction that required the pipeline be shutdown and emptied of oil by August 5, 2020. The Court of Appeals denied a stay of the D.D.C.’s March order, which required the EIS, and further denied a stay of the D.D.C.’s July order, which vacated the easement. In the D.D.C., briefing is ongoing for a renewed request for an injunction, which is expected to be completed by the end of 2020. Oral argument on the merits of the case at the Court of Appeals occurred on November 4, 2020. The pipeline remains operational.

67

If the pipeline is temporarily shutdown pending completion of the EIS, MPLX would have to contribute its 9.19 percent pro rata share of funds required to pay interest accruing on the notes and any portion of the principal that matures while the pipeline is shutdown. MPLX also expects to contribute its 9.19 percent pro rata share of any costs to remediate any deficiencies to reinstate the permit and/or return the pipeline into operation. If the vacatur of the easement permit results in a permanent shutdown of the pipeline, MPLX would have to contribute its 9.19 percent pro rata share of the cost to redeem the bonds (including the 1% redemption premium required pursuant to the indenture governing the notes) and any accrued and unpaid interest.

Tesoro High Plains Pipeline

In early July, MPLX received a Notification of Trespass Determination from the Bureau of Indian Affairs (“BIA”) relating to a portion of the pipeline that crosses the Fort Berthold Reservation in North Dakota. The notification covered the rights of way for 23 tracts of land and demanded the immediate cessation of pipeline operations. The notification also assessed trespass damages of approximately $187 million. We appealed this determination, which triggered an automatic stay of the requested pipeline shutdown and payment. On October 29, the Assistant Secretary - Indian Affairs issued an order vacating the BIA’s trespass order and requiring the Regional Director for the BIA Great Plains Region to issue a new decision on or before December 15 covering all 34 tracts at issue.

We continue to work towards a settlement of this matter with holders of the property rights at issue. Management does not believe the ultimate resolution of this matter will have a material adverse effect on our consolidated financial position, results of operations, or cash flows.

Environmental Proceedings

Gathering and Processing

As previously disclosed in our quarterly report on Form 10-Q for the period ended June 30, 2020, we had previously reached a settlement in principle to resolve allegations relating to MPLX’s compliance at its Sarsen facility. In August 2020, we finalized a settlement with the EPA, which resolved this matter with a cash penalty of $150,025.

Item 1A. Risk Factors

There have been no material changes from the risk factors previously disclosed in our Annual Report on Form 10-K for the year ended December 31, 2019, as updated in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2020.

Item 2. Unregistered Sales of Equity Securities

The following table sets forth a summary of our purchases during the quarter ended September 30, 2020, of equity securities that are registered by MPLX pursuant to Section 12 of the Securities Exchange Act of 1934, as amended.

Period	Total Number of Units Purchased(a)	Average Price Paid per Unit(a)		Total Number of Units Purchased as Part of Publicly Announced Plans or Programs	Maximum Dollar Value of Units that May Yet Be Purchased Under the Plans or Programs
07/01/2020-07/31/2020	18,582,088	$	18.30	—	$	—
08/01/2020-08/31/2020	—	—		—	—
09/01/2020-09/30/2020	—	—		—	—
Total	18,582,088	18.30		—

(a) On July 31, 2020, MPLX entered into a Redemption Agreement (the “Redemption Agreement”) with WRSW, an Arizona Corporation and wholly owned subsidiary of MPC, pursuant to which MPLX agreed to transfer to WRSW all of the outstanding membership interests in WRW in exchange for the redemption of MPLX common units held by WRSW. Per the terms of the Redemption Agreement, MPLX redeemed 18,582,088 common units (the “Redeemed Units”) held by WRSW on July 31, 2020. The number of Redeemed Units was calculated by dividing WRW’s aggregate valuation of $340 million by the simple average of the volume weighted average NYSE prices of an MPLX common unit for the ten trading days ending at market close on July 27, 2020. MPLX canceled the Redeemed Units immediately following the Wholesale Exchange.

68

Item 6. Exhibits

		Incorporated by Reference From
Exhibit Number	Exhibit Description	Form	Exhibit	Filing Date	SEC File No.	Filed Herewith	Furnished Herewith
2.1*	Agreement and Plan of Merger, dated as of May 7, 2019, by and among Andeavor Logistics LP, Tesoro Logistics GP, LLC, MPLX LP, MPLX GP LLC and MPLX MAX LLC.	8-K	2.1	5/8/2019	001-35714
3.1	Certificate of Limited Partnership of MPLX LP	S-1	3.1	7/2/2012	333-182500
3.2	Amendment to the Certificate of Limited Partnership of MPLX LP	S-1/A	3.2	10/9/2012	333-182500
3.3	Fifth Amended and Restated Agreement of Limited Partnership of MPLX LP, dated as of July 30, 2019	8-K/A	3.1	8/14/2019	001-35714
4.1	Twenty-Third Supplemental Indenture, dated as of August 18, 2020, by and between MPLX LP and The Bank of New York Mellon Trust Company, N.A., as Trustee (including Form of Notes)	8-K	4.1	8/18/2020	001-35714
4.2	Twenty-Fourth Supplemental Indenture, dated as of August 18, 2020, by and between MPLX LP and The Bank of New York Mellon Trust Company, N.A., as Trustee (including Form of Notes)	8-K	4.2	8/18/2020	001-35714
10.1	Redemption Agreement, dated July 31, 2020, between MPLX LP and Western Refining Southwest, Inc.	10-Q	10.1	8/3/2020	001-35714
10.2	Sixth Amendment to Third Amended and Restated Terminal Services Agreement, dated March 1, 2017, between MPLX Terminals LLC and Marathon Petroleum Company LP					X
10.3	Amendment to Amended and Restated Transportation Services Agreement, executed as of September 10, 2020, by and between Marathon Petroleum Company LP and Hardin Street Marine LLC					X
10.4	Notice of and Consent to Assignment, effective October 1, 2020, by and among Marathon Petroleum Company LP, Marathon Petroleum Trading and Supply LLC and Hardin Street Transportation LLC					X
10.5	Notice of and Consent to Assignment, effective October 1, 2020, by and among Marathon Petroleum Company LP, Marathon Petroleum Trading and Supply LLC and Marathon Pipe Line LLC					X

69

		Incorporated by Reference From
Exhibit Number	Exhibit Description	Form	Exhibit	Filing Date	SEC File No.	Filed Herewith	Furnished Herewith
10.6	Notice of and Consent to Assignment, effective October 1, 2020, by and among Marathon Petroleum Company LP, Marathon Petroleum Trading and Supply LLC and Marathon Pipe Line LLC (Commingled)					X
10.7	Terminal Services Agreement, dated as of November 1, 2020, by and among the MPLX LP and Marathon Petroleum Corporation subsidiaries party thereto.	8-K	10.1	11/5/2020	001-35714
31.1	Certification of Chief Executive Officer pursuant to Rule 13a-14 and 15d-14 under the Securities Exchange Act of 1934					X
31.2	Certification of Chief Financial Officer pursuant to Rule 13a-14 and 15d-14 under the Securities Exchange Act of 1934					X
32.1	Certification of Chief Executive Officer pursuant to 18 U.S.C. Section 1350						X
32.2	Certification of Chief Financial Officer pursuant to 18 U.S.C. Section 1350						X
101.INS	XBRL Instance Document: The instance document does not appear in the interactive data file because its XBRL tags are embedded within the Inline XBRL document.
101.SCH	Inline XBRL Taxonomy Extension Schema Document.					X
101.CAL	Inline XBRL Taxonomy Extension Calculation Linkbase Document.					X
101.DEF	Inline XBRL Taxonomy Extension Definition Linkbase Document.					X
101.LAB	Inline XBRL Taxonomy Extension Label Linkbase Document.					X
101.PRE	Inline XBRL Taxonomy Extension Presentation Linkbase Document.					X
104	Cover Page Interactive Data File (formatted as Inline XBRL and contained in Exhibit 101).

* Schedules have been omitted pursuant to Item 601(b)(2) of Regulation S-K. MPLX LP hereby undertakes to furnish supplementally a copy of any omitted schedule upon request by the SEC.

70

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

	MPLX LP
	By:	MPLX GP LLC
		Its general partner
Date: November 6, 2020	By:	/s/ C. Kristopher Hagedorn
		C. Kristopher Hagedorn
		Vice President and Controller of MPLX GP LLC (the general partner of MPLX LP)

71

EX-10.2

Exhibit 10.2

Sixth Amendment to the Third Amended and Restated Terminal Services Agreement

This Sixth Amendment to the Third Amended and Restated Terminal Services Agreement ("Amendment") is dated September 1, 2020 by and between Marathon Petroleum Company LP, a Delaware limited partnership with an address of 539 South Main Street, Findlay, Ohio 45840 ("MPC"), and MPLX Terminals LLC, a Delaware limited liability company with an address of 200 East Hardin Street, Findlay, Ohio 45840 ("Terminal Owner"). Each of MPC and Terminal Owner shall be referred to herein individually as a "Party" or collectively as the "Parties."

WHEREAS, MPC and Terminal Owner are the Parties to that certain Third Amended and Restated Terminal Services Agreement, dated March 1, 2017, as amended on September 1, 2017, October 31, 2017, March 20, 2018, July 1, 2019 and December 13, 2019 (as amended, the “Agreement”); and

WHEREAS, MPC and Terminal Owner desire to amend the Agreement to update Schedule 3.1 and Schedule 5.1.

NOW, THEREFORE, in consideration of the forgoing and for other goods and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto agree that the foregoing recitals are incorporated herein by reference and as follows:

1. Except for the provisions of the Agreement specifically addressed in this Amendment, all other provisions of the Agreement shall remain in full force and effect.

2. Capitalized terms used but not defined in this Amendment shall have the meaning ascribed to such terms in the Agreement.

3. Schedule 3.1 of the Agreement is hereby deleted in its entirety and replaced with the attached Schedule 3.1.

4. Schedule 5.1 of the Agreement is hereby deleted in its entirety and replaced with the attached Schedule 5.1.

5. The effective date of this Amendment is September 1, 2020.

6. This Amendment constitutes the entire agreement among the Parties regarding this subject matter and may be amended or modified only by a written instrument signed by each of the Parties and supersedes any other prior agreements or understandings of the Parties relating to this subject matter and the Parties are not relying on any statement, representation, promise or inducement not expressly set forth herein.

7. This Amendment may be executed in one or more counterparts, and in both original form and one or more photocopies, each of which shall be deemed to be an original, but all of which together shall be deemed to constitute one and the same instrument.

IN WITNESS WHEREOF, the Parties hereto have caused this Amendment to be executed by their respective authorized representatives.

Marathon Petroleum Company LP		MPLX Terminals LLC
By: MPC Investment LLC, its General Partner
By:	/s/ P. A. Melton	By:	/s/ L. A. Wilkins
Name:	P. A. Melton	Name:	L. A. Wilkins
Title:	Vice President	Title:	President

Schedule 3.1 - Terminals and Minimum Quarterly Terminal Volume Commitments

Terminal Name	State	Region	Facility Type	Loading Hours	Gallons	RC Assets
						Lanes	Docks	Shell Capacity
Bay City	MI	MW	Pipeline	24/7	71,625,000	3		437,600
Bellevue	OH	MW	Pipeline	24/7	5,664,000	1		-
Belton	SC	SE	Pipeline	24/7	74,949,000	3		370,500
Birmingham	AL	SE	Pipeline	24/7	58,131,000	2		251,000
Brecksville	OH	MW	Pipeline	24/7	30,912,000	2		454,800
Canton	OH	MW	Refinery	24/7	159,134,000	6		48,500
Champaign	IL	MW	Pipeline	24/7	96,441,000	4		554,500
Charleston	WV	MW	Barge	24/7	36,360,000	2	1	165,700
Charlotte (East)	NC	SE	Pipeline	24/7	152,622,000	4		451,800
Charlotte (West)*	NC	SE	Pipeline	24/7	0	0		0
Cincinnati	OH	MW	Barge	24/7	54,021,000	2	1	438,700
Columbus (East & West)	OH	MW	Pipeline	24/7	197,481,000	4		749,700
Columbus (GA)	GA	SE	Pipeline	24/7	22,335,000	1		132,600
Covington	KY	MW	Barge	24/7	100,056,000	4	1	342,100
Detroit	MI	MW	Refinery	24/7	260,460,000	6		-
Doraville	GA	SE	Pipeline	24/7	52,626,000	2		217,100
Evansville	IN	MW	Barge	24/7	37,686,000	2	1	126,000
Flint	MI	MW	Pipeline	24/7	37,401,000	2		223,800
Ft. Lauderdale (Eisenhower)	FL	SE	Marine	24/7	112,170,000	4	1	559,900
Ft. Lauderdale (Spangler)	FL	SE	Marine	24/7	107,451,000	3	1	473,800
Garyville	LA	SE	Refinery	24/7	61,788,000	2		96,700
Greensboro (Guilford County)	NC	SE	Pipeline	24/7	78,170,000			414,700
Hammond	IN	MW	Pipeline	24/7	117,831,000	3		1,193,800
Heath	OH	MW	Pipeline	24/7	49,524,000	2		11,100
Huntington	IN	MW	Pipeline	24/7	35,220,000	2		187,000
Indianapolis	IN	MW	Pipeline	24/7	64,806,000	3		951,600
Jackson	MI	MW	Pipeline	24/7	21,828,000	2		263,700
Jacksonville	FL	SE	Marine	24/7	139,122,000	5	1	1,142,000
Kenova/Catlettsburg Docks	WV/KY	MW	Marine Docks	24/7	712,500,000		4	1,421,100
Knoxville	TN	SE	Pipeline	24/7	77,520,000	4		332,800
Lansing	MI	MW	Pipeline	24/7	59,682,000	3		174,700
Lexington	KY	MW	Pipeline	24/7	79,470,000	3		205,300
Lima	OH	MW	Pipeline	24/7	92,961,000	2		854,000
Louisville (Algonquin)	KY	MW	Barge	24/7	202,890,000	6	1	1,215,400

Louisville (Kramers)	KY	MW	Barge	24/7	115,401,000	4	1	558,300
Macon	GA	SE	Pipeline	24/7	79,296,000	3		294,200
Marietta	OH	MW	Barge	24/7	46,947,000	3	2	170,700
Midland	PA	MW	Barge	24/7	54,573,000	2	1	390,400
Montgomery	AL	SE	Pipeline	24/7	53,745,000	2		191,700
Mt. Prospect	IL	MW	Pipeline	24/7	53,487,000	3		333,200
Mt. Vernon	IN	MW	Barge	24/7	105,945,000	1	1	630,000
Muncie	IN	MW	Pipeline	24/7	42,747,000	2		243,800
Nashville (Bordeaux)	TN	SE	Pipeline	24/7	64,008,000	3	1	233,800
Nashville (Downtown)	TN	SE	Barge	24/7	44,289,000	2	1	250,800
Nashville (51st)	TN	SE	Pipeline	24/7	60,903,000	3		331,100
Niles	MI	MW	Pipeline	24/7	74,589,000	2		631,100
North Muskegon	MI	MW	Pipeline	24/7	113,175,000	5		440,200
Oregon	OH	MW	Pipeline	24/7	53,250,000	2		247,800
Paducah	KY	MW	Barge	24/7	30,654,000	2	1	208,300
Powder Springs	GA	SE	Pipeline	24/7	78,300,000	3		338,300
Robinson	IL	MW	Refinery	24/7	74,736,000	4		7,300
Rockford	IL	MW	Pipeline	24/7	48,678,000	3		326,000
Romulus	MI	MW	Pipeline	24/7	27,309,000	3		268,400
Selma (Buffalo)	NC	SE	Pipeline	24/7	123,750,000	3		549,000
Selma (West Oak)	NC	SE	Pipeline	24/7	99,537,000	4		355,000
Speedway	IN	MW	Pipeline	24/7	124,647,000	5		526,300
Steubenville	OH	MW	Pipeline	24/7	16,599,000	2		111,400
Tampa	FL	SE	Marine	24/7	334,203,000	10	1	1,231,700
Viney Branch	KY	MW	Refinery	24/7	114,474,000	6		57,100
Youngstown	OH	MW	Pipeline	24/7	28,176,000	2		131,000

* Terminal Owner agrees to clean and idle the Charlotte (West) terminal in 2021 at Terminal Owner’s expense, allowing MPC to remove all existing inventory from this terminal.

Terminal Complexes:

1.    Brecksville and Canton

2.Cincinnati and Covington

3.Evansville and Mt. Vernon

4.Ft. Lauderdale (Spangler) and Ft. Lauderdale (Eisenhower)

5.Indianapolis and Speedway

6.Louisville (Kramers) and Louisville (Algonquin)

7.Nashville (Bordeaux), Nashville (Downtown) and Nashville (51^st)

8.Selma (Buffalo) and Selma (West Oak)

Schedule 5.1 – Fees

Terminal Name	Base Throughput Fee*	Excess Throughput Fee*
Bay City	0.01634260	0.01347734
Bellevue	0.01326510	0.01326510
Belton	0.01443243	0.01273450
Birmingham	0.01496303	0.01284062
Brecksville	0.03310969	0.01326510
Canton	0.01326510	0.01326510
Champaign	0.01411407	0.01326510
Charleston	0.02292209	0.01368958
Charlotte (East & West)	0.01464467	0.01305286
Cincinnati	0.02950158	0.01368958
Columbus (East & West)	0.01241613	0.01241613
Columbus (GA)	0.02727305	0.01294674
Covington	0.01655484	0.01623648
Detroit	0.01326510	0.01326510
Doraville	0.01963235	0.01294674
Evansville	0.02079968	0.01390182
Flint	0.02292209	0.01337122
Ft. Lauderdale (Eisenhower)	0.01782829	0.01337122
Ft. Lauderdale (Spangler)	0.01432631	0.01432631
Garyville	0.01400795	0.01241613
Greensboro (Friendship) – Guilford County	0.01273450	0.01273450
Hammond	0.01920786	0.01252225

Heath	0.01220389	0.01220389
Huntington	0.01931399	0.01347734
Indianapolis	0.02642408	0.01347734
Jackson	0.03947694	0.01347734
Jacksonville	0.02897098	0.01390182
Kenova/Catlettsburg Docks	0.00689785	0.00689785
Knoxville	0.01305286	0.01262838
Lansing	0.01496303	0.01347734
Lexington	0.01337122	0.01305286
Lima	0.01825278	0.01220389
Louisville (Algonquin)	0.01857114	0.01273450
Louisville (Kramers)	0.01581200	0.01337122
Macon	0.01411407	0.01241613
Marietta	0.02154252	0.01368958
Midland	0.02493839	0.01199165
Montgomery	0.01644872	0.01284062
Mt. Prospect	0.02313433	0.01326510
Mt. Vernon	0.01687321	0.01167329
Muncie	0.01697933	0.01326510
Nashville (Bordeaux)	0.01475079	0.01284062
Nashville (Downtown)	0.02090580	0.01284062
Nashville (51st)	0.01750993	0.01284062
Niles	0.01899562	0.01315898
North Muskegon	0.01347734	0.01347734

Oregon	0.01708545	0.01326510
Paducah	0.02706080	0.01326510
Powder Springs	0.01549364	0.01294674
Robinson	0.01390182	0.01294674
Rockford	0.02111804	0.01305286
Romulus	0.03703616	0.01358346
Selma (Buffalo)	0.01294674	0.01294674
Selma (West Oak)	0.01294674	0.01294674
Speedway	0.01347734	0.01347734
Steubenville	0.03194236	0.01315898
Tampa	0.01453855	0.01347734
Viney Branch	0.01337122	0.01337122
Youngstown	0.02313433	0.01284062

*The table above reflects the fees effective as of January 1, 2019, as adjusted per Section 5.3.

Marine Docks

Kenova/Catlettsburg Docks includes Kenova Light Product, and Catlettsburg Crude, Heavy Oil, and Light Oil Docks

Kenova/Catlettsburg Docks - $2,653,020 per month (reflects monthly fee effective as January 1, 2019, as adjusted per Section 5.3).

Butane/Natural Gasoline/Pentane Blending

A) Facilities with Third Party Licensed Blending Technology

From and after July 1, 2019, at facilities at which Energy Transfer Partners LP (“ETP”) licenses blending technology to MPC, Terminal Owner's fee for performing the butane blending service shall be calculated as follows:

Ninety-five percent (95%) of the difference between the Daily Gasoline Value (defined below) and the Daily Butane Value (defined below). Expressed as a formula, the Butane Blending Service Fee is:

Butane Blending Service Fee = (DGV-DBV)* 95%

NOTE: Terminal Owner will reflect an Annual True-Up, as defined in Section 4 of this Schedule 5.1, as a separate line item on any monthly invoices submitted pursuant to this Agreement.

Definitions:

1. Daily Gasoline Value ("DGV"): Expressed as a formula:

DGV = (GB)*(GPV+TF)

GB: number of Gallons of butane blended on a given day at the terminal site.

GPV: daily gasoline posted value per Gallon.

TF: the transportation fee for moving spot purchased gasoline to the terminal for the gasoline grade in which the butane is blended.

a. GPV is calculated by location as follows:

Location	Market	GPV Price Calculation
Bay City	Chicago	Daily posted Argus 85 CBOB and 91 PREM spot prices
CharlotteEast	Gulf Coast	Daily posted Argus 85 CBOB and 91 PREM spot prices
Jacksonville	Gulf Coast	Daily posted Argus 85 CBOB and 91 PREM spot prices
Lansing	Chicago	Daily posted Argus 85 CBOB and 91 PREM spot prices
Nashville 51st	Gulf Coast	Daily posted Argus 85 CBOB and 91 PREM spot prices
Selma Buffalo	Gulf Coast	Daily posted Argus 85 CBOB and 91 PREM spot prices
Selma Oak	Gulf Coast	Daily posted Argus 85 CBOB and 91 PREM spot prices
Speedway	Chicago	Daily posted Argus 85 CBOB and 91 PREM spot prices
North Muskegon	Chicago	Daily posted Argus 85 CBOB and 91 PREM spot prices
Tampa	Gulf Coast	Daily posted Argus 85 CBOB and 91 PREM spot prices

b. TF is the avoided MPC cost of transporting one Gallon of gasoline (in the most cost effective method possible) to a terminal blending location, as verified and provided by MPC's Supply Distribution & Planning - Light Products Project Analysis organization.

2. Daily Butane Value ("DBV"): the daily agreed upon butane purchase price ("BPP") from ETP plus the total daily RIN value (“DRV”), multiplied by the daily total number of butane gallons blended ("GB"). Expressed as a formula:

DBV = (GB)*(BPP+DRV)

Bay City DBV = (GB)*(BPP+1/2DRV)

a. DRV will be determined by using the percentage of each type of RINs specified by the Renewable Fuel Standard Program updated annually or the most recent requirements and will be adjusted retroactively for any difference between the requirements at the time of the calculation and the requirements contained in a final rule establishing Renewable Volume Obligations for the year. OPIS daily posting for the respective RINs pricing will be used. In order to minimize the daily average RINs Cost, postings for prior years RINs will be used up to the maximum allowable percentage.

3. Profit Sharing Payment: For each calendar month, a Profit Sharing Payment (“PSP”) is paid by ETP to MPC for volumes blended at the Bay City terminal. The PSP is calculated as the volume of gallons blended (“GB”) at Bay City in such month multiplied by fifty percent multiplied by the following value: (A) the volume weighted daily average of the high and low assessments of Argus posted Chicago Cycle 1 gasoline price (85 CBOB) minus (B) the volume weighted daily average of the high and low assessments of the OPIS posted Mt. Belvieu TET normal butane price minus (C) the average supply cost.

Fee calculations pursuant to this Schedule 5.1 for butane blending services completed prior to July 1, 2019 shall not be affected by changes in the foregoing formulas.

4. Annual True-Up: This cost or revenue is intended to cover changes in the estimated vs actual transportation costs, half of shared maintenance expenses, and estimated vs actual butane purchase costs. The cost or revenue is calculated ETP. MPC will pass ninety-five (95%) of this to Terminal Owner.

B) Facilities Without Third Party Blending Technology

From and after September 1, 2018, at facilities at which no third party licensed blending technology is utilized, Terminal Owner’s fee for performing the butane or pentane blending service shall be calculated as follows:

Ninety-five percent (95%) of the difference between the Tank Daily Gasoline Value (defined below) and the Tank Daily Butane Value (defined below). Expressed as a formula, the Tank Butane Blending Service Fee is:

Tank Butane Blending Service Fee = (TDGV-TDBV)* 95%

Or

Ninety-five percent (95%) of the difference between the Tank Daily Gasoline Value (defined below) and the Tank Daily Pentane Value (defined below). Expressed as a formula, the Tank Pentane Blending Service Fee is:

Tank Pentane Blending Service Fee = (TDGV-TDPV)* 95%

Definitions:

1. Tank Daily Gasoline Value (“TDGV”): Expressed as a formula:

TDGV = (GB)*(GPV+TF)

GB: number of Gallons of butane blended on a given day at the terminal site.

GPV: daily gasoline posted value per gallon.

TF: the avoided transportation fee for moving spot purchased gasoline to the terminal for the gasoline grade in which the butane is blended.

a. GPV is calculated by location using the daily posted average Argus 85 CBOB or Argus PREM spot prices for the respective blend and market derived from Schedule 3.1.

2. Tank Daily Butane Value (“TDBV”): the daily agreed upon tank butane purchase price (“TBPP”) from supplier, plus the total daily RIN value (“DRV”), multiplied by the daily total number of butane Gallons blended (“GB”). Expressed as a formula:

TDBV = (GB)*(TBPP+DRV+TC)

a. TC is the trucking cost of transporting one Gallon of butane (in the most cost effective method possible) to a terminal blending location.

b. DRV will be determined by using the percentage of each type of RINs specified by the Renewable Fuel Standard Program updated annually to the most recent requirements and will be adjusted retroactively for any difference between the requirements at the time of the calculation and the requirements contained in a final rule establishing Renewable Volume Obligations for the year. OPIS daily posting for the respective RINs pricing will be used. In order to minimize the daily average RINs Cost, posting for prior years RINs will be used up to the maximum allowable percentage.

3. Tank Daily Pentane Value (“TDPV”): the daily agreed upon tank pentane purchase price (“TPPP”) from supplier, plus the total daily RIN value (“DRV”), multiplied by the daily total number of butane Gallons blended (“GB”). Expressed as a formula:

TDPV = (GB) * (TPPP + DRV + TC)

a. TC is the trucking costs of transporting one Gallon of pentane (in the most cost-effective manner) to a terminal blending location.

b. DRV will be determined by using the percentage of each type of RINs specified by the Renewable Fuel Standard Program updated annually or the most recent requirements and will be adjusted retroactively for any difference between the requirements at the time of the calculation and the requirements contained in a final rule establishing Renewable Volume Obligations for the year. OPIS daily posting for the respective RINs pricing will be used. In order to minimize the daily average RINs Cost, postings for the prior years RINs will be used up to the maximum allowable percentage.

4. In the event MPC requests a butane skid for temporary use at an MPC owned terminal(s), MPC shall pay an MPLX Tank Butane Blending Equipment Service Fee equal to 5% of the blending value. Expressed as a formula:

a. MPLX Tank Butane Blending Equipment Service Fee = (TDGV-TDBV)* 5%.

5. Annual Adjustment to Revenue: This cost or revenue is intended to cover changes in the estimated vs actual transportation costs. Annually during the month of April, MPC will issue an adjustment of revenue to MPLX. This adjustment will be the result in changes of actual vs previously estimated trucking costs associated with delivery of butane to the terminals for the previous April- March.

C) Kenova Blending

From and after October 31^st, 2019, at the Kenova, WV terminal the Terminal Owner’s fee for performing in-line or barge loading blending service shall be calculated as follows:

Ninety-five percent (95%) of the difference between the Marathon Daily Gasoline Value (defined below) and the Marathon Daily Butane Value (defined below) or the Marathon Daily Pentane Value (defined below). Expressed as a formula the Inline or Barge Blending Service Fee is:

Inline or Barge Blending Service Fee = (MDGV – MDBV) * 0.95

Or

Inline or Barge Blending Service Fee = (MDGV – MDPV) * 0.95

Definitions:

1. Marathon Daily Gasoline Value (“MDGV”): Expressed as a formula:

MDGV = (GB) * (GPV + KTF)

GB: Number of Gallons of butane/pentane blended on a given day at the terminal site.

GPV: daily gasoline posted value per Gallon

KTF: the additional transportation costs for moving the gasoline barrel produced through butane or pentane blending to the terminal of sale

a.GPV is calculated by the location using the daily posted averages of either Argus 85 CBOB or Argus Prem spot prices for the respective blend and market derived from Schedule 3.1

2. Marathon Daily Butane Value (“MDBV”): the daily agreed upon Marathon butane purchase price (“MBPP”) from supplier, plus the total daily RIN value (“DRV”), multiplied by the daily total number of butane Gallons blended (“GB”). Expressed as a formula:

MDBV = (GB) * (MBPP + DRV + TC)

a.TC is the trucking costs of transporting one Gallon of butane (in the most cost-effective manner) to a terminal blending location.

b.DRV will be determined by using the percentage of each type of RINs specified by the Renewable Fuel Standard Program updated annually or the most recent requirements and will be adjusted retroactively for any difference between the requirements at the time of the calculation and the requirements contained in a final rule establishing Renewable Volume Obligations for the year. OPIS daily posting for the respective RINs pricing will be used. In order to minimize the daily average RINs Cost, postings for the prior year’s RINs will be used up to the maximum allowable percentage.

3. Marathon Daily Pentane Value (“MDPV”): the daily agreed upon Marathon pentane purchase price (“MPPP”) from supplier, plus the total daily RIN value (“DRV”), multiplied by the daily total number of butane Gallons blended (“GB”). Expressed as a formula:

MDPV = (GB) * (MPPP + DRV + TC)

a.TC is the trucking costs of transporting one Gallon of pentane (in the most cost-effective manner) to a terminal blending location.

b.DRV will be determined by using the percentage of each type of RINs specified by the Renewable Fuel Standard Program updated annually or the most recent requirements and will be adjusted retroactively for any difference between the requirements at the time of the calculation and the requirements contained in a final rule establishing Renewable Volume Obligations for the year. OPIS daily posting for the respective RINs pricing will be used. In order to minimize the daily average RINs Cost, postings for the prior year’s RINs will be used up to the maximum allowable percentage.

D) Butane Blending intoNatural Gasoline at Facilities Without Third Party Licensed Blending Technology

a. Butane Blending into Natural Gasoline Project Service Fee: Prior to MPC requesting Terminal Owner to provide natural gasoline blending services at a Terminal that does not have butane blending into natural gasoline service capabilities, MPC will pay a one-time fee to Terminal Owner as reimbursement for the project capital costs to be incurred by a Terminal to enable such Terminal to provide butane blending into natural gasoline services, as well as an additional charge of 15% of such project capital costs. Prior to any Terminal incurring any project capital costs to be able to provide butane blending into natural gasoline services for MPC, the Parties will agree upon the Butane Blending into Natural Gasoline Project Services Fee for each Terminal providing such services.

b. Butane Blending into Natural Gasoline Services Fee: From and after August 20^th, 2019 at any Terminal with no third-party licensed blending technology utilized, Terminal Owner’s fee for performing butane blending into natural gasoline services shall be calculated as follows, expressed as a formula:

Natural Gas Blending Services Fee = $1.58 * the number of barrels of butane blended into natural gasoline

Ethanol Denaturing

$0.02 per Gallon of undenatured ethanol.

Unit Train Ethanol Receipts

Beginning on January 15, 2017 and continuing thereafter for so long as the Master Terminal Services Agreement by and between MPC and ECO Energy Distribution Services, LLC dated October 19, 2015 (the "ECO Agreement") has not terminated, been cancelled or otherwise expired pursuant to its terms or agreement of the parties thereto, each of the following shall apply:

1. MPC shall pay Terminal Owner $0.0135 per Gallon for Unit Train Ethanol Receipts; provided that the invoice for the month ending March 31 of each year (or upon termination of the ECO Agreement, prorated according to the time of such termination) shall include an additional fee of $0.0135 per Gallon of Unit Train Ethanol Receipts that are less than 111,360,000 Gallons for the 12-month period ending on March 31 of the same year (prorated for the time period between January 15, 2017 through March 31, 2017. The $0.0135 per Gallon fee set forth in this Section shall be adjusted at the time of and in an amount equal to any adjustment to the Throughput Fees (as defined in the ECO Agreement) pursuant to Section 6.l(b) of the ECO Agreement, as may be amended from time to time.

At the end of each Calendar Quarter, Terminal Owner shall credit MPC on the monthly invoice (or upon termination of the ECO Agreement, prorated according to the time of such termination) an amount equal to the sum of (a) the Base Throughput Fee for Selma (Buffalo) set forth in Schedule

5.1 (as adjusted) multiplied by the volume (in Gallons) of ethanol redelivered by truck from the Selma (Buffalo) Terminal to the Selma (West Oak) Terminals during such Calendar Quarter; and (b) the Base Throughput Fee for Selma (Buffalo) set forth in Schedule 5.1 (as adjusted) multiplied by the volume (in Gallons) of ethanol redelivered per MPC's direction from the Selma (Buffalo) Terminal into trucks for ECO during such Calendar Quarter.

Ethanol Excess Volume Value Capture

MPC will pay Terminal Owner fees as calculated herein for EV at Terminals where sales volume is made on a temperature corrected basis.

The value will be calculated via the following method: Multiply the volume by the price per the calculations described in the following two paragraphs.

The volume will be calculated via the following method: The American Petroleum Institute’s Manual of Petroleum Measurement Standards Chapter 11.3.4 “Miscellaneous Hydrocarbon Properties – Denatured Ethanol and Gasoline Blend Densities and Volume Correction Factors” (“Chapter 11.3.4”) provides data-based equations for Blends of Gasoline and Ethanol (“BGE”). Chapter 11.3.4 addresses excess volumes of gasohol (“EV”) created when gasoline and ethanol components are blended together. EV for truck rack throughput at Terminals equipped with Terminal Automation Software (TAS) will be calculated using the equation in Chapter 11.3.4 performed by TAS for any BGE. The TAS will be programmed to calculate EV by multiplying these BGE volumes by the correction factors as calculated using the equation from Chapter 11.3.4. This process of crediting Terminal Owner with the EV based on the technology Terminal Owner installed and maintains at its Terminals is known as “Ethanol Excess Volume Value Capture.”

The price will be calculated via the following method: Each Terminal is assigned to the CHICAGO (Midwest-designated as ‘MW’) or US GULF COAST (Southeast-designated as ‘SE’) region based on Schedule 3.1. EV credited to Terminal Owner will be valued using the non-weighted monthly average ARGUS 85 Assessment MID CBOB price for given market based on the location of the Terminal. The Midwest (‘MW’) will be using West Shore and Gulf Coast (‘SE’) will be using Pasadena posted pricing.

EX-10.3

Exhibit 10.3

FIRST AMENDMENT TO

THE AMENDED AND RESTATED

TRANSPORTATION SERVICES AGREEMENT

THIS FIRST AMENDMENT (“Amendment”) TO THE AMENDED AND RESTATED TRANSPORTATION SERVICES AGREEMENT is effective this June 1, 2020 by and between Marathon Petroleum Company LP, a Delaware limited partnership (“MPC”) and Hardin Street Marine LLC, a Delaware limited liability company (“HSM”). MPC and HSM may be referred to collectively as the “Parties” and each individually as a “Party” as necessary.

WHEREAS, MPC and HSM entered into the Amended and Restated Transportation Services Agreement on December 18, 2015 (“Agreement”), pursuant to which HSM agreed to provide certain marine transportation services to MPC; and

WHEREAS, MPC and HSM desire to amend the Equipment used by HSM to provide services to MPC, and to amend the rates being charged by HSM.

NOW THEREFORE, in consideration of the premises and mutual covenants set forth hereinafter, MPC and HSM agree as follows:

1. Exhibit Band Exhibit Cof the Agreement are deleted in their entirety and replaced with attached Exhibit Band Exhibit C.

2. Except as amended herein, all other terms and conditions of the Agreement shall remain in full force and effect. In the event of any conflict between the terms of the provision of this Amendment and the terms and provisions of the Agreement, the terms and provisions of this Amendment shall prevail. Any terms not defined in this Amendment shall have the same meaning as specified in the Agreement.

Signature Page Follows

Page 1 of 2

IN WITNESS WHEREOF, the Parties have duly executed this Amendment as of the date first written above.
MARATHON PETROLEUM COMPANY LP		HARDIN STREET MARINE LLC
By: MPC Investment LLC, its General Partner
By:	/s/ Andy Melton	By:	/s/ Todd Sandifer
Name:	Andy Melton	Name:	M. Todd Sandifer
Title:	Light Products Supply Ops & Trading VP	Title:	President

Page 2 of 2

Exhibit B

TRANSPORTATION SERVICES AND RATES

Equipment Category	Daily Rate
C1 Barge Clean Small	$1,324.90
C2 Barge Clean 10K	$1,269.69
C3 Barge Clean 30K	$2,373.77
H2 Barge Heater 10K	$1,324.90
H3 Barge Heater 30K	$2,732.60
B1 Boat 1000-1999 HP	$6,182.85
B2 Boat 2000-2999 HP	$6,707.29
B3 Boat 3000-3999 HP	$7,535.35
B4 Boat 4000-4999 HP	$8,970.66
B5 Boat 6000-6999 HP	$9,050.00

Transportation Service Monthly Rate

Fleeting Services Mooring services for barges	Subject to Section 4.3(a): •June 1, 2020 and after: 190 spaces* at a rate of $103.69 per day.
Tankerman Services U.S. Coast Guard licensed tankerman services for assurance of safe transfer of refined, chemical and liquefied gas cargoes.	Billed in aggregate monthly at hourly rates for each barge transfer, plus overtime rates for time in excess of eight hours, as listed on Exhibit G, plus mileage for travel by a tankerman in a personally owned vehicle at the Internal Revenue Service published standard mileage rate when traveling between work sites, or when called from home to report tankerman duties.
Cleaning and Repair Facility Charges Cleaning of Cargo tanks, voids, boat bilges and fuel/slop tanks. This includes labor, materials, and services. Other routine repair and maintenance services at MPC facilities, including, but not limited to: labor and materials for welding, electrical, mechanical, and hose and pipe testing.	Billed in aggregate monthly at market rates for the number of hours required for each service. Labor is billed hourly; materials and supplies shall be billed at cost plus thirty percent.

*It is agreed between HSM and MPC that the number of fleeting spaces may adjust throughout this term which, subject Section 4.3(a). may require a rate adjustment.

Exhibit C

EQUIPMENT*

Equipment Category	Quantity
C1 Barge Clean Small	27
C2 Barge Clean 10K	18
C3 Barge Clean 30K	212
H2 Barge Heater 10K	2
H3 Barge Heater 30K	46
B1 Boat 1000-1999 HP	2
B2 Boat 2000-2999 HP	5
B3 Boat 3000-3999 HP	5
B4 Boat 4000-4999 HP	10
B5 Boat 6000-6999 HP	1

Note: This list may be updated by Memorandum to File pursuant to Section 3.1(a).

EX-10.4

Exhibit 10.4

September 28, 2020

Via Email and US Mail

Hardin Street Transportation LLC

Attn: President

200 E. Hardin Street

Findlay, OH 45840

Effective October 1, 2020, Marathon Petroleum Company LP (“MPC”) will be transitioning its crude procurement and logistics functions to Marathon Petroleum Supply and Trading LLC (“MPST”). This letter documents the intent of MPC, MPST and Hardin Street Transportation LLC (“HST”) with respect to certain agreements identified on the attached Schedule A that pertain to both crude oil and condensate (“Crude Oil”) and other commodities (the “Commingled Agreements”).

To make the transition of crude procurement and logistics functions from MPC to MPST as seamless and efficient as possible, MPC will assign its rights and obligations under Commingled Agreements that pertain to Crude Oil to MPST effective October 1, 2020. MPC will retain all rights and obligations under the Commingled Agreements that pertain to commodities other than Crude Oil. MPC will also retain all obligations and liabilities under the Commingled Agreements that pertain to Crude Oil that accrue prior to October 1, 2020.

It is the intent of the parties to execute amended and restated versions of the Commingled Agreements to reflect the assignment of Crude Oil rights and obligations to MPST, and to reflect the retained rights and obligations for other commodities that remain with MPC (the “A&R Agreements”). If, prior to the execution of the A&R Agreements, HST determines it is necessary to invoice MPC for all activity under a Commingled Agreement, MPC agrees to pay for all amounts attributable to Crude Oil and then MPST will pay MPC.

Please indicate your consent by signing where indicated below. By its signature below, MPST confirms to you that it will assume all obligations and liabilities arising under the Agreements after that date, and that it will pay MPC all amounts attributable to Crude Oil as referenced above. Thank you for your cooperation.

Sincerely,

Marathon Petroleum Company LP
By MPC Investment LLC, its general partner
By:	/s/ Daniel T. Kimmel
Name:	Daniel T. Kimmel
Title:	Vice President
ACKNOWLEDGED AND AGREED:		CONSENT TO ASSIGNMENT GRANTED:
Marathon Petroleum Trading and Supply LLC		Hardin Street Transportation LLC
By:	/s/ Dana S. Holden	By:	/s/ Shawn M. Lyon
Name:	Dana S. Holden	Name:	Shawn M. Lyon
Title:	Vice President	Title:	President

SCHEDULE A

COMMINGLED AGREEMENTS
(Marathon Pipe Line LLC)

1 Transportation Services Agreement between Hardin Street Transportation LLC and Marathon Petroleum Company LP dated 1/1/2015, as amended, to provide transportation services for Products and Crude Petroleum

EX-10.5

Exhibit 10.5

September 28, 2020

Via Email and US Mail

Marathon Pipe Line LLC

Attn: President

539 S. Main Street

Findlay, OH 45840

Dear Sir:

Effective October 1, 2020, Marathon Petroleum Company LP (“MPC”) will be transitioning its crude procurement and logistics functions to Marathon Petroleum Supply and Trading LLC (“MPST”).

To make this transition as seamless and efficient as possible, MPC will assign its rights and obligations under the agreements identified on the attached Schedule A (the “Agreements”) to MPST. MPC will retain all obligations and liabilities under the Agreements that accrue prior to October 1, 2020. However, your consent to these assignments is necessary.

Therefore, please indicate your consent by signing where indicated below. The assignments will be effective October 1, 2020. By its signature below, MPST confirms to you that it will assume all obligations and liabilities arising under the Agreements after that date. Thank you for your cooperation.

Sincerely,

Marathon Petroleum Company LP
By MPC Investment LLC, its general partner
By:	/s/ Daniel T. Kimmel
Name:	Daniel T. Kimmel
Title:	Vice President
ACKNOWLEDGED AND AGREED:		CONSENT TO ASSIGNMENT GRANTED:
Marathon Petroleum Trading and Supply LLC		Marathon Pipe Line LLC
By:	/s/ Dana S. Holden	By:	/s/ Shawn M. Lyon
Name:	Dana S. Holden	Name:	Shawn M. Lyon
Title:	Vice President	Title:	President

SCHEDULE A
(Marathon Pipe Line LLC)

1	Letter Agreement dated 5/2/2000 between Marathon Pipe Line LLC (fka Marathon Ashland Pipe Line LLC) and Marathon Petroleum Company LP (fka Marathon Ashland Petroleum LLC) relating to crude oil deliveries on the Capline Pipeline System.
2	Storage Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 9/24/2012, as amended, relating to storage at the Patoka, Illinois Tank Farm.
3	Storage Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 9/24/2012, as amended, relating to storage at the Lebanon, Indiana Tank Farm.
4	Storage Services Agr. between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 11/10/2017 relating to storage at the Texas City, Texas Tank Farm.
5	Transportation Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 10/31/2012 relating to the Crude Petroleum Pipeline System utilizing the Wood River or Roxanna to Patoka Pipeline Segments.
6	Transportation Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 10/31/2012 relating to the Crude Petroleum Pipeline System utilizing the Catlettsburg or Robinson Crude Pipeline Segments.
7	Transportation Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 10/31/2012 relating to the Crude Petroleum Pipeline System with origination points located in Patoka and Martinsville, Illinois and having a destination in Lima, Ohio.
8	Transportation Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 10/31/2012 relating to the Crude Petroleum Pipeline System utilizing the Samaria and Romulus to Detroit Pipeline Segments.
9	Woodpat Expanded Pipeline Transportation Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 9/6/2017.
10	Ozark-Woodpat Expanded Pipeline Transportation Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP effective 2/19/2018.
11	Transportation Services Agreement (Texas City) between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 4/1/2019.
12	Crude Oil Inline Mixing Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 8/19/2019, as amended.

EX-10.6

Exhibit 10.6

September 28, 2020

Via Email and US Mail

Marathon Pipe Line LLC

Attn: President

539 S. Main Street

Findlay, OH 45840

Effective October 1, 2020, Marathon Petroleum Company LP (“MPC”) will be transitioning its crude procurement and logistics functions to Marathon Petroleum Supply and Trading LLC (“MPST”). This letter documents the intent of MPC, MPST and Marathon Pipe Line LLC (“MPL”) with respect to certain agreements identified on the attached Schedule A that pertain to both crude oil and condensate (“Crude Oil”) and other commodities (the “Commingled Agreements”).

To make the transition of crude procurement and logistics functions from MPC to MPST as seamless and efficient as possible, MPC will assign its rights and obligations under Commingled Agreements that pertain to Crude Oil to MPST effective October 1, 2020. MPC will retain all rights and obligations under the Commingled Agreements that pertain to commodities other than Crude Oil. MPC will also retain all obligations and liabilities under the Commingled Agreements that pertain to Crude Oil that accrue prior to October 1, 2020.

It is the intent of the parties to execute amended and restated versions of the Commingled Agreements to reflect the assignment of Crude Oil rights and obligations to MPST, and to reflect the retained rights and obligations for other commodities that remain with MPC (the “A&R Agreements”). If, prior to the execution of the A&R Agreements, MPL determines it is necessary to invoice MPC for all activity under a Commingled Agreement, MPC agrees to pay for all amounts attributable to Crude Oil and then MPST will pay MPC.

Please indicate your consent by signing where indicated below. By its signature below, MPST confirms to you that it will assume all obligations and liabilities arising under the Agreements after that date, and that it will pay MPC all amounts attributable to Crude Oil as referenced above. Thank you for your cooperation.

Sincerely,

Marathon Petroleum Company LP
By MPC Investment LLC, its general partner
By:	/s/ Daniel T. Kimmel
Name:	Daniel T. Kimmel
Title:	Vice President
ACKNOWLEDGED AND AGREED:		CONSENT TO ASSIGNMENT GRANTED:
Marathon Petroleum Trading and Supply LLC		Marathon Pipe Line LLC
By:	/s/ Dana S. Holden	By:	/s/ Shawn M. Lyon
Name:	Dana S. Holden	Name:	Shawn M. Lyon
Title:	Vice President	Title:	President

SCHEDULE A

COMMINGLED AGREEMENTS
(Marathon Pipe Line LLC)

1	Storage Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 9/24/2012 relating to storage of Crude Petroleum and Products at the Wood River, Illinois Tank Farm
2	Storage Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 9/24/2012, as amended, relating to storage at the Martinsville, Illinois Tank Farm
3	Transportation Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 10/31/2012, as amended, relating to Crude Petroleum and Condensate transportation services at the MPL barge facility located in Wood River, Illinois
4	Transportation Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 6/11/2015 relating to Product (Condensate)
5	Transportation Services Agreement between Marathon Pipe Line LLC and Marathon Petroleum Company LP dated 11/1/2017 relating to the transport of Commodities on the Pipeline System utilizing the Lima-Canton and St James -Garyville Crude Pipeline Segments.
6	Kankakee, Hammond, East Chicago Incentive Program Transportation Services Agreement dated 4/1/2020 between Marathon Pipe Line LLC and Marathon Petroleum Company LP.

EX-31.1

Exhibit 31.1

CERTIFICATION PURSUANT TO SECTION 302 OF

THE SARBANES-OXLEY ACT OF 2002

I, Michael J. Hennigan, certify that:

1. I have reviewed this report on Form 10-Q of MPLX LP;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant's other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant's auditors and the audit committee of the registrant's board of directors (or persons performing the equivalent functions):

(a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant's ability to record, process, summarize and report financial information; and

(b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant's internal control over financial reporting.

Date: November 6, 2020	/s/ Michael J. Hennigan
	Michael J. Hennigan
	Chairman of the Board, President and Chief Executive Officer of MPLX GP LLC (the general partner of MPLX LP)

EX-31.2

Exhibit 31.2

CERTIFICATION PURSUANT TO SECTION 302 OF

THE SARBANES-OXLEY ACT OF 2002

I, Pamela K.M. Beall, certify that:

1. I have reviewed this report on Form 10-Q of MPLX LP;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant's other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant's auditors and the audit committee of the registrant's board of directors (or persons performing the equivalent functions):

(a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant's ability to record, process, summarize and report financial information; and

(b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant's internal control over financial reporting.

Date: November 6, 2020	/s/ Pamela K.M. Beall
	Pamela K.M. Beall
	Director, Executive Vice President and Chief Financial Officer of MPLX GP LLC (the general partner of MPLX LP)

EX-32.1

Exhibit 32.1

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report of MPLX LP (the “Partnership”) on Form 10-Q for the quarterly period ended September 30, 2020 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Michael J. Hennigan, Chairman of the Board, President and Chief Executive Officer of MPLX GP LLC, the general partner of the Partnership, certify, pursuant to 18 U.S.C. §1350, as adopted pursuant to §906 of the Sarbanes-Oxley Act of 2002, that to the best of my knowledge:

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Partnership.

Date: November 6, 2020

/s/ Michael J. Hennigan

Michael J. Hennigan

Chairman of the Board, President and Chief Executive Officer of MPLX GP LLC (the general partner of MPLX LP)

EX-32.2

Exhibit 32.2

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report of MPLX LP (the “Partnership”) on Form 10-Q for the quarterly period ended September 30, 2020 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Pamela K.M. Beall, Director, Executive Vice President and Chief Financial Officer of MPLX GP LLC, the general partner of the Partnership, certify, pursuant to 18 U.S.C. §1350, as adopted pursuant to §906 of the Sarbanes-Oxley Act of 2002, that to the best of my knowledge:

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Partnership.

Date: November 6, 2020

/s/ Pamela K.M. Beall

Pamela K.M. Beall

Director, Executive Vice President and Chief Financial Officer of MPLX GP LLC (the general partner of MPLX LP)

XML

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 29, 2020
Document Information [Line Items]
Document Transition Report	false
Document Quarterly Report	true
Title of 12(b) Security	Common Units Representing Limited Partnership Interests
Entity Incorporation, State or Country Code	DE
Document Type	10-Q
Document Period End Date	Sep. 30, 2020
Amendment Flag	false
Entity File Number	001-35714
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Trading Symbol	MPLX
Entity Registrant Name	MPLX LP
Entity Central Index Key	0001552000
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		1,040,169,324
Entity Address, Address Line One	200 E. Hardin Street,
Entity Address, City or Town	Findlay,
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	45840
City Area Code	419
Local Phone Number	421-2414
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Security Exchange Name	NYSE
Entity Tax Identification Number	27-0005456

XML

Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019
Restructuring Charges		$ 36		$ 0		$ 36		$ 0
Revenues and other income:
Total revenues from contracts with customers		1,756		1,760		5,129		5,185
Rental income		102		99		296		291
Rental income - related parties		241		293		712		904
Income/(loss) from equity method investments(1)		83		95		(1,012)	[1],[2]	255
Other income		2		2		5		6
Other income - related parties		63		31		190		84
Revenues		2,247		2,280		5,320		6,725
Costs and expenses:
Rental cost of sales		33		37		101		103
Rental cost of sales - related parties		32		45		119		124
Purchases - related parties		297		303		853		894
Depreciation and amortization	[3]	346		302		992		916
Goodwill and Intangible Asset Impairment		0		0		2,165		0
General and administrative expenses		96		102		289		293
Other taxes		33		29		94		84
Costs and Expenses		1,348		1,354		6,029		4,002
Income/(loss) from operations		899		926		(709)		2,723
Related party interest and other financial costs		0		5		4		8
Interest expense (net of amounts capitalized of $8 million, $13 million, $31 million and $36 million, respectively)		207		212		624		640
Other financial costs		17		16		49		38
Income/(loss) before income taxes		675		693		(1,386)		2,037
Provision for income taxes		1		4		1		2
Net income		674		689		(1,387)		2,035
Less: Net income (loss) attributable to noncontrolling interest		9		8		24		20
Income (Loss) Attributable to Predecessor		0		52		0		401
Net income (loss) attributable to MPLX LP		665	[4]	629	[5]	(1,411)	[6]	1,614	[7]
Limited partners' interest in net income (loss) attributable to MPLX LP		635		602		(1,503)		1,546
Weighted average limited partner units outstanding:
Equity Method Investment, Other than Temporary Impairment						1,264
Limited Partners Common Units
Costs and expenses:
Net income (loss) attributable to MPLX LP		$ 635	[4]	$ 599	[5]	$ (1,503)	[6]	$ 1,522	[7]
Net income (loss) attributable to MPLX LP per limited partner unit:
Common - basic (in USD per unit)		$ 0.61		$ 0.61		$ (1.43)		$ 1.78
Common - diluted (in USD per unit)		$ 0.61		$ 0.61		$ (1.43)		$ 1.78
Weighted average limited partner units outstanding:
Common - basic (in shares)		1,046		974	[8]	1,054		855	[9]
Common - diluted (in shares)		1,047		975	[8]	1,054		855	[9]
Service [Member]
Revenues and other income:
Total revenues from contracts with customers		$ 604		$ 632		$ 1,779		$ 1,865
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		909		899		2,694		2,549
Service, Other [Member]
Revenues and other income:
Total revenues from contracts with customers		41		26		102		86
Product [Member]
Revenues and other income:
Total revenues from contracts with customers		165		171		454		576
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		37		32		100		109
Oil and Gas, Refining and Marketing [Member]
Costs and expenses:
Cost of Goods and Services Sold		323		407		1,006		1,099
Natural Gas, Midstream [Member]
Costs and expenses:
Cost of Goods and Services Sold		152		129		374		489
Series A Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Net income (loss) attributable to MPLX LP		20	[4]	20	[5]	61	[6]	61	[7]
Dividends, Preferred Stock		20		20		61		61
Series B Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Net income (loss) attributable to MPLX LP		10	[4]	10	[5]	31	[6]	31	[7]
Dividends, Preferred Stock		10		7		31		7
MPC
Revenues and other income:
Rental income - related parties		241		293		712		904
Other income - related parties		48		14		144		34
MPC | Service [Member]
Revenues and other income:
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		908		899		2,692		2,549
MPC | Product [Member]
Revenues and other income:
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[10]	$ 37		$ 32		$ 100		$ 109

[1] The 2020 period includes $1,264 million of impairment expense. See Note 4.

[2] The nine months ended September 30, 2020 includes $1,264 million of impairment expense. See Note 4.

[3] Depreciation and amortization attributable to L&S was $164 million and $440 million for the three and nine months ended September 30, 2020, respectively, and $113 million and $373 million for the three and nine months ended September 30, 2019, respectively. Depreciation and amortization attributable to G&P was $182 million and $552 million for the three and nine months ended September 30, 2020, respectively, and $189 million and $543 million for the three and nine months ended September 30, 2019, respectively.

[4] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[5] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[6] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[7] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[8] The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire three months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

[9] The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire nine months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

[10] There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For the three and nine months ended September 30, 2020, these sales totaled $107 million and $332 million, respectively. For the three and nine months ended September 30, 2019, these sales totaled $301 million and $819 million, respectively.

XML

Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Interest Costs Capitalized	$ 8	$ 13	$ 31	$ 36

XML

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net (loss)/income	$ 674	$ 689	$ (1,387)	$ 2,035
Other comprehensive income/(loss), net of tax:
Remeasurements of pension and other postretirement benefits related to equity method investments, net of tax	0	0	(1)	1
Comprehensive income/(loss)	674	689	(1,388)	2,036
Less comprehensive income attributable to:
Noncontrolling interests	9	8	24	20
Comprehensive Income (loss), Net of Tax, Attributable to Predecessor	0	52	0	401
Comprehensive income/(loss) attributable to MPLX LP	$ 665	$ 629	$ (1,412)	$ 1,615

XML

Consolidated Balance Sheets - USD ($) $ in Millions		Sep. 30, 2020	Dec. 31, 2019
Assets
Cash and cash equivalents		$ 28.0	$ 15.0
Receivables, net		477.0	593.0
Current Assets, Related Parties		591.0	656.0
Inventories		117.0	110.0
Other current assets		59.0	110.0
Total current assets		1,272.0	1,484.0
Equity method investments		4,081.0	5,275.0
Property, plant and equipment, net		21,615.0	22,145.0
Intangibles, net		991.0	1,270.0
Goodwill		7,657.0	9,536.0
Operating Lease, Right-of-Use Asset		323.0	365.0
Other Assets, Related Parties, Noncurrent		675.0	303.0
Other noncurrent assets		48.0	52.0
Total assets		36,662.0	40,430.0
Current liabilities:
Accounts payable		140.0	242.0
Accrued Liabilities, Current		169.0	187.0
Current Liabilities, Related Parties		364.0	1,008.0
Accrued Property Plant and Equipment Current		121.0	283.0
Accrued interest payable		207.0	210.0
Operating Lease, Liability, Current		65.0	66.0
Other current liabilities		158.0	127.0
Total current liabilities		1,531.0	2,132.0
Long-term deferred revenue		291.0	217.0
Liabilities, Related Parties, Noncurrent		281.0	290.0
Long-term debt		20,042.0	19,704.0
Deferred income taxes		12.0	12.0
Operating Lease, Liability, Noncurrent		258.0	302.0
Debt, Current		307.0	9.0
Deferred credits and other liabilities		184.0	192.0
Total liabilities		22,599.0	22,849.0
Commitments and contingencies (see Note 21)
Series A preferred units		968.0	968.0
Equity
Total MPLX LP partners’ capital		12,848.0	16,364.0
Accumulated other comprehensive loss	[1]	(16.0)	(15.0)
Noncontrolling interests		247.0	249.0
Total equity		13,095.0	16,613.0
Total liabilities, preferred units and equity		36,662.0	40,430.0
MPC
Assets
Other current assets		1.0	0.0
Operating Lease, Right-of-Use Asset		231.0	232.0
Current liabilities:
Operating Lease, Liability, Current		1.0	1.0
Operating Lease, Liability, Noncurrent		230.0	230.0
Series B Preferred Stock [Member]
Equity
Total MPLX LP partners’ capital		601.0	611.0
Limited Partners Common Units | Public
Equity
Total MPLX LP partners’ capital		9,436.0	10,800.0
Total equity		9,436.0	10,800.0
Limited Partners Common Units | MPC
Equity
Total MPLX LP partners’ capital		2,827.0	4,968.0
Total equity		2,827.0	4,968.0
LOOP and Explorer
Equity
Accumulated other comprehensive loss		(16.0)	(15.0)
Retained Earnings [Member] | MPC
Equity
Total equity		$ 0.0	$ 0.0

[1] These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on the Consolidated Statements of Income under the caption “Income/(loss) from equity method investments.”

XML

Consolidated Balance Sheets (Parenthetical) - shares shares in Millions	Sep. 30, 2020	Dec. 31, 2019
Limited Partners Common Units | Public
Units issued	393.0	392.0
Units Outstanding	393.0	392.0
Limited Partners Common Units | MPC
Units issued	647.0	666.0
Units Outstanding	647.0	666.0
Series B Preferred Stock [Member]
Units issued	0.6	0.6
Units Outstanding	0.6	0.6

XML

Consolidated Statements of Cash Flows - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2020		Sep. 30, 2019
Operating activities:
Net (loss)/income		$ (1,387)		$ 2,035
Adjustments to reconcile net income/(loss) to net cash provided by operating activities:
Amortization of deferred financing costs		44		29
Depreciation and amortization	[1]	992		916
Goodwill and Intangible Asset Impairment		2,165		0
Deferred income taxes		(1)		1
Retirement Expenditures		0		1
Loss/(gain) on disposal of assets		1		(3)
Loss/(income) from equity method investments(1)		1,012	[2],[3]	(255)
Distributions from unconsolidated affiliates		350		379
Changes in:
Current receivables		69		38
Inventories		(8)		(3)
Fair value of derivatives		1		(4)
Current accounts payable and accrued liabilities		(27)		(81)
Current assets/current liabilities - related parties		36		(148)
Increase (Decrease) in Other Operating Assets and Liabilities, Net		(2)		6
Deferred revenue		85		58
All other, net		6		23
Net cash provided by operating activities		3,336		2,990
Investing activities:
Additions to property, plant and equipment		(982)		(1,720)
Proceeds from Contributions from Affiliates		0		6
Disposal of assets		54		14
Investments in unconsolidated affiliates		(244)		(494)
Distributions from unconsolidated affiliates - return of capital		112		2
Payments for (Proceeds from) Other Investing Activities		0		(3)
Net cash used in investing activities		(1,060)		(2,189)
Financing activities:
Long-term debt - borrowings		5,990		8,674
Long-term debt - repayments		(5,372)		(7,423)
Related party debt - borrowings		4,870		7,708
Related party debt - repayments		(5,464)		(7,583)
Distributions to noncontrolling interests		(26)		(20)
Distributions to unitholders and general partner		(2,162)		(1,731)
Proceeds from Contributions from Parent		34		52
Contributions from noncontrolling interests		0		94
All other, net		(8)		(12)
Net cash used in financing activities		(2,263)		(845)
Net increase/(decrease) in cash, cash equivalents and restricted cash		13		(44)
Cash, cash equivalents and restricted cash at beginning of period		15		85
Cash, cash equivalents and restricted cash at end of period		28		41
Equity Method Investment, Other than Temporary Impairment		1,264
Payments of Debt Issuance Costs		23		20
Series A Preferred Stock [Member] | Preferred Partner [Member]
Financing activities:
Distributions to preferred unitholders		(61)		(61)
Series B Preferred Stock [Member] | Preferred Partner [Member]
Financing activities:
Distributions to preferred unitholders		(41)		(21)
Payments of Distributions on Preferred Units from Predecessor		$ 0		$ 502

[1] Depreciation and amortization attributable to L&S was $164 million and $440 million for the three and nine months ended September 30, 2020, respectively, and $113 million and $373 million for the three and nine months ended September 30, 2019, respectively. Depreciation and amortization attributable to G&P was $182 million and $552 million for the three and nine months ended September 30, 2020, respectively, and $189 million and $543 million for the three and nine months ended September 30, 2019, respectively.

[2] The 2020 period includes $1,264 million of impairment expense. See Note 4.

[3] The nine months ended September 30, 2020 includes $1,264 million of impairment expense. See Note 4.

XML

Consolidated Statements of Equity - USD ($)	Total	Preferred Class B [Member]	Public Limited Partners Common Units	MPC Limited Partners Common Units	Accumulated Other Comprehensive Loss	Noncontrolling Interests	Equity of Predecessor MPC
Beginning Balance at Dec. 31, 2018	$ 17,731,000,000	$ 0	$ 8,336,000,000	$ (1,612,000,000)	$ (16,000,000)	$ 156,000,000	$ 10,867,000,000
Distributions to:	(669,000,000)	0	176,000,000	307,000,000	0	(6,000,000)	(180,000,000)
Contributions from:	15,000,000	0	0	0	0	0	15,000,000
Unitholders and general partner	(776,000,000)	0	(188,000,000)	(327,000,000)	0	0	(261,000,000)
Noncontrolling interests	(6,000,000)	0	0	0	0	(6,000,000)	0
Contributions from noncontrolling interests	(94,000,000)	0	0	0	0	(94,000,000)	0
Other	3,000,000	0	2,000,000	0	1,000,000	0	0
Ending Balance at Mar. 31, 2019	17,730,000,000	0	8,326,000,000	(1,632,000,000)	(15,000,000)	250,000,000	10,801,000,000
Beginning Balance at Dec. 31, 2018	17,731,000,000	0	8,336,000,000	(1,612,000,000)	(16,000,000)	156,000,000	10,867,000,000
Contributions from noncontrolling interests	(94,000,000)
Ending Balance at Sep. 30, 2019	17,892,000,000	601,000,000	11,289,000,000	5,767,000,000	(15,000,000)	250,000,000	0
Beginning Balance at Mar. 31, 2019	17,730,000,000	0	8,326,000,000	(1,632,000,000)	(15,000,000)	250,000,000	10,801,000,000
Distributions to:	(636,000,000)	0	168,000,000	293,000,000	0	(6,000,000)	(169,000,000)
Contributions from:	13,000,000	0	0	0	0	0	13,000,000
Unitholders and general partner	(764,000,000)	0	(191,000,000)	(332,000,000)	0	0	241,000,000
Noncontrolling interests	(6,000,000)	0	0	0	0	(6,000,000)	0
Other	2,000,000	0	2,000,000	0	0	0	0
Ending Balance at Jun. 30, 2019	17,611,000,000	0	8,305,000,000	(1,671,000,000)	(15,000,000)	250,000,000	10,742,000,000
Distributions to:	(669,000,000)	(7,000,000)	(222,000,000)	(380,000,000)	0	(8,000,000)	(52,000,000)
Stockholders' Equity, Change in Reporting Entity	0	615,000,000	2,983,000,000	7,199,000,000	0	0	(10,797,000,000)
Contributions from:	295,000,000	0	0	292,000,000	0	0	3,000,000
Unitholders and general partner	(715,000,000)	(21,000,000)	(262,000,000)	(432,000,000)	0	0	0
Noncontrolling interests	(8,000,000)	0	0	0	0	(8,000,000)	0
Partners' Capital Account, Exchanges and Conversions	36,000,000	0	36,000,000	0	0	0	0
Other	4,000,000	0	5,000,000	(1,000,000)	0	0	0
Ending Balance at Sep. 30, 2019	17,892,000,000	601,000,000	11,289,000,000	5,767,000,000	(15,000,000)	250,000,000	0
Beginning Balance at Dec. 31, 2019	16,613,000,000	611,000,000	10,800,000,000	4,968,000,000	(15,000,000)	249,000,000	0
Distributions to:	2,736,000,000	(11,000,000)	(1,022,000,000)	(1,733,000,000)	0	(8,000,000)	0
Contributions from:	225,000,000	0	0	225,000,000	0	0	0
Unitholders and general partner	(738,000,000)	(21,000,000)	(271,000,000)	(446,000,000)	0	0	0
Noncontrolling interests	(9,000,000)	0	0	0	0	(9,000,000)	0
Other	1,000,000	0	2,000,000	0	(1,000,000)	0	0
Ending Balance at Mar. 31, 2020	13,356,000,000	601,000,000	9,509,000,000	3,014,000,000	(16,000,000)	248,000,000	0
Beginning Balance at Dec. 31, 2019	16,613,000,000	611,000,000	10,800,000,000	4,968,000,000	(15,000,000)	249,000,000	0
Distributions to:		(31,000,000)
Unitholders and general partner		(41,000,000)
Contributions from noncontrolling interests	0
Ending Balance at Sep. 30, 2020	13,095,000,000	601,000,000	9,436,000,000	2,827,000,000	(16,000,000)	247,000,000	0
Beginning Balance at Mar. 31, 2020	13,356,000,000	601,000,000	9,509,000,000	3,014,000,000	(16,000,000)	248,000,000	0
Distributions to:	(634,000,000)	(10,000,000)	229,000,000	388,000,000	0	(7,000,000)	0
Contributions from:	6,000,000	0	0	6,000,000	0	0	0
Unitholders and general partner	(728,000,000)	0	(270,000,000)	(458,000,000)	0	0	0
Noncontrolling interests	(8,000,000)	0	0	0	0	(8,000,000)	0
Other	2,000,000	0	1,000,000	1,000,000	0	0	0
Ending Balance at Jun. 30, 2020	13,262,000,000	611,000,000	9,469,000,000	2,951,000,000	(16,000,000)	247,000,000	0
Distributions to:	(654,000,000)	(10,000,000)	236,000,000	399,000,000	0	(9,000,000)	0
Stockholders' Equity, Change in Reporting Entity	(90,000,000)	0	0	(90,000,000)	0	0	0
Contributions from:	13,000,000	0	0	13,000,000	0	0	0
Unitholders and general partner	(736,000,000)	(20,000,000)	(271,000,000)	(445,000,000)	0	0	0
Noncontrolling interests	(9,000,000)	0	0	0	0	(9,000,000)	0
Other	1,000,000	0	2,000,000	(1,000,000)	0	0	0
Ending Balance at Sep. 30, 2020	$ 13,095,000,000	$ 601,000,000	$ 9,436,000,000	$ 2,827,000,000	$ (16,000,000)	$ 247,000,000	$ 0

XML

Description of the Business and Basis of Presentation

9 Months Ended

Sep. 30, 2020

Accounting Policies [Abstract]

Business Description and Basis of Presentation [Text Block]

Description of the Business and Basis of Presentation

Description of the Business – MPLX LP is a diversified, large-cap master limited partnership formed by Marathon Petroleum Corporation that owns and operates midstream energy infrastructure and logistics assets, and provides fuels distribution services. References in this report to “MPLX LP,” “MPLX,” “the Partnership,” “we,” “ours,” “us,” or like terms refer to MPLX LP and its subsidiaries. References to “MPC” refer collectively to Marathon Petroleum Corporation as our sponsor and its subsidiaries, other than the Partnership. We are engaged in the transportation, storage and distribution of crude oil, asphalt and refined petroleum products; the gathering, processing and transportation of natural gas; and the gathering, transportation, fractionation, storage and marketing of NGLs. MPLX’s principal executive office is located in Findlay, Ohio.

MPLX’s business consists of two segments based on the nature of services it offers: Logistics and Storage (“L&S”), which relates primarily to crude oil, asphalt and refined petroleum products; and Gathering and Processing (“G&P”), which relates primarily to natural gas and NGLs. See Note 9 for additional information regarding the operations and results of these segments.

On July 30, 2019, MPLX completed its acquisition by merger (the “Merger”) of Andeavor Logistics LP (“ANDX”). At the effective time of the Merger, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units. ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. See Note 3 for additional information regarding the Merger.

On July 31, 2020, MPLX completed the exchange of Western Refining Wholesale, LLC (WRW”) to Western Refining Southwest, Inc. (“WRSW”), a wholly owned subsidiary of MPC, in exchange for the redemption of 18,582,088 MPLX common units held by WRSW (the “Wholesale Exchange”). See Note 3 for additional information regarding the Wholesale Exchange. These financial statements include the results of WRSW through July 31, 2020.

Impairments – The outbreak of COVID-19 and its development into a pandemic in March 2020 resulted in significant economic disruption globally. Actions taken by various governmental authorities, individuals and companies around the world to prevent the spread of COVID-19 through social distancing have restricted travel, many business operations, public gatherings and the overall level of individual movement and in-person interaction across the globe. Although there have been some signs of economic improvement, these events significantly reduced global economic activity and resulted in a decline in the demand for the midstream services we provide beginning with the first quarter of 2020. Macroeconomic conditions and global geopolitical events have also resulted in significant price volatility related to those aforementioned products.

The overall deterioration in the economy and the environment in which MPLX and its customers operate, as well as a sustained decrease in unit price, were considered triggering events resulting in impairments of the carrying value of certain assets during the first quarter of 2020. We recognized impairments related to goodwill, certain equity method investments and certain long-lived assets (including intangibles), within our G&P segment. Many of our producer customers refined and updated production forecasts in response to the current environment, which impacted their current and expected future demand for our services, including the future utilization of our assets. Additionally, certain of our contracts have commodity price exposure, including NGL prices, which have experienced increased volatility as noted above. The table below provides information related to the impairments recognized during the first quarter of 2020 as well as the corresponding footnote where additional information can be found. No additional events or circumstances arose during the second or third quarters of 2020 which would indicate the need for any additional impairment beyond those recognized during the first quarter.

(In millions)	Impairment		Footnote Reference
Goodwill	$	1,814	12
Equity method investments	1,264		4
Intangibles, net	177		12
Property, plant and equipment, net	174		11
Total impairments	$	3,429

Basis of Presentation – The accompanying interim consolidated financial statements are unaudited; however, in the opinion of MPLX’s management, these statements reflect all adjustments necessary for a fair statement of the results for the periods reported. All such adjustments are of a normal, recurring nature unless otherwise disclosed. These interim consolidated financial statements, including the notes, have been prepared in accordance with the rules and regulations of the SEC

applicable to interim period financial statements and do not include all of the information and disclosures required by GAAP for complete financial statements. Certain amounts in prior years have been reclassified to conform to current year presentation.

These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the year ended December 31, 2019. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results to be expected for the full year.

In relation to the Merger described above and in Note 3, ANDX’s assets, liabilities and results of operations prior to the Merger are collectively included in what we refer to as the “Predecessor” from October 1, 2018, which was the date that MPC acquired Andeavor. MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s relationship with ANDX prior to the Merger. As an entity under common control with MPC, MPLX recorded the assets acquired and liabilities assumed on its consolidated balance sheets at MPC’s historical carrying value. For the acquiring entity, transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the accompanying financial statements and related notes of MPLX LP have been retrospectively adjusted to include the historical results of ANDX beginning October 1, 2018.

MPLX’s consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly owned consolidated subsidiaries, the interests owned by third parties have been recorded as “Noncontrolling interests” on the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. MPLX’s investments in which MPLX exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. MPLX’s investments in VIEs in which MPLX exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method.

In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule. Distributions, although earned, are not accrued until declared. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in Note 6.

XML

Accounting Standards Accounting Standards

9 Months Ended

Sep. 30, 2020

Accounting Changes and Error Corrections [Abstract]

Accounting Standards Update and Change in Accounting Principle [Text Block]

Recently Adopted

ASU 2016-13, Credit Losses - Measurement of Credit Losses on Financial Instruments

Effective January 1, 2020, we adopted ASU 2016-13 using the modified retrospective transition method. This ASU requires entities to consider a broader range of information to estimate expected credit losses, which may result in earlier recognition of losses. The ASU requires the company to utilize an expected loss methodology in place of the incurred loss methodology for financial instruments, including trade receivables, and off-balance sheet credit exposures. Adoption of the standard did not have a material impact on our financial statements.

We are exposed to credit losses, primarily as a result of the midstream services that we provide. We assess each customer’s ability to pay through our credit review process, which considers various factors such as external credit ratings; a review of financial statements to determine liquidity, leverage, trends and business specific risks; market information; pay history and our business strategy. We monitor our ongoing credit exposure through timely review of customer payment activity. At September 30, 2020, we reported $477 million of accounts receivable, net of allowances of $4 million.

We also adopted the following ASUs during the first nine months of 2020, which did not have a material impact to our financial statements or financial statement disclosures:

ASU		Effective Date
2018-13	Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement	January 1, 2020
2020-04	Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting	April 1, 2020

XML

Acquisitions

9 Months Ended

Sep. 30, 2020

Business Combinations [Abstract]

Acquisitions

Acquisitions and Dispositions

Wholesale Exchange

On July 31, 2020, MPLX entered into a Redemption Agreement (the “Redemption Agreement”) with WRSW, an Arizona corporation and wholly owned subsidiary of MPC, pursuant to which MPLX agreed to transfer to WRSW all of the outstanding membership interests in WRW in exchange for the redemption of MPLX common units held by WRSW. The transaction effects the transfer to MPC of the Western wholesale distribution business that MPLX acquired as a result of its acquisition of ANDX as described below. Per the terms of the Redemption Agreement, MPLX redeemed 18,582,088 common units (the “Redeemed Units”) held by WRSW on July 31, 2020. The number of Redeemed Units was calculated by dividing WRW’s aggregate valuation of $340 million by the simple average of the volume weighted average NYSE prices of an MPLX common unit for the ten trading days ending at market close on July 27, 2020. MPLX canceled the Redeemed Units immediately following the Wholesale Exchange. The carrying value of the net assets of WRW transferred to MPC was approximately $90 million as of July 31, 2020, resulting in $250 million being recorded to “Common Unit-holder MPC” within the Consolidated Statements of Equity, in addition to the fair value of the redeemed units. Included within the $90 million carrying value of the WRW net assets was approximately $65 million of goodwill.

Acquisition of Andeavor Logistics LP

On May 7, 2019, ANDX, Tesoro Logistics GP, LLC (then the general partner of ANDX (“TLGP”)), MPLX, MPLX GP LLC (the general partner of MPLX (“MPLX GP”)), and MPLX MAX LLC, a wholly owned subsidiary of MPLX (“Merger Sub”), entered into an Agreement and Plan of Merger (the “Merger Agreement”) that provided for, among other things, the merger of Merger Sub with and into ANDX. On July 30, 2019, the Merger was completed, and ANDX survived the Merger as a wholly owned subsidiary of MPLX. At the effective time of the Merger, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units. ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. See Note 7 for information on units issued in connection with the Merger.

Additionally, as a result of the Merger, each ANDX TexNew Mex Unit issued and outstanding immediately prior to the effective time of the Merger was converted into a right for WRSW, a wholly owned subsidiary of MPC, as the holder of all such units, to receive a unit representing a substantially equivalent limited partner interest in MPLX (the “MPLX TexNew Mex Units”). By virtue of the conversion, all ANDX TexNew Mex Units were cancelled and ceased to exist as of the effective time of the Merger. The MPLX TexNew Mex Units are a new class of units in MPLX substantially equivalent to the ANDX TexNew Mex Units, including substantially equivalent rights, powers, duties and obligations that the ANDX TexNew Mex Units had immediately prior to the closing of the Merger.

As a result of the Merger, the ANDX Special Limited Partner Interest outstanding immediately prior to the effective time of the Merger was converted into a right for WRSW, as the holder of all such interest, to receive a substantially equivalent special limited partner interest in MPLX (the “MPLX Special Limited Partner Interest”). By virtue of the conversion, the ANDX Special Limited Partner Interest was cancelled and ceased to exist as of the effective time of the Merger. For information on ANDX’s preferred units, please see Note 7.

The assets of ANDX consist of a network of owned and operated crude oil, refined product and natural gas pipelines; crude oil and water gathering systems; refining logistics assets; terminals with crude oil and refined products storage capacity; rail facilities; marine terminals including storage; bulk petroleum distribution facilities; a trucking fleet; and natural gas processing and fractionation systems and complexes. The assets are located in the western and inland regions of the United States and complement MPLX’s existing business and assets.

MPC accounted for its October 1, 2018 acquisition of Andeavor (through which it acquired control of ANDX), using the acquisition method of accounting, which required Andeavor assets and liabilities to be recorded by MPC at the acquisition date fair value. The Merger was closed on July 30, 2019, and the results of ANDX have been incorporated into the results of MPLX as of October 1, 2018, which is the date that common control was established. As a result of MPC’s relationship with both MPLX and ANDX, the Merger has been treated as a common control transaction, which requires the recasting of MPLX’s historical results and the recognition of assets acquired and liabilities assumed using MPC’s historical carrying value. We recognized $14 million in acquisition costs during the first nine months of 2019 related to the Merger, which are reflected in general and administrative expenses. For the three and nine months ended September 30, 2019, we recognized $612 million and $1,789 million of revenues and other income, respectively, related to ANDX. For the three and nine months ended September 30, 2019 we recognized $191 million and $539 million, respectively, of net income related to ANDX.

XML

Equity Method Investments

9 Months Ended

Sep. 30, 2020

Equity Method Investments and Joint Ventures [Abstract]

Investments and Noncontrolling Interests [Text Block]

Investments and Noncontrolling Interests

The following table presents MPLX’s equity method investments at the dates indicated:

	Ownership as of	Carrying value at
	September 30,	September 30,		December 31,
(In millions, except ownership percentages)	2020	2020		2019
L&S
MarEn Bakken Company LLC(1)	25%	$	469	$	481
Illinois Extension Pipeline Company, L.L.C.	35%	261		265
LOOP LLC	41%	249		238
Andeavor Logistics Rio Pipeline LLC(2)	67%	195		202
Minnesota Pipe Line Company, LLC	17%	189		190
Whistler Pipeline LLC(2)	38%	184		134
Explorer Pipeline Company	25%	78		83
W2W Holdings LLC(2)(3)	50%	77		—
Wink to Webster Pipeline LLC(2)(3)	15%	—		126
Other(2)		100		55
Total L&S		1,802		1,774
G&P
MarkWest Utica EMG, L.L.C.(2)	57%	720		1,984
Sherwood Midstream LLC(2)	50%	560		537
MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C.(2)	67%	307		302
Rendezvous Gas Services, L.L.C.(2)	78%	164		170
Sherwood Midstream Holdings LLC(2)	51%	151		157
Centrahoma Processing LLC	40%	147		153
Other(2)		230		198
Total G&P		2,279		3,501
Total		$	4,081	$	5,275

(1) The investment in MarEn Bakken Company LLC includes our 9.19 percent indirect interest in a joint venture (“Dakota Access”) that owns and operates the Dakota Access Pipeline and Energy Transfer Crude Oil Pipeline projects, collectively referred to as the Bakken Pipeline system or DAPL.    

(2) Investments deemed to be VIEs. Some investments included within “Other” have also been deemed to be VIEs.

(3) During the nine months ended September 30, 2020, we contributed our ownership in Wink to Webster Pipeline LLC to W2W Holdings LLC.

For those entities that have been deemed to be VIEs, neither MPLX nor any of its subsidiaries have been deemed to be the primary beneficiary due to voting rights on significant matters. While we have the ability to exercise influence through participation in the management committees which make all significant decisions, we have equal influence over each committee as a joint interest partner and all significant decisions require the consent of the other investors without regard to economic interest and as such we have determined that these entities should not be consolidated and apply the equity method of accounting with respect to our investments in each entity.

Sherwood Midstream has been deemed the primary beneficiary of Sherwood Midstream Holdings due to its controlling financial interest through its authority to manage the joint venture. As a result, Sherwood Midstream consolidates Sherwood Midstream Holdings. Therefore, MPLX also reports its portion of Sherwood Midstream Holdings’ net assets as a component of its investment in Sherwood Midstream. As of September 30, 2020, MPLX has a 24.51 percent indirect ownership interest in Sherwood Midstream Holdings through Sherwood Midstream.

MPLX’s maximum exposure to loss as a result of its involvement with equity method investments includes its equity investment, any additional capital contribution commitments and any operating expenses incurred by the subsidiary operator in excess of its compensation received for the performance of the operating services. MPLX did not provide any financial support to equity method investments that it was not contractually obligated to provide during the nine months ended September 30, 2020.

During the first quarter of 2020, we recorded an other than temporary impairment for three joint ventures in which we have an interest as discussed in Note 1. Impairment of these investments was $1,264 million, of which $1,251 million was related to MarkWest Utica EMG and its investment in Ohio Gathering Company, L.L.C. The fair value of the investments was determined based upon applying the discounted cash flow method, which is an income approach. The discounted cash flow fair value estimate is based on known or knowable information at the interim measurement date. The significant assumptions that were used to develop the estimate of the fair value under the discounted cash flow method include management’s best estimates of the expected future cash flows, including prices and volumes, the weighted average cost of capital and the long-term growth rate. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As such, the fair value of these equity method investments represents a Level 3 measurement. As a result, there can be no assurance that the estimates and assumptions made for purposes of the impairment test will prove to be an accurate prediction of the future. The impairment was recorded through “Income from equity method investments.” The impairments were largely due to a reduction in forecasted volumes gathered and processed by the systems operated by the joint ventures. There were no additional impairments recorded during the second or third quarters of 2020.

Summarized financial information for MPLX’s equity method investments for the nine months ended September 30, 2020 and 2019 is as follows:

	Nine Months Ended September 30, 2020
(In millions)	VIEs			Non-VIEs		Total
Revenues and other income	$	132		$	933	$	1,065
Costs and expenses	308			405		713
Income from operations	(176		)	528		352
Net income	(230		)	477		247
(Loss)/income from equity method investments(1)	$	(1,138	)	$	126	$	(1,012	)

(1) Includes the impact of any basis differential amortization or accretion in addition to the impairment of $1,264 million.

	Nine Months Ended September 30, 2019
(In millions)	VIEs		Non-VIEs		Total
Revenues and other income	$	479	$	1,116	$	1,595
Costs and expenses	251		434		685
Income from operations	228		682		910
Net income	192		605		797
Income from equity method investments(1)	$	89	$	166	$	255

(1) Includes the impact of any basis differential amortization or accretion.

Summarized balance sheet information for MPLX’s equity method investments as of September 30, 2020 and December 31, 2019 is as follows:

	September 30, 2020
(In millions)	VIEs		Non-VIEs		Total
Current assets	$	774	$	367	$	1,141
Noncurrent assets	6,398		5,024		11,422
Current liabilities	304		194		498
Noncurrent liabilities	$	1,611	$	857	$	2,468

	December 31, 2019
(In millions)	VIEs		Non-VIEs		Total
Current assets	$	534	$	330	$	864
Noncurrent assets	5,862		5,134		10,996
Current liabilities	192		245		437
Noncurrent liabilities	$	305	$	822	$	1,127

As of September 30, 2020, the underlying net assets of MPLX’s investees in the G&P segment exceeded the carrying value of its equity method investments by approximately $58 million. At December 31, 2019, the carrying value of MPLX’s equity method investments in the G&P segment exceeded the underlying net assets of its investees by approximately $1.0 billion. As of September 30, 2020 and December 31, 2019, the carrying value of MPLX’s equity method investments in the L&S segment exceeded the underlying net assets of its investees by $331 million and $329 million, respectively. At September 30, 2020 and December 31, 2019, the G&P basis difference was being amortized into net income over the remaining estimated useful lives of the underlying assets, except for $31 million and $498 million of excess related to goodwill, respectively. At September 30, 2020 and December 31, 2019, the L&S basis difference was being amortized into net income over the remaining estimated useful lives of the underlying assets, except for $167 million of excess related to goodwill.

XML

Related Party Agreements and Transactions

9 Months Ended

Sep. 30, 2020

Related Party Transactions [Abstract]

Related Party Agreements and Transactions

Related Party Agreements and Transactions

MPLX engages in transactions with both MPC and certain of its equity method investments as part of its normal business; however, transactions with MPC make up the majority of MPLX’s related party transactions. Transactions with related parties are further described below.

MPLX has various long-term, fee-based commercial agreements with MPC. Under these agreements, MPLX provides transportation, terminal, fuels distribution, marketing, storage, management, operational and other services to MPC. MPC has committed to provide MPLX with minimum throughput volumes on crude oil and refined products and other fees for storage capacity; operating and management fees; as well as reimbursements for certain direct and indirect costs. MPC has also committed to provide a fixed fee for 100 percent of available capacity for boats, barges and third-party chartered equipment under the marine transportation service agreement. MPLX also has a keep-whole commodity agreement with MPC under which MPC pays us a processing fee for NGLs related to keep-whole agreements and delivers shrink gas to the producers on our behalf. We pay MPC a marketing fee in exchange for assuming the commodity risk. Additionally, MPLX has obligations to MPC for services provided to MPLX by MPC under omnibus and employee services-type agreements as well as other various agreements.

MPC has also been advancing certain strategic priorities to lay a foundation for long-term success, including plans to optimize its assets and structurally lower costs in 2021 and beyond, which included an involuntary workforce reduction plan. The workforce reduction plan, together with employee reductions resulting from MPC's indefinite idling of its Martinez, California and Gallup, New Mexico refineries, affected approximately 2,050 employees. All of the employees that conduct MPLX’s business are directly employed by affiliates of MPC, and certain of those employees were affected by MPC’s workforce reductions. During the third quarter of 2020, MPLX reimbursed MPC for $36 million related to severance and employee benefits related expenses that MPC recorded in connection with its workforce reductions. These costs are shown on the Consolidated Statements of Income as “Restructuring expenses.”

Related Party Loan

MPLX is party to a loan agreement with MPC Investment LLC (“MPC Investment”) (the “MPC Loan Agreement”). Under the terms of the agreement, MPC Investment makes a loan or loans to MPLX on a revolving basis as requested by MPLX and as agreed to by MPC Investment. In connection with the Merger, on July 31, 2019, MPLX and MPC Investment amended and restated the MPC Loan Agreement to increase the borrowing capacity under the MPC Loan Agreement to $1.5 billion in aggregate principal amount of all loans outstanding at any one time. The entire unpaid principal amount of the loan, together with all accrued and unpaid interest and other amounts (if any), shall become due and payable on July 31, 2024, provided that MPC Investment may demand payment of all or any portion of the outstanding principal amount of the loan, together with all accrued and unpaid interest and other amounts (if any), at any time prior to July 31, 2024. Borrowings under the MPC Loan Agreement prior to July 31, 2019 bore interest at LIBOR plus 1.50 percent while borrowings as of and after July 31, 2019 bear interest at LIBOR plus 1.25 percent or such lower rate as would be applicable to such loans under the MPLX Credit Agreement as discussed in Note 15. Activity on the MPC Loan Agreement was as follows:

(In millions)	Nine Months Ended September 30, 2020			Year Ended December 31, 2019
Borrowings	$	4,870		$	8,540
Average interest rate of borrowings	2.380		%	3.441		%
Repayments	$	5,464		$	7,946
Outstanding balance at end of period(1)	$	—		$	594

(1) Included in “Current liabilities - related parties” on the Consolidated Balance Sheets.

Prior to the Merger, ANDX was also party to a loan agreement with MPC (“ANDX-MPC Loan Agreement”). This facility was entered into on December 21, 2018, with a borrowing capacity of $500 million. In connection with the Merger, on July 31, 2019, MPLX repaid the entire outstanding balance and terminated the ANDX-MPC Loan Agreement. Activity on the ANDX-MPC Loan Agreement prior to the Merger was as follows:

(In millions)	Year Ended December 31, 2019
Borrowings	$	773
Average interest rate of borrowings	4.249		%
Repayments	$	773
Outstanding balance at end of period	$	—

Related Party Revenue

Related party sales to MPC consist of crude oil and refined products pipeline and trucking transportation services based on tariff/contracted rates; storage, terminal and fuels distribution services based on contracted rates; and marine transportation services. Related party sales to MPC also consist of revenue related to volume deficiency credits.

MPLX also has operating agreements with MPC under which it receives a fee for operating MPC’s retained pipeline assets and a fixed annual fee for providing oversight and management services required to run the marine business. MPLX also receives management fee revenue for engineering, construction and administrative services for operating certain of its equity method investments.

Revenue received from related parties included on the Consolidated Statements of Income was as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020		2019
Service revenues - related parties
MPC	$	908	$	899	$	2,692	$	2,549
Other	1		—		2		—
Total Service revenue - related parties	909		899		2,694		2,549
Rental income - related parties
MPC	241		293		712		904
Product sales - related parties(1)
MPC	37		32		100		109
Other income - related parties
MPC	48		14		144		34
Other	15		17		46		50
Total Other income - related parties	$	63	$	31	$	190	$	84

(1) There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For the three and nine months ended September 30, 2020, these sales totaled $107 million and $332 million, respectively. For the three and nine months ended September 30, 2019, these sales totaled $301 million and $819 million, respectively.

Related Party Expenses

MPC provides executive management services and certain general and administrative services to MPLX under the terms of our omnibus agreements (“Omnibus charges”). Omnibus charges included in “Rental cost of sales - related parties” primarily relate to services that support MPLX’s rental operations and maintenance of assets available for rent. Omnibus charges included in “Purchases - related parties” primarily relate to services that support MPLX’s operations and maintenance activities, as well as compensation expenses. Omnibus charges included in “General and administrative expenses” primarily relate to services that support MPLX’s executive management, accounting and human resources activities. MPLX also obtains employee services from MPC under employee services agreements (“ESA charges”). ESA charges for personnel directly involved in or supporting operations and maintenance activities related to rental services are classified as “Rental cost of sales - related parties.” ESA charges for personnel directly involved in or supporting operations and maintenance activities related to other services are classified as “Purchases - related parties.” ESA charges for personnel involved in executive management, accounting and

human resources activities are classified as “General and administrative expenses.” In addition to these agreements, MPLX purchases products from MPC, makes payments to MPC in its capacity as general contractor to MPLX, and has certain lease agreements with MPC.

Expenses incurred from MPC under the omnibus and employee services agreements as well as other purchases from MPC included on the Consolidated Statements of Income are as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020		2019
Rental cost of sales - related parties
MPC	$	32	$	45	$	119	$	124
Purchases - related parties
MPC	293		297		840		878
Other	4		6		13		16
Total Purchase - related parties	297		303		853		894
General and administrative expenses
MPC	63		59		195		174
Restructuring expenses
MPC	$	36	$	—	$	36	$	—

Some charges incurred under the omnibus and ESA agreements are related to engineering services and are associated with assets under construction. These charges are added to “Property, plant and equipment, net” on the Consolidated Balance Sheets. For the three and nine months ended September 30, 2020, these charges totaled $29 million and $80 million, respectively. For the three and nine months ended September 30, 2019, these charges totaled $48 million and $127 million, respectively.

Related Party Assets and Liabilities

Assets and liabilities with related parties appearing on the Consolidated Balance Sheets are detailed in the table below. This table identifies the various components of related party assets and liabilities, including those associated with leases (see Note 20 for additional information) and deferred revenue on minimum volume commitments. If MPC fails to meet its minimum committed volumes, MPC will pay MPLX a deficiency payment based on the terms of the agreement. The deficiency amounts are recorded as “Current liabilities - related parties.” In many cases, MPC may then apply the amount of any such deficiency payments as a credit for volumes in excess of its minimum volume commitment in future periods under the terms of the applicable agreements. MPLX recognizes related party revenues for the deficiency payments when credits are used for volumes in excess of minimum quarterly volume commitments, where it is probable the customer will not use the credit in future periods or upon the expiration of the credits. The use or expiration of the credits is a decrease in “Current liabilities - related parties.” In addition, capital projects MPLX is undertaking at the request of MPC are reimbursed in cash and recognized in income over the remaining term of the applicable agreements or in some cases as an equity contribution from its sponsor.

(In millions)	September 30, 2020		December 31, 2019
Current assets - related parties
Receivables - MPC	$	543	$	621
Receivables - Other	7		22
Prepaid - MPC	11		9
Other - MPC	1		—
Lease Receivables - MPC	29		4
Total	591		656
Noncurrent assets - related parties
Long-term receivables - MPC	32		21
Right of use assets - MPC	231		232
Long-term lease receivables - MPC	390		43
Unguaranteed residual asset - MPC	22		7
Total	675		303
Current liabilities - related parties
Payables - MPC	247		911
Payables - Other	42		37
Operating lease liabilities - MPC	1		1
Deferred revenue - Minimum volume deficiencies - MPC	54		42
Deferred revenue - Project reimbursements - MPC	19		16
Deferred revenue - Project reimbursements - Other	1		1
Total	364		1,008
Long-term liabilities - related parties
Long-term operating lease liabilities - MPC	230		230
Long-term deferred revenue - Project reimbursements - MPC	45		53
Long-term deferred revenue - Project reimbursements - Other	6		7
Total	$	281	$	290

Other Related Party Transactions

From time to time, MPLX may also sell to or purchase from related parties, assets and inventory at the lesser of average unit cost or net realizable value. Sales to and purchases from related parties were immaterial for the nine months ended September 30, 2020 and 2019, respectively.

XML

Net Income Per Limited Partner Unit

9 Months Ended

Sep. 30, 2020

Earnings Per Share [Abstract]

Net Income Per Limited Partner Unit

Net Income/(Loss) Per Limited Partner Unit

Net income/(loss) per unit applicable to common units is computed by dividing net income/(loss) attributable to MPLX LP less income/(loss) allocated to participating securities by the weighted average number of common units outstanding.

Classes of participating securities for the three and nine months ended September 30, 2020 and 2019 include:

	Nine Months Ended September 30,
	2020	2019
Common Units	ü	ü
Equity-based compensation awards	ü	ü
Series A preferred units	ü	ü
Series B preferred units	ü	ü

For the three and nine months ended September 30, 2020 and 2019, MPLX had dilutive potential common units consisting of certain equity-based compensation awards. Potential common units omitted from the diluted earnings per unit calculation for the three and nine months ended September 30, 2020 and 2019 were less than 1 million.

	Three Months Ended September 30,						Nine Months Ended September 30,
(In millions)	2020			2019			2020			2019
Net income/(loss) attributable to MPLX LP	$	665		$	629		$	(1,411	)	$	1,614
Less: Distributions declared on Series A preferred units(1)	20			20			61			61
Distributions declared on Series B preferred units(1)	10			10			31			31
Limited partners’ distributions declared on MPLX common units (including common units of general partner)(1)(2)	715			704			2,158			1,919
Undistributed net loss attributable to MPLX LP	$	(80	)	$	(105	)	$	(3,661	)	$	(397	)

(1) See Note 7 for distribution information.

(2) The three and nine months ended September 30, 2019 amounts are net of $12.5 million and $25 million, respectively, of waived distributions with respect to units held by MPC and its affiliates.

	Three Months Ended September 30, 2020
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	715		$	20	$	10	$	745
Undistributed net loss attributable to MPLX LP	(80		)	—		—		(80		)
Net income attributable to MPLX LP(1)	$	635		$	20	$	10	$	665
Weighted average units outstanding:
Basic	1,046
Diluted	1,047
Net income attributable to MPLX LP per limited partner unit:
Basic	$	0.61
Diluted	$	0.61

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

	Three Months Ended September 30, 2019
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	704		$	20	$	10	$	734
Undistributed net loss attributable to MPLX LP	(105		)	—		—		(105		)
Net income attributable to MPLX LP(1)	$	599		$	20	$	10	$	629
Weighted average units outstanding:
Basic(2)	974
Diluted(2)	975
Net income attributable to MPLX LP per limited partner unit:
Basic	$	0.61
Diluted	$	0.61

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

(2) The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire three months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

	Nine Months Ended September 30, 2020
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	2,158		$	61	$	31	$	2,250
Undistributed net loss attributable to MPLX LP	(3,661		)	—		—		(3,661		)
Net (loss)/income attributable to MPLX LP(1)	$	(1,503	)	$	61	$	31	$	(1,411	)
Weighted average units outstanding:
Basic	1,054
Diluted	1,054
Net income attributable to MPLX LP per limited partner unit:
Basic	$	(1.43	)
Diluted	$	(1.43	)

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

	Nine Months Ended September 30, 2019
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	1,919		$	61	$	31	$	2,011
Undistributed net loss attributable to MPLX LP	(397		)	—		—		(397		)
Net income attributable to MPLX LP(1)	$	1,522		$	61	$	31	$	1,614
Weighted average units outstanding:
Basic(2)	855
Diluted(2)	855
Net income attributable to MPLX LP per limited partner unit:
Basic	$	1.78
Diluted	$	1.78

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

(2)

The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire nine months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

XML

Equity

9 Months Ended

Sep. 30, 2020

Equity [Abstract]

Equity

Equity

The changes in the number of common units outstanding during the nine months ended September 30, 2020 are summarized below:

(In units)	Common
Balance at December 31, 2019	1,058,355,471
Unit-based compensation awards	395,091
Units redeemed in Wholesale Exchange	(18,582,088	)
Balance at September 30, 2020	1,040,168,474

Wholesale Exchange and Merger

In connection with the Wholesale Exchange as discussed in Note 3, 18,582,088 units were redeemed by MPC in exchange for all of the outstanding membership interests in WRW. These units were cancelled by MPLX immediately following the transaction.

In connection with the Merger and as discussed in Note 3, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units while ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. This resulted in the issuance of MPLX common units of approximately 102 million units to public unitholders and approximately 161 million units to MPC on July 30, 2019.

Series B Preferred Units

Prior to the Merger, ANDX had outstanding 600,000 units of 6.875 percent Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Units representing limited partner interests of ANDX at a price to the public of $1,000 per unit. Upon completion of the Merger, the ANDX preferred units converted to preferred units of MPLX representing substantially equivalent limited partnership interests in MPLX (the “Series B preferred units”). The Series B preferred units are pari passu with the Series A preferred units with respect to distribution rights and rights upon liquidation. Distributions on the Series B preferred units are payable semi-annually in arrears on the 15th day, or the first business day thereafter, of February and August of each year up to and including February 15, 2023. After February 15, 2023, the holders of Series B preferred units are entitled to receive cumulative, quarterly distributions payable in arrears on the 15th day of February, May, August and November of each year, or the first business day thereafter, based on a floating annual rate equal to the three-month LIBOR plus 4.652 percent.

The changes in the Series B preferred unit balance from December 31, 2019 through September 30, 2020 are summarized below. Series B preferred units are included in the Consolidated Balance Sheets and Consolidated Statements of Equity within “Equity of Predecessor” for the period prior to the Merger and within “Series B preferred units” for the period following the Merger.

(In millions)	Series B Preferred Units
Balance at December 31, 2019	$	611
Net income allocated	31
Distributions received by Series B preferred unitholders	(41		)
Balance at September 30, 2020	$	601

TexNew Mex Units - Prior to the Merger, MPC held 80,000 ANDX TexNew Mex units, representing all outstanding units. At the time of the Merger, each ANDX TexNew Mex unit was automatically converted into TexNew Mex units of MPLX with substantially the same rights and obligations as the ANDX TexNew Mex units. The TexNew Mex units represent the right to receive quarterly distribution payments in an amount calculated using the distributable cash flow generated by a particular portion of the TexNew Mex pipeline system, in excess of a base amount and adjusted for previously agreed upon stipulations and contingencies. Distributions earned by TexNew Mex units during the fourth quarter of 2019 and during the six months ended June 30, 2020 were immaterial. Distributions of $5 million were earned by TexNew Mex units during the three months ended September 30, 2020.

Cash distributions – In accordance with the MPLX partnership agreement, on October 27, 2020, MPLX declared a quarterly cash distribution for the third quarter of 2020, totaling $715 million, or $0.6875 per common unit. This rate will also be received by Series A preferred unitholders. These distributions will be paid on November 13, 2020 to common unitholders of record on November 6, 2020. Series B preferred unitholders are entitled to receive a fixed distribution of $68.75 per unit, per annum, payable semi-annually in arrears on February 15 and August 15, or the first business day thereafter, up to and including February 15, 2023. After February 15, 2023, the holders of Series B preferred units are entitled to receive cumulative, quarterly distributions payable in arrears on the 15th day of February, May, August and November of each year, or the first business day thereafter, based on a floating annual rate equal to the three-month LIBOR plus 4.652 percent, in each case assuming a distribution is declared by the Board of Directors. Accordingly, MPLX made a cash distribution payment totaling $21 million to Series B unitholders on August 17, 2020.

Quarterly distributions for 2020 and 2019 are summarized below:

(Per common unit)	2020		2019
March 31,	$	0.6875	$	0.6575
June 30,	0.6875		0.6675
September 30,	$	0.6875	$	0.6775

The allocation of total quarterly cash distributions to limited and preferred unitholders is as follows for the three and nine months ended September 30, 2020 and 2019. MPLX’s distributions are declared subsequent to quarter end; therefore, the following table represents total cash distributions applicable to the period in which the distributions were earned.

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020		2019
Common and preferred unit distributions:
Common unitholders, includes common units of general partner	$	715	$	704	$	2,158	$	1,919
Series A preferred unit distributions	20		20		61		61
Series B preferred unit distributions	10		10		31		31
Total cash distributions declared	$	745	$	734	$	2,250	$	2,011

The distribution on common units for the three and nine months ended September 30, 2019 includes the impact of the issuance of approximately 102 million units issued to public unitholders and approximately 161 million units issued to MPC in connection with the Merger. Due to the timing of the closing, distributions presented in the table above include second quarter

distributions for MPLX common units and Series B preferred units issued to former ANDX unitholders in connection with the Merger. The distributions on common units exclude $12.5 million of waived distributions for the three months ended September 30, 2019 and $25 million of waived distributions for the nine months ended September 30, 2019.

XML

Series A Preferred Units

9 Months Ended

Sep. 30, 2020

Temporary Equity Disclosure [Abstract]

Redeemable Preferred Units

Series A Preferred Units

On May 13, 2016, MPLX LP issued approximately 30.8 million 6.5 percent Series A Convertible preferred units for a cash purchase price of $32.50 per unit. The Series A preferred units rank senior to all common units and pari passu with all Series B preferred units with respect to distributions and rights upon liquidation. The holders of the Series A preferred units are entitled to receive, when and if declared by the board, a quarterly distribution equal to the greater of $0.528125 per unit or the amount of distributions they would have received on an as converted basis. On October 27, 2020, MPLX declared a quarterly cash distribution of $0.6875 per common unit for the third quarter of 2020. Holders of the Series A preferred units will receive the common unit rate in lieu of the lower $0.528125 base amount.

The holders may convert their Series A preferred units into common units at any time, in full or in part, subject to minimum conversion amounts and conditions. After the fourth anniversary of the issuance date, MPLX may convert the Series A preferred units into common units at any time, in whole or in part, subject to certain minimum conversion amounts and conditions, if the closing price of MPLX common units is greater than $48.75 for the 20-day trading period immediately preceding the conversion notice date. The conversion rate for the Series A preferred units shall be the quotient of (a) the sum of (i) $32.50, plus (ii) any unpaid cash distributions on the applicable preferred unit, divided by (b) $32.50, subject to adjustment for unit distributions, unit splits and similar transactions. The holders of the Series A preferred units are entitled to vote on an as-converted basis with the common unitholders and have certain other class voting rights with respect to any amendment to the MPLX partnership agreement that would adversely affect any rights, preferences or privileges of the preferred units. In addition, upon certain events involving a change of control, the holders of preferred units may elect, among other potential elections, to convert their Series A preferred units to common units at the then change of control conversion rate.

Approximately 29.6 million Series A preferred units remaining outstanding as of September 30, 2020. The changes in the redeemable preferred balance from December 31, 2019 through September 30, 2020 are summarized below:

(In millions)	Redeemable Series A Preferred Units
Balance at December 31, 2019	$	968
Net income allocated	61
Distributions received by Series A preferred unitholders	(61		)
Balance at September 30, 2020	$	968

The Series A preferred units are considered redeemable securities under GAAP due to the existence of redemption provisions upon a deemed liquidation event which is outside MPLX’s control. Therefore, they are presented as temporary equity in the mezzanine section of the Consolidated Balance Sheets. The Series A preferred units have been recorded at their issuance date fair value, net of issuance costs. Income allocations increase the carrying value and declared distributions decrease the carrying value of the Series A preferred units. As the Series A preferred units are not currently redeemable and not probable of becoming redeemable, adjustment to the initial carrying amount is not necessary and would only be required if it becomes probable that the Series A preferred units would become redeemable.

XML

Segment Information

9 Months Ended

Sep. 30, 2020

Segment Reporting [Abstract]

Segment Reporting Disclosure [Text Block]

Segment Information

MPLX’s chief operating decision maker is the chief executive officer (“CEO”) of its general partner. The CEO reviews MPLX’s discrete financial information, makes operating decisions, assesses financial performance and allocates resources on a type of service basis. MPLX has two reportable segments: L&S and G&P. Each of these segments is organized and managed based upon the nature of the products and services it offers.

• L&S – transports, stores, distributes and markets crude oil, asphalt, refined petroleum products and water. Also includes an inland marine business, terminals, rail facilities, storage caverns and refining logistics.

• G&P – gathers, processes and transports natural gas; and gathers, transports, fractionates, stores and markets NGLs.

Our CEO evaluates the performance of our segments using Segment Adjusted EBITDA. Amounts included in net income and excluded from Segment Adjusted EBITDA include: (i) depreciation and amortization; (ii) provision/(benefit) for income taxes; (iii) amortization of deferred financing costs; (iv) extinguishment of debt; (v) non-cash equity-based compensation; (vi)

impairment expense; (vii) net interest and other financial costs; (viii) income/(loss) from equity method investments; (ix) distributions and adjustments related to equity method investments; (x) unrealized derivative gains/(losses); (xi) acquisition costs; (xii) noncontrolling interest; and (xiii) other adjustments as deemed necessary. These items are either: (i) believed to be non-recurring in nature; (ii) not believed to be allocable or controlled by the segment; or (iii) are not tied to the operational performance of the segment.

The tables below present information about revenues and other income, capital expenditures and investments in unconsolidated affiliates as well as total assets for our reportable segments:

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020			2019
L&S
Service revenue	$	989	$	976	$	2,924		$	2,787
Rental income	249		304		737			935
Product related revenue	9		22		49			57
Income from equity method investments	36		60		126			159
Other income	51		17		154			45
Total segment revenues and other income(1)	1,334		1,379		3,990			3,983
Segment Adjusted EBITDA(2)	893		766		2,604			1,895
Restructuring expenses	27		—		27			—
Capital expenditures	118		272		410			700
Investments in unconsolidated affiliates	4		95		132			163
G&P
Service revenue	524		555		1,549			1,627
Rental income	94		88		271			260
Product related revenue	234		207		607			714
Income/(loss) from equity method investments	47		35		(1,138		)	96
Other income	14		16		41			45
Total segment revenues and other income(1)	913		901		1,330			2,742
Segment Adjusted EBITDA(2)	442		399		1,252			1,120
Restructuring expenses	9		—		9			—
Capital expenditures	131		321		375			953
Investments in unconsolidated affiliates	$	18	$	76	$	112		$	331

(1) Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $139 million and $443 million for the three and nine months ended September 30, 2020, respectively, and $182 million and $498 million for the three and nine months ended September 30, 2019, respectively. Third party revenues for the G&P segment were $858 million and $1,181 million for the three and nine months ended September 30, 2020, respectively, and $843 million and $2,581 million for the three and nine months ended September 30, 2019, respectively.

(2) See below for the reconciliation from Segment Adjusted EBITDA to net income.

(In millions)	September 30, 2020		December 31, 2019
Segment assets
Cash and cash equivalents	$	28	$	15
L&S	21,144		20,810
G&P	15,490		19,605
Total assets	$	36,662	$	40,430

The table below provides a reconciliation between net (loss)/income and Segment Adjusted EBITDA.

	Three Months Ended September 30,						Nine Months Ended September 30,
(In millions)	2020			2019			2020			2019
Reconciliation to Net income/(loss):
L&S Segment Adjusted EBITDA	$	893		$	766		$	2,604		$	1,895
G&P Segment Adjusted EBITDA	442			399			1,252			1,120
Total reportable segments	1,335			1,165			3,856			3,015
Depreciation and amortization(1)	(346		)	(302		)	(992		)	(916		)
Provision for income taxes	(1		)	(4		)	(1		)	(2		)
Amortization of deferred financing costs	(15		)	(10		)	(44		)	(29		)
Non-cash equity-based compensation	(4		)	(5		)	(12		)	(17		)
Impairment expense	—			—			(2,165		)	—
Net interest and other financial costs	(223		)	(223		)	(647		)	(657		)
Gain on extinguishment of debt	14			—			14			—
Income/(loss) from equity method investments	83			95			(1,012		)	255
Distributions/adjustments related to equity method investments	(130		)	(145		)	(369		)	(399		)
Unrealized derivative (losses)/gains(2)	(10		)	11			(1		)	7
Acquisition costs	—			(9		)	—			(14		)
Restructuring expenses	(36		)	—			(36		)	—
Other	(3		)	(1		)	(5		)	(1		)
Adjusted EBITDA attributable to noncontrolling interests	10			9			27			23
Adjusted EBITDA attributable to Predecessor(3)	—			108			—			770
Net income/(loss)	$	674		$	689		$	(1,387	)	$	2,035

(1) Depreciation and amortization attributable to L&S was $164 million and $440 million for the three and nine months ended September 30, 2020, respectively, and $113 million and $373 million for the three and nine months ended September 30, 2019, respectively. Depreciation and amortization attributable to G&P was $182 million and $552 million for the three and nine months ended September 30, 2020, respectively, and $189 million and $543 million for the three and nine months ended September 30, 2019, respectively.

(2) MPLX makes a distinction between realized and unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

(3)

The adjusted EBITDA adjustments related to Predecessor are excluded from adjusted EBITDA attributable to MPLX LP prior to the Merger.

XML

Inventories

9 Months Ended

Sep. 30, 2020

Inventory Disclosure [Abstract]

Inventories

Inventories

Inventories consist of the following:

(In millions)	September 30, 2020		December 31, 2019
NGLs	$	3	$	5
Line fill	11		10
Spare parts, materials and supplies	103		95
Total inventories	$	117	$	110

XML

Property, Plant and Equipment

9 Months Ended

Sep. 30, 2020

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Property, Plant and Equipment

Property, plant and equipment with associated accumulated depreciation is shown below:

(In millions)	Estimated Useful Lives	September 30, 2020		December 31, 2019
L&S
Pipelines	2-51 years	$	6,001	$	5,572
Refining Logistics	13-40 years	2,196		2,870
Terminals	4-40 years	1,534		1,109
Marine	15-20 years	961		906
Land, building and other	1-61 years	1,576		1,817
Construction-in progress		403		660
Total L&S property, plant and equipment		12,671		12,934
G&P
Gathering and transportation	5-40 years	7,413		7,159
Processing and fractionation	10-40 years	5,944		5,545
Land, building and other	3-40 years	509		484
Construction-in-progress		382		745
Total G&P property, plant and equipment		14,248		13,933
Total property, plant and equipment		26,919		26,867
Less accumulated depreciation(1)		5,304		4,722
Property, plant and equipment, net		$	21,615	$	22,145

(1) The September 30, 2020 balance includes property, plant and equipment impairment charges recorded during the first quarter of 2020 as discussed below.

Long-lived assets used in operations are assessed for impairment whenever changes in facts and circumstances indicate that the carrying value of the assets may not be recoverable based on the expected undiscounted future cash flow of an asset group. For purposes of impairment evaluation, long-lived assets must be grouped at the lowest level for which independent cash flows can be identified, which is at least at the segment level and in some cases for similar assets in the same geographic region where cash flows can be separately identified. If the sum of the undiscounted cash flows is less than the carrying value of an asset group, fair value is calculated, and the carrying value is written down if greater than the calculated fair value.

No impairment triggers were identified in the second or third quarters of 2020; however, during the first quarter of 2020, we did identify an impairment trigger relating to asset groups within our Western G&P reporting unit as a result of significant impacts to forecasted cash flows for these asset groups resulting from the first quarter events and circumstances as discussed in Note 1. The cash flows associated with these assets were significantly impacted by volume declines reflecting decreased forecasted producer customer production as a result of lower commodity prices. After assessing each asset group within the Western G&P reporting unit for impairment, only the East Texas G&P asset group had a carrying value in excess of the fair value of its underlying assets. As a result, an impairment of $174 million was recorded to “Impairment expense” on the Consolidated Statements of Income in the first quarter of 2020. Fair value of the assets was determined using a combination of an income and cost approach. The income approach utilized significant assumptions including management’s best estimates of the expected future cash flows, the estimated useful life of the asset group and discount rate. The cost approach utilized assumptions for the current replacement costs of similar assets adjusted for estimated depreciation and deterioration of the existing equipment and economic obsolescence. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of our impairment analysis will prove to be an accurate prediction of the future. The fair value measurements for the asset group fair values represent Level 3 measurements.

XML

Goodwill and Intangibles (Notes)

9 Months Ended

Sep. 30, 2020

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets Disclosure [Text Block]

Goodwill and Intangibles

Goodwill

MPLX annually evaluates goodwill for impairment as of November 30, as well as whenever events or changes in circumstances indicate it is more likely than not that the fair value of a reporting unit with goodwill is less than its carrying amount.

There were no events or changes in circumstances noted in the second or third quarters of 2020 which would indicate it is more likely than not that the fair value of our reporting units with goodwill is less than their carrying amount. During the first quarter of 2020, we determined that an interim impairment analysis of the goodwill recorded was necessary based on consideration of a number of first quarter events and circumstances as discussed in Note 1. Our producer customers in our Eastern G&P region reduced production forecasts and drilling activity in response to the global economic downturn. Additionally, a decline in NGL prices impacted our future revenue forecast. After performing our evaluations related to the interim impairment of goodwill during the first quarter of 2020, we recorded an impairment of $1,814 million within the Eastern G&P reporting unit, which was recorded to “Impairment expense” on the Consolidated Statements of Income. The impairment was primarily driven by additional guidance related to the slowing of drilling activity, which has reduced production growth forecasts from our producer customers. This resulted in goodwill totaling approximately $7.7 billion as of March 31, 2020 within four reporting units. The fair value of the remaining reporting units with goodwill were in excess of their carrying value by percentages ranging from 8.5 percent to 270.0 percent. The reporting unit whose fair value exceeded its carrying amount by 8.5 percent, our Crude Gathering reporting unit, had goodwill totaling $1.1 billion at March 31, 2020. The operations which make up this reporting unit were acquired through the merger with ANDX. MPC accounted for its October 1, 2018 acquisition of Andeavor (through which it acquired control of ANDX), using the acquisition method of accounting, which required Andeavor assets and liabilities to be recorded by MPC at the acquisition date fair value. The Merger was closed on July 30, 2019 and has been treated as a common control transaction, which required the recognition of assets acquired and liabilities assumed using MPC’s historical carrying value. As such, given the short amount of time from when fair value was established to the date of the impairment test, the amount by which the fair value exceeded the carrying value within this reporting unit was not unexpected.

Our reporting units are one level below our operating segments and are determined based on the way in which segment management operates and reviews each operating segment. The fair value of our six reporting units was determined based on applying both a discounted cash flow or income approach as well as a market approach. The discounted cash flow fair value estimate is based on known or knowable information at the measurement date. The significant assumptions that were used to develop the estimates of the fair values under the discounted cash flow method included management’s best estimates of the expected future results and discount rate, which ranged from 9.5 percent to 11.5 percent. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of the interim goodwill impairment test will prove to be an accurate prediction of the future. The fair value measurements for the individual reporting units represent Level 3 measurements.

After performing our evaluations related to the impairment of goodwill during the fiscal year ending December 31, 2019, we recorded an impairment of $1,197 million within the Western G&P reporting unit. The remainder of the reporting units’ fair values were in excess of their carrying values. The impairment was primarily driven by updated guidance related to the slowing of drilling activity, which has reduced production growth forecasts from our producer customers. This resulted in goodwill totaling approximately $9.5 billion as of December 31, 2019, with all but one of our six reporting units having goodwill.

The changes in carrying amount of goodwill were as follows:

(In millions)	L&S			G&P			Total
Gross goodwill as of December 31, 2018	$	7,234		$	2,912		$	10,146
Accumulated impairment losses	—			(130		)	(130		)
Balance as of December 31, 2018	7,234			2,782			10,016
Impairment losses	—			(1,197		)	(1,197		)
Acquisitions	488			229			717
Balance as of December 31, 2019	7,722			1,814			9,536
Impairment losses	—			(1,814		)	(1,814		)
Wholesale Exchange (Note 3)	(65		)	—			(65		)
Balance as of September 30, 2020	7,657			—			7,657
Gross goodwill as of September 30, 2020	7,657			3,141			10,798
Accumulated impairment losses	—			(3,141		)	(3,141		)
Balance as of September 30, 2020	$	7,657		$	—		$	7,657

Intangible Assets

During the first quarter of 2020, we also determined that an impairment analysis of intangibles within our Western G&P reporting unit was necessary. See Note 11 for additional information regarding our assessment around the Western G&P reporting unit, and more specifically our East Texas G&P asset group. The fair value of the intangibles in our East Texas G&P asset group was determined based on applying the multi-period excess earnings method, which is an income approach. Key assumptions included management’s best estimates of the expected future cash flows from existing customers, customer attrition rates and the discount rate. After performing our evaluations related to the impairment of intangible assets associated with our East Texas G&P asset group during the first quarter of 2020, we recorded an impairment of $177 million to “Impairment expense” on the Consolidated Statements of Income related to our customer relationships.

MPLX’s remaining intangible assets are comprised of customer contracts and relationships. Gross intangible assets with accumulated amortization as of September 30, 2020 and December 31, 2019 is shown below:

		September 30, 2020							December 31, 2019
(In millions)	Useful Lives	Gross		Accumulated Amortization(1)(2)			Net		Gross		Accumulated Amortization			Net
L&S	6 - 8 years	$	283	$	(72	)	$	211	$	283	$	(45	)	$	238
G&P	6 - 25 years	1,288		(508		)	780		1,288		(256		)	1,032
		$	1,571	$	(580	)	$	991	$	1,571	$	(301	)	$	1,270

(1) Amortization expense attributable to the G&P and L&S segments for the nine months ended September 30, 2020 was $75 million and $27 million, respectively.

(2) Impairment charge of $177 million is included within the G&P accumulated amortization.

Estimated future amortization expense related to the intangible assets at September 30, 2020 is as follows:

(In millions)
2020	$	32
2021	128
2022	128
2023	128
2024	124
Thereafter	451
Total	$	991

XML

Fair Value Measurements

9 Months Ended

Sep. 30, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

Fair Value Measurements

Fair Values – Recurring

Fair value measurements and disclosures relate primarily to MPLX’s derivative positions as discussed in Note 14. The following table presents the financial instruments carried at fair value on a recurring basis as of September 30, 2020 and December 31, 2019 by fair value hierarchy level. MPLX has elected to offset the fair value amounts recognized for multiple derivative contracts executed with the same counterparty.

	September 30, 2020					December 31, 2019
(In millions)	Assets		Liabilities			Assets		Liabilities
Significant unobservable inputs (Level 3)
Embedded derivatives in commodity contracts	$	—	$	(61	)	$	—	$	(60	)
Total carrying value on Consolidated Balance Sheets	$	—	$	(61	)	$	—	$	(60	)

Level 3 instruments include all NGL transactions and embedded derivatives in commodity contracts. The embedded derivative liability relates to a natural gas purchase commitment embedded in a keep-whole processing agreement. The fair value calculation for these Level 3 instruments used significant unobservable inputs including: (1) NGL prices interpolated and extrapolated due to inactive markets ranging from $0.46 to $0.97 per gallon with a weighted average of $0.58 per gallon and

(2) the probability of renewal of 100 percent for the first five-year term and second five-year term of the gas purchase commitment and related keep-whole processing agreement, respectively. Increases or decreases in the fractionation spread result in an increase or decrease in the fair value of the embedded derivative liability, respectively. Beyond the embedded derivative discussed above, we had no outstanding commodity contracts as of September 30, 2020 or December 31, 2019.

Changes in Level 3 Fair Value Measurements

The following table is a reconciliation of the net beginning and ending balances recorded for net assets and liabilities classified as Level 3 in the fair value hierarchy.

	Three Months Ended September 30, 2020					Three Months Ended September 30, 2019
(In millions)	Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)			Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)
Fair value at beginning of period	$	—	$	(51	)	$	—	$	(65	)
Total (losses)/gains (realized and unrealized) included in earnings(1)	—		(12		)	—		9
Settlements	—		2			—		2
Fair value at end of period	—		(61		)	—		(54		)
The amount of total (losses)/gains for the period included in earnings attributable to the change in unrealized gains/(losses) relating to liabilities still held at end of period	$	—	$	(11	)	$	—	$	9

	Nine Months Ended September 30, 2020					Nine Months Ended September 30, 2019
(In millions)	Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)			Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)
Fair value at beginning of period	$	—	$	(60	)	$	—	$	(61	)
Total (losses)/gains (realized and unrealized) included in earnings(1)	—		(5		)	—		2
Settlements	—		4			—		5
Fair value at end of period	—		(61		)	—		(54		)
The amount of total (losses)/gains for the period included in earnings attributable to the change in unrealized gains/(losses) relating to liabilities still held at end of period	$	—	$	(2	)	$	—	$	5

(1) Gains and losses on commodity derivative contracts classified as Level 3 are recorded in “Product sales” on the Consolidated Statements of Income. Gains and losses on derivatives embedded in commodity contracts are recorded in “Purchased product costs” and “Cost of revenues” on the Consolidated Statements of Income.

Fair Values – Reported

MPLX’s primary financial instruments are cash and cash equivalents, receivables, receivables from related parties, lease receivables from related parties, accounts payable, payables to related parties and long-term debt. MPLX’s fair value assessment incorporates a variety of considerations, including (1) the duration of the instruments, (2) MPC’s investment-grade credit rating and (3) the historical incurrence of and expected future insignificance of bad debt expense, which includes an evaluation of counterparty credit risk. MPLX believes the carrying values of its current assets and liabilities approximate fair value. The recorded value of the amounts outstanding under the bank revolving credit facility, if any, approximates fair value due to the variable interest rate that approximates current market rates. Derivative instruments are recorded at fair value, based on available market information (see Note 14).

The fair value of MPLX’s long-term debt is estimated based on recent market non-binding indicative quotes. The fair value of the SMR liability is estimated using a discounted cash flow approach based on the contractual cash flows and MPLX’s unsecured borrowing rate. The long-term debt and SMR liability fair values are considered Level 3 measurements. The following table summarizes the fair value and carrying value of our debt, excluding finance leases, and SMR liability:

	September 30, 2020				December 31, 2019
(In millions)	Fair Value		Carrying Value		Fair Value		Carrying Value
Long-term debt (including amounts due within one year)	$	21,721	$	20,455	$	21,054	$	19,800
SMR liability	$	87	$	76	$	90	$	80

XML

Derivative Financial Instruments

9 Months Ended

Sep. 30, 2020

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Instruments and Hedging Activities Disclosure [Text Block]

Derivative Financial Instruments

As of September 30, 2020, MPLX had no outstanding commodity contracts beyond the embedded derivative discussed below.

Embedded Derivative - MPLX has a natural gas purchase commitment embedded in a keep-whole processing agreement with a producer customer in the Southern Appalachian region expiring in December 2022. The customer has the unilateral option to extend the agreement for two consecutive five-year terms through December 2032. For accounting purposes, the natural gas purchase commitment and the term extending options have been aggregated into a single compound embedded derivative. The probability of the customer exercising its options is determined based on assumptions about the customer’s potential business strategy decision points that may exist at the time they would elect whether to renew the contract. The changes in fair value of this compound embedded derivative are based on the difference between the contractual and index pricing and the probability of the producer customer exercising its option to extend. The changes in fair value are recorded in earnings through “Purchased product costs” on the Consolidated Statements of Income. As of September 30, 2020 and December 31, 2019, the estimated fair value of this contract was a liability of $61 million and $60 million, respectively.

Certain derivative positions are subject to master netting agreements, therefore, MPLX has elected to offset derivative assets and liabilities that are legally permissible to be offset. As of September 30, 2020 and December 31, 2019, there were no derivative assets or liabilities that were offset on the Consolidated Balance Sheets. The impact of MPLX’s derivative instruments on its Consolidated Balance Sheets is summarized below:

(In millions)	September 30, 2020					December 31, 2019
Derivative contracts not designated as hedging instruments and their balance sheet location	Asset		Liability			Asset		Liability
Commodity contracts(1)
Other current assets / Other current liabilities	$	—	$	(4	)	$	—	$	(5	)
Other noncurrent assets / Deferred credits and other liabilities	—		(57		)	—		(55		)
Total	$	—	$	(61	)	$	—	$	(60	)

(1) Includes embedded derivatives in commodity contracts as discussed above.

For further information regarding the fair value measurement of derivative instruments, see Note 13. There were no material changes to MPLX’s policy regarding the accounting for Level 2 and Level 3 instruments as previously disclosed in MPLX’s Annual Report on Form 10-K for the year ended December 31, 2019. MPLX does not designate any of its commodity derivative positions as hedges for accounting purposes.

The impact of MPLX’s derivative contracts not designated as hedging instruments and the location of gains and losses recognized on the Consolidated Statements of Income is summarized below:

	Three Months Ended September 30,						Nine Months Ended September 30,
(In millions)	2020			2019			2020			2019
Purchased product costs
Realized (loss)/gain	$	(2	)	$	(2	)	$	(4	)	$	(5	)
Unrealized (loss)/gain	(10		)	11			(1		)	7
Purchased product costs derivative (loss)/gain	(12		)	9			(5		)	2
Total derivative (loss)/gain	$	(12	)	$	9		$	(5	)	$	2

XML

Debt

9 Months Ended

Sep. 30, 2020

Debt Disclosure [Abstract]

Debt

Debt

MPLX’s outstanding borrowings consist of the following:

(In millions)	September 30, 2020			December 31, 2019
MPLX LP:
Bank revolving credit facility	$	95		$	—
Term loan facility	—			1,000
Floating rate senior notes	1,000			2,000
Fixed rate senior notes	19,506			16,887
Consolidated subsidiaries:
MarkWest	23			23
ANDX	121			190
Financing lease obligations(1)	12			19
Total	20,757			20,119
Unamortized debt issuance costs	(118		)	(106		)
Unamortized discount/premium	(290		)	(300		)
Amounts due within one year	(307		)	(9		)
Total long-term debt due after one year	$	20,042		$	19,704

(1)    See Note 20 for lease information.

Credit Agreement

Effective July 30, 2019, in connection with the closing of the Merger, MPLX amended and restated its revolving credit facility (as amended, the “MPLX Credit Agreement”) to, among other things, increase borrowing capacity to up to $3.5 billion and extend its term from July 2022 to July 2024. During the nine months ended September 30, 2020, MPLX borrowed $2.995 billion under the MPLX Credit Agreement, at an average interest rate of 1.510 percent, and repaid $2.9 billion. At September 30, 2020, MPLX had $95 million in outstanding borrowings and less than $1 million in letters of credit outstanding under the MPLX Credit Agreement, resulting in total availability of $3.405 billion, or 97.3 percent of the borrowing capacity.

Term Loan Agreement

On September 26, 2019, MPLX entered into a Term Loan Agreement which provides for a committed term loan facility for up to an aggregate of $1 billion. Borrowings under the Term Loan Agreement bear interest, at MPLX’s election, at either (i) the Adjusted LIBO Rate (as defined in the Term Loan Agreement) plus a margin ranging from 75.0 basis points to 100.0 basis points per annum, depending on MPLX’s credit ratings, or (ii) the Alternate Base Rate (as defined in the Term Loan Agreement). On August 18, 2020 MPLX fully repaid the $1.0 billion of outstanding borrowings on the Term Loan Agreement, which resulted in the recognition of $1 million of unamortized issuance costs, which is included on the Consolidated Statements of Income as “Other financial costs”.

Floating Rate Senior Notes

On September 9, 2019, MPLX issued $2.0 billion aggregate principal amount of floating rate senior notes in a public offering, consisting of $1.0 billion aggregate principal amount of notes due September 2021 and $1.0 billion aggregate principal amount of notes due September 2022 (collectively, the “Floating Rate Senior Notes”). The Floating Rate Senior Notes were offered at a price to the public of 100 percent of par. The Floating Rate Senior Notes are callable, in whole or in part, at par plus accrued and unpaid interest at any time on or after September 10, 2020. Interest on the Floating Rate Senior Notes is payable quarterly in March, June, September and December, commencing on December 9, 2019. The interest rate applicable to the floating rate senior notes due September 2021 is LIBOR plus 0.9 percent per annum. The interest rate applicable to the floating rate senior notes due September 2022 is LIBOR plus 1.1 percent per annum.

On September 14, 2020 MPLX redeemed, at par value, all of the $1.0 billion aggregate principal amount of notes due September 2021 which resulted in the recognition of $3 million of unamortized issuance costs, which is included on the Consolidated Statements of Income as “Other financial costs”.

Fixed Rate Senior Notes

MPLX’s senior notes, including those issued by consolidated subsidiaries, consist of various series of senior notes expiring between 2022 and 2058 with interest rates ranging from 1.750 percent to 6.250 percent. Interest on each series of notes is payable semi-annually in arrears on various dates depending on the series of the notes.

On August 18, 2020 MPLX issued $3 billion aggregate principal amount of senior notes in a public offering, consisting of $1.5 billion aggregate principal amount of 1.750 percent senior notes due March 2026 and $1.5 billion aggregate principal amount of 2.650 percent senior notes due August 2030 (collectively, the “August 2020 New Senior Notes”). The August 2020 New Senior Notes were offered at a price to the public of 99.785 percent and 99.913 percent of par, respectively. Interest on each series of notes in the August 2020 New Senior Notes is payable semi-annually in arrears, commencing on March 1, 2021 for the senior notes due March 2026 and commencing on February 15, 2021 for the senior notes due August 2030. The net proceeds were used to repay the $1.0 billion of outstanding borrowings under the MPLX Term Loan Agreement, to repay the $1.0 billion floating rate notes due September 2021 and to redeem all of the $450 million aggregate principal amount of 6.375 percent senior notes due May 2024, $69 million of which was issued by ANDX. These notes were redeemed at 103.2 percent of the aggregate principal amount, which resulted in a payment of $14 million related to the note premium offset by the immediate recognition of $18 million of unamortized debt premium/discount and issuance costs, both of which are included on the Consolidated Statements of Income as “Other financial costs.” Proceeds were also used to reduce amounts outstanding under the MPLX Credit Agreement at the time and will be used to redeem the $300 million aggregate principal amount of 6.250 percent senior notes due October 15, 2022, including approximately $34 million in aggregate principal amount of senior notes issued by ANDX, in October of 2020. The 6.250 percent senior notes are included on the Consolidated Balance Sheets as “Long-term debt due within one year” at September 30, 2020.

XML

Revenue

9 Months Ended

Sep. 30, 2020

Revenue from Contract with Customer [Abstract]

Revenue from Contract with Customer [Text Block]

Revenue

Disaggregation of Revenue

The following tables represent a disaggregation of revenue for each reportable segment for the three and nine months ended September 30, 2020 and 2019:

	Three Months Ended September 30, 2020
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	87	$	517	$	604
Service revenue - related parties	902		7		909
Service revenue - product related	—		41		41
Product sales	7		158		165
Product sales - related parties	2		35		37
Total revenues from contracts with customers	$	998	$	758	1,756
Non-ASC 606 revenue(1)					491
Total revenues and other income					$	2,247

	Three Months Ended September 30, 2019
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	95	$	537	$	632
Service revenue - related parties	881		18		899
Service revenue - product related	—		26		26
Product sales	14		157		171
Product sales - related parties	8		24		32
Total revenues from contracts with customers	$	998	$	762	1,760
Non-ASC 606 revenue(1)					520
Total revenues and other income					$	2,280

	Nine Months Ended September 30, 2020
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	248	$	1,531	$	1,779
Service revenue - related parties	2,676		18		2,694
Service revenue - product related	—		102		102
Product sales	39		415		454
Product sales - related parties	10		90		100
Total revenues from contracts with customers	$	2,973	$	2,156	5,129
Non-ASC 606 loss(1)					191
Total revenues and other income					$	5,320

	Nine Months Ended September 30, 2019
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	260	$	1,605	$	1,865
Service revenue - related parties	2,527		22		2,549
Service revenue - product related	—		86		86
Product sales	40		536		576
Product sales - related parties	17		92		109
Total revenues from contracts with customers	$	2,844	$	2,341	5,185
Non-ASC 606 revenue(1)					1,540
Total revenues and other income					$	6,725

(1) Non-ASC 606 Revenue includes rental income, income/(loss) from equity method investments, derivative gains and losses, mark-to-market adjustments, and other income.

Contract Balances

Contract assets typically relate to aid in construction agreements where the revenue recognized and MPLX’s rights to consideration for work completed exceeds the amount billed to the customer or for deficiency payments associated with minimum volume commitments which have not been billed to customers. Contract assets are generally classified as current and included in “Other current assets” on the Consolidated Balance Sheets.

Contract liabilities, which we refer to as “Deferred revenue” and “Long-term deferred revenue,” typically relate to advance payments for aid in construction agreements and deferred customer credits associated with makeup rights and minimum volume commitments. Related to minimum volume commitments, breakage is estimated and recognized into service revenue in instances where it is probable the customer will not use the credit in future periods. We classify contract liabilities as current or long-term based on the timing of when we expect to recognize revenue.

“Receivables, net” primarily relate to our commodity sales. Portions of the “Receivables, net” balance are attributed to the sale of commodity product controlled by MPLX prior to sale while a significant portion of the balance relates to the sale of commodity product on behalf of our producer customers. Both types of transactions are commingled and excluded from the table below. MPLX remits the net sales price back to our producer customers upon completion of the sale. Each period end, certain amounts within accounts payable relate to our payments to producer customers. Such amounts are not deemed material at period end as a result of when we settle with each producer.

The tables below reflect the changes in our contract balances for the nine-month periods ended September 30, 2020 and 2019:

(In millions)	Balance at December 31, 2019(1)		Additions/ (Deletions)			Revenue Recognized(2)			Balance at September 30, 2020
Contract assets	$	39	$	(9	)	$	(1	)	$	29
Deferred revenue	23		16			(6		)	33
Deferred revenue - related parties	53		77			(60		)	70
Long-term deferred revenue	90		25			—			115
Long-term deferred revenue - related parties	$	55	$	(7	)	$	—		$	48

(In millions)	Balance at December 31, 2018(1)		Additions/ (Deletions)			Revenue Recognized(2)			Balance at September 30, 2019
Contract assets	$	36	$	(6	)	$	(2	)	$	28
Deferred revenue	13		11			(4		)	20
Deferred revenue - related parties	65		34			(50		)	49
Long-term deferred revenue	56		26			—			82
Long-term deferred revenue - related parties	$	52	$	5		$	—		$	57

(1) Balance represents ASC 606 portion of each respective line item.

(2) No significant revenue was recognized related to past performance obligations in the current periods.

Remaining Performance Obligations

The table below includes estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period.

As of September 30, 2020, the amounts allocated to contract assets and contract liabilities on the Consolidated Balance Sheets are $264 million and are reflected in the amounts below. This will be recognized as revenue as the obligations are satisfied, which is expected to occur over the next 30 years. Further, MPLX does not disclose variable consideration due to volume variability in the table below.

(In millions)
2020	$	461
2021	1,727
2022	1,701
2023	1,591
2024 and thereafter	5,869
Total revenue on remaining performance obligations(1),(2),(3)	$	11,349

(1) All fixed consideration from contracts with customers is included in the amounts presented above. Variable consideration that is constrained or not required to be estimated as it reflects our efforts to perform is excluded.

(2) Arrangements deemed implicit leases are included in “Rental income” and are excluded from this table.

(3) Only minimum volume commitments that are deemed fixed are included in the table above. MPLX has various minimum volume commitments in processing arrangements that vary based on the actual Btu content of the gas received. These amounts are deemed variable consideration and are excluded from the table above.

We do not disclose information on the future performance obligations for any contract with an original expected duration of

one year or less.

XML

Supplemental Cash Flow Information

9 Months Ended

Sep. 30, 2020

Supplemental Cash Flow Elements [Abstract]

Supplemental Cash Flow Information [Text Block]

Supplemental Cash Flow Information

	Nine Months Ended September 30,
(In millions)	2020			2019
Net cash provided by operating activities included:
Interest paid (net of amounts capitalized)	$	631		$	648
Income taxes paid	1			—
Non-cash investing and financing activities:
Net transfers of property, plant and equipment (to)/from materials and supplies inventories	(1		)	1
Fair value of common units redeemed for Wholesale Exchange	$	340		$	—

The Consolidated Statements of Cash Flows exclude changes to the Consolidated Balance Sheets that did not affect cash. The following is the change of additions to property, plant and equipment related to capital accruals:

	Nine Months Ended September 30,
(In millions)	2020			2019
(Decrease)/increase in capital accruals	$	(197	)	$	(67	)

XML

Accumulated Other Comprehensive Income

9 Months Ended

Sep. 30, 2020

Accumulated Other Comprehensive Income (Loss) [Line Items]

Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]

Accumulated Other Comprehensive Loss

MPLX LP records an accumulated other comprehensive loss on the Consolidated Balance Sheets relating to pension and other post-retirement benefits provided by LOOP LLC (“LOOP”) and Explorer Pipeline Company (“Explorer”) to their employees. MPLX LP is not a sponsor of these benefit plans.

The following table shows the changes in “Accumulated other comprehensive loss” by component during the period December 31, 2019 through September 30, 2020.

(In millions)	Pension Benefits			Other Post-Retirement Benefits			Total
Balance at December 31, 2019(1)	$	(14	)	$	(1	)	$	(15	)
Other comprehensive loss - remeasurements(2)	—			(1		)	(1		)
Balance at September 30, 2020(1)	$	(14	)	$	(2	)	$	(16	)

The following table shows the changes in “Accumulated other comprehensive loss” by component during the period December 31, 2018 through September 30, 2019.

(In millions)	Pension Benefits			Other Post-Retirement Benefits			Total
Balance at December 31, 2018(1)	$	(14	)	$	(2	)	$	(16	)
Other comprehensive income - remeasurements(2)	—			1			1
Balance at September 30, 2019(1)	$	(14	)	$	(1	)	$	(15	)

(1) These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on the Consolidated Statements of Income under the caption “Income/(loss) from equity method investments.”

(2)

Components of other comprehensive income/loss - remeasurements relate to actuarial gains and losses as well as amortization of prior service costs. MPLX records an adjustment to “Comprehensive income” in accordance with its ownership interest in LOOP and Explorer.

XML

Equity-Based Compensation Plan

9 Months Ended

Sep. 30, 2020

Share-based Payment Arrangement [Abstract]

Share-based Payment Arrangement [Text Block]

Equity-Based Compensation

Phantom Units

The following is a summary of phantom unit award activity of MPLX LP common units for the nine months ended September 30, 2020:

	Number of Units		Weighted Average Fair Value
Outstanding at December 31, 2019	1,109,568		$	35.97
Granted	215,677		19.31
Settled	(558,398	)	37.73
Forfeited	(5,383	)	35.87
Outstanding at September 30, 2020	761,464		$	29.96

Performance Units – MPLX grants performance units to certain officers of the general partner and certain eligible MPC officers who make significant contributions to its business. These performance units pay out 75 percent in cash and 25 percent in MPLX LP common units and often contain both market and performance conditions based on various metrics. Market conditions are valued using a Monte Carlo valuation while performance conditions are reevaluated periodically and valued at the compensation cost associated with the performance outcome deemed most probable.

The performance units granted in 2020 are hybrid awards having a three-year performance period of January 1, 2020 through December 31, 2022. The payout of the award is dependent on two independent conditions, each constituting 50 percent of the overall target units granted. The awards have a performance condition based on MPLX LP’s distributable cash flow, and a market condition based on MPLX LP’s total unitholder return. The market condition was valued using a Monte Carlo valuation, resulting in a grant date fair value of $0.80 per unit for the 2020 equity-classified performance units. Grant date fair value of the performance condition is based on potential payouts per unit of up to $2.00 per unit. Compensation cost associated with the performance condition is based on the grant date fair value of the payout deemed most probable to occur and is adjusted as the expectation for payout changes.

During the first quarter of 2018, a performance award was granted; however, due to the nature of the award terms, the grant date for this award was not established until the first quarter of 2020 and we began recognizing units and expense related to this award at that time. The performance units granted in 2018 are hybrid awards having a three-year performance period of January 1, 2018 through December 31, 2020. The payout of the award is dependent on two independent conditions, each constituting 50 percent of the overall target units granted. The awards have a performance condition based on an average of MPLX LP’s distributable cash flow and a market condition based on MPLX LP’s total unitholder return. The market condition was valued using a Monte Carlo valuation, resulting in a grant date fair value of $0.45 per unit for the 2018 equity-classified performance units. Grant date fair value of the performance condition is based on potential payouts per unit of up to $2.00 per unit. Compensation cost associated with the performance condition is based on the grant date fair value of the payout deemed most probable to occur and is adjusted as the expectation for payout changes.

The following is a summary of the activity for performance unit awards to be settled in MPLX LP common units for the nine months ended September 30, 2020:

	Number of Units
Outstanding at December 31, 2019	2,157,347
Granted	2,147,211
Settled	(1,169,354	)
Forfeited	(31,668	)
Outstanding at September 30, 2020	3,103,536

XML

Leases Leases (Notes)

9 Months Ended

Sep. 30, 2020

Disclosure Text Block [Abstract]

Leases of Lessor Disclosure [Text Block]

Leases

During the first quarter of 2020, reimbursements for projects at certain MPLX refining logistics locations were agreed to between MPLX and MPC. These reimbursements relate to the storage services agreements between MPLX and MPC at these locations and required the embedded leases within these agreements to be reassessed under the leasing standard. As a result of the reassessment, one of our leases was reclassified from an operating lease to a sales-type lease. As a result, the underlying assets previously shown on the Consolidated Balance Sheets associated with the sales-type lease were derecognized and the net investment in the lease (i.e., the sum of the present value of the future lease payments and the unguaranteed residual value of the assets) was recorded as a lease receivable. See Note 5 for the location of lease receivables and unguaranteed residual assets on the Consolidated Balance Sheets. The difference between the net book value of the underlying assets and the net investment in the lease has been recorded as a Contribution from MPC in the Consolidated Statements of Equity given that the transaction related to refining logistics was a common control transaction. During the first quarter of 2020, MPLX derecognized approximately $171 million of property, plant and equipment, recorded a lease receivable of approximately $370 million, recorded an unguaranteed residual asset of approximately $10 million and a Contribution from MPC of $209 million.

Lease revenues included on the Consolidated Statements of Income were as follows:

	Three Months Ended September 30, 2020				Three Months Ended September 30, 2019
(In millions)	Related Party		Third Party		Related Party		Third Party
Operating leases:
Operating lease revenue(1)	$	208	$	70	$	248	$	63
Sales-type leases:
Profit/(loss) recognized at the commencement date	—		—		—		N/A
Interest income (Sales-type lease revenue- fixed minimum)	37		—		3		N/A
Interest income (Revenue from variable lease payments)	$	1	$	—	$	1	N/A

	Nine Months Ended September 30, 2020				Nine Months Ended September 30, 2019
(In millions)	Related Party		Third Party		Related Party		Third Party
Operating leases:
Operating lease revenue(1)	$	589	$	199	$	773	$	196
Sales-type leases:
Profit/(loss) recognized at the commencement date	—		—		—		N/A
Interest income (Sales-type lease revenue- fixed minimum)	113		—		3		N/A
Interest income (Revenue from variable lease payments)	$	1	$	—	$	1	N/A

(1) These amounts are presented net of executory costs.

See Note 5 for additional information on where related party lease assets are recorded in the Consolidated Balance Sheets. Third party lease assets are less than $1 million as of September 30, 2020 and are included within the “Receivables, net” and “Other noncurrent assets” captions within the Consolidated Balance Sheets.

The following is a schedule of future payments on the sales-type leases as of September 30, 2020:

(In millions)	Related Party
2020	$	39
2021	157
2022	157
2023	158
2024	158
2025 and thereafter	473
Total minimum future rentals	1,142
Less: present value discount	723
Lease receivable	$	419

XML

Commitments and Contingencies

9 Months Ended

Sep. 30, 2020

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies Disclosure [Text Block]

Commitments and Contingencies

MPLX is the subject of, or a party to, a number of pending or threatened legal actions, contingencies and commitments involving a variety of matters, including laws and regulations relating to the environment. Some of these matters are discussed below. For matters for which MPLX has not recorded a liability, MPLX is unable to estimate a range of possible loss because

the issues involved have not been fully developed through pleadings, discovery or court proceedings. However, the ultimate resolution of some of these contingencies could, individually or in the aggregate, be material.

Environmental Matters – MPLX is subject to federal, state and local laws and regulations relating to the environment. These laws generally provide for control of pollutants released into the environment and require responsible parties to undertake remediation of hazardous waste disposal sites. Penalties may be imposed for non-compliance.

At September 30, 2020 and December 31, 2019, accrued liabilities for remediation totaled $18 million and $19 million, respectively. It is not presently possible to estimate the ultimate amount of all remediation costs that might be incurred or the penalties, if any, that may be imposed. At September 30, 2020 and December 31, 2019, there were no balances with MPC for indemnification of environmental costs.

MPLX is involved in environmental enforcement matters arising in the ordinary course of business. While the outcome and impact to MPLX cannot be predicted with certainty, management believes the resolution of these environmental matters will not, individually or collectively, have a material adverse effect on its consolidated results of operations, financial position or cash flows.

MPLX is also a party to a number of other lawsuits and other proceedings arising in the ordinary course of business. While the ultimate outcome and impact to MPLX cannot be predicted with certainty, management believes the resolution of these other lawsuits and proceedings will not, individually or collectively, have a material adverse effect on its consolidated financial position, results of operations or cash flows.

Guarantees – Over the years, MPLX has sold various assets in the normal course of its business. Certain of the related agreements contain performance and general guarantees, including guarantees regarding inaccuracies in representations, warranties, covenants and agreements, and environmental and general indemnifications that require MPLX to perform upon the occurrence of a triggering event or condition. These guarantees and indemnifications are part of the normal course of selling assets. MPLX is typically not able to calculate the maximum potential amount of future payments that could be made under such contractual provisions because of the variability inherent in the guarantees and indemnities. Most often, the nature of the guarantees and indemnities is such that there is no appropriate method for quantifying the exposure because the underlying triggering event has little or no past experience upon which a reasonable prediction of the outcome can be based.

In connection with our 9.19 percent indirect interest in a joint venture (“Dakota Access”) that owns and operates the Dakota Access Pipeline and Energy Transfer Crude Oil Pipeline projects, collectively referred to as the Bakken Pipeline system or DAPL, we have entered into a Contingent Equity Contribution Agreement whereby MPLX LP, along with the other joint venture owners in the Bakken Pipeline system, has agreed to make equity contributions to the joint venture upon certain events occurring to allow the entities that own and operate the Bakken Pipeline system to satisfy their senior note payment obligations. The senior notes were issued to repay amounts owed by the pipeline companies to fund the cost of construction of the Bakken Pipeline system.

In March 2020, the U.S. District Court for the District of Columbia (the “D.D.C.”) ordered the U.S. Army Corps of Engineers (“Army Corps”), which granted permits and an easement for the Bakken Pipeline system, to conduct a full environmental impact statement (“EIS”), and further requested briefing on whether an easement necessary for the operation of the Bakken Pipeline system should be vacated while the EIS is being prepared.

On July 6, 2020, the D.D.C. ordered vacatur of the easement to cross Lake Oahe during the pendency of an EIS and further ordered a shut down of the pipeline by August 5, 2020. The D.D.C. denied a motion to stay that order. Dakota Access and the Army Corps appealed the D.D.C.’s order to the U.S. Court of Appeals for the District of Columbia Circuit (the “Court of Appeals”). On July 14, 2020, the Court of Appeals issued an administrative stay while the court considered Dakota Access and the Army Corps’ emergency motion for stay pending appeal. On August 5, 2020, the Court of Appeals stayed the D.D.C.’s injunction that required the pipeline be shutdown and emptied of oil by August 5, 2020. The Court of Appeals denied a stay of the D.D.C.’s March order, which required the EIS, and further denied a stay of the D.D.C.’s July order, which vacated the easement. In the D.D.C., briefing is ongoing for a renewed request for an injunction, which is expected to be completed by the end of 2020. Oral argument on the merits of the case at the Court of Appeals occurred on November 4, 2020. The pipeline remains operational.

If the pipeline is temporarily shutdown pending completion of the EIS, MPLX would have to contribute its 9.19 percent pro rata share of funds required to pay interest accruing on the notes and any portion of the principal that matures while the pipeline is shutdown. MPLX also expects to contribute its 9.19 percent pro rata share of any costs to remediate any deficiencies to reinstate the permit and/or return the pipeline into operation. If the vacatur of the easement permit results in a permanent

shutdown of the pipeline, MPLX would have to contribute its 9.19 percent pro rata share of the cost to redeem the bonds (including the 1% redemption premium required pursuant to the indenture governing the notes) and any accrued and unpaid interest. As of September 30, 2020, our maximum potential undiscounted payments under the Contingent Equity Contribution Agreement were approximately $230 million.

Other Legal Proceedings – In early July, MPLX received a Notification of Trespass Determination from the Bureau of Indian Affairs (“BIA”) relating to a portion of the Tesoro High Plains Pipeline that crosses the Fort Berthold Reservation in North Dakota. The notification covered the rights of way for 23 tracts of land and demanded the immediate cessation of pipeline operations. The notification also assessed trespass damages of approximately $187 million. We appealed this determination, which triggered an automatic stay of the requested pipeline shutdown and payment. On October 29, the Assistant Secretary - Indian Affairs issued an order vacating the BIA’s trespass order and requiring the Regional Director for the BIA Great Plains Region to issue a new decision on or before December 15 covering all 34 tracts at issue.

We continue to work towards a settlement of this matter with holders of the property rights at issue. Management does not believe the ultimate resolution of this matter will have a material adverse effect on our consolidated financial position, results of operations, or cash flows.

Contractual Commitments and Contingencies – At September 30, 2020, MPLX’s contractual commitments to acquire property, plant and equipment totaled $181 million. These commitments were primarily related to G&P plant expansion, terminal and pipeline projects. In addition, from time to time and in the ordinary course of business, MPLX and its affiliates provide guarantees of MPLX’s subsidiaries payment and performance obligations in the G&P segment. Certain natural gas processing and gathering arrangements require MPLX to construct new natural gas processing plants, natural gas gathering pipelines and NGL pipelines and contain certain fees and charges if specified construction milestones are not achieved for reasons other than force majeure. In certain cases, certain producers may have the right to cancel the processing arrangements if there are significant delays that are not due to force majeure. As of September 30, 2020, management does not believe there are any indications that MPLX will not be able to meet the construction milestones, that force majeure does not apply or that such fees and charges will otherwise be triggered.

XML

Description of the Business and Basis of Presentation Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2020

Accounting Policies [Abstract]

Business Description and Basis of Presentation [Text Block]

Description of the Business and Basis of Presentation

Description of the Business – MPLX LP is a diversified, large-cap master limited partnership formed by Marathon Petroleum Corporation that owns and operates midstream energy infrastructure and logistics assets, and provides fuels distribution services. References in this report to “MPLX LP,” “MPLX,” “the Partnership,” “we,” “ours,” “us,” or like terms refer to MPLX LP and its subsidiaries. References to “MPC” refer collectively to Marathon Petroleum Corporation as our sponsor and its subsidiaries, other than the Partnership. We are engaged in the transportation, storage and distribution of crude oil, asphalt and refined petroleum products; the gathering, processing and transportation of natural gas; and the gathering, transportation, fractionation, storage and marketing of NGLs. MPLX’s principal executive office is located in Findlay, Ohio.

MPLX’s business consists of two segments based on the nature of services it offers: Logistics and Storage (“L&S”), which relates primarily to crude oil, asphalt and refined petroleum products; and Gathering and Processing (“G&P”), which relates primarily to natural gas and NGLs. See Note 9 for additional information regarding the operations and results of these segments.

On July 30, 2019, MPLX completed its acquisition by merger (the “Merger”) of Andeavor Logistics LP (“ANDX”). At the effective time of the Merger, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units. ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. See Note 3 for additional information regarding the Merger.

On July 31, 2020, MPLX completed the exchange of Western Refining Wholesale, LLC (WRW”) to Western Refining Southwest, Inc. (“WRSW”), a wholly owned subsidiary of MPC, in exchange for the redemption of 18,582,088 MPLX common units held by WRSW (the “Wholesale Exchange”). See Note 3 for additional information regarding the Wholesale Exchange. These financial statements include the results of WRSW through July 31, 2020.

Impairments – The outbreak of COVID-19 and its development into a pandemic in March 2020 resulted in significant economic disruption globally. Actions taken by various governmental authorities, individuals and companies around the world to prevent the spread of COVID-19 through social distancing have restricted travel, many business operations, public gatherings and the overall level of individual movement and in-person interaction across the globe. Although there have been some signs of economic improvement, these events significantly reduced global economic activity and resulted in a decline in the demand for the midstream services we provide beginning with the first quarter of 2020. Macroeconomic conditions and global geopolitical events have also resulted in significant price volatility related to those aforementioned products.

The overall deterioration in the economy and the environment in which MPLX and its customers operate, as well as a sustained decrease in unit price, were considered triggering events resulting in impairments of the carrying value of certain assets during the first quarter of 2020. We recognized impairments related to goodwill, certain equity method investments and certain long-lived assets (including intangibles), within our G&P segment. Many of our producer customers refined and updated production forecasts in response to the current environment, which impacted their current and expected future demand for our services, including the future utilization of our assets. Additionally, certain of our contracts have commodity price exposure, including NGL prices, which have experienced increased volatility as noted above. The table below provides information related to the impairments recognized during the first quarter of 2020 as well as the corresponding footnote where additional information can be found. No additional events or circumstances arose during the second or third quarters of 2020 which would indicate the need for any additional impairment beyond those recognized during the first quarter.

(In millions)	Impairment		Footnote Reference
Goodwill	$	1,814	12
Equity method investments	1,264		4
Intangibles, net	177		12
Property, plant and equipment, net	174		11
Total impairments	$	3,429

Basis of Presentation – The accompanying interim consolidated financial statements are unaudited; however, in the opinion of MPLX’s management, these statements reflect all adjustments necessary for a fair statement of the results for the periods reported. All such adjustments are of a normal, recurring nature unless otherwise disclosed. These interim consolidated financial statements, including the notes, have been prepared in accordance with the rules and regulations of the SEC

applicable to interim period financial statements and do not include all of the information and disclosures required by GAAP for complete financial statements. Certain amounts in prior years have been reclassified to conform to current year presentation.

These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the year ended December 31, 2019. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results to be expected for the full year.

In relation to the Merger described above and in Note 3, ANDX’s assets, liabilities and results of operations prior to the Merger are collectively included in what we refer to as the “Predecessor” from October 1, 2018, which was the date that MPC acquired Andeavor. MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s relationship with ANDX prior to the Merger. As an entity under common control with MPC, MPLX recorded the assets acquired and liabilities assumed on its consolidated balance sheets at MPC’s historical carrying value. For the acquiring entity, transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the accompanying financial statements and related notes of MPLX LP have been retrospectively adjusted to include the historical results of ANDX beginning October 1, 2018.

MPLX’s consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly owned consolidated subsidiaries, the interests owned by third parties have been recorded as “Noncontrolling interests” on the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. MPLX’s investments in which MPLX exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. MPLX’s investments in VIEs in which MPLX exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method.

In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule. Distributions, although earned, are not accrued until declared. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in Note 6.

Use of Estimates, Policy [Policy Text Block]

The accompanying interim consolidated financial statements are unaudited; however, in the opinion of MPLX’s management, these statements reflect all adjustments necessary for a fair statement of the results for the periods reported. All such adjustments are of a normal, recurring nature unless otherwise disclosed. These interim consolidated financial statements, including the notes, have been prepared in accordance with the rules and regulations of the SEC

applicable to interim period financial statements and do not include all of the information and disclosures required by GAAP for complete financial statements. Certain amounts in prior years have been reclassified to conform to current year presentation.

Earnings Per Share, Policy [Policy Text Block]

In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule. Distributions, although earned, are not accrued until declared. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in Note 6.

Net income/(loss) per unit applicable to common units is computed by dividing net income/(loss) attributable to MPLX LP less income/(loss) allocated to participating securities by the weighted average number of common units outstanding.

XML

Net Income Per Limited Partner Unit Accounting Policy (Policies)

9 Months Ended

Sep. 30, 2020

Accounting Policies [Abstract]

Earnings Per Share, Policy [Policy Text Block]

In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule. Distributions, although earned, are not accrued until declared. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in Note 6.

Net income/(loss) per unit applicable to common units is computed by dividing net income/(loss) attributable to MPLX LP less income/(loss) allocated to participating securities by the weighted average number of common units outstanding.

XML

Equity Method Investments (Tables)

9 Months Ended

Sep. 30, 2020

Schedule of Equity Method Investments [Line Items]

Equity Method Investments [Table Text Block]

The following table presents MPLX’s equity method investments at the dates indicated:

	Ownership as of	Carrying value at
	September 30,	September 30,		December 31,
(In millions, except ownership percentages)	2020	2020		2019
L&S
MarEn Bakken Company LLC(1)	25%	$	469	$	481
Illinois Extension Pipeline Company, L.L.C.	35%	261		265
LOOP LLC	41%	249		238
Andeavor Logistics Rio Pipeline LLC(2)	67%	195		202
Minnesota Pipe Line Company, LLC	17%	189		190
Whistler Pipeline LLC(2)	38%	184		134
Explorer Pipeline Company	25%	78		83
W2W Holdings LLC(2)(3)	50%	77		—
Wink to Webster Pipeline LLC(2)(3)	15%	—		126
Other(2)		100		55
Total L&S		1,802		1,774
G&P
MarkWest Utica EMG, L.L.C.(2)	57%	720		1,984
Sherwood Midstream LLC(2)	50%	560		537
MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C.(2)	67%	307		302
Rendezvous Gas Services, L.L.C.(2)	78%	164		170
Sherwood Midstream Holdings LLC(2)	51%	151		157
Centrahoma Processing LLC	40%	147		153
Other(2)		230		198
Total G&P		2,279		3,501
Total		$	4,081	$	5,275

(1) The investment in MarEn Bakken Company LLC includes our 9.19 percent indirect interest in a joint venture (“Dakota Access”) that owns and operates the Dakota Access Pipeline and Energy Transfer Crude Oil Pipeline projects, collectively referred to as the Bakken Pipeline system or DAPL.    

(2) Investments deemed to be VIEs. Some investments included within “Other” have also been deemed to be VIEs.

(3) During the nine months ended September 30, 2020, we contributed our ownership in Wink to Webster Pipeline LLC to W2W Holdings LLC.

Summarized Financial Information For Equity Method Investees Table [Table Text Block]

Summarized financial information for MPLX’s equity method investments for the nine months ended September 30, 2020 and 2019 is as follows:

	Nine Months Ended September 30, 2020
(In millions)	VIEs			Non-VIEs		Total
Revenues and other income	$	132		$	933	$	1,065
Costs and expenses	308			405		713
Income from operations	(176		)	528		352
Net income	(230		)	477		247
(Loss)/income from equity method investments(1)	$	(1,138	)	$	126	$	(1,012	)

(1) Includes the impact of any basis differential amortization or accretion in addition to the impairment of $1,264 million.

	Nine Months Ended September 30, 2019
(In millions)	VIEs		Non-VIEs		Total
Revenues and other income	$	479	$	1,116	$	1,595
Costs and expenses	251		434		685
Income from operations	228		682		910
Net income	192		605		797
Income from equity method investments(1)	$	89	$	166	$	255

(1) Includes the impact of any basis differential amortization or accretion.

Summarized balance sheet information for MPLX’s equity method investments as of September 30, 2020 and December 31, 2019 is as follows:

	September 30, 2020
(In millions)	VIEs		Non-VIEs		Total
Current assets	$	774	$	367	$	1,141
Noncurrent assets	6,398		5,024		11,422
Current liabilities	304		194		498
Noncurrent liabilities	$	1,611	$	857	$	2,468

	December 31, 2019
(In millions)	VIEs		Non-VIEs		Total
Current assets	$	534	$	330	$	864
Noncurrent assets	5,862		5,134		10,996
Current liabilities	192		245		437
Noncurrent liabilities	$	305	$	822	$	1,127

XML

Related Party Agreements and Transactions (Tables)

9 Months Ended

Sep. 30, 2020

Related Party Transactions [Abstract]

Other Long-term Debt, Noncurrent

Activity on the MPC Loan Agreement was as follows:

(In millions)	Nine Months Ended September 30, 2020			Year Ended December 31, 2019
Borrowings	$	4,870		$	8,540
Average interest rate of borrowings	2.380		%	3.441		%
Repayments	$	5,464		$	7,946
Outstanding balance at end of period(1)	$	—		$	594

(1) Included in “Current liabilities - related parties” on the Consolidated Balance Sheets.

Prior to the Merger, ANDX was also party to a loan agreement with MPC (“ANDX-MPC Loan Agreement”). This facility was entered into on December 21, 2018, with a borrowing capacity of $500 million. In connection with the Merger, on July 31, 2019, MPLX repaid the entire outstanding balance and terminated the ANDX-MPC Loan Agreement. Activity on the ANDX-MPC Loan Agreement prior to the Merger was as follows:

(In millions)	Year Ended December 31, 2019
Borrowings	$	773
Average interest rate of borrowings	4.249		%
Repayments	$	773
Outstanding balance at end of period	$	—

Schedule of Sales to Related Parties

Revenue received from related parties included on the Consolidated Statements of Income was as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020		2019
Service revenues - related parties
MPC	$	908	$	899	$	2,692	$	2,549
Other	1		—		2		—
Total Service revenue - related parties	909		899		2,694		2,549
Rental income - related parties
MPC	241		293		712		904
Product sales - related parties(1)
MPC	37		32		100		109
Other income - related parties
MPC	48		14		144		34
Other	15		17		46		50
Total Other income - related parties	$	63	$	31	$	190	$	84

(1) There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For the three and nine months ended September 30, 2020, these sales totaled $107 million and $332 million, respectively. For the three and nine months ended September 30, 2019, these sales totaled $301 million and $819 million, respectively.

Schedule of Employee Services Expenses from Related Parties

Expenses incurred from MPC under the omnibus and employee services agreements as well as other purchases from MPC included on the Consolidated Statements of Income are as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020		2019
Rental cost of sales - related parties
MPC	$	32	$	45	$	119	$	124
Purchases - related parties
MPC	293		297		840		878
Other	4		6		13		16
Total Purchase - related parties	297		303		853		894
General and administrative expenses
MPC	63		59		195		174
Restructuring expenses
MPC	$	36	$	—	$	36	$	—

Schedule of Related Party Transactions [Table Text Block]

(In millions)	September 30, 2020		December 31, 2019
Current assets - related parties
Receivables - MPC	$	543	$	621
Receivables - Other	7		22
Prepaid - MPC	11		9
Other - MPC	1		—
Lease Receivables - MPC	29		4
Total	591		656
Noncurrent assets - related parties
Long-term receivables - MPC	32		21
Right of use assets - MPC	231		232
Long-term lease receivables - MPC	390		43
Unguaranteed residual asset - MPC	22		7
Total	675		303
Current liabilities - related parties
Payables - MPC	247		911
Payables - Other	42		37
Operating lease liabilities - MPC	1		1
Deferred revenue - Minimum volume deficiencies - MPC	54		42
Deferred revenue - Project reimbursements - MPC	19		16
Deferred revenue - Project reimbursements - Other	1		1
Total	364		1,008
Long-term liabilities - related parties
Long-term operating lease liabilities - MPC	230		230
Long-term deferred revenue - Project reimbursements - MPC	45		53
Long-term deferred revenue - Project reimbursements - Other	6		7
Total	$	281	$	290

XML

Net Income Per Limited Partner Unit (Tables)

9 Months Ended

Sep. 30, 2020

Earnings Per Share [Abstract]

Schedule of Distributions By Partner By Class

For the three and nine months ended September 30, 2020 and 2019, MPLX had dilutive potential common units consisting of certain equity-based compensation awards. Potential common units omitted from the diluted earnings per unit calculation for the three and nine months ended September 30, 2020 and 2019 were less than 1 million.

	Three Months Ended September 30,						Nine Months Ended September 30,
(In millions)	2020			2019			2020			2019
Net income/(loss) attributable to MPLX LP	$	665		$	629		$	(1,411	)	$	1,614
Less: Distributions declared on Series A preferred units(1)	20			20			61			61
Distributions declared on Series B preferred units(1)	10			10			31			31
Limited partners’ distributions declared on MPLX common units (including common units of general partner)(1)(2)	715			704			2,158			1,919
Undistributed net loss attributable to MPLX LP	$	(80	)	$	(105	)	$	(3,661	)	$	(397	)

(1) See Note 7 for distribution information.

(2) The three and nine months ended September 30, 2019 amounts are net of $12.5 million and $25 million, respectively, of waived distributions with respect to units held by MPC and its affiliates.

	Three Months Ended September 30, 2020
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	715		$	20	$	10	$	745
Undistributed net loss attributable to MPLX LP	(80		)	—		—		(80		)
Net income attributable to MPLX LP(1)	$	635		$	20	$	10	$	665
Weighted average units outstanding:
Basic	1,046
Diluted	1,047
Net income attributable to MPLX LP per limited partner unit:
Basic	$	0.61
Diluted	$	0.61

Schedule of Basic and Diluted Earnings Per Unit

	Three Months Ended September 30, 2020
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	715		$	20	$	10	$	745
Undistributed net loss attributable to MPLX LP	(80		)	—		—		(80		)
Net income attributable to MPLX LP(1)	$	635		$	20	$	10	$	665
Weighted average units outstanding:
Basic	1,046
Diluted	1,047
Net income attributable to MPLX LP per limited partner unit:
Basic	$	0.61
Diluted	$	0.61

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

	Three Months Ended September 30, 2019
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	704		$	20	$	10	$	734
Undistributed net loss attributable to MPLX LP	(105		)	—		—		(105		)
Net income attributable to MPLX LP(1)	$	599		$	20	$	10	$	629
Weighted average units outstanding:
Basic(2)	974
Diluted(2)	975
Net income attributable to MPLX LP per limited partner unit:
Basic	$	0.61
Diluted	$	0.61

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

(2) The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire three months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

	Nine Months Ended September 30, 2020
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	2,158		$	61	$	31	$	2,250
Undistributed net loss attributable to MPLX LP	(3,661		)	—		—		(3,661		)
Net (loss)/income attributable to MPLX LP(1)	$	(1,503	)	$	61	$	31	$	(1,411	)
Weighted average units outstanding:
Basic	1,054
Diluted	1,054
Net income attributable to MPLX LP per limited partner unit:
Basic	$	(1.43	)
Diluted	$	(1.43	)

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

	Nine Months Ended September 30, 2019
(In millions, except per unit data)	Limited Partners’ Common Units			Series A Preferred Units		Series B Preferred Units		Total
Basic and diluted net income attributable to MPLX LP per unit
Net income attributable to MPLX LP:
Distributions declared	$	1,919		$	61	$	31	$	2,011
Undistributed net loss attributable to MPLX LP	(397		)	—		—		(397		)
Net income attributable to MPLX LP(1)	$	1,522		$	61	$	31	$	1,614
Weighted average units outstanding:
Basic(2)	855
Diluted(2)	855
Net income attributable to MPLX LP per limited partner unit:
Basic	$	1.78
Diluted	$	1.78

(1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

(2)

The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire nine months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

XML

Equity (Tables)

9 Months Ended

Sep. 30, 2020

Equity [Abstract]

Schedule of Stockholders Equity [Table Text Block]

The changes in the number of common units outstanding during the nine months ended September 30, 2020 are summarized below:

(In units)	Common
Balance at December 31, 2019	1,058,355,471
Unit-based compensation awards	395,091
Units redeemed in Wholesale Exchange	(18,582,088	)
Balance at September 30, 2020	1,040,168,474

Wholesale Exchange and Merger

In connection with the Wholesale Exchange as discussed in Note 3, 18,582,088 units were redeemed by MPC in exchange for all of the outstanding membership interests in WRW. These units were cancelled by MPLX immediately following the transaction.

In connection with the Merger and as discussed in Note 3, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units while ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. This resulted in the issuance of MPLX common units of approximately 102 million units to public unitholders and approximately 161 million units to MPC on July 30, 2019.

Series B Preferred Units

Prior to the Merger, ANDX had outstanding 600,000 units of 6.875 percent Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Units representing limited partner interests of ANDX at a price to the public of $1,000 per unit. Upon completion of the Merger, the ANDX preferred units converted to preferred units of MPLX representing substantially equivalent limited partnership interests in MPLX (the “Series B preferred units”). The Series B preferred units are pari passu with the Series A preferred units with respect to distribution rights and rights upon liquidation. Distributions on the Series B preferred units are payable semi-annually in arrears on the 15th day, or the first business day thereafter, of February and August of each year up to and including February 15, 2023. After February 15, 2023, the holders of Series B preferred units are entitled to receive cumulative, quarterly distributions payable in arrears on the 15th day of February, May, August and November of each year, or the first business day thereafter, based on a floating annual rate equal to the three-month LIBOR plus 4.652 percent.

The changes in the Series B preferred unit balance from December 31, 2019 through September 30, 2020 are summarized below. Series B preferred units are included in the Consolidated Balance Sheets and Consolidated Statements of Equity within “Equity of Predecessor” for the period prior to the Merger and within “Series B preferred units” for the period following the Merger.

(In millions)	Series B Preferred Units
Balance at December 31, 2019	$	611
Net income allocated	31
Distributions received by Series B preferred unitholders	(41		)
Balance at September 30, 2020	$	601

Distributions Made to Limited Partner, by Distribution [Table Text Block]

The allocation of total quarterly cash distributions to limited and preferred unitholders is as follows for the three and nine months ended September 30, 2020 and 2019. MPLX’s distributions are declared subsequent to quarter end; therefore, the following table represents total cash distributions applicable to the period in which the distributions were earned.

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020		2019
Common and preferred unit distributions:
Common unitholders, includes common units of general partner	$	715	$	704	$	2,158	$	1,919
Series A preferred unit distributions	20		20		61		61
Series B preferred unit distributions	10		10		31		31
Total cash distributions declared	$	745	$	734	$	2,250	$	2,011

The distribution on common units for the three and nine months ended September 30, 2019 includes the impact of the issuance of approximately 102 million units issued to public unitholders and approximately 161 million units issued to MPC in connection with the Merger. Due to the timing of the closing, distributions presented in the table above include second quarter

distributions for MPLX common units and Series B preferred units issued to former ANDX unitholders in connection with the Merger. The distributions on common units exclude $12.5 million of waived distributions for the three months ended September 30, 2019 and $25 million of waived distributions for the nine months ended September 30, 2019.

XML

Series A Preferred Units (Tables)

9 Months Ended

Sep. 30, 2020

Temporary Equity Disclosure [Abstract]

Rollforward of Redeemable Preferred Units

The changes in the redeemable preferred balance from December 31, 2019 through September 30, 2020 are summarized below:

(In millions)	Redeemable Series A Preferred Units
Balance at December 31, 2019	$	968
Net income allocated	61
Distributions received by Series A preferred unitholders	(61		)
Balance at September 30, 2020	$	968

XML

Segment Information (Tables)

9 Months Ended

Sep. 30, 2020

Segment Reporting [Abstract]

Schedule of Segment Reporting Information, by Segment [Table Text Block]

The tables below present information about revenues and other income, capital expenditures and investments in unconsolidated affiliates as well as total assets for our reportable segments:

	Three Months Ended September 30,				Nine Months Ended September 30,
(In millions)	2020		2019		2020			2019
L&S
Service revenue	$	989	$	976	$	2,924		$	2,787
Rental income	249		304		737			935
Product related revenue	9		22		49			57
Income from equity method investments	36		60		126			159
Other income	51		17		154			45
Total segment revenues and other income(1)	1,334		1,379		3,990			3,983
Segment Adjusted EBITDA(2)	893		766		2,604			1,895
Restructuring expenses	27		—		27			—
Capital expenditures	118		272		410			700
Investments in unconsolidated affiliates	4		95		132			163
G&P
Service revenue	524		555		1,549			1,627
Rental income	94		88		271			260
Product related revenue	234		207		607			714
Income/(loss) from equity method investments	47		35		(1,138		)	96
Other income	14		16		41			45
Total segment revenues and other income(1)	913		901		1,330			2,742
Segment Adjusted EBITDA(2)	442		399		1,252			1,120
Restructuring expenses	9		—		9			—
Capital expenditures	131		321		375			953
Investments in unconsolidated affiliates	$	18	$	76	$	112		$	331

(1) Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $139 million and $443 million for the three and nine months ended September 30, 2020, respectively, and $182 million and $498 million for the three and nine months ended September 30, 2019, respectively. Third party revenues for the G&P segment were $858 million and $1,181 million for the three and nine months ended September 30, 2020, respectively, and $843 million and $2,581 million for the three and nine months ended September 30, 2019, respectively.

(2)

See below for the reconciliation from Segment Adjusted EBITDA to net income.

Reconciliation of Assets from Segment to Consolidated [Table Text Block]

(In millions)	September 30, 2020		December 31, 2019
Segment assets
Cash and cash equivalents	$	28	$	15
L&S	21,144		20,810
G&P	15,490		19,605
Total assets	$	36,662	$	40,430

Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table Text Block]

The table below provides a reconciliation between net (loss)/income and Segment Adjusted EBITDA.

	Three Months Ended September 30,						Nine Months Ended September 30,
(In millions)	2020			2019			2020			2019
Reconciliation to Net income/(loss):
L&S Segment Adjusted EBITDA	$	893		$	766		$	2,604		$	1,895
G&P Segment Adjusted EBITDA	442			399			1,252			1,120
Total reportable segments	1,335			1,165			3,856			3,015
Depreciation and amortization(1)	(346		)	(302		)	(992		)	(916		)
Provision for income taxes	(1		)	(4		)	(1		)	(2		)
Amortization of deferred financing costs	(15		)	(10		)	(44		)	(29		)
Non-cash equity-based compensation	(4		)	(5		)	(12		)	(17		)
Impairment expense	—			—			(2,165		)	—
Net interest and other financial costs	(223		)	(223		)	(647		)	(657		)
Gain on extinguishment of debt	14			—			14			—
Income/(loss) from equity method investments	83			95			(1,012		)	255
Distributions/adjustments related to equity method investments	(130		)	(145		)	(369		)	(399		)
Unrealized derivative (losses)/gains(2)	(10		)	11			(1		)	7
Acquisition costs	—			(9		)	—			(14		)
Restructuring expenses	(36		)	—			(36		)	—
Other	(3		)	(1		)	(5		)	(1		)
Adjusted EBITDA attributable to noncontrolling interests	10			9			27			23
Adjusted EBITDA attributable to Predecessor(3)	—			108			—			770
Net income/(loss)	$	674		$	689		$	(1,387	)	$	2,035

(1) Depreciation and amortization attributable to L&S was $164 million and $440 million for the three and nine months ended September 30, 2020, respectively, and $113 million and $373 million for the three and nine months ended September 30, 2019, respectively. Depreciation and amortization attributable to G&P was $182 million and $552 million for the three and nine months ended September 30, 2020, respectively, and $189 million and $543 million for the three and nine months ended September 30, 2019, respectively.

(2) MPLX makes a distinction between realized and unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

(3)

The adjusted EBITDA adjustments related to Predecessor are excluded from adjusted EBITDA attributable to MPLX LP prior to the Merger.

XML

Inventories (Tables)

9 Months Ended

Sep. 30, 2020

Inventory Disclosure [Abstract]

Summary of Inventories

Inventories consist of the following:

(In millions)	September 30, 2020		December 31, 2019
NGLs	$	3	$	5
Line fill	11		10
Spare parts, materials and supplies	103		95
Total inventories	$	117	$	110

XML

Property, Plant and Equipment (Tables)

9 Months Ended

Sep. 30, 2020

Property, Plant and Equipment [Abstract]

Summary of Property, Plant and Equipment

Property, plant and equipment with associated accumulated depreciation is shown below:

(In millions)	Estimated Useful Lives	September 30, 2020		December 31, 2019
L&S
Pipelines	2-51 years	$	6,001	$	5,572
Refining Logistics	13-40 years	2,196		2,870
Terminals	4-40 years	1,534		1,109
Marine	15-20 years	961		906
Land, building and other	1-61 years	1,576		1,817
Construction-in progress		403		660
Total L&S property, plant and equipment		12,671		12,934
G&P
Gathering and transportation	5-40 years	7,413		7,159
Processing and fractionation	10-40 years	5,944		5,545
Land, building and other	3-40 years	509		484
Construction-in-progress		382		745
Total G&P property, plant and equipment		14,248		13,933
Total property, plant and equipment		26,919		26,867
Less accumulated depreciation(1)		5,304		4,722
Property, plant and equipment, net		$	21,615	$	22,145

(1) The September 30, 2020 balance includes property, plant and equipment impairment charges recorded during the first quarter of 2020 as discussed below.

XML

Goodwill and Intangibles (Tables)

9 Months Ended

Sep. 30, 2020

Finite-Lived Intangible Assets [Line Items]

Schedule of Finite-Lived Intangible Assets [Table Text Block]

Gross intangible assets with accumulated amortization as of September 30, 2020 and December 31, 2019 is shown below:

		September 30, 2020							December 31, 2019
(In millions)	Useful Lives	Gross		Accumulated Amortization(1)(2)			Net		Gross		Accumulated Amortization			Net
L&S	6 - 8 years	$	283	$	(72	)	$	211	$	283	$	(45	)	$	238
G&P	6 - 25 years	1,288		(508		)	780		1,288		(256		)	1,032
		$	1,571	$	(580	)	$	991	$	1,571	$	(301	)	$	1,270

(1) Amortization expense attributable to the G&P and L&S segments for the nine months ended September 30, 2020 was $75 million and $27 million, respectively.

(2)

Impairment charge of $177 million is included within the G&P accumulated amortization.

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]

Estimated future amortization expense related to the intangible assets at September 30, 2020 is as follows:

(In millions)
2020	$	32
2021	128
2022	128
2023	128
2024	124
Thereafter	451
Total	$	991

XML

Goodwill and Intangibles Goodwill and Intangibles (Tables)

9 Months Ended

Sep. 30, 2020

Goodwill [Line Items]

Schedule of Goodwill [Table Text Block]

The changes in carrying amount of goodwill were as follows:

(In millions)	L&S			G&P			Total
Gross goodwill as of December 31, 2018	$	7,234		$	2,912		$	10,146
Accumulated impairment losses	—			(130		)	(130		)
Balance as of December 31, 2018	7,234			2,782			10,016
Impairment losses	—			(1,197		)	(1,197		)
Acquisitions	488			229			717
Balance as of December 31, 2019	7,722			1,814			9,536
Impairment losses	—			(1,814		)	(1,814		)
Wholesale Exchange (Note 3)	(65		)	—			(65		)
Balance as of September 30, 2020	7,657			—			7,657
Gross goodwill as of September 30, 2020	7,657			3,141			10,798
Accumulated impairment losses	—			(3,141		)	(3,141		)
Balance as of September 30, 2020	$	7,657		$	—		$	7,657

XML

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2020

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

The following table presents the financial instruments carried at fair value on a recurring basis as of September 30, 2020 and December 31, 2019 by fair value hierarchy level. MPLX has elected to offset the fair value amounts recognized for multiple derivative contracts executed with the same counterparty.

	September 30, 2020					December 31, 2019
(In millions)	Assets		Liabilities			Assets		Liabilities
Significant unobservable inputs (Level 3)
Embedded derivatives in commodity contracts	$	—	$	(61	)	$	—	$	(60	)
Total carrying value on Consolidated Balance Sheets	$	—	$	(61	)	$	—	$	(60	)

Fair Value Inputs Assets and Liabilities Quantitative Information [Table Text Block]

Level 3 instruments include all NGL transactions and embedded derivatives in commodity contracts. The embedded derivative liability relates to a natural gas purchase commitment embedded in a keep-whole processing agreement. The fair value calculation for these Level 3 instruments used significant unobservable inputs including: (1) NGL prices interpolated and extrapolated due to inactive markets ranging from $0.46 to $0.97 per gallon with a weighted average of $0.58 per gallon and

(2) the probability of renewal of 100 percent for the first five-year term and second five-year term of the gas purchase commitment and related keep-whole processing agreement, respectively. Increases or decreases in the fractionation spread result in an increase or decrease in the fair value of the embedded derivative liability, respectively. Beyond the embedded derivative discussed above, we had no outstanding commodity contracts as of September 30, 2020 or December 31, 2019.

Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]

The following table is a reconciliation of the net beginning and ending balances recorded for net assets and liabilities classified as Level 3 in the fair value hierarchy.

	Three Months Ended September 30, 2020					Three Months Ended September 30, 2019
(In millions)	Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)			Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)
Fair value at beginning of period	$	—	$	(51	)	$	—	$	(65	)
Total (losses)/gains (realized and unrealized) included in earnings(1)	—		(12		)	—		9
Settlements	—		2			—		2
Fair value at end of period	—		(61		)	—		(54		)
The amount of total (losses)/gains for the period included in earnings attributable to the change in unrealized gains/(losses) relating to liabilities still held at end of period	$	—	$	(11	)	$	—	$	9

	Nine Months Ended September 30, 2020					Nine Months Ended September 30, 2019
(In millions)	Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)			Commodity Derivative Contracts (net)		Embedded Derivatives in Commodity Contracts (net)
Fair value at beginning of period	$	—	$	(60	)	$	—	$	(61	)
Total (losses)/gains (realized and unrealized) included in earnings(1)	—		(5		)	—		2
Settlements	—		4			—		5
Fair value at end of period	—		(61		)	—		(54		)
The amount of total (losses)/gains for the period included in earnings attributable to the change in unrealized gains/(losses) relating to liabilities still held at end of period	$	—	$	(2	)	$	—	$	5

(1) Gains and losses on commodity derivative contracts classified as Level 3 are recorded in “Product sales” on the Consolidated Statements of Income. Gains and losses on derivatives embedded in commodity contracts are recorded in “Purchased product costs” and “Cost of revenues” on the Consolidated Statements of Income.

Fair Value Carrying Value by Balance Sheet Grouping [Table Text Block]

The following table summarizes the fair value and carrying value of our debt, excluding finance leases, and SMR liability:

	September 30, 2020				December 31, 2019
(In millions)	Fair Value		Carrying Value		Fair Value		Carrying Value
Long-term debt (including amounts due within one year)	$	21,721	$	20,455	$	21,054	$	19,800
SMR liability	$	87	$	76	$	90	$	80

XML

Derivative Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2020

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]

As of September 30, 2020, MPLX had no outstanding commodity contracts beyond the embedded derivative discussed below.

Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]

The impact of MPLX’s derivative instruments on its Consolidated Balance Sheets is summarized below:

(In millions)	September 30, 2020					December 31, 2019
Derivative contracts not designated as hedging instruments and their balance sheet location	Asset		Liability			Asset		Liability
Commodity contracts(1)
Other current assets / Other current liabilities	$	—	$	(4	)	$	—	$	(5	)
Other noncurrent assets / Deferred credits and other liabilities	—		(57		)	—		(55		)
Total	$	—	$	(61	)	$	—	$	(60	)

(1)

Includes embedded derivatives in commodity contracts as discussed above.

Derivative Instruments, Gain (Loss) [Table Text Block]

The impact of MPLX’s derivative contracts not designated as hedging instruments and the location of gains and losses recognized on the Consolidated Statements of Income is summarized below:

	Three Months Ended September 30,						Nine Months Ended September 30,
(In millions)	2020			2019			2020			2019
Purchased product costs
Realized (loss)/gain	$	(2	)	$	(2	)	$	(4	)	$	(5	)
Unrealized (loss)/gain	(10		)	11			(1		)	7
Purchased product costs derivative (loss)/gain	(12		)	9			(5		)	2
Total derivative (loss)/gain	$	(12	)	$	9		$	(5	)	$	2

XML

Debt (Tables)

9 Months Ended

Sep. 30, 2020

Debt Disclosure [Abstract]

Summary of Outstanding Borrowings

MPLX’s outstanding borrowings consist of the following:

(In millions)	September 30, 2020			December 31, 2019
MPLX LP:
Bank revolving credit facility	$	95		$	—
Term loan facility	—			1,000
Floating rate senior notes	1,000			2,000
Fixed rate senior notes	19,506			16,887
Consolidated subsidiaries:
MarkWest	23			23
ANDX	121			190
Financing lease obligations(1)	12			19
Total	20,757			20,119
Unamortized debt issuance costs	(118		)	(106		)
Unamortized discount/premium	(290		)	(300		)
Amounts due within one year	(307		)	(9		)
Total long-term debt due after one year	$	20,042		$	19,704

(1)    See Note 20 for lease information.

XML

Revenue (Tables)

9 Months Ended

Sep. 30, 2020

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue [Table Text Block]

The following tables represent a disaggregation of revenue for each reportable segment for the three and nine months ended September 30, 2020 and 2019:

	Three Months Ended September 30, 2020
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	87	$	517	$	604
Service revenue - related parties	902		7		909
Service revenue - product related	—		41		41
Product sales	7		158		165
Product sales - related parties	2		35		37
Total revenues from contracts with customers	$	998	$	758	1,756
Non-ASC 606 revenue(1)					491
Total revenues and other income					$	2,247

	Three Months Ended September 30, 2019
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	95	$	537	$	632
Service revenue - related parties	881		18		899
Service revenue - product related	—		26		26
Product sales	14		157		171
Product sales - related parties	8		24		32
Total revenues from contracts with customers	$	998	$	762	1,760
Non-ASC 606 revenue(1)					520
Total revenues and other income					$	2,280

	Nine Months Ended September 30, 2020
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	248	$	1,531	$	1,779
Service revenue - related parties	2,676		18		2,694
Service revenue - product related	—		102		102
Product sales	39		415		454
Product sales - related parties	10		90		100
Total revenues from contracts with customers	$	2,973	$	2,156	5,129
Non-ASC 606 loss(1)					191
Total revenues and other income					$	5,320

	Nine Months Ended September 30, 2019
(In millions)	L&S		G&P		Total
Revenues and other income:
Service revenue	$	260	$	1,605	$	1,865
Service revenue - related parties	2,527		22		2,549
Service revenue - product related	—		86		86
Product sales	40		536		576
Product sales - related parties	17		92		109
Total revenues from contracts with customers	$	2,844	$	2,341	5,185
Non-ASC 606 revenue(1)					1,540
Total revenues and other income					$	6,725

(1) Non-ASC 606 Revenue includes rental income, income/(loss) from equity method investments, derivative gains and losses, mark-to-market adjustments, and other income.

Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block]

The tables below reflect the changes in our contract balances for the nine-month periods ended September 30, 2020 and 2019:

(In millions)	Balance at December 31, 2019(1)		Additions/ (Deletions)			Revenue Recognized(2)			Balance at September 30, 2020
Contract assets	$	39	$	(9	)	$	(1	)	$	29
Deferred revenue	23		16			(6		)	33
Deferred revenue - related parties	53		77			(60		)	70
Long-term deferred revenue	90		25			—			115
Long-term deferred revenue - related parties	$	55	$	(7	)	$	—		$	48

(In millions)	Balance at December 31, 2018(1)		Additions/ (Deletions)			Revenue Recognized(2)			Balance at September 30, 2019
Contract assets	$	36	$	(6	)	$	(2	)	$	28
Deferred revenue	13		11			(4		)	20
Deferred revenue - related parties	65		34			(50		)	49
Long-term deferred revenue	56		26			—			82
Long-term deferred revenue - related parties	$	52	$	5		$	—		$	57

(1) Balance represents ASC 606 portion of each respective line item.

(2) No significant revenue was recognized related to past performance obligations in the current periods.

Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]

As of September 30, 2020, the amounts allocated to contract assets and contract liabilities on the Consolidated Balance Sheets are $264 million and are reflected in the amounts below. This will be recognized as revenue as the obligations are satisfied, which is expected to occur over the next 30 years. Further, MPLX does not disclose variable consideration due to volume variability in the table below.

(In millions)
2020	$	461
2021	1,727
2022	1,701
2023	1,591
2024 and thereafter	5,869
Total revenue on remaining performance obligations(1),(2),(3)	$	11,349

(1) All fixed consideration from contracts with customers is included in the amounts presented above. Variable consideration that is constrained or not required to be estimated as it reflects our efforts to perform is excluded.

(2) Arrangements deemed implicit leases are included in “Rental income” and are excluded from this table.

(3)

Only minimum volume commitments that are deemed fixed are included in the table above. MPLX has various minimum volume commitments in processing arrangements that vary based on the actual Btu content of the gas received. These amounts are deemed variable consideration and are excluded from the table above.

XML

Supplemental Cash Flow Information (Tables)

9 Months Ended

Sep. 30, 2020

Supplemental Cash Flow Elements [Abstract]

Summary of Supplemental Cash Flow Information [Table Text Block]

	Nine Months Ended September 30,
(In millions)	2020			2019
Net cash provided by operating activities included:
Interest paid (net of amounts capitalized)	$	631		$	648
Income taxes paid	1			—
Non-cash investing and financing activities:
Net transfers of property, plant and equipment (to)/from materials and supplies inventories	(1		)	1
Fair value of common units redeemed for Wholesale Exchange	$	340		$	—

Summary of Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures [Table Text Block]

The following is the change of additions to property, plant and equipment related to capital accruals:

	Nine Months Ended September 30,
(In millions)	2020			2019
(Decrease)/increase in capital accruals	$	(197	)	$	(67	)

XML

Accumulated Other Comprehensive Income (Tables)

9 Months Ended

Sep. 30, 2020

Accumulated Other Comprehensive Income (Loss) [Line Items]

Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]

The following table shows the changes in “Accumulated other comprehensive loss” by component during the period December 31, 2019 through September 30, 2020.

(In millions)	Pension Benefits			Other Post-Retirement Benefits			Total
Balance at December 31, 2019(1)	$	(14	)	$	(1	)	$	(15	)
Other comprehensive loss - remeasurements(2)	—			(1		)	(1		)
Balance at September 30, 2020(1)	$	(14	)	$	(2	)	$	(16	)

The following table shows the changes in “Accumulated other comprehensive loss” by component during the period December 31, 2018 through September 30, 2019.

(In millions)	Pension Benefits			Other Post-Retirement Benefits			Total
Balance at December 31, 2018(1)	$	(14	)	$	(2	)	$	(16	)
Other comprehensive income - remeasurements(2)	—			1			1
Balance at September 30, 2019(1)	$	(14	)	$	(1	)	$	(15	)

(1) These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on the Consolidated Statements of Income under the caption “Income/(loss) from equity method investments.”

(2)

Components of other comprehensive income/loss - remeasurements relate to actuarial gains and losses as well as amortization of prior service costs. MPLX records an adjustment to “Comprehensive income” in accordance with its ownership interest in LOOP and Explorer.

XML

Equity-Based Compensation Plan (Tables)

9 Months Ended

Sep. 30, 2020

Phantom Units

Equity Transactions And Share Based Compensation [Line Items]

Summary of Share-based Compensation, Restricted Stock Units Award Activity

The following is a summary of phantom unit award activity of MPLX LP common units for the nine months ended September 30, 2020:

	Number of Units		Weighted Average Fair Value
Outstanding at December 31, 2019	1,109,568		$	35.97
Granted	215,677		19.31
Settled	(558,398	)	37.73
Forfeited	(5,383	)	35.87
Outstanding at September 30, 2020	761,464		$	29.96

Performance Shares [Member]

Equity Transactions And Share Based Compensation [Line Items]

Summary of Share-based Compensation, Restricted Stock Units Award Activity

Performance Units – MPLX grants performance units to certain officers of the general partner and certain eligible MPC officers who make significant contributions to its business. These performance units pay out 75 percent in cash and 25 percent in MPLX LP common units and often contain both market and performance conditions based on various metrics. Market conditions are valued using a Monte Carlo valuation while performance conditions are reevaluated periodically and valued at the compensation cost associated with the performance outcome deemed most probable.

The performance units granted in 2020 are hybrid awards having a three-year performance period of January 1, 2020 through December 31, 2022. The payout of the award is dependent on two independent conditions, each constituting 50 percent of the overall target units granted. The awards have a performance condition based on MPLX LP’s distributable cash flow, and a market condition based on MPLX LP’s total unitholder return. The market condition was valued using a Monte Carlo valuation, resulting in a grant date fair value of $0.80 per unit for the 2020 equity-classified performance units. Grant date fair value of the performance condition is based on potential payouts per unit of up to $2.00 per unit. Compensation cost associated with the performance condition is based on the grant date fair value of the payout deemed most probable to occur and is adjusted as the expectation for payout changes.

During the first quarter of 2018, a performance award was granted; however, due to the nature of the award terms, the grant date for this award was not established until the first quarter of 2020 and we began recognizing units and expense related to this award at that time. The performance units granted in 2018 are hybrid awards having a three-year performance period of January 1, 2018 through December 31, 2020. The payout of the award is dependent on two independent conditions, each constituting 50 percent of the overall target units granted. The awards have a performance condition based on an average of MPLX LP’s distributable cash flow and a market condition based on MPLX LP’s total unitholder return. The market condition was valued using a Monte Carlo valuation, resulting in a grant date fair value of $0.45 per unit for the 2018 equity-classified performance units. Grant date fair value of the performance condition is based on potential payouts per unit of up to $2.00 per unit. Compensation cost associated with the performance condition is based on the grant date fair value of the payout deemed most probable to occur and is adjusted as the expectation for payout changes.

The following is a summary of the activity for performance unit awards to be settled in MPLX LP common units for the nine months ended September 30, 2020:

	Number of Units
Outstanding at December 31, 2019	2,157,347
Granted	2,147,211
Settled	(1,169,354	)
Forfeited	(31,668	)
Outstanding at September 30, 2020	3,103,536

XML

Leases Lessor Disclosure (Tables)

9 Months Ended

Sep. 30, 2020

Lessor Disclosure [Abstract]

Operating Lease, Lease Income [Table Text Block]

Lease revenues included on the Consolidated Statements of Income were as follows:

	Three Months Ended September 30, 2020				Three Months Ended September 30, 2019
(In millions)	Related Party		Third Party		Related Party		Third Party
Operating leases:
Operating lease revenue(1)	$	208	$	70	$	248	$	63
Sales-type leases:
Profit/(loss) recognized at the commencement date	—		—		—		N/A
Interest income (Sales-type lease revenue- fixed minimum)	37		—		3		N/A
Interest income (Revenue from variable lease payments)	$	1	$	—	$	1	N/A

	Nine Months Ended September 30, 2020				Nine Months Ended September 30, 2019
(In millions)	Related Party		Third Party		Related Party		Third Party
Operating leases:
Operating lease revenue(1)	$	589	$	199	$	773	$	196
Sales-type leases:
Profit/(loss) recognized at the commencement date	—		—		—		N/A
Interest income (Sales-type lease revenue- fixed minimum)	113		—		3		N/A
Interest income (Revenue from variable lease payments)	$	1	$	—	$	1	N/A

(1) These amounts are presented net of executory costs.

Sales-type Lease, Lease Income [Table Text Block]

Lease revenues included on the Consolidated Statements of Income were as follows:

	Three Months Ended September 30, 2020				Three Months Ended September 30, 2019
(In millions)	Related Party		Third Party		Related Party		Third Party
Operating leases:
Operating lease revenue(1)	$	208	$	70	$	248	$	63
Sales-type leases:
Profit/(loss) recognized at the commencement date	—		—		—		N/A
Interest income (Sales-type lease revenue- fixed minimum)	37		—		3		N/A
Interest income (Revenue from variable lease payments)	$	1	$	—	$	1	N/A

	Nine Months Ended September 30, 2020				Nine Months Ended September 30, 2019
(In millions)	Related Party		Third Party		Related Party		Third Party
Operating leases:
Operating lease revenue(1)	$	589	$	199	$	773	$	196
Sales-type leases:
Profit/(loss) recognized at the commencement date	—		—		—		N/A
Interest income (Sales-type lease revenue- fixed minimum)	113		—		3		N/A
Interest income (Revenue from variable lease payments)	$	1	$	—	$	1	N/A

(1) These amounts are presented net of executory costs.

Sales-type and Direct Financing Leases, Lease Receivable, Maturity [Table Text Block]

The following is a schedule of future payments on the sales-type leases as of September 30, 2020:

(In millions)	Related Party
2020	$	39
2021	157
2022	157
2023	158
2024	158
2025 and thereafter	473
Total minimum future rentals	1,142
Less: present value discount	723
Lease receivable	$	419

XML

Description of Business and Basis of Presentation - Additional Information (Detail) $ in Millions			3 Months Ended	9 Months Ended	12 Months Ended
	Jul. 31, 2020 shares	Jul. 30, 2019 shares	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($) shares	Dec. 31, 2019 USD ($)
Description Of Business And Basis Of Presentation [Line Items]
Goodwill, Impairment Loss				$ 1,814	$ 1,197
Equity Method Investment, Other than Temporary Impairment			$ 1,264	$ 1,264
Impairment of Intangible Assets, Finite-lived			177
Number of reportable segments				2
Impairment of Long-Lived Assets Held-for-use			174
Impairment Charges			3,429
G&P
Description Of Business And Basis Of Presentation [Line Items]
Goodwill, Impairment Loss			$ 1,814	$ 1,814	$ 1,197
ANDX LP [Member] | Public
Description Of Business And Basis Of Presentation [Line Items]
Common Units Conversion Ratio - ANDX to MPLX | shares		1.135
ANDX LP [Member] | Nonpublic [Member]
Description Of Business And Basis Of Presentation [Line Items]
Common Units Conversion Ratio - ANDX to MPLX | shares		1.0328
Western Refining Wholesale & Western Refining Product Transport [Member]
Description Of Business And Basis Of Presentation [Line Items]
Partners' Capital Account, Units, Redeemed | shares	18,582,088			18,582,088

XML

Accounting Standards Impact of Adoption (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounting Changes and Error Corrections [Abstract]
Receivables, net	$ 477	$ 593
Accounts Receivable, Allowance for Credit Loss	$ 4

XML

Acquisitions Andeavor Logistics (Details) - USD ($) $ in Millions			3 Months Ended				9 Months Ended
		Jul. 30, 2019	Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019		Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 09, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Cash and cash equivalents			$ 28				$ 28						$ 15
Receivables, net			477				477						593
Inventories			117				117						110
Other current assets			59				59						110
Assets, Current			1,272				1,272						1,484
Equity method investments			4,081				4,081						5,275
Property, plant and equipment, net			21,615				21,615						22,145
Intangibles, net			991				991						1,270
Other noncurrent assets			48				48						52
Assets			36,662				36,662						40,430
Accounts payable			140				140						242
Accrued Liabilities, Current			169				169						187
Accrued interest payable			207				207						210
Other current liabilities			158				158						127
Liabilities, Current			1,531				1,531						2,132
Long-term deferred revenue			291				291						217
Liabilities, Related Parties, Noncurrent			281				281						290
Long-term debt			20,042				20,042						19,704
Deferred credits and other liabilities			184				184						192
Liabilities			22,599				22,599						22,849
Series A preferred units			968				968						968
Total MPLX LP partners’ capital			12,848				12,848						16,364
Accumulated other comprehensive loss	[1]		(16)		$ (15)		(16)		$ (15)				(15)				$ (16)
Revenues			2,247		2,280		5,320		6,725
Goodwill			7,657				7,657					$ 7,700	9,536				10,016
Net Income (Loss) Attributable to Parent			665	[2]	629	[3]	(1,411)	[4]	1,614	[5]
Acquisition Costs, Period Cost			0		9		0		14
Noncontrolling interests			247				247						249
Partners' Capital, Including Portion Attributable to Noncontrolling Interest			13,095		17,892		13,095		17,892		$ 13,262	$ 13,356	16,613		$ 17,611	$ 17,730	17,731
Liabilities and Equity			36,662				36,662						40,430
Net (loss)/income			674		689		(1,387)		2,035
Andeavor Logistics [Member]
Business Acquisition [Line Items]
Revenues					612				1,789
Acquisition Costs, Period Cost									14
Net (loss)/income					$ 191				$ 539
ANDX LP [Member] | Public
Business Acquisition [Line Items]
Common Units Conversion Ratio - ANDX to MPLX		1.135
ANDX LP [Member] | Nonpublic [Member]
Business Acquisition [Line Items]
Common Units Conversion Ratio - ANDX to MPLX		1.0328
Senior Notes [Member]
Business Acquisition [Line Items]
Long-term Debt, Gross														$ 2,000
L&S
Business Acquisition [Line Items]
Intangibles, net			211				211						238
Goodwill			7,657				$ 7,657						7,722				7,234
L&S | Minimum [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life							6 years
L&S | Maximum [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life							8 years
G&P
Business Acquisition [Line Items]
Intangibles, net			780				$ 780						1,032
Goodwill			$ 0				$ 0						$ 1,814				$ 2,782
G&P | Minimum [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life							6 years
G&P | Maximum [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life							25 years

[1] These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on the Consolidated Statements of Income under the caption “Income/(loss) from equity method investments.”

[2] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[3] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[4] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[5] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

XML

Acquisitions Western Transportation Reverse Drop (Details) - USD ($) $ in Millions		9 Months Ended
	Jul. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Noncash or Part Noncash Divestitures [Line Items]
Goodwill		$ 7,657	$ 7,700	$ 9,536	$ 10,016
Western Refining Wholesale & Western Refining Product Transport [Member]
Noncash or Part Noncash Divestitures [Line Items]
Partners' Capital Account, Units, Contributed	18,582,088	18,582,088
Partner Capital, Units, contributed, fair value assigned	$ 340
Fair Value, Net Asset (Liability)	90
Excess of Fair Value over Book Value	250
Goodwill	$ 65

XML

Equity Method Investments - Summary of Equity Method Investment Financial Information (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019		Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Revenues		$ 2,247		$ 2,280	$ 5,320		$ 6,725
Equity method investments		4,081			4,081				$ 5,275
Costs and Expenses		1,348		1,354	6,029		4,002
Net (loss)/income		674		689	(1,387)		2,035
Income/(loss) from equity method investments(1)		83		95	(1,012)	[1],[2]	255
Assets, Current		1,272			1,272				1,484
Liabilities, Current		$ 1,531			1,531				2,132
Equity Method Investment, Other than Temporary Impairment			$ 1,264		$ 1,264
MarEn Bakken Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		25.00%			25.00%
Illinois Extension
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		35.00%			35.00%
LOOP
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		41.00%			41.00%
Whistler Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		38.00%			38.00%
W2W Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		50.00%			50.00%
Wink to Webster Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		15.00%			15.00%
Explorer
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		25.00%			25.00%
MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		57.00%			57.00%
Equity Method Investment, Other than Temporary Impairment			$ 1,251
Sherwood Midstream
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		50.00%			50.00%
MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		67.00%			67.00%
Centrahoma Processing LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		40.00%			40.00%
Indirect Ownership Interest [Member] | Bakken Pipeline System [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		9.19%			9.19%
Indirect Ownership Interest [Member] | Sherwood Midstream Holdings
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		24.51%			24.51%
Direct Ownership Interest [Member] | Andeavor Logistics Rio Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		67.00%			67.00%
Direct Ownership Interest [Member] | Minnesota Pipe Line Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		17.00%			17.00%
Direct Ownership Interest [Member] | Rendezvous Gas Services, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		78.00%			78.00%
Direct Ownership Interest [Member] | Sherwood Midstream Holdings
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		51.00%			51.00%
G&P
Schedule of Equity Method Investments [Line Items]
Difference between carrying amount and underlying equity		$ (58)			$ (58)				1,000
Difference between carrying amount and underlying equity portion related to goodwill		31			31				498
G&P | MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity method investments	[3]	720			720				1,984
G&P | Sherwood Midstream
Schedule of Equity Method Investments [Line Items]
Equity method investments	[3]	560			560				537
G&P | MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[3]	307			307				302
G&P | Rendezvous Gas Services, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[3]	164			164				170
G&P | Sherwood Midstream Holdings
Schedule of Equity Method Investments [Line Items]
Equity method investments	[3]	151			151				157
G&P | Centrahoma Processing LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		147			147				153
G&P | Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[3]	230			230				198
L&S
Schedule of Equity Method Investments [Line Items]
Difference between carrying amount and underlying equity		331			331				329
Difference between carrying amount and underlying equity portion related to goodwill		167			167				167
L&S | MarEn Bakken Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[4]	469			469				481
L&S | Illinois Extension
Schedule of Equity Method Investments [Line Items]
Equity method investments		261			261				265
L&S | LOOP
Schedule of Equity Method Investments [Line Items]
Equity method investments		249			249				238
L&S | Andeavor Logistics Rio Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[3]	195			195				202
L&S | Minnesota Pipe Line Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		189			189				190
L&S | Whistler Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[3]	184			184				134
L&S | W2W Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[3],[5]	77			77				0
L&S | Wink to Webster Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[3],[5]	0			0				126
L&S | Explorer
Schedule of Equity Method Investments [Line Items]
Equity method investments		78			78				83
L&S | Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[3]	100			100				55
Operating Segments | G&P
Schedule of Equity Method Investments [Line Items]
Revenues	[6]	913		901	1,330		2,742
Equity method investments		2,279			2,279				3,501
Income/(loss) from equity method investments(1)		47		35	(1,138)		96
Operating Segments | L&S
Schedule of Equity Method Investments [Line Items]
Revenues	[6]	1,334		1,379	3,990		3,983
Equity method investments		1,802			1,802				1,774
Income/(loss) from equity method investments(1)		36		$ 60	126		159
Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Revenues					1,065		1,595
Costs and Expenses					713		685
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest					352		910
Net (loss)/income					247		797
Income/(loss) from equity method investments(1)					(1,012)	[7]	255	[8]
Assets, Current		1,141			1,141				864
Assets, Noncurrent		11,422			11,422				10,996
Liabilities, Current		498			498				437
Liabilities, Noncurrent		2,468			2,468				1,127
Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Revenues					933		1,116
Costs and Expenses					405		434
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest					528		682
Net (loss)/income					477		605
Income/(loss) from equity method investments(1)					126	[7]	166	[8]
Assets, Current		367			367				330
Assets, Noncurrent		5,024			5,024				5,134
Liabilities, Current		194			194				245
Liabilities, Noncurrent		857			857				822
Other VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Revenues					132		479
Costs and Expenses					308		251
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest					(176)		228
Net (loss)/income					(230)		192
Income/(loss) from equity method investments(1)					(1,138)	[7]	$ 89	[8]
Assets, Current		774			774				534
Assets, Noncurrent		6,398			6,398				5,862
Liabilities, Current		304			304				192
Liabilities, Noncurrent		$ 1,611			$ 1,611				$ 305

[1] The 2020 period includes $1,264 million of impairment expense. See Note 4.

[2] The nine months ended September 30, 2020 includes $1,264 million of impairment expense. See Note 4.

[3] Investments deemed to be VIEs. Some investments included within “Other” have also been deemed to be VIEs.

[4] The investment in MarEn Bakken Company LLC includes our 9.19 percent indirect interest in a joint venture (“Dakota Access”) that owns and operates the Dakota Access Pipeline and Energy Transfer Crude Oil Pipeline projects, collectively referred to as the Bakken Pipeline system or DAPL.

[5] During the nine months ended September 30, 2020, we contributed our ownership in Wink to Webster Pipeline LLC to W2W Holdings LLC.

[6] Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $139 million and $443 million for the three and nine months ended September 30, 2020, respectively, and $182 million and $498 million for the three and nine months ended September 30, 2019, respectively. Third party revenues for the G&P segment were $858 million and $1,181 million for the three and nine months ended September 30, 2020, respectively, and $843 million and $2,581 million for the three and nine months ended September 30, 2019, respectively.

[7] Includes the impact of any basis differential amortization or accretion in addition to the impairment of $1,264 million.

[8] Includes the impact of any basis differential amortization or accretion.

XML

Related Party Agreements and Transactions - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Related Party Transaction [Line Items]
Restructuring Charges	$ 36	$ 0	$ 36	$ 0
MPC Investment [Member]
Related Party Transaction [Line Items]
Restructuring Charges	$ 36

XML

Related Party Agreements and Transactions MPC Loan Agreement (Details) - Related Party Revolving Credit Agreement [Member] - MPC Investment [Member] - USD ($) $ in Millions				9 Months Ended	12 Months Ended
		Jul. 31, 2019	Apr. 27, 2018	Sep. 30, 2020	Dec. 31, 2019	Dec. 21, 2018
Related Party Transaction [Line Items]
Line of Credit Facility, Current Borrowing Capacity		$ 1,500
Debt Instrument, Description of Variable Rate Basis		LIBOR plus 1.25 percent	LIBOR plus 1.50 percent
Proceeds from Lines of Credit				$ 4,870	$ 8,540
Line of Credit Facility, Interest Rate During Period				2.38%	3.441%
Repayments of Lines of Credit				$ 5,464	$ 7,946
Long-term Line of Credit	[1]			$ 0	594
ANDX LP [Member]
Related Party Transaction [Line Items]
Line of Credit Facility, Current Borrowing Capacity						$ 500
Proceeds from Lines of Credit					$ 773
Line of Credit Facility, Interest Rate During Period					4.249%
Repayments of Lines of Credit					$ 773
Long-term Line of Credit	[1]				$ 0

[1] Included in “Current liabilities - related parties” on the Consolidated Balance Sheets.

XML

Sales to Related Parties (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Related Party Transaction [Line Items]
Rental income - related parties		$ 241	$ 293	$ 712	$ 904
Other income - related parties		63	31	190	84
MPC
Related Party Transaction [Line Items]
Rental income - related parties		241	293	712	904
Other income - related parties		48	14	144	34
Product sales to MPC that net to zero		107	301	332	819
Other Affiliates [Member]
Related Party Transaction [Line Items]
Other income - related parties		15	17	46	50
Product [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		37	32	100	109
Product [Member] | MPC
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[1]	37	32	100	109
Service [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		909	899	2,694	2,549
Service [Member] | MPC
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		908	899	2,692	2,549
Service [Member] | Other Affiliates [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		$ 1	$ 0	$ 2	$ 0

[1] There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For the three and nine months ended September 30, 2020, these sales totaled $107 million and $332 million, respectively. For the three and nine months ended September 30, 2019, these sales totaled $301 million and $819 million, respectively.

XML

Summary of Charges for Employee Services and Omnibus Agreements (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Related Party Transaction [Line Items]
Restructuring Charges	$ 36	$ 0	$ 36	$ 0
Purchases - related parties
Related Party Transaction [Line Items]
Labor and Related Expense	297	303	853	894
MPC | Rental cost of sales - related parties
Related Party Transaction [Line Items]
Labor and Related Expense	32	45	119	124
MPC | Purchases - related parties
Related Party Transaction [Line Items]
Labor and Related Expense	293	297	840	878
MPC | General and administrative expenses
Related Party Transaction [Line Items]
Labor and Related Expense	63	59	195	174
Other Affiliates [Member] | Purchases - related parties
Related Party Transaction [Line Items]
Labor and Related Expense	4	6	13	16
Construction-in-progress | MPC
Related Party Transaction [Line Items]
Property, Plant and Equipment, Additions	$ 29	$ 48	$ 80	$ 127

XML

Other Assets and Liabilities from Related Parties (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Other current assets	$ 59	$ 110
Current Assets, Related Parties	591	656
Operating Lease, Right-of-Use Asset	323	365
Other Assets, Related Parties, Noncurrent	675	303
Operating Lease, Liability, Current	65	66
Current Liabilities, Related Parties	364	1,008
Operating Lease, Liability, Noncurrent	258	302
Liabilities, Related Parties, Noncurrent	281	290
MPC
Related Party Transaction [Line Items]
Receivables - related parties	543	621
Prepaid Insurance	11	9
Other current assets	1	0
Sales-type Lease, Interest Income	29	4
Sales-type Lease, Unguaranteed Residual Asset	22	7
Due from Related Parties, Noncurrent	32	21
Operating Lease, Right-of-Use Asset	231	232
Net Investment in Lease, Noncurrent	390	43
Due to Related Parties, Current	247	911
Operating Lease, Liability, Current	1	1
Operating Lease, Liability, Noncurrent	230	230
Other Affiliates [Member]
Related Party Transaction [Line Items]
Receivables - related parties	7	22
Due to Related Parties, Current	42	37
Minimum Committed Volume Contracts [Member] | MPC
Related Party Transaction [Line Items]
Deferred Revenue Related Parties	54	42
Reimbursable Projects [Member] | MPC
Related Party Transaction [Line Items]
Deferred Revenue Related Parties	19	16
Deferred Revenue, Noncurrent, Related Parties	45	53
Other Noncurrent Liabilities [Member] | Other Affiliates [Member]
Related Party Transaction [Line Items]
Deferred Revenue Related Parties	1	1
Other Noncurrent Liabilities [Member] | Other Affiliates [Member]
Related Party Transaction [Line Items]
Deferred Revenue, Noncurrent, Related Parties	$ 6	$ 7

XML

Net Income Per Limited Partner Unit - Schedule of Distributions by Partner by Class (Detail) - USD ($) shares in Millions		3 Months Ended								9 Months Ended
		Sep. 30, 2020		Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019		Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020		Sep. 30, 2019
Net Income Per Share [Line Items]
Potentially dilutive units		1				1				1		1
Net income attributable to MPLX LP		$ 665,000,000	[1]			$ 629,000,000	[2]			$ (1,411,000,000)	[3]	$ 1,614,000,000	[4]
Less: Distribution declared		745,000,000				734,000,000				2,250,000,000		2,011,000,000
Undistributed net income (loss) attributable to MPLX LP		(80,000,000)				(105,000,000)				(3,661,000,000)		(397,000,000)
Undistributed net loss attributable to MPLX LP		(80,000,000)				(105,000,000)				(3,661,000,000)		(397,000,000)
Capital Contribution By Related Party		13,000,000		$ 6,000,000	$ 225,000,000	295,000,000		$ 13,000,000	$ 15,000,000
Limited Partners Common Units
Net Income Per Share [Line Items]
Net income attributable to MPLX LP		635,000,000	[1]			599,000,000	[2]			(1,503,000,000)	[3]	1,522,000,000	[4]
Less: Distribution declared	[5]	715,000,000				704,000,000	[6]			2,158,000,000		1,919,000,000	[6]
Undistributed net income (loss) attributable to MPLX LP		(80,000,000)				(105,000,000)				(3,661,000,000)		(397,000,000)
MPC | Limited Partners Common Units
Net Income Per Share [Line Items]
Capital Contribution By Related Party		13,000,000		$ 6,000,000	$ 225,000,000	292,000,000		$ 0	$ 0
MPC | ANDX LP [Member]
Net Income Per Share [Line Items]
Capital Contribution By Related Party						12,500,000						25,000,000
Series A Preferred Stock [Member] | Series A Preferred Stock [Member]
Net Income Per Share [Line Items]
Net income attributable to MPLX LP		20,000,000	[1]			20,000,000	[2]			61,000,000	[3]	61,000,000	[4]
Less: Distribution declared	[5]	20,000,000				20,000,000				61,000,000		61,000,000
Undistributed net income (loss) attributable to MPLX LP		0				0				0		0
Series B Preferred Stock [Member] | Series A Preferred Stock [Member]
Net Income Per Share [Line Items]
Net income attributable to MPLX LP		10,000,000	[1]			10,000,000	[2]			31,000,000	[3]	31,000,000	[4]
Less: Distribution declared	[5]	10,000,000				10,000,000				31,000,000		31,000,000
Undistributed net income (loss) attributable to MPLX LP		$ 0				$ 0				$ 0		$ 0

[1] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[2] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[3] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[4] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[5] See Note 7 for distribution information.

[6] The three and nine months ended September 30, 2019 amounts are net of $12.5 million and $25 million, respectively, of waived distributions with respect to units held by MPC and its affiliates.

XML

Net Income Per Limited Partner Unit - Basic and Diluted Earnings Per Unit (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Potentially dilutive units		1		1		1		1
Distribution Made to Limited Partner, Cash Distributions Declared		$ 745		$ 734		$ 2,250		$ 2,011
Net income (loss) attributable to MPLX LP:
Undistributed net income (loss) attributable to MPLX LP		(80)		(105)		(3,661)		(397)
Net income attributable to MPLX LP		665	[1]	629	[2]	(1,411)	[3]	1,614	[4]
Limited Partners Common Units
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared	[5]	715		704	[6]	2,158		1,919	[6]
Net income (loss) attributable to MPLX LP:
Undistributed net income (loss) attributable to MPLX LP		(80)		(105)		(3,661)		(397)
Net income attributable to MPLX LP		$ 635	[1]	$ 599	[2]	$ (1,503)	[3]	$ 1,522	[4]
Weighted average units outstanding:
Common - basic (in shares)		1,046		974	[7]	1,054		855	[8]
Common - diluted (in shares)		1,047		975	[7]	1,054		855	[8]
Net income attributable to MPLX LP per limited partner unit:
Basic (in USD per unit)		$ 0.61		$ 0.61		$ (1.43)		$ 1.78
Diluted (in USD per unit)		$ 0.61		$ 0.61		$ (1.43)		$ 1.78
Series A Preferred Stock [Member] | Series A Preferred Stock [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared	[5]	$ 20		$ 20		$ 61		$ 61
Net income (loss) attributable to MPLX LP:
Undistributed net income (loss) attributable to MPLX LP		0		0		0		0
Net income attributable to MPLX LP		20	[1]	20	[2]	61	[3]	61	[4]
Series B Preferred Stock [Member] | Series A Preferred Stock [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared	[5]	10		10		31		31
Net income (loss) attributable to MPLX LP:
Undistributed net income (loss) attributable to MPLX LP		0		0		0		0
Net income attributable to MPLX LP		$ 10	[1]	$ 10	[2]	$ 31	[3]	$ 31	[4]

[1] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[2] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[3] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[4] Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[5] See Note 7 for distribution information.

[6] The three and nine months ended September 30, 2019 amounts are net of $12.5 million and $25 million, respectively, of waived distributions with respect to units held by MPC and its affiliates.

[7] The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire three months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

[8] The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire nine months ended September 30, 2019. See Notes 3 and 7 for additional information about the treatment of these units.

XML

Equity - Changes in Partners Capital, Unit Rollforward (Details) - USD ($)							3 Months Ended							9 Months Ended
		Oct. 27, 2020	Aug. 17, 2020	Jul. 31, 2020	Jul. 30, 2019	Jul. 29, 2019	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019		Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019		Dec. 31, 2019	Dec. 31, 2018
Stockholders Equity [Line Items]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Temporary Equity							$ (654,000,000)	$ (634,000,000)	$ 2,736,000,000	$ (669,000,000)		$ (636,000,000)	$ (669,000,000)
Partners, Total Subsequent Distribution Amount							745,000,000			734,000,000				$ 2,250,000,000	$ 2,011,000,000
Contributions from:							13,000,000	6,000,000	225,000,000	295,000,000		13,000,000	15,000,000
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders							(736,000,000)	(728,000,000)	(738,000,000)	(715,000,000)		(764,000,000)	(776,000,000)
Partners' Capital, Including Portion Attributable to Noncontrolling Interest							13,095,000,000	13,262,000,000	13,356,000,000	17,892,000,000		17,611,000,000	17,730,000,000	13,095,000,000	17,892,000,000		$ 16,613,000,000	$ 17,731,000,000
Distribution Made to Limited Partner, Cash Distributions Declared							745,000,000			734,000,000				2,250,000,000	2,011,000,000
Preferred Class B [Member]
Stockholders Equity [Line Items]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Temporary Equity							(10,000,000)	(10,000,000)	(11,000,000)	(7,000,000)		0	0	(31,000,000)
Contributions from:							0	0	0	0		0	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders							(20,000,000)	0	(21,000,000)	(21,000,000)		0	0	(41,000,000)
Partners' Capital, Including Portion Attributable to Noncontrolling Interest							$ 601,000,000	611,000,000	$ 601,000,000	601,000,000		0	0	$ 601,000,000	601,000,000		$ 611,000,000	0
Limited Partners Common Units
Stockholders Equity [Line Items]
Balance at December 31, 2019									1,058,355,471					1,058,355,471
Unit-based compensation awards														395,091
Balance at September 30, 2020							1,040,168,474							1,040,168,474
Distribution Made to Limited Partner, Cash Distributions Declared	[1]						$ 715,000,000			704,000,000	[2]			$ 2,158,000,000	1,919,000,000	[2]
Andeavor Logistics [Member]
Stockholders Equity [Line Items]
Preferred Units, Outstanding						600,000
ANDX LP [Member]
Stockholders Equity [Line Items]
Dividend rate, percentage						6.875%
Price per share						$ 1,000
Subsequent Event | Limited Partners Common Units
Stockholders Equity [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared		$ 715,000,000
Limited Partners Common Units
Stockholders Equity [Line Items]
Partners, Total Subsequent Distribution Amount							715,000,000			704,000,000				2,158,000,000	1,919,000,000
Series B Preferred Stock [Member] | Preferred Partner [Member]
Stockholders Equity [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared	[1]						10,000,000			10,000,000				$ 31,000,000	31,000,000
Series B Preferred Stock [Member] | MPLX LP
Stockholders Equity [Line Items]
Dividend rate, percentage														4.652%
Preferred Stock, Dividend Payment Rate, Variable														LIBOR plus
Preferred Class B [Member]
Stockholders Equity [Line Items]
Partners, Total Subsequent Distribution Amount							10,000,000			10,000,000				$ 31,000,000	31,000,000
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders			$ (21,000,000)
Preferred Class A [Member]
Stockholders Equity [Line Items]
Partners, Total Subsequent Distribution Amount							20,000,000			20,000,000				$ 61,000,000	61,000,000
MPC | Limited Partners Common Units
Stockholders Equity [Line Items]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Temporary Equity							$ 399,000,000	388,000,000	$ (1,733,000,000)	(380,000,000)		293,000,000	307,000,000
Units issued					161,000,000		647,000,000							647,000,000			666,000,000
Contributions from:							$ 13,000,000	6,000,000	225,000,000	292,000,000		0	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders							(445,000,000)	(458,000,000)	(446,000,000)	(432,000,000)		(332,000,000)	(327,000,000)
Partners' Capital, Including Portion Attributable to Noncontrolling Interest							$ 2,827,000,000	2,951,000,000	3,014,000,000	5,767,000,000		(1,671,000,000)	(1,632,000,000)	$ 2,827,000,000	5,767,000,000		$ 4,968,000,000	(1,612,000,000)
Units Outstanding							647,000,000							647,000,000			666,000,000
MPC | ANDX LP [Member]
Stockholders Equity [Line Items]
Contributions from:										12,500,000					25,000,000
Public | Limited Partners Common Units
Stockholders Equity [Line Items]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Temporary Equity							$ 236,000,000	229,000,000	(1,022,000,000)	(222,000,000)		168,000,000	176,000,000
Units issued					102,000,000		393,000,000							393,000,000			392,000,000
Contributions from:							$ 0	0	0	0		0	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders							(271,000,000)	(270,000,000)	(271,000,000)	(262,000,000)		(191,000,000)	(188,000,000)
Partners' Capital, Including Portion Attributable to Noncontrolling Interest							$ 9,436,000,000	$ 9,469,000,000	$ 9,509,000,000	$ 11,289,000,000		$ 8,305,000,000	$ 8,326,000,000	$ 9,436,000,000	$ 11,289,000,000		$ 10,800,000,000	$ 8,336,000,000
Units Outstanding							393,000,000							393,000,000			392,000,000
Western Refining Wholesale & Western Refining Product Transport [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Contributed				(18,582,088)										(18,582,088)
Nonpublic [Member] | ANDX LP [Member]
Stockholders Equity [Line Items]
Common Units Conversion Ratio - ANDX to MPLX					1.0328
Public | ANDX LP [Member]
Stockholders Equity [Line Items]
Common Units Conversion Ratio - ANDX to MPLX					1.135
TexNew Mex units [Member] | MPLX LP
Stockholders Equity [Line Items]
Units Outstanding					80,000
Distribution Made to Limited Partner, Cash Distributions Declared							$ 5,000,000

[1] See Note 7 for distribution information.

[2] The three and nine months ended September 30, 2019 amounts are net of $12.5 million and $25 million, respectively, of waived distributions with respect to units held by MPC and its affiliates.

XML

Equity - Cash Distributions (Details) - USD ($) $ / shares in Units, shares in Millions							3 Months Ended							9 Months Ended
		Nov. 13, 2020	Nov. 06, 2020	Oct. 27, 2020	Aug. 17, 2020	Jul. 29, 2019	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019		Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019		Dec. 31, 2019	Jul. 30, 2019	Dec. 31, 2018
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Contributions from:							$ 13,000,000	$ 6,000,000	$ 225,000,000	$ 295,000,000		$ 13,000,000	$ 15,000,000
Distribution Made to Limited Partner, Cash Distributions Declared							745,000,000			734,000,000				$ 2,250,000,000	$ 2,011,000,000
Partners' Capital Account, Distributions							736,000,000	728,000,000	738,000,000	715,000,000		764,000,000	776,000,000
Partners' Capital, Including Portion Attributable to Noncontrolling Interest							13,095,000,000	$ 13,262,000,000	$ 13,356,000,000	17,892,000,000		$ 17,611,000,000	$ 17,730,000,000	13,095,000,000	17,892,000,000		$ 16,613,000,000		$ 17,731,000,000
Preferred Class B [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution date					Aug. 17, 2020
Partners' Capital Account, Distributions					$ 21,000,000
Subsequent Event
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Declaration Date				Oct. 27, 2020
Cash distributions declared per limited partner common unit				$ 0.6875
Date of record			Nov. 06, 2020
Subsequent Event | Limited Partners Common Units
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution date		Nov. 13, 2020
Limited Partners Common Units
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared	[1]						$ 715,000,000			$ 704,000,000	[2]			2,158,000,000	1,919,000,000	[2]
Cash distributions declared per limited partner common unit							$ 0.6875	$ 0.6875	$ 0.6875	$ 0.6775		$ 0.6675	$ 0.6575
Limited Partners Common Units | Subsequent Event
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared				$ 715,000,000
Series A Preferred Stock [Member] | Series B Preferred Stock [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared	[1]						$ 10,000,000			$ 10,000,000				31,000,000	31,000,000
Series A Preferred Stock [Member] | Preferred Class B [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Cash distributions declared per limited partner common unit							$ 68.75
Preferred Class B [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Contributions from:							$ 0	$ 0	$ 0	0		$ 0	$ 0
Partners' Capital Account, Distributions							20,000,000	0	21,000,000	21,000,000		0	0	41,000,000
Partners' Capital, Including Portion Attributable to Noncontrolling Interest							$ 601,000,000	611,000,000	601,000,000	601,000,000		0	0	$ 601,000,000	601,000,000		$ 611,000,000		0
MPC | Limited Partners Common Units
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Limited Partners' Capital Account, Units Issued							647							647			666	161
Contributions from:							$ 13,000,000	6,000,000	225,000,000	292,000,000		0	0
Partners' Capital Account, Distributions							445,000,000	458,000,000	446,000,000	432,000,000		332,000,000	327,000,000
Partners' Capital, Including Portion Attributable to Noncontrolling Interest							2,827,000,000	2,951,000,000	3,014,000,000	5,767,000,000		(1,671,000,000)	(1,632,000,000)	$ 2,827,000,000	5,767,000,000		$ 4,968,000,000		(1,612,000,000)
MPC | ANDX LP [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Contributions from:										12,500,000					25,000,000
ANDX LP [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Preferred Stock, Dividend Rate, Percentage						6.875%
MPLX LP | Series B Preferred Stock [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Preferred Stock, Dividend Payment Rate, Variable														LIBOR plus
Preferred Stock, Dividend Rate, Percentage														4.652%
TexNew Mex units [Member] | MPLX LP
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared							$ 5,000,000
Public | Limited Partners Common Units
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Limited Partners' Capital Account, Units Issued							393							393			392	102
Contributions from:							$ 0	0	0	0		0	0
Partners' Capital Account, Distributions							271,000,000	270,000,000	271,000,000	262,000,000		191,000,000	188,000,000
Partners' Capital, Including Portion Attributable to Noncontrolling Interest							$ 9,436,000,000	$ 9,469,000,000	$ 9,509,000,000	$ 11,289,000,000		$ 8,305,000,000	$ 8,326,000,000	$ 9,436,000,000	$ 11,289,000,000		$ 10,800,000,000		$ 8,336,000,000

[1] See Note 7 for distribution information.

[2] The three and nine months ended September 30, 2019 amounts are net of $12.5 million and $25 million, respectively, of waived distributions with respect to units held by MPC and its affiliates.

XML

Series A Preferred Units (Narrative) (Details) - $ / shares shares in Millions	Oct. 27, 2020	May 13, 2016	Sep. 30, 2020
Series A Convertible Preferred Units
Redeemable Noncontrolling Interest [Line Items]
Issuance of preferred units		30.8
Dividend rate, percentage		6.50%
Price per share		$ 32.50
Dividend rate, per-dollar-amount		$ 0.528125
Description		The holders may convert their Series A preferred units into common units at any time, in full or in part, subject to minimum conversion amounts and conditions. After the fourth anniversary of the issuance date, MPLX may convert the Series A preferred units into common units at any time, in whole or in part, subject to certain minimum conversion amounts and conditions, if the closing price of MPLX common units is greater than $48.75 for the 20-day trading period immediately preceding the conversion notice date. The conversion rate for the Series A preferred units shall be the quotient of (a) the sum of (i) $32.50, plus (ii) any unpaid cash distributions on the applicable preferred unit, divided by (b) $32.50, subject to adjustment for unit distributions, unit splits and similar transactions. The holders of the Series A preferred units are entitled to vote on an as-converted basis with the common unitholders and have certain other class voting rights with respect to any amendment to the MPLX partnership agreement that would adversely affect any rights, preferences or privileges of the preferred units. In addition, upon certain events involving a change of control, the holders of preferred units may elect, among other potential elections, to convert their Series A preferred units to common units at the then change of control conversion rate.
Partners' Capital Account, Units			29.6
Subsequent Event
Redeemable Noncontrolling Interest [Line Items]
Distribution Made to Limited Partner, Declaration Date	Oct. 27, 2020
Distribution Made to Limited Partner, Distributions Declared, Per Unit	$ 0.6875

XML

Series A Preferred Units (Rollforward of Redeemable Preferred Units) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Redeemable Noncontrolling Interest [Line Items]
Balance at December 31, 2019	$ 968
Distributions to unitholders and general partner	(2,162)	$ (1,731)
Balance at September 30, 2020	968
Series A Convertible Preferred Units
Redeemable Noncontrolling Interest [Line Items]
Balance at December 31, 2019	968
Net income allocated	61
Distributions to unitholders and general partner	(61)
Balance at September 30, 2020	$ 968

XML

Segment Information (Details)	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Number of reportable segments	2

XML

Segment Information - Segment Adjusted EBITDA (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019		Sep. 30, 2020		Sep. 30, 2019
Segment Reporting Information [Line Items]
Restructuring Charges		$ 36	$ 0		$ 36		$ 0
Depreciation and amortization	[1]	346	302		992		916
Total revenues from contracts with customers		1,756	1,760		5,129		5,185
Rental income		102	99		296		291
Income/(loss) from equity method investments(1)		83	95		(1,012)	[2],[3]	255
Other income		2	2		5		6
Total segment revenues and other income		(2,247)	(2,280)		(5,320)		(6,725)
Investments in unconsolidated affiliates					(244)		(494)
L&S
Segment Reporting Information [Line Items]
Depreciation and amortization		164	113		440		373
Total revenues from contracts with customers		998	998		2,973		2,844
Investments in unconsolidated affiliates		(4)	(95)		(132)		(163)
G&P
Segment Reporting Information [Line Items]
Depreciation and amortization		182	189		552		543
Total revenues from contracts with customers		758	762		2,156		2,341
Investments in unconsolidated affiliates		(18)	(76)		(112)		(331)
Operating Segments
Segment Reporting Information [Line Items]
Adjusted EBITDA		1,335	1,165		3,856		3,015
Operating Segments | L&S
Segment Reporting Information [Line Items]
Restructuring Charges		27	0		27		0
Rental income		249	304		737		935
Income/(loss) from equity method investments(1)		36	60		126		159
Other income		51	17		154		45
Total segment revenues and other income	[4]	(1,334)	(1,379)		(3,990)		(3,983)
Adjusted EBITDA	[5]	893	766		2,604		1,895
Capital Expenditure		118	272		410		700
Operating Segments | G&P
Segment Reporting Information [Line Items]
Restructuring Charges		9	0		9		0
Rental income		94	88		271		260
Income/(loss) from equity method investments(1)		47	35		(1,138)		96
Other income		14	16		41		45
Total segment revenues and other income	[4]	(913)	(901)		(1,330)		(2,742)
Adjusted EBITDA	[5]	442	399		1,252		1,120
Capital Expenditure		131	321		375		953
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA attributable to Predecessor		0	108	[6]	0		770	[6]
Service [Member]
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		604	632		1,779		1,865
Service [Member] | L&S
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		87	95		248		260
Service [Member] | G&P
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		517	537		1,531		1,605
Service [Member] | Operating Segments | L&S
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		989	976		2,924		2,787
Service [Member] | Operating Segments | G&P
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		524	555		1,549		1,627
Product [Member]
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		165	171		454		576
Product [Member] | Operating Segments | L&S
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		9	22		49		57
Product [Member] | Operating Segments | G&P
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		234	207		607		714
Third Party [Member] | L&S
Segment Reporting Information [Line Items]
Total segment revenues and other income		(139)	(182)		(443)		(498)
Third Party [Member] | G&P
Segment Reporting Information [Line Items]
Total segment revenues and other income		$ (858)	$ (843)		$ (1,181)		$ (2,581)

[1] Depreciation and amortization attributable to L&S was $164 million and $440 million for the three and nine months ended September 30, 2020, respectively, and $113 million and $373 million for the three and nine months ended September 30, 2019, respectively. Depreciation and amortization attributable to G&P was $182 million and $552 million for the three and nine months ended September 30, 2020, respectively, and $189 million and $543 million for the three and nine months ended September 30, 2019, respectively.

[2] The 2020 period includes $1,264 million of impairment expense. See Note 4.

[3] The nine months ended September 30, 2020 includes $1,264 million of impairment expense. See Note 4.

[4] Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $139 million and $443 million for the three and nine months ended September 30, 2020, respectively, and $182 million and $498 million for the three and nine months ended September 30, 2019, respectively. Third party revenues for the G&P segment were $858 million and $1,181 million for the three and nine months ended September 30, 2020, respectively, and $843 million and $2,581 million for the three and nine months ended September 30, 2019, respectively.

[5] See below for the reconciliation from Segment Adjusted EBITDA to net income.

[6] The adjusted EBITDA adjustments related to Predecessor are excluded from adjusted EBITDA attributable to MPLX LP prior to the Merger.

XML

Segment Information - Assets by Segment (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Segment Reporting, Other Significant Reconciling Item [Line Items]
Cash and cash equivalents	$ 28	$ 15
Assets	36,662	40,430
L&S | Operating Segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	21,144	20,810
G&P | Operating Segments
Segment Reporting, Other Significant Reconciling Item [Line Items]
Assets	$ 15,490	$ 19,605

XML

Segment Information - Reconciliation to Net Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Restructuring Charges		$ (36)	$ 0	$ (36)		$ 0
Depreciation and amortization	[1]	346	302	992		916
Income Tax Expense (Benefit)		(1)	(4)	(1)		(2)
Amortization of Debt Issuance Costs				(44)		(29)
Share-based Payment Arrangement, Expense		(4)	(5)	(12)		(17)
Goodwill and Intangible Asset Impairment		0	0	(2,165)		0
Interest and Other Financial Costs		(223)	(223)	(647)		(657)
Extinguishment of Debt, Gain (Loss), Net of Tax		14	0	14		0
Income/(loss) from equity method investments(1)		83	95	(1,012)	[2],[3]	255
Proceeds from Equity Method Investment, Distribution, Return of Capital				(350)		(379)
Acquisition Costs, Period Cost		0	(9)	0		(14)
Other Cost and Expense, Operating		3	1	5		1
Net income		674	689	(1,387)		2,035
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted EBITDA		1,335	1,165	3,856		3,015
Amortization of Debt Issuance Costs		(15)	(10)	(44)		(29)
Segment Reconciling Items [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Proceeds from Equity Method Investment, Distribution, Return of Capital		(130)	(145)	(369)		(399)
Adjusted EBITDA attributable to noncontrolling interests		10	9	27		23
L&S
Segment Reporting, Revenue Reconciling Item [Line Items]
Depreciation and amortization		164	113	440		373
L&S | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Restructuring Charges		(27)	0	(27)		0
Adjusted EBITDA	[4]	893	766	2,604		1,895
Income/(loss) from equity method investments(1)		36	60	126		159
G&P
Segment Reporting, Revenue Reconciling Item [Line Items]
Depreciation and amortization		182	189	552		543
G&P | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Restructuring Charges		(9)	0	(9)		0
Adjusted EBITDA	[4]	442	399	1,252		1,120
Income/(loss) from equity method investments(1)		47	35	(1,138)		96
Not Designated as Hedging Instrument [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	[5]	$ (10)	$ 11	$ (1)		$ 7

[1] Depreciation and amortization attributable to L&S was $164 million and $440 million for the three and nine months ended September 30, 2020, respectively, and $113 million and $373 million for the three and nine months ended September 30, 2019, respectively. Depreciation and amortization attributable to G&P was $182 million and $552 million for the three and nine months ended September 30, 2020, respectively, and $189 million and $543 million for the three and nine months ended September 30, 2019, respectively.

[2] The 2020 period includes $1,264 million of impairment expense. See Note 4.

[3] The nine months ended September 30, 2020 includes $1,264 million of impairment expense. See Note 4.

[4] See below for the reconciliation from Segment Adjusted EBITDA to net income.

[5] MPLX makes a distinction between realized and unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

XML

Inventories (Summary of Inventories) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
NGLs	$ 3	$ 5
Line fill	11	10
Spare parts, materials and supplies	103	95
Total inventories	$ 117	$ 110

XML

Property, Plant and Equipment (Summary of Property, Plant and Equipment) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020		Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use	$ 174
Property, plant and equipment, gross		$ 26,919		$ 26,867
Less accumulated depreciation(1)		5,304	[1]	4,722
Property, plant and equipment, net		21,615		22,145
L&S
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		12,671		12,934
L&S | Terminals
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		6,001		5,572
L&S | Marine
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		961		906
L&S | Terminals and related assets
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,534		1,109
L&S | Refineries and related assets
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		2,196		2,870
L&S | Land, building and other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,576		1,817
L&S | Construction-in-progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		403		660
G&P
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		14,248		13,933
G&P | Pipelines
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		7,413		7,159
G&P | Processing, fractionation and storage facilities
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		5,944		5,545
G&P | Land, building and other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		509		484
G&P | Construction-in-progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 382		$ 745
Maximum [Member] | L&S | Terminals
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		51 years
Maximum [Member] | L&S | Marine
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		20 years
Maximum [Member] | L&S | Terminals and related assets
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		40 years
Maximum [Member] | L&S | Refineries and related assets
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		40 years
Maximum [Member] | L&S | Land, building and other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		61 years
Maximum [Member] | G&P | Pipelines
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		40 years
Maximum [Member] | G&P | Processing, fractionation and storage facilities
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		40 years
Maximum [Member] | G&P | Land, building and other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		40 years
Minimum [Member] | L&S | Terminals
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		2 years
Minimum [Member] | L&S | Marine
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		15 years
Minimum [Member] | L&S | Terminals and related assets
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		4 years
Minimum [Member] | L&S | Refineries and related assets
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		13 years
Minimum [Member] | L&S | Land, building and other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		1 year
Minimum [Member] | G&P | Pipelines
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		5 years
Minimum [Member] | G&P | Processing, fractionation and storage facilities
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		10 years
Minimum [Member] | G&P | Land, building and other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		3 years

[1] The September 30, 2020 balance includes property, plant and equipment impairment charges recorded during the first quarter of 2020 as discussed below.

XML

Goodwill and Intangibles Goodwill (Details)		3 Months Ended	9 Months Ended	12 Months Ended
	Nov. 30, 2019	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jul. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)
Goodwill [Line Items]
Goodwill, Gross			$ 10,798,000,000			$ 10,146,000,000
Goodwill, Impaired, Accumulated Impairment Loss			(3,141,000,000)			(130,000,000)
Goodwill		$ (7,700,000,000)	(7,657,000,000)	$ (9,536,000,000)		(10,016,000,000)
Goodwill, Impairment Loss			(1,814,000,000)	(1,197,000,000)
Goodwill, Acquired During Period				717,000,000
Total Number of Reporting Units		6
Reporting Unit, Zero or Negative Carrying Amount, Amount of Allocated Goodwill				1
Number of Reporting Units	6	4
Crude Gathering [Member]
Goodwill [Line Items]
Goodwill		$ (1,100,000,000)
Minimum [Member]
Goodwill [Line Items]
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount		8.50%
Maximum [Member]
Goodwill [Line Items]
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount		270.00%
L&S
Goodwill [Line Items]
Goodwill, Gross			7,657,000,000			7,234,000,000
Goodwill, Impaired, Accumulated Impairment Loss			0			0
Goodwill			(7,657,000,000)	(7,722,000,000)		(7,234,000,000)
Goodwill, Impairment Loss			0	0
Goodwill, Acquired During Period				488,000,000
G&P
Goodwill [Line Items]
Goodwill, Gross			3,141,000,000			2,912,000,000
Goodwill, Impaired, Accumulated Impairment Loss			(3,141,000,000)			(130,000,000)
Goodwill			0	(1,814,000,000)		$ (2,782,000,000)
Goodwill, Impairment Loss		$ (1,814,000,000)	$ (1,814,000,000)	(1,197,000,000)
Goodwill, Acquired During Period				$ 229,000,000
Valuation, Income Approach [Member] | Measurement Input, Discount Rate [Member] | Goodwill [Member] | Minimum [Member]
Goodwill [Line Items]
Fair Value Inputs		9.50%
Valuation, Income Approach [Member] | Measurement Input, Discount Rate [Member] | Goodwill [Member] | Maximum [Member]
Goodwill [Line Items]
Fair Value Inputs		11.50%
Western Refining Wholesale & Western Refining Product Transport [Member]
Goodwill [Line Items]
Goodwill					$ (65,000,000)
Western Refining Wholesale & Western Refining Product Transport [Member] | L&S
Goodwill [Line Items]
Goodwill					(65,000,000)
Western Refining Wholesale & Western Refining Product Transport [Member] | G&P
Goodwill [Line Items]
Goodwill					$ 0

XML

Goodwill and Intangibles Intangibles (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020		Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Impairment of Intangible Assets, Finite-lived	$ 177
Finite-Lived Intangible Assets, Gross		$ 1,571		$ 1,571
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months		32
Finite-Lived Intangible Asset, Expected Amortization, Year Two		128
Finite-Lived Intangible Asset, Expected Amortization, Year Three		128
Finite-Lived Intangible Asset, Expected Amortization, Year Four		128
Finite-Lived Intangible Asset, Expected Amortization, Year Five		124
Finite-Lived Intangible Asset, Expected Amortization, after Year Five		451
Finite-Lived Intangible Assets, Net		991
Finite-Lived Intangible Assets, Accumulated Amortization		(580)	[1]	(301)
Intangibles, net		991		1,270
L&S
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets		27
Finite-Lived Intangible Assets, Gross		283		283
Finite-Lived Intangible Assets, Accumulated Amortization		(72)	[1]	(45)
Intangibles, net		$ 211		238
L&S | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		6 years
L&S | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		8 years
G&P
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets		$ 75
Finite-Lived Intangible Assets, Gross		1,288		1,288
Finite-Lived Intangible Assets, Accumulated Amortization		(508)	[1],[2]	(256)
Intangibles, net		$ 780		$ 1,032
G&P | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		6 years
G&P | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		25 years

[1] Amortization expense attributable to the G&P and L&S segments for the nine months ended September 30, 2020 was $75 million and $27 million, respectively.

[2] Impairment charge of $177 million is included within the G&P accumulated amortization.

XML

Fair Value Measurements - Recurring - Financial Instruments by Valuation Hierarchy (Details) - Fair Value, Recurring [Member] - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	$ 0	$ 0
Derivative liability	61	60
Embedded derivatives in commodity contracts | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Derivative liability	$ 61	$ 60

XML

Fair Value Measurments - Recurring - Significant Unobservable Inputs in Level 3 Valuation (Details)	9 Months Ended
	Sep. 30, 2020 USD ($) $ / gal
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivative, Average Forward Price | $ / gal	0.58
Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Embedded Derivative Renewal Term	5 years
Embedded Derivative Second Renewal Term	5 years
Fair Value, Inputs, Level 3 [Member] | Embedded derivatives in commodity contracts
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Probability of Renewal Second Term	100.00%
Fair Value Inputs Probability of Renewal	100.00%
Minimum [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity contracts
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	$ 0.46
Maximum [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity contracts
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	$ 0.97

XML

Fair Value Measurements - Recurring - Changes in Level 3 Measurements (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Commodity Derivative Contracts (net)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value at beginning of period		$ 0	$ 0	$ 0	$ 0
Total gains (losses) (realized and unrealized) included in earnings	[1]	0	0	0	0
Settlements		0	0	0	0
Fair value at end of period		0	0	0	0
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized losses relating to liabilities still held at end of period		0	0	0	0
Embedded Derivatives in Commodity Contracts (net)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value at beginning of period		(51)	(65)	(60)	(61)
Total gains (losses) (realized and unrealized) included in earnings	[1]	(12)	9	(5)	2
Settlements		2	2	4	5
Fair value at end of period		(61)	(54)	(61)	(54)
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized losses relating to liabilities still held at end of period		$ (11)	$ 9	$ (2)	$ 5

[1] Gains and losses on commodity derivative contracts classified as Level 3 are recorded in “Product sales” on the Consolidated Statements of Income. Gains and losses on derivatives embedded in commodity contracts are recorded in “Purchased product costs” and “Cost of revenues” on the Consolidated Statements of Income.

XML

Fair Value Measurements - Reported (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 20,455	$ 19,800
SMR liability	76	80
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	21,721	21,054
SMR liability	$ 87	$ 90

XML

Derivative Financial Instruments - Embedded Derivatives in Commodity Contracts (Details) - Natural Gas [Member] - Embedded derivatives in commodity contracts $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Derivative [Line Items]
Number of Renewals	2
Embedded Derivative Renewal Term	5 years
Embedded Derivative Fair Value of Embedded Derivative Liability Including Inception Value Allocable to Host Contract	$ 61	$ 60

XML

Derivative Financial Instruments - Derivatives Balance Sheet Location (Details) - Not Designated as Hedging Instrument [Member] - Commodity contracts - USD ($) $ in Millions		Sep. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	$ 0	$ 0
Derivative Liability, Fair Value, Gross Liability	[1]	61	60
Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	0	0
Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[1]	4	5
Other noncurrent assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	0	0
Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[1]	$ 57	$ 55

[1] Includes embedded derivatives in commodity contracts as discussed above.

XML

Derivatives Financial Instruments - Derivative Income Statement Location (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative [Line Items]
Total gain (loss)		$ (12)	$ 9	$ (5)	$ 2
Purchased product costs
Derivative [Line Items]
Realized gain (loss)		(2)	(2)	(4)	(5)
Total gain (loss)		(12)	9	(5)	2
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	[1]	(10)	11	(1)	7
Not Designated as Hedging Instrument [Member] | Purchased product costs
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts		$ (10)	$ 11	$ (1)	$ 7

[1] MPLX makes a distinction between realized and unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

XML

Debt - Summary of Outstanding Borrowings (Detail) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Oct. 15, 2020	Aug. 18, 2020	Dec. 31, 2019	Sep. 09, 2019
Debt Instrument [Line Items]
Amortization of deferred financing costs		$ 44.0	$ 29.0
Total		20,757.0				$ 20,119.0
Unamortized debt issuance costs		(118.0)				(106.0)
Unamortized discount/premium		(290.0)				(300.0)
Amounts due within one year		(307.0)				(9.0)
Total long-term debt due after one year		20,042.0				19,704.0
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross							$ 2,000.0
Senior Notes [Member] | MPLX LP
Debt Instrument [Line Items]
Long-term Debt, Gross					$ 3,000.0
Senior Notes [Member] | MarkWest [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		23.0				23.0
Senior Notes [Member] | ANDX LP [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		121.0				190.0
Variable Rate Senior Notes [Member] | MPLX LP
Debt Instrument [Line Items]
Long-term Debt, Gross		1,000.0				2,000.0
Fixed Rate Senior Notes [Member] | MPLX LP
Debt Instrument [Line Items]
Long-term Debt, Gross		19,506.0				16,887.0
Finance Lease [Member] | Marathon Pipe Line LLC [Member]
Debt Instrument [Line Items]
Financing lease obligations(1)	[1]	12.0				19.0
Floating Rate Senior Notes Due September 2021 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross							1,000.0
Floating Rate Senior Notes Due September 2022 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross							$ 1,000.0
MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Long-term Line of Credit		95.0				0.0
MPLX Term Loan [Member]
Debt Instrument [Line Items]
Long-term Line of Credit		$ 0.0			$ 1,000.0	$ 1,000.0
Senior Notes Due October 2022 [Member] | Senior Notes [Member] | MPLX LP
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		6.25%
Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		1.75%
Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		6.25%
Subsequent Event | Senior Notes Due October 2022 [Member] | Senior Notes [Member] | MPLX LP
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 300.0
Subsequent Event | Senior Notes Due October 2022 [Member] | Senior Notes [Member] | ANDX LP [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 34.0

[1] See Note 20 for lease information.

XML

Debt Debt - Summary of Outstanding Borrowings - Interest Rates and Table Due Dates (Details)	9 Months Ended
	Sep. 30, 2020
MPLX LP | Line of Credit [Member] | MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Expiration Date	Jul. 30, 2024
MPLX LP | Senior Notes [Member] | Senior Notes Due October 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.25%
MPLX LP | Senior Notes [Member] | Floating Rate Senior Notes Due September 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Sep. 09, 2021
MPLX LP | Senior Notes [Member] | Floating Rate Senior Notes Due September 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Sep. 09, 2022
Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.75%
Minimum [Member] | MPLX LP | Senior Notes [Member] | Senior Notes Due October 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Oct. 15, 2022
Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.25%
Maximum [Member] | MPLX LP | Senior Notes [Member] | Senior Notes Due April 2058 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Apr. 15, 2058

XML

Debt - Additional Information (Detail) - USD ($) $ in Millions				3 Months Ended		9 Months Ended
		Sep. 26, 2019	Sep. 09, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Oct. 15, 2020	Aug. 31, 2020	Aug. 28, 2020	Aug. 18, 2020	Dec. 31, 2019	Jul. 30, 2019
Debt Instrument [Line Items]
Payments of Debt Issuance Costs						$ 23.0	$ 20.0
Repayments of Long-term Debt						5,372.0	7,423.0
Payment for Debt Extinguishment or Debt Prepayment Cost				$ (14.0)	$ 0.0	(14.0)	$ 0.0
Debt and Lease Obligation				20,757.0		20,757.0						$ 20,119.0
Unamortized Debt Issuance Expense				118.0		118.0						106.0
Debt Instrument, Unamortized Discount				290.0		290.0						300.0
Debt, Current				307.0		307.0						9.0
Long-term debt				20,042.0		20,042.0						19,704.0
MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity													$ 3,500.0
Long-term Line of Credit				$ 95.0		95.0						0.0
MPLX Revolving Credit Facility due July 2024 [Member] | MPLX LP
Debt Instrument [Line Items]
Proceeds from Lines of Credit						$ 2,995.0
Debt Instrument, Interest Rate, Effective Percentage				1.51%		1.51%
Repayments of Long-term Lines of Credit						$ 2,900.0
Letters of Credit Outstanding				$ 1.0		1.0
Line of Credit Facility, Remaining Borrowing Capacity				$ 3,405.0		$ 3,405.0
Line of Credit Facility, Remaining Borrowing Capacity, Percentage				97.30%		97.30%
MPLX Term Loan [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 1,000.0
Debt Instrument, Description of Variable Rate Basis		(i) the Adjusted LIBO Rate (as defined in the Term Loan Agreement) plus a margin ranging from 75.0 basis points to 100.0 basis points per annum, depending on MPLX’s credit ratings, or (ii) the Alternate Base Rate (as defined in the Term Loan Agreement).
Long-term Line of Credit				$ 0.0		$ 0.0					$ 1,000.0	1,000.0
Repayments of Long-term Debt						1,000.0
Payment for Debt Extinguishment or Debt Prepayment Cost						(1.0)
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 2,000.0
Percent of Par			100.00%
Senior Notes [Member] | MPLX LP
Debt Instrument [Line Items]
Long-term Debt, Gross											$ 3,000.0
Senior Notes [Member] | ANDX LP [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				121.0		121.0						190.0
Senior Notes [Member] | MarkWest [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				23.0		23.0						23.0
Senior Notes [Member] | Floating Rate Senior Notes Due September 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 1,000.0
Debt Instrument, Description of Variable Rate Basis			LIBOR plus 0.9 percent per annum
Payment for Debt Extinguishment or Debt Prepayment Cost						(3.0)
Senior Notes [Member] | Floating Rate Senior Notes Due September 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 1,000.0
Debt Instrument, Description of Variable Rate Basis			LIBOR plus 1.1 percent per annum
Senior Notes [Member] | Senior Notes Due March 2026 [Member] | MPLX LP
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 1,500.0		$ 1,500.0
Debt Instrument, Interest Rate, Stated Percentage				1.75%		1.75%
Percent of Par											99.785%
Senior Notes [Member] | Senior Notes Due August 2030 [Member] | MPLX LP
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 1,500.0		$ 1,500.0
Debt Instrument, Interest Rate, Stated Percentage				2.65%		2.65%
Percent of Par											99.913%
Senior Notes [Member] | Senior Notes Due October 2022 [Member] | MPLX LP
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				6.25%		6.25%
Senior Notes [Member] | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Payment for Debt Extinguishment or Debt Prepayment Cost						$ (18.0)
Senior Notes [Member] | Senior Notes Due May 2024 [Member] | MPLX LP
Debt Instrument [Line Items]
Long-term Debt, Gross									$ 450.0
Percent of Par										103.20%
Senior Notes [Member] | Senior Notes Due May 2024 [Member] | ANDX LP [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross										$ 69.0
Debt Instrument, Interest Rate, Stated Percentage										6.375%
Fixed Rate Senior Notes [Member] | MPLX LP
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 19,506.0		19,506.0						16,887.0
Variable Rate Senior Notes [Member] | MPLX LP
Debt Instrument [Line Items]
Long-term Debt, Gross				1,000.0		1,000.0						2,000.0
Finance Lease [Member] | Marathon Pipe Line LLC [Member]
Debt Instrument [Line Items]
Finance Lease, Liability	[1]			$ 12.0		$ 12.0						$ 19.0
Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				1.75%		1.75%
Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				6.25%		6.25%
Subsequent Event | Senior Notes [Member] | Senior Notes Due October 2022 [Member] | MPLX LP
Debt Instrument [Line Items]
Long-term Debt, Gross								$ 300.0
Subsequent Event | Senior Notes [Member] | Senior Notes Due October 2022 [Member] | ANDX LP [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross								$ 34.0
Debt Premium [Member] | Senior Notes [Member] | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Payment for Debt Extinguishment or Debt Prepayment Cost						$ (14.0)

[1] See Note 20 for lease information.

XML

Revenue Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		$ 1,756	$ 1,760	$ 5,129		$ 5,185
Rental income		102	99	296		291
Rental income - related parties		241	293	712		904
Income/(loss) from equity method investments(1)		83	95	(1,012)	[1],[2]	255
Other income		2	2	5		6
Other income - related parties		63	31	190		84
Operating Income (Loss)	[3]	491	520	191		1,540
Total segment revenues and other income		2,247	2,280	5,320		6,725
L&S
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		998	998	2,973		2,844
G&P
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		758	762	2,156		2,341
Service [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		604	632	1,779		1,865
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		909	899	2,694		2,549
Service [Member] | L&S
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		87	95	248		260
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		902	881	2,676		2,527
Service [Member] | G&P
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		517	537	1,531		1,605
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		7	18	18		22
Service, Other [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		41	26	102		86
Service, Other [Member] | L&S
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		0	0	0		0
Service, Other [Member] | G&P
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		41	26	102		86
Product [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		165	171	454		576
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		37	32	100		109
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue		165	171	454		576
Product [Member] | L&S
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		2	8	10		17
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue		7	14	39		40
Product [Member] | G&P
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		35	24	90		92
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue		$ 158	$ 157	$ 415		$ 536

[1] The 2020 period includes $1,264 million of impairment expense. See Note 4.

[2] The nine months ended September 30, 2020 includes $1,264 million of impairment expense. See Note 4.

[3] Non-ASC 606 Revenue includes rental income, income/(loss) from equity method investments, derivative gains and losses, mark-to-market adjustments, and other income.

XML

Revenue Contract Balances (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019
Long-term deferred revenue, beginning balance		$ 217
Long-term deferred revenue, ending balance		291
Liability, change in timeframe, performance obligation satisfied, revenue recognized		0	$ 0
ASC 606
Contract assets, beginning balance	[1]	39	36
Contract assets, additions/(deletions)		(9)	(6)
Contract assets, revenue recognized	[2]	(1)	(2)
Contract assets, ending balance		29	28
Deferred revenue, beginning balance	[1]	23	13
Deferred revenue, additions/(deletions)		16	11
Deferred revenue, revenue recognized	[2]	(6)	(4)
Deferred revenue, ending balance		33	20
Deferred revenue - related parties, beginning balance	[1]	53	65
Deferred revenue - related party, additions/(deletions)		77	34
Deferred revenue - related parties, revenue recognized	[2]	(60)	(50)
Deferred revenue - related parties, ending balance		70	49
Long-term deferred revenue, beginning balance	[1]	90	56
Long-term deferred revenue, additions/(deletions)		25	26
Long-term deferred revenue, revenue recognized	[2]	0	0
Long-term deferred revenue, ending balance		115	82
Long-term deferred revenue - related parties, beginning balance	[1]	55	52
Long-term deferred revenue - related party, additions/(deletions)		(7)	5
Long-term deferred revenue - related parties, revenue recognized	[2]	0	0
Long-term deferred revenue - related parties, ending balance		$ 48	$ 57

[1] Balance represents ASC 606 portion of each respective line item.

[2] No significant revenue was recognized related to past performance obligations in the current periods.

XML

Revenue Remaining Performance Obligations (Details) $ in Millions	Sep. 30, 2020 USD ($)
Revenue from Contract with Customer [Abstract]
Contract with customer, liability	$ 264
Revenue, Remaining Performance Obligation, Amount	11,349	[1],[2],[3]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 461
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, years	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 1,727
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, years	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 1,701
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, years	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 1,591
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, years	3 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 5,869
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, years	30 years

[1] All fixed consideration from contracts with customers is included in the amounts presented above. Variable consideration that is constrained or not required to be estimated as it reflects our efforts to perform is excluded.

[2] Arrangements deemed implicit leases are included in “Rental income” and are excluded from this table.

[3] Only minimum volume commitments that are deemed fixed are included in the table above. MPLX has various minimum volume commitments in processing arrangements that vary based on the actual Btu content of the gas received. These amounts are deemed variable consideration and are excluded from the table above.

XML

Supplemental Cash Flow Information - Summary of Supplemental Cash Flow Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jul. 31, 2020
Net cash provided by operating activities included:
Interest paid (net of amounts capitalized)	$ 631	$ 648
Income Taxes Paid, Net	1	0
Non-cash investing and financing activities
Net transfers of property, plant and equipment (to)/from materials and supplies inventories	$ (1)	$ 1
Western Refining Wholesale & Western Refining Product Transport [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Partner Capital, Units, contributed, fair value assigned			$ 340

XML

Supplemental Cash Flow Information - Summary of Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Supplemental Cash Flow Elements [Abstract]
(Decrease)/increase in capital accruals	$ (197)	$ (67)

XML

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	[1]	$ (16)	$ (15)	$ (15)	$ (16)
Other Comprehensive Income (Loss), Net of Tax	[2]	(1)	1
Pension Plan [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	[1]	(14)	(14)	(14)	(14)
Other Comprehensive Income (Loss), Net of Tax	[2]	0	0
Other Postretirement Benefits Plan [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	[1]	(2)	(1)	$ (1)	$ (2)
Other Comprehensive Income (Loss), Net of Tax	[2]	$ (1)	$ 1

[1] These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on the Consolidated Statements of Income under the caption “Income/(loss) from equity method investments.”

[2] Components of other comprehensive income/loss - remeasurements relate to actuarial gains and losses as well as amortization of prior service costs. MPLX records an adjustment to “Comprehensive income” in accordance with its ownership interest in LOOP and Explorer.

XML

Equity-Based Compensation Plan - Summary of Phantom Unit Award Activity (Details) - Phantom Units	9 Months Ended
	Sep. 30, 2020 $ / shares shares
Number of Units
Outstanding at December 31, 2019 | shares	1,109,568
Granted | shares	215,677
Settled | shares	558,398
Forfeited | shares	5,383
Outstanding at September 30, 2020 | shares	761,464
Weighted Average Fair Value
Outstanding at December 31, 2019 | $ / shares	$ 35.97
Granted | $ / shares	19.31
Settled | $ / shares	37.73
Forfeited | $ / shares	35.87
Outstanding at September 30, 2020 | $ / shares	$ 29.96

XML

Equity-Based Compensation Plan - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2020 $ / shares
Officer | Performance Shares [Member] | MPLX LP 2012 Incentive Compensation Plan [Member]
Equity Transactions And Share Based Compensation [Line Items]
Percentage paid out in cash	75.00%
Share Based Compensation Arrangement By Share Based Payment Award Percentage Paid Out In Stock	25.00%
2020 [Member] | Performance Units Market Condition [Member]
Equity Transactions And Share Based Compensation [Line Items]
Performance units grant date fair value (in USD per unit)	$ 0.80
2018 [Member] | Performance Units Market Condition [Member]
Equity Transactions And Share Based Compensation [Line Items]
Performance units grant date fair value (in USD per unit)	0.45
Maximum [Member] | 2020 [Member] | Performance Unit Performance Condition [Member]
Equity Transactions And Share Based Compensation [Line Items]
Performance units grant date fair value (in USD per unit)	2.00
Maximum [Member] | 2018 [Member] | Performance Unit Performance Condition [Member]
Equity Transactions And Share Based Compensation [Line Items]
Performance units grant date fair value (in USD per unit)	$ 2.00

XML

Equity-Based Compensation Plan - Summary of Performance Unit Award Activity (Detail) - Performance Shares [Member]	9 Months Ended
	Sep. 30, 2020 shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at December 31, 2019	2,157,347
Granted	2,147,211
Settled	1,169,354
Forfeited	(31,668)
Outstanding at September 30, 2020	3,103,536

XML

Leases Leases Narrative (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Lessor, Sales-type Lease, Assumptions and Judgments, Value of Underlying Asset, Amount			$ 171
Sales-type Lease, Lease Receivable			370
Sales-type Lease, Selling Profit (Loss)			209
MPC
Operating Lease, Lease Income	[1]	$ 208		$ 248	$ 589	$ 773
Sales-type Lease, Lease Receivable		419			419
Sales-type Lease, Unguaranteed Residual Asset		22			22		$ 7
Refining Logistics [Member] | MPC
Sales-type Lease, Unguaranteed Residual Asset			$ 10
Third Party [Member]
Operating Lease, Lease Income	[1]	70		$ 63	199	$ 196
Sales-type Lease, Lease Receivable		1			1
Sales-type Lease, Selling Profit (Loss)		$ 0			$ 0

[1] These amounts are presented net of executory costs.

XML

Leases Lessor Maturity Table (Details) - USD ($) $ in Millions	Sep. 30, 2020	Mar. 31, 2020
Lessor, Lease, Description [Line Items]
Sales-type Lease, Lease Receivable		$ 370
MPC
Lessor, Lease, Description [Line Items]
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Current Year	$ 39
Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, Year One	157
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Three Years	157
Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, Year Three	158
Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, Year Four	158
Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, after Year Five	473
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received	1,142
Sales-type and Direct Financing Leases, Lease Receivable, Undiscounted Excess Amount	723
Sales-type Lease, Lease Receivable	419
Third Party [Member]
Lessor, Lease, Description [Line Items]
Sales-type Lease, Lease Receivable	$ 1

XML

Leases Lessor Lease Revenues (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Lessor, Lease, Description [Line Items]
Sales-type Lease, Selling Profit (Loss)			$ 209
MPC
Lessor, Lease, Description [Line Items]
Operating Lease, Lease Income	[1]	$ 208		$ 248	$ 589	$ 773
Sales-type Lease, Interest Income		37		3	113	3
Sales-type Lease, Variable Lease Income		1		1	1	1
Third Party [Member]
Lessor, Lease, Description [Line Items]
Operating Lease, Lease Income	[1]	70		63	199	196
Sales-type Lease, Selling Profit (Loss)		0			0
Sales-type Lease, Interest Income		0			0
Sales-type Lease, Variable Lease Income		0			0
MPC
Lessor, Lease, Description [Line Items]
Sales-type Lease, Selling Profit (Loss)		$ 0		$ 0	$ 0	$ 0

[1] These amounts are presented net of executory costs.

XML

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Commitments And Contingencies [Line Items]
Accrued liabilities for environmental remediation	$ 18	$ 19
Loss Contingency, Damages Sought, Value	187
Contractual commitments to acquire property, plant and equipment	181
MPC
Commitments And Contingencies [Line Items]
Due to Related Parties, Current	247	911
Environmental Loss Contingency [Member] | MPC
Commitments And Contingencies [Line Items]
Due to Related Parties, Current	$ 0	$ 0
Whistler Pipeline LLC [Member]
Commitments And Contingencies [Line Items]
Equity method investment, ownership percentage	38.00%
Indirect Ownership Interest [Member] | Bakken Pipeline System [Member]
Commitments And Contingencies [Line Items]
Equity method investment, ownership percentage	9.19%
Guarantee Type, Other [Member]
Commitments And Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 230