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Pension and Other Postretirement Benefits
 12 Months Ended
Dec. 31, 2023
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]  
Defined Benefit Pension and Other Postretirement Plans Pension and Other Postretirement Benefits
We have two noncontributory defined benefit pension plans. One plan is frozen and covered certain employees of our former Speedway LLC subsidiary. The other plan is active and covers substantially all of our employees. Benefits under these plans are based on a now frozen final average pay type of benefit based on age, years of service and final average pensionable earnings, and a cash balance type of benefit. The years of service component for the final average pay type of benefit was frozen as of December 31, 2009, and certain of the pensionable earnings components were frozen as of December 31, 2012. Benefits for the cash balance type of benefit began on January 1, 2010 for our continuing active plan, and began on January 1, 2016 for our frozen plan, and are based on a cash balance formula with an annual percentage of eligible pay credited based upon age and years of service or at a flat rate of eligible pay, depending on covered employee group. Substantially all of our employees also accrue benefits under a defined contribution plan.
(Millions of dollars)202320222021
Cash balance weighted average interest crediting rates3.57 %3.00 %3.00 %
We also have other postretirement benefits covering most employees. Retiree health care benefits are provided through comprehensive hospital, surgical, major medical benefit, prescription drug and related health benefit provisions subject to various cost sharing features. Retiree life insurance benefits are provided to a closed group of retirees. Other postretirement benefits are not funded in advance.
In connection with the Andeavor acquisition, we assumed a number of additional qualified and nonqualified noncontributory benefit pension plans, covering substantially all former Andeavor employees. Benefits under these plans are determined based on final average compensation and years of service through December 31, 2010 and a cash balance formula for service beginning January 1, 2011. These plans were frozen as of December 31, 2018. Further, as of December 31, 2019, the qualified plans were merged with our existing qualified plans in which the actuarial assumptions were materially the same between the plans. We also assumed a number of additional postretirement benefits covering eligible employees. These benefits were merged with our existing benefits beginning January 1, 2019.
Obligations and Funded Status
The accumulated benefit obligation for all defined benefit pension plans was $2,441 million and $2,272 million as of December 31, 2023 and 2022.
The following summarizes the projected benefit obligations and funded status for our defined benefit pension and other postretirement plans:
 Pension BenefitsOther Benefits
(Millions of dollars)2023202220232022
Benefit obligations at January 1$2,359 $3,295 $650 $828 
Service cost195 228 18 26 
Interest cost116 102 31 21 
Actuarial loss/(gain)184 (653)31 (168)
Benefits paid(a)
(291)(613)(51)(57)
Benefit obligations at December 312,563 2,359 679 650 
Fair value of plan assets at January 11,838 3,043 — — 
Actual return on plan assets266 (622)— — 
Employer contributions269 30 51 57 
Benefits paid from plan assets(291)(613)(51)(57)
Fair value of plan assets at December 312,082 1,838 — — 
Funded status at December 31$(481)$(521)$(679)$(650)
(a)Of the $613 million in benefits paid in 2022, $285 million is related to the pension annuity lift-out.
Amounts recognized in the consolidated balance sheet for our pension and other postretirement benefit plans at December 31 include:
 Pension BenefitsOther Benefits
(Millions of dollars)2023202220232022
Current liabilities(8)(7)(50)(50)
Noncurrent liabilities(473)(514)(629)(600)
Accrued benefit cost$(481)$(521)$(679)$(650)
Included in accumulated other comprehensive loss at December 31 were the following before-tax amounts that had not been recognized in net periodic benefit cost:
 Pension BenefitsOther Benefits
(Millions of dollars)2023202220232022
Net actuarial loss$467 $386 $50 $19 
Prior service credit(69)(114)(202)(224)
Amounts exclude those related to LOOP and Explorer, equity method investees with defined benefit pension and postretirement plans for which net losses (gains) of $10 million and $(5) million were recorded in accumulated other comprehensive income (loss) in 2023, reflecting our ownership share.
Components of Net Periodic Benefit Cost and Other Comprehensive (Income) Loss
The following summarizes the net periodic benefit costs and the amounts recognized as other comprehensive loss (pretax) for our defined benefit pension and other postretirement plans.
 Pension BenefitsOther Benefits
(Millions of dollars)202320222021202320222021
Service cost$201 $230 $287 $18 $26 $34 
Interest cost116 102 93 31 21 30 
Expected return on plan assets(163)(142)(139)— — — 
Amortization of prior service cost (credit)(45)(45)(45)(22)(22)2 
Amortization of actuarial (gain) loss(5)4 37 — 6 10 
Settlement (gain) loss(1)79 75 — — 1 
Net periodic benefit cost(a)
$103 $228 $308 $27 $31 $77 
Actuarial (gain) loss$75 $109 $(227)$31 $(167)$(16)
Prior service credit— — — — — (276)
Amortization of actuarial (gain) loss6 (83)(112)— (6)(11)
Amortization of prior service (cost) credit45 45 45 22 22 (2)
Total recognized in other comprehensive (income) loss$126 $71 $(294)$53 $(151)$(305)
Total recognized in net periodic benefit cost and other comprehensive (income) loss$229 $299 $14 $80 $(120)$(228)
(a)Net periodic benefit cost reflects a calculated market-related value of plan assets which recognizes changes in fair value over three years.
For certain of our pension plans, lump sum payments to employees retiring in 2023, 2022 and 2021 exceeded the plan’s total service and interest costs expected for those years. Settlement losses are required to be recorded when lump sum payments exceed total service and interest costs. As a result, pension settlement expenses were recorded in 2023, 2022 and 2021.
Plan Assumptions
The following summarizes the assumptions used to determine the benefit obligations at December 31, and net periodic benefit cost for the defined benefit pension and other postretirement plans for 2023, 2022 and 2021.
Pension BenefitsOther Benefits
 202320222021202320222021
Benefit obligation:
Discount rate4.85 %5.04 %2.82 %4.88 %5.08 %2.93 %
Rate of compensation increase4.18 %4.18 %5.70 %4.18 %4.18 %5.70 %
Net periodic benefit cost:
Discount rate5.10 %3.33 %2.70 %5.08 %2.93 %2.55 %
Expected long-term return on plan assets7.00 %5.75 %5.75 %— %— %— %
Rate of compensation increase4.18 %4.18 %5.70 %4.18 %4.18 %5.70 %
Expected Long-term Return on Plan Assets
The overall expected long-term return on plan assets assumption is determined based on an asset rate-of-return modeling tool developed by a third-party investment group. The tool utilizes underlying assumptions based on actual returns by asset category and inflation and takes into account our asset allocation to derive an expected long-term rate of return on those assets. Capital market assumptions reflect the long-term capital market outlook. The assumptions for equity and fixed income investments are developed using a building-block approach, reflecting observable inflation information and interest rate information available in the fixed income markets. Long-term assumptions for other asset categories are based on historical results, current market characteristics and the professional judgment of our internal and external investment teams.
Assumed Health Care Cost Trend
The following summarizes the assumed health care cost trend rates.
 December 31,
 202320222021
Health care cost trend rate assumed for the following year:
Medical: Pre-657.70 %6.60 %5.80 %
Prescription drugs10.80 %8.90 %6.40 %
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate):
Medical: Pre-654.50 %4.50 %4.50 %
Prescription drugs4.50 %4.50 %4.50 %
Year that the rate reaches the ultimate trend rate:
Medical: Pre-65203220312030
Prescription drugs203220312030
Increases in the post-65 medical plan premium for the Marathon Petroleum Health Plan and the Marathon Petroleum Retiree Health Plan have been permanently eliminated.
Plan Investment Policies and Strategies
The investment policies for our pension plan assets reflect the funded status of the plans and expectations regarding our future ability to make further contributions. Long-term investment goals are to: (1) manage the assets in accordance with the legal requirements of all applicable laws; (2) diversify plan investments across asset classes to achieve an optimal balance between risk and return and between income and growth of assets through capital appreciation; and (3) source benefit payments primarily through existing plan assets and anticipated future returns.
The investment goals are implemented to manage the plans’ funded status volatility and minimize future cash contributions. The asset allocation strategy will change over time in response to changes primarily in funded status, which is dictated by current and anticipated market conditions, the independent actions of our investment committee, required cash flows to and from the plans and other factors deemed appropriate. Such changes in asset allocation are intended to allocate additional assets to the fixed income asset class should the funded status improve. The fixed income asset class shall be invested in such a manner that its
interest rate sensitivity correlates highly with that of the plans’ liabilities. Other asset classes are intended to provide additional return with associated higher levels of risk. Investment performance and risk is measured and monitored on an ongoing basis through quarterly investment meetings and periodic asset and liability studies. At December 31, 2023, the primary plan’s targeted asset allocation was 50 percent equity, private equity, real estate, and timber securities and 50 percent fixed income securities.
Fair Value Measurements
Plan assets are measured at fair value. The following provides a description of the valuation techniques employed for each major plan asset category at December 31, 2023 and 2022.
Cash and cash equivalents
Cash and cash equivalents include a collective fund serving as the investment vehicle for the cash reserves and cash held by third-party investment managers. The collective fund is valued at net asset value (“NAV”) on a scheduled basis using a cost approach, and is considered a Level 2 asset. Cash and cash equivalents held by third-party investment managers are valued using a cost approach and are considered Level 2.
Equity
Equity investments includes common stock, mutual and pooled funds. Common stock investments are valued using a market approach, which are priced daily in active markets and are considered Level 1. Mutual and pooled equity funds are well diversified portfolios, representing a mix of strategies in domestic, international and emerging market strategies. Mutual funds are publicly registered, valued at NAV on a daily basis using a market approach and are considered Level 1 assets. Pooled funds are valued at NAV using a market approach and are considered Level 2.
Fixed Income
Fixed income investments include corporate bonds, U.S. dollar treasury bonds and municipal bonds. These securities are priced on observable inputs using a combination of market, income and cost approaches. These securities are considered Level 2 assets. Fixed income also includes a well diversified bond portfolio structured as a pooled fund. This fund is valued at NAV on a daily basis using a market approach and is considered Level 2. Other investments classified as Level 1 include mutual funds that are publicly registered, valued at NAV on a daily basis using a market approach.
Private Equity
Private equity investments include interests in limited partnerships which are valued using information provided by external managers for each individual investment held in the fund. These holdings are considered Level 3.
Real Estate
Real estate investments consist of interests in limited partnerships. These holdings are either appraised or valued using the investment manager’s assessment of assets held. These holdings are considered Level 3.
Other
Other investments include two limited liability companies (“LLCs”) with no public market. The LLCs were formed to acquire timberland in the northwest U.S. These holdings are either appraised or valued using the investment manager’s assessment of assets held. These holdings are considered Level 3. Other investments classified as Level 1 include publicly traded depository receipts, while Level 2 include derivative transactions.
The following tables present the fair values of our defined benefit pension plans’ assets, by level within the fair value hierarchy, as of December 31, 2023 and 2022.
 December 31, 2023December 31, 2022
(Millions of dollars)Level 1Level 2Level 3TotalLevel 1Level 2Level 3Total
Cash and cash equivalents$— $63 $— $63 $— $3 $— $3 
Equity:
Common stocks50 — — 50 40 — — 40 
Mutual funds115 — — 115 104 — — 104 
Pooled funds— 791 — 791 — 742 — 742 
Fixed income:
Corporate— 588 — 588 — 582 — 582 
Government— 330 — 330 211 41 — 252 
Pooled funds— 118 — 118 — 79 — 79 
Private equity— — 10 10 — — 13 13 
Real estate— — 12 12 — — 14 14 
Other— 2 3 5 — 5 4 9 
Total investments, at fair value$165 $1,892 $25 $2,082 $355 $1,452 $31 $1,838 
Cash Flows
Contributions to defined benefit plans
Our funding policy with respect to the funded pension plans is to contribute amounts necessary to satisfy minimum pension funding requirements, including requirements of the Pension Protection Act of 2006, plus such additional, discretionary, amounts from time to time as determined appropriate by management. In 2023, we made contributions totaling $258 million to our funded pension plans. For 2024, we do not project any required funding, but we may make voluntary contributions to our funded pension plans at our discretion. Cash contributions to be paid from our general assets for the unfunded pension and postretirement plans are estimated to be approximately $8 million and $50 million, respectively, in 2024.
Estimated future benefit payments
The following gross benefit payments, which reflect expected future service, as appropriate, are expected to be paid in the years indicated.
(Millions of dollars)Pension BenefitsOther Benefits
2024$147 $50 
2025168 51 
2026177 51 
2027183 52 
2028194 52 
2029 through 20331,100 266 
Contributions to defined contribution plan
We also contribute to a defined contribution plan for eligible employees. Contributions to this plan totaled $176 million, $167 million and $165 million in 2023, 2022 and 2021, respectively.
Multiemployer Pension Plan
We contribute to one multiemployer defined benefit pension plan under the terms of a collective-bargaining agreement that covers some of our union-represented employees. The risks of participating in this multiemployer plan are different from single-employer plans in the following aspects:
•Assets contributed to the multiemployer plan by one employer may be used to provide benefits to employees of other participating employers.
•If a participating employer stops contributing to the plan, the unfunded obligations of the plan may be borne by the remaining participating employers.
•If we choose to stop participating in the multiemployer plan, we may be required to pay that plan an amount based on the underfunded status of the plan, referred to as a withdrawal liability.
Our participation in this plan for 2023, 2022 and 2021 is outlined in the table below. The “EIN” column provides the Employee Identification Number for the plan. The most recent Pension Protection Act zone status available in 2023 and 2022 is for the plan years ending on December 31, 2022 and December 31, 2021, respectively. The zone status is based on information that we received from the plan and is certified by the plan’s actuary. Among other factors, plans in the red zone are generally less than 65 percent funded. The “FIP/RP Status Pending/Implemented” column indicates a financial improvement plan or a rehabilitation plan has been implemented. The last column lists the expiration date of the collective-bargaining agreement to which the plan is subject. There have been no significant changes that affect the comparability of 2023, 2022 and 2021 contributions. Our portion of the contributions does not make up more than five percent of total contributions to the plan.
  Pension 
Protection
Act Zone 
Status		FIP/RP Status
Pending/Implemented
MPC Contributions 
(Millions of dollars)
Surcharge
Imposed		Expiration Date of
Collective – Bargaining
Agreement
Pension FundEIN20232022202320222021
Central States, Southeast and Southwest Areas Pension Plan(a)(b)
366044243RedRedImplemented$5 $5 $5 NoJanuary 31, 2024
(a)This agreement has a minimum contribution requirement of $338 per week per employee for 2024. A total of 278 employees participated in the plan as of December 31, 2023.
(b)    The parties to the expired agreement continue operating under the relevant terms of the expired agreement while negotiating a successor agreement.
Multiemployer Health and Welfare Plan
We contribute to one multiemployer health and welfare plan that covers both active employees and retirees. Through the health and welfare plan, employees receive medical, dental, vision, prescription and disability coverage. Our contributions to this plan totaled $7 million, $7 million and $7 million for 2023, 2022 and 2021, respectively.