10-Q

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C.  20549

FORM 10-Q

(Mark One)

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

For the quarterly period ended June 30, 2018

or

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

Commission File Number: 001-31387

Northern States Power Company

(Exact name of registrant as specified in its charter)

Minnesota	41-1967505
(State or other jurisdiction of incorporation or organization)	(I.R.S. Employer Identification No.)
414 Nicollet Mall
Minneapolis, Minnesota	55401
(Address of principal executive offices)	(Zip Code)

(612) 330-5500

(Registrant’s telephone number, including area code)

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. x Yes ¨ No

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 and 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 and post such files). x Yes ¨ No

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, 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 ¨	Accelerated filer ¨
Non-accelerated filer x	Smaller reporting company ¨
(Do not check if 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 x No

Indicate the number of shares outstanding of each of the issuer’s classes of common stock, as of the latest practicable date.

Class	Outstanding at July 27, 2018
Common Stock, $0.01 par value	1,000,000 shares

Northern States Power Company (a Minnesota corporation) meets the conditions set forth in General Instruction H (1)(a) and (b) of Form 10-Q and is therefore filing this Form 10-Q with the reduced disclosure format specified in General Instruction H (2) to such Form 10-Q.

TABLE OF CONTENTS

PARTI —	FINANCIAL INFORMATION
Item l —	Financial Statements (Unaudited)	3
Item 2 —	Management’s Discussion and Analysis of Financial Condition and Results of Operations	29
Item 4 —	Controls and Procedures	35
PART II —	OTHER INFORMATION
Item 1 —	Legal Proceedings	35
Item 1A —	Risk Factors	35
Item 6 —	Exhibits	36
SIGNATURES		37
Certifications Pursuant to Section 302		1
Certifications Pursuant to Section 906		1
Statement Pursuant to Private Litigation		1

This Form 10-Q is filed by Northern States Power Company, a Minnesota corporation (NSP-Minnesota). NSP-Minnesota is a wholly owned subsidiary of Xcel Energy Inc. Xcel Energy Inc. wholly owns the following subsidiaries: NSP-Minnesota; Northern States Power Company, a Wisconsin corporation (NSP-Wisconsin); Public Service Company of Colorado (PSCo); and Southwestern Public Service Company (SPS). NSP-Minnesota, NSP-Wisconsin, PSCo and SPS are also referred to collectively as utility subsidiaries. The electric production and transmission system of NSP-Minnesota and NSP-Wisconsin, which is operated on an integrated basis and is managed by NSP-Minnesota, is referred to collectively as the NSP System. Additional information on Xcel Energy Inc. and its subsidiaries (collectively, Xcel Energy) is available on various filings with the Securities and Exchange Commission (SEC).

PART I — FINANCIAL INFORMATION

Item 1 — FINANCIAL STATEMENTS

NSP-MINNESOTA AND SUBSIDIARIES

CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED)

(amounts in thousands)

	Three Months Ended June 30						Six Months Ended June 30
	2018			2017			2018			2017
Operating revenues
Electric, non-affiliates	$	978,991		$	960,394		$	1,924,282		$	1,915,735
Electric, affiliates	117,417			119,385			234,389			243,074
Natural gas	83,112			78,006			324,544			299,189
Other	8,215			7,155			15,271			14,082
Total operating revenues	1,187,735			1,164,940			2,498,486			2,472,080
Operating expenses
Electric fuel and purchased power	416,502			383,947			824,274			780,068
Cost of natural gas sold and transported	36,818			35,500			192,084			178,245
Cost of sales — other	4,655			4,594			8,836			8,772
Operating and maintenance expenses	309,196			305,189			601,491			613,815
Conservation program expenses	27,518			28,065			58,328			60,564
Depreciation and amortization	178,654			173,152			360,132			345,331
Taxes (other than income taxes)	64,285			61,445			131,830			129,769
Total operating expenses	1,037,628			991,892			2,176,975			2,116,564
Operating income	150,107			173,048			321,511			355,516
Other expense, net	(2,234		)	(3,632		)	(2,018		)	(5,166		)
Allowance for funds used during construction — equity	6,903			6,425			13,651			12,708
Interest charges and financing costs
Interest charges — includes other financing costs of  $1,833 $1,806, $3,648 and $3,592, respectively	56,767			57,707			114,119			114,971
Allowance for funds used during construction — debt	(3,352		)	(3,298		)	(6,787		)	(6,526		)
Total interest charges and financing costs	53,415			54,409			107,332			108,445
Income before income taxes	101,361			121,432			225,812			254,613
Income taxes	8,974			33,770			21,685			72,785
Net income	$	92,387		$	87,662		$	204,127		$	181,828

See Notes to Consolidated Financial Statements

3

NSP-MINNESOTA AND SUBSIDIARIES

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED)

(amounts in thousands)

	Three Months Ended June 30				Six Months Ended June 30
	2018		2017		2018			2017
Net income	$	92,387	$	87,662	$	204,127		$	181,828
Other comprehensive income
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, net of tax of $22, $22, $45 and $47, respectively	54		36		107			71
Derivative instruments:
Net fair value decrease, net of tax of $9, $17, $11 and $17, respectively	22		26		27			26
Reclassification of losses to net income, net of tax of $64, $141, $129 and $280, respectively	165		204		332			407
	187		230		359			433
Marketable securities:
Reclassification of gains to net income, net of tax of $0, $0, $(51) and $0, respectively	—		—		(128		)	—
Other comprehensive income	241		266		338			504
Comprehensive income	$	92,628	$	87,928	$	204,465		$	182,332

See Notes to Consolidated Financial Statements

4

NSP-MINNESOTA AND SUBSIDIARIES

CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED)

(amounts in thousands)

	Six Months Ended June 30,
	2018			2017
Operating activities
Net income	$	204,127		$	181,828
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	363,310			348,442
Nuclear fuel amortization	62,294			57,003
Deferred income taxes	41,204			90,927
Amortization of investment tax credits	(817		)	(827		)
Allowance for equity funds used during construction	(13,651		)	(12,708		)
Net realized and unrealized hedging and derivative transactions	(1,497		)	(2,973		)
Other, net	(998		)	(946		)
Changes in operating assets and liabilities:
Accounts receivable	(16,025		)	(23,008		)
Accrued unbilled revenues	31,354			45,497
Inventories	44,093			18,901
Other current assets	59,683			(56,145		)
Accounts payable	(31,673		)	(17,828		)
Net regulatory assets and liabilities	43,782			2,613
Other current liabilities	(105,681		)	(94,500		)
Pension and other employee benefit obligations	(59,371		)	(57,698		)
Change in other noncurrent assets	1,224			(2,505		)
Change in other noncurrent liabilities	(17,885		)	(11,878		)
Net cash provided by operating activities	603,473			464,195
Investing activities
Utility capital/construction expenditures	(439,868		)	(484,172		)
Allowance for equity funds used during construction	13,651			12,708
Purchases investment securities	(367,159		)	(361,881		)
Proceeds from the sale of investment securities	356,973			350,446
Investments in utility money pool arrangement	(627,000		)	(192,000		)
Repayments from utility money pool arrangement	627,000			192,000
Other, net	(2,065		)	(4,097		)
Net cash used in investing activities	(438,468		)	(486,996		)
Financing activities
Repayments of short-term borrowings, net	(20,000		)	(2,000		)
Borrowings under utility money pool arrangement	131,000			465,000
Repayments under utility money pool arrangement	(154,000		)	(374,000		)
Repayments of long-term debt	(9		)	—
Capital contributions from parent	49,622			89,487
Dividends paid to parent	(183,245		)	(175,115		)
Other, net	(68		)	—
Net cash (used in) provided by financing activities	(176,700		)	3,372
Net change in cash and cash equivalents	(11,695		)	(19,429		)
Cash and cash equivalents at beginning of period	43,781			47,595
Cash and cash equivalents at end of period	$	32,086		$	28,166
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	$	(101,005	)	$	(104,020	)
Cash received (paid) for income taxes, net	64,212			(33,014		)
Supplemental disclosure of non-cash investing transactions:
Property, plant and equipment additions in accounts payable	$	50,370		$	60,361

See Notes to Consolidated Financial Statements

5

NSP-MINNESOTA AND SUBSIDIARIES

CONSOLIDATED BALANCE SHEETS (UNAUDITED)

(amounts in thousands, except share and per share data)

	June 30, 2018			Dec. 31, 2017
Assets
Current assets
Cash and cash equivalents	$	32,086		$	43,781
Accounts receivable, net	361,144			345,110
Accounts receivable from affiliates	19,462			48,494
Accrued unbilled revenues	246,362			277,716
Inventories	294,602			337,712
Regulatory assets	300,150			276,392
Derivative instruments	31,268			25,230
Prepaid taxes	41,763			79,145
Prepayments and other	36,717			43,682
Total current assets	1,363,554			1,477,262
Property, plant and equipment, net	13,075,676			13,033,612
Other assets
Nuclear decommissioning fund and other investments	2,195,458			2,192,344
Regulatory assets	1,343,820			1,190,429
Derivative instruments	26,790			28,102
Other	11,936			4,142
Total other assets	3,578,004			3,415,017
Total assets	$	18,017,234		$	17,925,891
Liabilities and Equity
Current liabilities
Current portion of long-term debt	$	8		$	7
Short-term debt	—			20,000
Borrowings under utility money pool arrangement	62,000			85,000
Accounts payable	348,475			368,342
Accounts payable to affiliates	53,790			80,070
Regulatory liabilities	135,725			83,403
Taxes accrued	193,465			229,335
Accrued interest	67,765			65,896
Dividends payable to parent	88,714			98,687
Derivative instruments	18,029			17,697
Customer deposits	66,764			95,369
Other	153,256			152,965
Total current liabilities	1,187,991			1,296,771
Deferred credits and other liabilities
Deferred income taxes	1,655,863			1,612,341
Deferred investment tax credits	21,710			22,528
Regulatory liabilities	2,013,411			1,978,527
Asset retirement obligations	2,134,741			2,083,874
Derivative instruments	92,122			102,742
Pension and employee benefit obligations	271,228			331,087
Other	178,347			89,440
Total deferred credits and other liabilities	6,367,422			6,220,539
Commitments and contingencies
Capitalization
Long-term debt	4,935,060			4,933,011
Common stock — authorized 5,000,000 shares of $0.01 par value; 1,000,000 shares outstanding at June 30, 2018 and Dec. 31, 2017, respectively	10			10
Additional paid in capital	3,600,234			3,580,234
Retained earnings	1,950,716			1,919,863
Accumulated other comprehensive loss	(24,199		)	(24,537		)
Total common stockholder’s equity	5,526,761			5,475,570
Total liabilities and equity	$	18,017,234		$	17,925,891

See Notes to Consolidated Financial Statements

6

NSP-MINNESOTA AND SUBSIDIARIES

Notes to Consolidated Financial Statements (UNAUDITED)

In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly, in accordance with accounting principles generally accepted in the United States of America (GAAP), the financial position of NSP-Minnesota and its subsidiaries as of June 30, 2018 and Dec. 31, 2017; the results of its operations, including the components of net income and comprehensive income, for the three and six months ended June 30, 2018 and 2017; and its cash flows for the six months endedJune 30, 2018 and 2017. All adjustments are of a normal, recurring nature, except as otherwise disclosed. Management has also evaluated the impact of events occurring after June 30, 2018 up to the date of issuance of these consolidated financial statements. These statements contain all necessary adjustments and disclosures resulting from that evaluation. The Dec. 31, 2017 balance sheet information has been derived from the audited 2017 consolidated financial statements included in the NSP-Minnesota Annual Report on Form 10-K for the year ended Dec. 31, 2017. These notes to the consolidated financial statements have been prepared pursuant to the rules and regulations of the SEC for Quarterly Reports on Form 10-Q. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP on an annual basis have been condensed or omitted pursuant to such rules and regulations. For further information, refer to the consolidated financial statements and notes thereto, included in the NSP-Minnesota Annual Report on Form 10-K for the year ended Dec. 31, 2017, filed with the SEC on Feb. 26, 2018. Due to the seasonality of NSP-Minnesota’s electric and natural gas sales, interim results are not necessarily an appropriate base from which to project annual results.

1. Summary of Significant Accounting Policies

The significant accounting policies set forth in Note 1 to the consolidated financial statements in the NSP-Minnesota Annual Report on Form 10-K for the year ended Dec. 31, 2017, appropriately represent, in all material respects, the current status of accounting policies and are incorporated herein by reference.

2. Accounting Pronouncements

Recently Issued

Leases —In February 2016, the Financial Accounting Standards Board (FASB) issued Leases, Topic 842 (Accounting Standards Update (ASU) No. 2016-02), which for lessees requires balance sheet recognition of right-of-use assets and lease liabilities for most leases. This guidance will be effective for interim and annual reporting periods beginning after Dec. 15, 2018. NSP-Minnesota has not yet fully determined the impacts of implementation. However, adoption is expected to occur on Jan. 1, 2019 utilizing the practical expedients provided by the standard and proposed in Targeted Improvements, Topic 842 (Proposed ASU 2018-200). On Jan. 1, 2019 agreements considered leases for the use of office space, equipment and natural gas storage assets, as well as certain purchased power agreements (PPAs) for fossil-fueled generating facilities are expected to be recognized on the consolidated balance sheet.

Recently Adopted

Revenue Recognition— In May 2014, the FASB issued Revenue from Contracts with Customers, Topic 606 (ASU No. 2014-09), which provides a new framework for the recognition of revenue. NSP-Minnesota implemented the guidance on a modified retrospective basis on Jan. 1, 2018. Results for reporting periods beginning after Dec. 31, 2017 are presented in accordance with Topic 606, while prior period results have not been adjusted and continue to be reported in accordance with prior accounting guidance. Other than increased disclosures regarding revenues related to contracts with customers, the implementation did not have a significant impact on NSP-Minnesota’s consolidated financial statements. For related disclosures, see Note 13 to the consolidated financial statements.

Classification and Measurement of Financial Instruments — In January 2016, the FASB issued Recognition and Measurement of Financial Assets and Financial Liabilities, Subtopic 825-10 (ASU No. 2016-01), which eliminated the available-for-sale classification for marketable equity securities and also replaced the cost method of accounting for non-marketable equity securities with a model for recognizing impairments and observable price changes. Under the new standard, other than when the consolidation or equity method of accounting is utilized, changes in the fair value of equity securities are recognized in earnings. NSP-Minnesota implemented the guidance on Jan. 1, 2018. As a result of application of accounting principles for rate regulated entities, changes in the fair value of the securities in the nuclear decommissioning fund, historically classified as available-for-sale, continue to be deferred to a regulatory asset, and the overall adoption impacts were not material.

7

Presentation of Net Periodic Benefit Cost —In March 2017, the FASB issued Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost, Topic 715 (ASU No. 2017-07), which establishes that only the service cost element of pension cost may be presented as a component of operating income in the income statement. Also under the guidance, only the service cost component of pension cost is eligible for capitalization. As a result of the application of accounting principles for rate regulated entities, a similar amount of pension cost, including non-service components, will be recognized consistent with the historical ratemaking treatment, and the impacts of adoption will be limited to changes in classification of non-service costs in the consolidated statement of income. NSP-Minnesota implemented the new guidance on Jan. 1, 2018, and as a result, $6.8 million of pension costs were retrospectively reclassified from operating and maintenance expenses to other income, net on the consolidated income statement for the six months ended June 30, 2017. Under a practical expedient permitted by the standard, NSP-Minnesota used benefit cost amounts disclosed for prior periods as the basis for retrospective application.

3. Selected Balance Sheet Data

(Thousands of Dollars)	June 30, 2018			Dec. 31, 2017
Accounts receivable, net
Accounts receivable	$	380,606		$	366,388
Less allowance for bad debts	(19,462		)	(21,278		)
	$	361,144		$	345,110

(Thousands of Dollars)	June 30, 2018		Dec. 31, 2017
Inventories
Materials and supplies	$	208,596	$	209,236
Fuel	73,737		94,483
Natural gas	12,269		33,993
	$	294,602	$	337,712

(Thousands of Dollars)	June 30, 2018			Dec. 31, 2017
Property, plant and equipment, net
Electric plant	$	17,276,273		$	17,024,925
Natural gas plant	1,407,523			1,370,330
Common and other property	719,069			724,066
Construction work in progress	528,079			530,126
Total property, plant and equipment	19,930,944			19,649,447
Less accumulated depreciation	(7,210,566		)	(7,018,249		)
Nuclear fuel	2,712,590			2,697,412
Less accumulated amortization	(2,357,292		)	(2,294,998		)
	$	13,075,676		$	13,033,612

4. Income Taxes

Except to the extent noted below, Note 6 to the consolidated financial statements included in NSP-Minnesota’s Annual Report on Form 10-K for the year ended Dec. 31, 2017 appropriately represents, in all material respects, the current status of other income tax matters, and are incorporated herein by reference.

8

Total income tax expense from operations differs from the amount computed by applying the statutory federal income tax rate to income before income tax expense. The following reconciles such differences:

	Six Months Ended June 30
	2018		2017
Federal statutory rate	21.0	%	35.0	%
State tax, net of federal tax effect	7.1		5.8
Increases (decreases) in tax from:
Wind production tax credits (PTCs)	(17.1	)	(11.4	)
Regulatory differences - ARAM (a)	(8.5	)	(0.2	)
Regulatory differences - ARAM deferral (b)	7.9		—
Other tax credits, net of federal income tax expense	(1.5	)	(1.0	)
Other, net	0.7		0.4
Effective income tax rate	9.6	%	28.6	%

^(a)   The average rate assumption method (ARAM); a method to flow back excess deferred taxes to customers.

^(b) As we receive direction from our regulatory commissions regarding the return of excess deferred taxes (to our customers resulting from the Tax Cuts and Jobs Act

(TCJA)), the ARAM deferral may decrease during the year, which would result in a reduction to tax expense with a corresponding reduction to revenue.

Federal Audits — NSP-Minnesota is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. The statute of limitations applicable to Xcel Energy’s federal income tax returns expire as follows:

Tax Year(s)	Expiration
2009 - 2011	December 2018
2012 - 2014	October 2019
2015	September 2019
2016	September 2020

In 2012, the Internal Revenue Service (IRS) commenced an examination of tax years 2010 and 2011, including the 2009 carryback claim. The IRS proposed an adjustment to the federal tax loss carryback claims and in 2015 the IRS forwarded the issue to the Office of Appeals (Appeals). In 2017 Xcel Energy and Appeals reached an agreement and the benefit related to the agreed upon portions was recognized. In the second quarter of 2018, the Joint Committee on Taxation completed its review and took no exception to the agreement. As a result, the remaining unrecognized tax benefit was released and recorded as a payable to the IRS.

In the third quarter of 2015, the IRS commenced an examination of tax years 2012 and 2013. In the third quarter of 2017, the IRS concluded the audit of tax years 2012 and 2013 and proposed an adjustment that would impact Xcel Energy’s net operating loss (NOL) and effective tax rate (ETR). After evaluating the proposed adjustment Xcel Energy filed a protest with the IRS. As of June 30, 2018 the case has been forwarded to Appeals and Xcel Energy has recognized its best estimate of income tax expense that will result from a final resolution of this issue; however, the outcome and timing of a resolution is unknown.

State Audits — NSP-Minnesota is a member of the Xcel Energy affiliated group that files consolidated state income tax returns. As of June 30, 2018, NSP-Minnesota’s earliest open tax year that is subject to examination by state taxing authorities under applicable statutes of limitations is 2009. In 2016, the state of Minnesota began an audit of years 2010 through 2014. As of June 30, 2018, Minnesota had not proposed any material adjustments.

Unrecognized Benefits — The unrecognized tax benefit balance includes permanent tax positions, which if recognized would affect the annual ETR. In addition, the unrecognized tax benefit balance includes temporary tax positions for which the ultimate deductibility is highly certain but for which there is uncertainty about the timing of such deductibility. A change in the period of deductibility would not affect the ETR but would accelerate the payment of cash to the taxing authority to an earlier period.

9

A reconciliation of the amount of unrecognized tax benefit is as follows:

(Millions of Dollars)	June 30, 2018		Dec. 31, 2017
Unrecognized tax benefit — Permanent tax positions	$	10.2	$	10.2
Unrecognized tax benefit — Temporary tax positions	5.5		7.9
Total unrecognized tax benefit	$	15.7	$	18.1

The unrecognized tax benefit amounts were reduced by the tax benefits associated with NOL and tax credit carryforwards. The amounts of tax benefits associated with NOL and tax credit carryforwards are as follows:

(Millions of Dollars)	June 30, 2018			Dec. 31, 2017
NOL and tax credit carryforwards	$	(15.0	)	$	(12.8	)

It is reasonably possible that NSP-Minnesota’s amount of unrecognized tax benefits could significantly change in the next 12 months as the IRS Appeals progresses and audit resumes, the Minnesota audit progresses, and other state audits resume. As the IRS Appeals and Minnesota audit progress and the IRS audit resumes, it is reasonably possible that the amount of unrecognized tax benefit could decrease up to approximately $13 million.

The payable for interest related to unrecognized tax benefits is partially offset by the interest benefit associated with NOL and tax credit carryforwards. A reconciliation of the beginning and ending amount of the payable for interest related to unrecognized tax benefits are as follows:

(Millions of Dollars)	June 30, 2018			Dec. 31, 2017
Payable for interest related to unrecognized tax benefits at beginning of period	$	(0.9	)	$	(2.0	)
Interest (expense) income related to unrecognized tax benefits recorded during the period	(1.0		)	1.1
Payable for interest related to unrecognized tax benefits at end of period	$	(1.9	)	$	(0.9	)

No amounts were accrued for penalties related to unrecognized tax benefits as of June 30, 2018 or Dec. 31, 2017.

5. Rate Matters

Except to the extent noted below, the circumstances set forth in Note 10 to the consolidated financial statements included in NSP-Minnesota’s Annual Report on Form 10-K for the year ended Dec. 31, 2017 and in Note 5 to the consolidated financial statements to NSP-Minnesota’s Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018, appropriately represent, in all material respects, the current status of other rate matters, and are incorporated herein by reference.

Tax Reform — Regulatory Proceedings

The specific impacts of the TCJA on customer rates are subject to regulatory approval. Each of the states in NSP-Minnesota’s service areas have opened dockets to address the impacts of the TCJA.

In April 2018, NSP-Minnesota updated the estimated impact of the TCJA, which reflected an overall reduction in 2018 revenue requirements of approximately $136 million for electric and $7 million for natural gas, and made recommendations regarding the sharing of those benefits with ratepayers. The proposed electric options included: customer refunds and rider impacts of $68 million, deferral of $44 million to allow for a rate case stay-out for 2020, acceleration of depreciation for the King coal plant of $22 million and low income program funding of $2 million. The proposed natural gas options included customer refunds and rider impacts of $3 million, with the remaining TCJA benefits deferred to mitigate increased costs in the next natural gas rate case.

In June 2018, the Minnesota Department of Commerce (DOC) recommended to implement refunds for the current tax impacts (approximately $90 million), and incorporate the deferred tax impacts (approximately $53 million) in NSP-Minnesota’s next electric and gas rate cases. A decision from the Minnesota Public Utilities Commission (MPUC) is expected in 2018.

North and South Dakota — In February 2018, NSP-Minnesota proposed using the reduced revenue requirements from the TCJA to defer planned future rate filings in North Dakota and South Dakota. In July 2018, the South Dakota Public Utilities Commission (SDPUC) approved a settlement which proposed a one-time customer refund of $11 million for the 2018 impact of the TCJA and a 2-year rate case moratorium.

10

Dockets have also been opened in North Dakota and South Dakota. In February 2018, NSP-Minnesota proposed using the reduced revenue requirements from the TCJA to defer planned future rate filings in both jurisdictions.

Recently Concluded Regulatory Proceedings — MPUC and the North Dakota Public Service Commission (NDPSC)

PPA Terminations and Amendments — In June 2018, NSP-Minnesota executed the terminations of the Benson and Laurentian PPAs, and purchased the Benson biomass facility. As a result, a $103 million regulatory asset was recognized for the costs of the Benson transaction, including payments to Benson of $93 million, as well as other transaction costs and future estimated facility removal costs. For Laurentian, a regulatory asset of $109 million was recognized for annual termination payments over 6 years. The regulatory approvals provide for recovery of the Benson regulatory asset over approximately 10 years, and for recovery of the Laurentian termination payments as they occur, through fuel and purchased energy recovery mechanisms.

Pending Regulatory Proceeding — Federal Energy Regulatory Commission (FERC)

Midcontinent Independent System Operator, Inc. (MISO) Return on Equity (ROE) Complaints — In November 2013, a group of customers filed a complaint at the FERC against MISO transmission owners (TOs), including NSP-Minnesota and NSP-Wisconsin. The complaint argued for a reduction in the ROE in transmission formula rates in the MISO region from 12.38 percent to 9.15 percent, and the removal of ROE adders (including those for Regional Transmission Organization (RTO) membership), effective Nov. 12, 2013.

In September 2016, the FERC approved an Administrative Law Judge (ALJ) recommendation that MISO TOs be granted a 10.32 percent base ROE using the methodology adopted by FERC in June 2014 (Opinion 531). This ROE would be applicable for the 15-month refund period from Nov. 12, 2013 to Feb. 11, 2015, and prospectively from the date of the FERC order. The total prospective ROE would be 10.82 percent, including a 50 basis point adder for RTO membership. The requests are pending FERC action.

In February 2015, a second complaint seeking to reduce the MISO ROE from 12.38 percent to 8.67 percent prior to any RTO adder was filed, resulting in a second period of potential refunds from Feb. 12, 2015 to May 11, 2016. In June 2016, an ALJ recommended a base ROE of 9.7 percent, applying the FERC Opinion 531 methodology. FERC action is pending. In April 2017, the United States Court of Appeals for the District of Columbia Circuit (D.C. Circuit) vacated and remanded Opinion 531. It is unclear how the D.C. Circuit’s opinion to vacate and remand Opinion 531 will affect the September 2016 FERC order or the timing and outcome of the second ROE complaint.

NSP-Minnesota has recognized a current refund liability consistent with the best estimate of the final ROE.

6. Commitments and Contingencies

Except to the extent noted below and in Note 5 to the consolidated financial statements, the circumstances set forth in Notes 10, 11 and 12 to the consolidated financial statements included in the NSP-Minnesota Annual Report on Form 10-K for the year ended Dec. 31, 2017 and in Notes 5 and 6 to NSP-Minnesota’s Quarterly Report of Form 10-Q for the quarterly period ended March 31, 2018, appropriately represent, in all material respects, the current status of commitments and contingent liabilities and are incorporated herein by reference. The following include commitments, contingencies and unresolved contingencies that are material to NSP-Minnesota’s financial position.

PPAs

NSP-Minnesota purchases power from independent power producing entities for which NSP-Minnesota is required to reimburse natural gas or biomass fuel costs, or to participate in tolling arrangements under which NSP-Minnesota procures the natural gas required to produce the energy that it purchases. These specific PPAs create a variable interest in the associated independent power producing entity.

NSP-Minnesota had approximately 1,002 Megawatts (MW) of capacity under long-term PPAs as of June 30, 2018 and 1,069 MW as of Dec. 31, 2017, with entities that have been determined to be variable interest entities. NSP-Minnesota has concluded that these entities are not required to be consolidated in its consolidated financial statements because it does not have the power to direct the activities that most significantly impact the entities’ economic performance. These agreements have various expiration dates through 2027.

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Guarantees

Under NSP-Minnesota’s railcar lease agreement, accounted for as an operating lease, NSP-Minnesota guarantees the lessor proceeds from sale of the leased assets at the end of the lease term will at least equal the guaranteed residual value. The guarantee issued by NSP-Minnesota has a stated maximum amount; however, NSP-Minnesota expects sale proceeds to exceed the guaranteed amount. This agreement expires in 2019.

The following table presents the guarantee issued and outstanding for NSP-Minnesota:

(Millions of Dollars)	June 30, 2018		Dec. 31, 2017
Guarantee issued and outstanding	$	4.8	$	4.8

Environmental Contingencies

Fargo, N.D. Manufactured Gas Plant (MGP) Site — In May 2015, underground pipes, tars and impacted soils were discovered in a right-of-way in Fargo, N.D. that appeared to be associated with a former MGP operated by NSP-Minnesota or prior companies. NSP-Minnesota removed impacted soils and other materials and commenced an investigation of the historic MGP and adjacent properties (the Fargo MGP Site). The North Dakota Department of Health approved NSP-Minnesota’s proposed cleanup plan in January 2017, which involves targeted source removal of impacted soils and historic MGP infrastructure. Remediation activities commenced in June 2018. NSP-Minnesota has also initiated insurance recovery litigation in North Dakota. The U.S. District Court for the District of North Dakota has set a trial date for Spring of 2020.

NSP-Minnesota recorded an estimated liability of $10 million as of June 30, 2018 and $16 million as of Dec. 31, 2017, for the Fargo MGP Site. The current cost estimate for the remediation of the site is approximately $22 million, of which approximately $12 million has been spent. NSP-Minnesota has deferred Fargo MGP Site costs allocable to the North Dakota jurisdiction, or approximately 88 percent of all remediation costs, as approved by the NDPSC. In December 2017, NSP-Minnesota filed a request with the MPUC to defer post-2017 MGP remediation expenditures allocable to the Minnesota jurisdiction, including the Fargo MGP Site. In March 2018, the DOC recommended that the MPUC deny NSP-Minnesota’s deferral request. A MPUC decision is expected in the third quarter of 2018.

Other MGP, Landfill or Disposal Sites — NSP-Minnesota is currently involved in investigating and/or remediating several MGP, landfill or other disposal sites. NSP-Minnesota has identified five sites, in addition to the Fargo MGP Site, where contamination is present and where investigation and/or remediation activities are currently underway. Other parties may have responsibility for some portion of the investigation and/or remediation activities. NSP-Minnesota anticipates that these investigation or remediation activities will continue through at least 2018. NSP-Minnesota accrued $3 million as of June 30, 2018 and Dec. 31, 2017 for all of these sites. There may be insurance recovery and/or recovery from other PRPs that will offset any costs incurred. Xcel Energy anticipates that any amounts spent will be fully recovered from customers.

Legal Contingencies

NSP-Minnesota is involved in various litigation matters that are being defended and handled in the ordinary course of business. The assessment of whether a loss is probable or is a reasonable possibility, and whether the loss or a range of loss is estimable, often involves a series of complex judgments about future events. Management maintains accruals for such losses that are probable of being incurred and subject to reasonable estimation. Management is sometimes unable to estimate an amount or range of a reasonably possible loss in certain situations, including but not limited to when (1) the damages sought are indeterminate, (2) the proceedings are in the early stages, or (3) the matters involve novel or unsettled legal theories. In such cases, there is considerable uncertainty regarding the timing or ultimate resolution of such matters, including a possible eventual loss. For current proceedings not specifically reported herein, management does not anticipate that the ultimate liabilities, if any, arising from such current proceedings would have a material effect on NSP-Minnesota’s financial statements. Unless otherwise required by GAAP, legal fees are expensed as incurred.

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7. Borrowings and Other Financing Instruments

Short-Term Borrowings

Money Pool — Xcel Energy Inc. and its utility subsidiaries have established a money pool arrangement that allows for short-term investments in and borrowings between the utility subsidiaries. Xcel Energy Inc. may make investments in the utility subsidiaries at market-based interest rates; however, the money pool arrangement does not allow the utility subsidiaries to make investments in Xcel Energy Inc. Money pool borrowings for NSP-Minnesota were as follows:

(Amounts in Millions, Except Interest Rates)	Three Months Ended June 30, 2018			Year Ended Dec. 31, 2017
Borrowing limit	$	250		$	250
Amount outstanding at period end	62			85
Average amount outstanding	1			25
Maximum amount outstanding	62			142
Weighted average interest rate, computed on a daily basis	1.85		%	1.14		%
Weighted average interest rate at period end	1.85			1.18

Commercial Paper — NSP-Minnesota meets its short-term liquidity requirements primarily through the issuance of commercial paper and borrowings under its credit facility and the money pool. Commercial paper outstanding for NSP-Minnesota was as follows:

(Amounts in Millions, Except Interest Rates)	Three Months Ended June 30, 2018		Year Ended Dec. 31, 2017
Borrowing limit	$	500	$	500
Amount outstanding at period end	—		20
Average amount outstanding	—		62
Maximum amount outstanding	—		237
Weighted average interest rate, computed on a daily basis	N/A		1.10		%
Weighted average interest rate at period end	N/A		1.93

Letters of Credit — NSP-Minnesota uses letters of credit, generally with terms of one year, to provide financial guarantees for certain operating obligations. At June 30, 2018 and Dec. 31, 2017, there were $36 million and $24 million, respectively, of letters of credit outstanding under the credit facility. The contract amounts of these letters of credit approximate their fair value and are subject to fees.

Credit Facility — In order to use its commercial paper program to fulfill short-term funding needs, NSP-Minnesota must have a revolving credit facility in place at least equal to the amount of its commercial paper borrowing limit and cannot issue commercial paper in an amount exceeding available capacity under this credit facility. The line of credit provides short-term financing in the form of notes payable to banks, letters of credit and back-up support for commercial paper borrowings.

At June 30, 2018, NSP-Minnesota had the following committed credit facility available (in millions of dollars):

Credit Facility (a)		Drawn(b)		Available
$	500	$	36	$	464

^(a)  This credit facility expires in June 2021.

^(b)  Includes outstanding letters of credit.

All credit facility bank borrowings, outstanding letters of credit and outstanding commercial paper reduce the available capacity under the credit facility. NSP-Minnesota had no direct advances on the credit facility outstanding at June 30, 2018 and Dec. 31, 2017.

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8. Fair Value of Financial Assets and Liabilities

Fair Value Measurements

The accounting guidance for fair value measurements and disclosuresprovides a single definition of fair value and requires certain disclosures about assets and liabilities measured at fair value. A hierarchical framework for disclosing the observability of the inputs utilized in measuring assets and liabilities at fair value is established by this guidance. The three levels in the hierarchy are as follows:

Level 1 — Quoted prices are available in active markets for identical assets or liabilities as of the reporting date. The types of assets and liabilities included in Level 1 are highly liquid and actively traded instruments with quoted prices.

Level 2 — Pricing inputs are other than quoted prices in active markets, but are either directly or indirectly observable as of the reporting date. The types of assets and liabilities included in Level 2 are typically either comparable to actively traded securities or contracts, or priced with models using highly observable inputs.

Level 3 — Significant inputs to pricing have little or no observability as of the reporting date. The types of assets and liabilities included in Level 3 are those valued with models requiring significant management judgment or estimation.

Specific valuation methods include the following:

Cash equivalents— The fair values of cash equivalents are generally based on cost plus accrued interest; money market funds are measured using quoted net asset value (NAV).

Investments in equity securities and other funds— Equity securities are valued using quoted prices in active markets. The fair values for commingled funds are measured using NAVs, which take into consideration the value of underlying fund investments, as well as the other accrued assets and liabilities of a fund, in order to determine a per-share market value. The investments in commingled funds may be redeemed for NAV with proper notice. Proper notice varies by fund and can range from daily with one or two days notice to annually with 90 days notice. Private equity investments require approval of the fund for any unscheduled redemption, and such redemptions may be approved or denied by the fund at its sole discretion. Unscheduled distributions from real estate investments may be redeemed with proper notice, which is typically quarterly with 45-90 days notice; however, withdrawals from real estate investments may be delayed or discounted as a result of fund illiquidity.

Investments in debt securities— Fair values for debt securities are determined by a third party pricing service using recent trades and observable spreads from benchmark interest rates for similar securities.

Interest rate derivatives— The fair values of interest rate derivatives are based on broker quotes that utilize current market interest rate forecasts.

Commodity derivatives— The methods used to measure the fair value of commodity derivative forwards and options utilize forward prices and volatilities, as well as pricing adjustments for specific delivery locations, and are generally assigned a Level 2 classification. When contractual settlements extend to periods beyond those readily observable on active exchanges or quoted by brokers, the significance of the use of less observable forecasts of long-term forward prices and volatilities on a valuation is evaluated, and may result in Level 3 classification.

Electric commodity derivatives held by NSP-Minnesota include transmission congestion instruments, generally referred to as financial transmission rights (FTRs), purchased from MISO. FTRs purchased from a RTO are financial instruments that entitle or obligate the holder to monthly revenues or charges based on transmission congestion across a given transmission path. The value of an FTR is derived from, and designed to offset, the cost of transmission congestion. In addition to overall transmission load, congestion is also influenced by the operating schedules of power plants and the consumption of electricity pertinent to a given transmission path. Unplanned plant outages, scheduled plant maintenance, changes in the relative costs of fuels used in generation, weather and overall changes in demand for electricity can each impact the operating schedules of the power plants on the transmission grid and the value of an FTR. NSP-Minnesota’s valuation process for FTRs utilizes the cleared prices for each FTR for the most recent auction.

If forecasted costs of electric transmission congestion increase or decrease for a given FTR path, the value of that particular FTR instrument will likewise increase or decrease. Given the limited transparency in the auction process, fair value measurements for FTRs have been assigned a Level 3. Non-trading monthly FTR settlements are included in fuel and purchased energy cost recovery mechanisms, and therefore changes in the fair value of the yet to be settled portions of most FTRs are deferred as a regulatory asset or liability. Given this regulatory treatment and the limited magnitude of NSP-Minnesota’s FTRs, the limited transparency associated with the valuation of FTRs are insignificant to the consolidated financial statements of NSP-Minnesota.

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Non-Derivative Instruments Fair Value Measurements

Nuclear Decommissioning Fund

The Nuclear Regulatory Commission requires NSP-Minnesota to maintain a portfolio of investments to fund the costs of decommissioning its nuclear generating plants. Together with all accumulated earnings or losses, the assets of the nuclear decommissioning fund are legally restricted for the decommissioning the Monticello and Prairie Island (PI) nuclear generating plants. The fund contains cash equivalents, debt securities, equity securities and other investments. NSP-Minnesota plans to reinvest matured securities until decommissioning begins. NSP-Minnesota uses the asset class target allocations approved by the MPUC for the qualified trust.

NSP-Minnesota recognizes the costs of funding the decommissioning of its nuclear generating plants over the lives of the plants, assuming rate recovery of all costs. Given the purpose and legal restrictions on the use of nuclear decommissioning fund assets, realized and unrealized gains on fund investments over the life of the fund are deferred as an offset of NSP-Minnesota’s regulatory asset for nuclear decommissioning costs. Consequently, any realized and unrealized gains and losses on securities in the nuclear decommissioning fund, including any impairments, are deferred as a component of the regulatory asset for nuclear decommissioning.

Unrealized gains for the nuclear decommissioning fund were $547 million and $560 million as of June 30, 2018 and Dec. 31, 2017, respectively, and unrealized losses and amounts recorded as other-than-temporary impairments were $23 million and $7 million as of June 30, 2018 and Dec. 31, 2017, respectively.

The following tables present the cost and fair value of NSP-Minnesota’s non-derivative instruments with recurring fair value measurements in the nuclear decommissioning fund as of June 30, 2018 and Dec. 31, 2017:

	June 30, 2018
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Investments Measured at NAV (b)		Total
Nuclear decommissioning fund (a)
Cash equivalents	$	30,868	$	30,868	$	—	$	—	$	—	$	30,868
Commingled funds:
Non U.S. equities	262,468		197,545		—		—		90,402		287,947
Emerging market debt funds	158,296		—		—		—		158,075		158,075
Private equity investments	150,565		—		—		—		220,460		220,460
Real estate	128,115		—		—		—		197,032		197,032
Debt securities:
Government securities	75,806		—		75,477		—		—		75,477
U.S. corporate bonds	330,170		—		322,689		—		—		322,689
Non U.S. corporate bonds	57,902		—		56,422		—		—		56,422
Equity securities:
U.S. equities	269,483		568,134		—		—		—		568,134
Non U.S. equities	156,756		227,226		—		—		—		227,226
Total	$	1,620,429	$	1,023,773	$	454,588	$	—	$	665,969	$	2,144,330

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $51 million of rabbi trust assets and miscellaneous investments.

^(b)  Due to limited availability of published pricing and a lack of immediate redeemability, certain fund investments measured at NAV are not required to be categorized within the fair value hierarchy.

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	Dec. 31, 2017
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Investments Measured at NAV (b)		Total
Nuclear decommissioning fund (a)
Cash equivalents	$	28,741	$	28,741	$	—	$	—	$	—	$	28,741
Commingled funds:
Non U.S. equities	263,694		216,551		—		—		89,857		306,408
Emerging market debt funds	156,057		—		—		—		166,375		166,375
Private equity investments	141,413		—		—		—		198,037		198,037
Real estate	130,787		—		—		—		201,842		201,842
Other commingled funds	9,340		6,286		—		—		2,975		9,261
Debt securities:
Government securities	67,760		—		69,413		—		—		69,413
U.S. corporate bonds	319,809		—		322,129		—		—		322,129
Non U.S. corporate bonds	50,121		—		50,102		—		—		50,102
Equity securities:
U.S. equities	271,166		556,974		—		—		—		556,974
Non U.S. equities	151,961		233,999		—		—		—		233,999
Total	$	1,590,849	$	1,042,551	$	441,644	$	—	$	659,086	$	2,143,281

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $49 million of rabbi trust assets and miscellaneous investments.

^(b)  Due to limited availability of published pricing and a lack of immediate redeemability, certain fund investments measured at NAV are not required to be categorized within the fair value hierarchy.

For the three and six months ended June 30, 2018 and 2017 there were no Level 3 nuclear decommissioning fund investments and no transfers of amounts between levels.

The following table summarizes the final contractual maturity dates of the debt securities in the nuclear decommissioning fund, by asset class, as of June 30, 2018:

	Final Contractual Maturity
(Thousands of Dollars)	Due in 1Year or Less		Due in 1 to 5 Years		Due in 5 to 10 Years		Due after 10 Years		Total
Government securities	$	—	$	3,930	$	2,300	$	69,247	$	75,477
U.S. corporate bonds	4,919		89,594		172,423		55,753		322,689
Non U.S. corporate bonds	2,007		19,925		30,316		4,174		56,422
Debt securities	$	6,926	$	113,449	$	205,039	$	129,174	$	454,588

Rabbi Trusts

In 2016, NSP-Minnesota established a rabbi trust to provide partial funding for future deferred compensation plan distributions. The following tables present the cost and fair value of the assets held in rabbi trust at June 30, 2018 and Dec. 31, 2017:

	June 30, 2018
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trust (a)
Cash equivalents	$	394	$	394	$	—	$	—	$	394
Mutual funds	10,423		11,374		—		—		11,374
Total	$	10,817	$	11,768	$	—	$	—	$	11,768

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	Dec. 31, 2017
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trusts (a)
Cash equivalents	$	783	$	783	$	—	$	—	$	783
Mutual funds	10,332		11,283		—		—		11,283
Total	$	11,115	$	12,066	$	—	$	—	$	12,066

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet.

Derivative Instruments Fair Value Measurements

NSP-Minnesota enters into derivative instruments, including forward contracts, futures, swaps and options, for trading purposes and to manage risk in connection with changes in interest rates, utility commodity prices and vehicle fuel prices.

Interest Rate Derivatives — NSP-Minnesota enters into various instruments that effectively fix the interest payments on certain floating rate debt obligations or effectively fix the yield or price on a specified benchmark interest rate for an anticipated debt issuance for a specific period. These derivative instruments are generally designated as cash flow hedges for accounting purposes.

At June 30, 2018, accumulated other comprehensive losses related to interest rate derivatives included $0.8 million of net losses expected to be reclassified into earnings during the next 12 months as the related hedged interest rate transactions impact earnings, including forecasted amounts for unsettled hedges, as applicable.

Wholesale and Commodity Trading Risk — NSP-Minnesota conducts various wholesale and commodity trading activities, including the purchase and sale of electric capacity, energy, energy-related instruments and natural gas related instruments, including derivatives. NSP-Minnesota’s risk management policy allows management to conduct these activities within guidelines and limitations as approved by its risk management committee, which is made up of management personnel not directly involved in the activities governed by this policy.

Commodity Derivatives — NSP-Minnesota enters into derivative instruments to manage variability of future cash flows from changes in commodity prices in its electric and natural gas operations, as well as for trading purposes. This could include the purchase or sale of energy or energy-related products, natural gas to generate electric energy, natural gas for resale, FTRs, vehicle fuel, and weather derivatives.

At June 30, 2018, NSP-Minnesota had various vehicle fuel contracts designated as cash flow hedges extending through December 2018. NSP-Minnesota enters into derivative instruments that mitigate commodity price risk on behalf of electric and natural gas customers, but may not be designated as qualifying hedging transactions. Changes in the fair value of non-trading commodity derivative instruments are recorded in other comprehensive income or deferred as a regulatory asset or liability. The classification as a regulatory asset or liability is based on commission approved regulatory recovery mechanisms. NSP-Minnesota recorded immaterial amounts to income related to the ineffectiveness of cash flow hedges for the three and six months ended June 30, 2018 and 2017.

At June 30, 2018, net gains related to commodity derivative cash flow hedges recorded as a component of accumulated other comprehensive losses included $0.1 million of net gains expected to be reclassified into earnings during the next 12 months as the hedged transactions occur.

Additionally, NSP-Minnesota enters into commodity derivative instruments for trading purposes not directly related to commodity price risks associated with serving its electric and natural gas customers. Changes in the fair value of these commodity derivatives are recorded in electric operating revenues, net of amounts credited to customers under margin-sharing mechanisms.

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The following table details the gross notional amounts of commodity forwards, options and FTRs at June 30, 2018 and Dec. 31, 2017:

(Amounts in Thousands)(a)(b)	June 30, 2018	Dec. 31, 2017
Megawatt hours of electricity	73,771	41,711
Million British thermal units of natural gas	7,403	23,829
Gallons of vehicle fuel	120	240

^(a)  Amounts are not reflective of net positions in the underlying commodities.

^(b)  Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.

The following tables detail the impact of derivative activity during the three and six months ended June 30, 2018 and 2017 on accumulated other comprehensive loss, regulatory assets and liabilities and income:

	Three Months Ended June 30, 2018
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:							Pre-Tax Gains Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	264		(a)	$	—		$	—
Vehicle fuel and other commodity	31		—			(35		)	(b)	—			—
Total	$	31	$	—		$	229			$	—		$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—		$	2,263	(c)
Electric commodity	—		24,262			—				1,142		(d)	—
Natural gas commodity	—		(18		)	—				—			—
Total	$	—	$	24,244		$	—			$	1,142		$	2,263

	Six Months Ended June 30, 2018
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:								Pre-Tax Gains (Losses) Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	525		(a)	$	—			$	—
Vehicle fuel and other commodity	38		—			(64		)	(b)	—				—
Total	$	38	$	—		$	461			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	8,981		(c)
Electric commodity	—		(5,615		)	—				3,311			(d)	—
Natural gas commodity	—		830			—				(521		)	(e)	(404		)	(e)
Total	$	—	$	(4,785	)	$	—			$	2,790			$	8,577

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	Three Months Ended June 30, 2017
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:								Pre-Tax Gains Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	350		(a)	$	—			$	—
Vehicle fuel and other commodity	43		—			(5		)	(b)	—				—
Total	$	43	$	—		$	345			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	5,977	(c)
Electric commodity	—		(1,526		)	—				(1,149		)	(d)	—
Natural gas commodity	—		(51		)	—				—				—
Total	$	—	$	(1,577	)	$	—			$	(1,149	)		$	5,977

	Six Months Ended June 30, 2017
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:								Pre-Tax Gains (Losses) Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	692		(a)	$	—			$	—
Vehicle fuel and other commodity	43		—			(5		)	(b)	—				—
Total	$	43	$	—		$	687			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	6,599		(c)
Electric commodity	—		(2,772		)	—				(3,937		)	(d)	—
Natural gas commodity	—		(717		)	—				698			(e)	(945		)	(e)
Total	$	—	$	(3,489	)	$	—			$	(3,239	)		$	5,654

^(a)  Amounts are recorded to interest charges.

^(b)  Amounts are recorded to operating and maintenance (O&M) expenses.

^(c)  Amounts are recorded to electric operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue, as appropriate.

^(d)  Amounts are recorded to electric fuel and purchased power. These derivative settlement gains and losses are shared with electric customers through fuel and purchased energy cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.

(e) Amounts are recorded to cost of natural gas sold and transported. These derivative settlement gains and losses are shared with natural gas customers through purchased natural gas cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.

NSP-Minnesota had no derivative instruments designated as fair value hedges during the three and six months ended June 30, 2018 and 2017. Therefore, no gains or losses from fair value hedges or related hedged transactions were recognized for these periods.

Consideration of Credit Risk and Concentrations — NSP-Minnesota continuously monitors the creditworthiness of the counterparties to its interest rate derivatives and commodity derivative contracts prior to settlement, and assesses each counterparty’s ability to perform on the transactions set forth in the contracts. Given this assessment, as well as an assessment of the impact of NSP-Minnesota’s own credit risk when determining the fair value of derivative liabilities, the impact of credit risk was immaterial to the fair value of unsettled commodity derivatives presented in the consolidated balance sheets.

NSP-Minnesota employs additional credit risk control mechanisms when appropriate, such as letters of credit, parental guarantees, standardized master netting agreements and termination provisions that allow for offsetting of positive and negative exposures. Credit exposure is monitored and, when necessary, the activity with a specific counterparty is limited until credit enhancement is provided.

19

NSP-Minnesota’s most significant concentrations of credit risk with particular entities or industries are contracts with counterparties to its wholesale, trading and non-trading commodity activities. At June 30, 2018, five of NSP-Minnesota’s 10 most significant counterparties for these activities, comprising $39.7 million or 48 percent of this credit exposure, had investment grade credit ratings from Standard & Poor’s, Moody’s or Fitch Ratings. Five of the 10 most significant counterparties, comprising $20.1 million or 24 percent of this credit exposure, were not rated by these external agencies, but based on NSP-Minnesota’s internal analysis, had credit quality consistent with investment grade. All ten of these significant counterparties are municipal or cooperative electric entities, or other utilities.

Credit Related Contingent Features — Contract provisions for derivative instruments that NSP-Minnesota enters into, including those accounted for as normal purchase-normal sale contracts and therefore not reflected on the balance sheet, may require the posting of collateral or settlement of the contracts for various reasons, including if NSP-Minnesota’s credit ratings are downgraded below its investment grade credit rating by any of the major credit rating agencies or for cross-default contractual provisions that could result in the settlement of such contracts if there was a failure under other financing arrangements related to payment terms or other covenants. At June 30, 2018 and Dec. 31, 2017, there were no derivative instruments in a material liability position with such underlying contract provisions.

Certain derivative instruments are also subject to contract provisions that contain adequate assurance clauses. These provisions allow counterparties to seek performance assurance, including cash collateral, in the event that NSP-Minnesota’s ability to fulfill its contractual obligations is reasonably expected to be impaired. NSP-Minnesota had no collateral posted related to adequate assurance clauses in derivative contracts as of June 30, 2018 and Dec. 31, 2017.

Recurring Fair Value Measurements — The following table presents for each of the fair value hierarchy levels, NSP-Minnesota’s derivative assets and liabilities measured at fair value on a recurring basis at June 30, 2018:

	June 30, 2018
	Fair Value						Fair Value Total		Counterparty Netting(b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative assets
Derivatives designated as cash flow hedges:
Vehicle fuel and other commodity	$	—	$	81	$	—	$	81	$	—		$	81
Other derivative instruments:
Commodity trading	480		14,737		1,661		16,878		(8,601		)	8,277
Electric commodity	—		—		22,896		22,896		(177		)	22,719
Natural gas commodity	—		167		—		167		—			167
Total current derivative assets	$	480	$	14,985	$	24,557	$	40,022	$	(8,778	)	31,244
PPAs (a)												24
Current derivative instruments												$	31,268
Noncurrent derivative assets
Other derivative instruments:
Commodity trading	$	—	$	33,171	$	5,596	$	38,767	$	(12,085	)	$	26,682
Total noncurrent derivative assets	$	—	$	33,171	$	5,596	$	38,767	$	(12,085	)	26,682
PPAs (a)												108
Noncurrent derivative instruments												$	26,790

20

	June 30, 2018
	Fair Value						Fair Value Total		Counterparty Netting(b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative liabilities
Other derivative instruments:
Commodity trading	$	286	$	12,147	$	1,550	$	13,983	$	(9,805	)	$	4,178
Electric commodity	—		—		177		177		(177		)	—
Total current derivative liabilities	$	286	$	12,147	$	1,727	$	14,160	$	(9,982	)	4,178
PPAs (a)												13,851
Current derivative instruments												$	18,029
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	—	$	24,476	$	397	$	24,873	$	(15,738	)	$	9,135
Total noncurrent derivative liabilities	$	—	$	24,476	$	397	$	24,873	$	(15,738	)	9,135
PPAs (a)												82,987
Noncurrent derivative instruments												$	92,122

^(a)  During 2006, NSP-Minnesota qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts is being amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

^(b)  NSP-Minnesota nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at June 30, 2018. At June 30, 2018, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $4.9 million. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

The following table presents for each of the fair value hierarchy levels, NSP-Minnesota’s derivative assets and liabilities measured at fair value on a recurring basis at Dec. 31, 2017:

	Dec. 31, 2017
	Fair Value						Fair Value Total		Counterparty Netting (b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative assets
Derivatives designated as cash flow hedges:
Vehicle fuel and other commodity	$	—	$	107	$	—	$	107	$	—		$	107
Other derivative instruments:
Commodity trading	1,691		17,144		142		18,977		(11,744		)	7,233
Electric commodity	—		—		17,581		17,581		(425		)	17,156
Natural gas commodity	—		77		—		77		—			77
Total current derivative assets	$	1,691	$	17,328	$	17,723	$	36,742	$	(12,169	)	24,573
PPAs (a)												657
Current derivative instruments												$	25,230
Noncurrent derivative assets
Other derivative instruments:
Commodity trading	$	—	$	29,121	$	5,363	$	34,484	$	(6,502	)	$	27,982
Total noncurrent derivative assets	$	—	$	29,121	$	5,363	$	34,484	$	(6,502	)	27,982
PPAs (a)												120
Noncurrent derivative instruments												$	28,102

21

	Dec. 31, 2017
	Fair Value						Fair Value Total		Counterparty Netting (b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative liabilities
Other derivative instruments:
Commodity trading	$	1,713	$	13,853	$	—	$	15,566	$	(11,974	)	$	3,592
Electric commodity	—		—		425		425		(425		)	—
Total current derivative liabilities	$	1,713	$	13,853	$	425	$	15,991	$	(12,399	)	3,592
PPAs (a)												14,105
Current derivative instruments												$	17,697
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	—	$	22,163	$	—	$	22,163	$	(9,334	)	$	12,829
Total noncurrent derivative liabilities	$	—	$	22,163	$	—	$	22,163	$	(9,334	)	12,829
PPAs (a)												89,913
Noncurrent derivative instruments												$	102,742

^(a)  During 2006, NSP-Minnesota qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts is being amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

^(b)  NSP-Minnesota nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2017. At Dec. 31, 2017, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $3.1 million. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

The following table presents the changes in Level 3 commodity derivatives for the three and six months ended June 30, 2018 and 2017:

	Three Months Ended June 30
(Thousands of Dollars)	2018			2017
Balance at April 1	$	13,516		$	4,643
Purchases	26,395			40,460
Settlements	(5,170		)	(8,166		)
Net transactions recorded during the period:
(Losses) gains recognized in earnings (a)	(2,654		)	6,007
Net losses recognized as regulatory assets and liabilities	(4,058		)	(2,372		)
Balance at June 30	$	28,029		$	40,572
	Six Months Ended June 30
(Thousands of Dollars)	2018			2017
Balance at Jan. 1	$	22,662		$	15,320
Purchases	26,397			40,740
Settlements	(7,104		)	(11,592		)
Net transactions recorded during the period:
(Losses) gains recognized in earnings (a)	(374		)	5,215
Net gains recognized as regulatory assets and liabilities	(13,552		)	(9,111		)
Balance at June 30	$	28,029		$	40,572

^(a)  These amounts relate to commodity derivatives held at the end of the period.

NSP-Minnesota recognizes transfers between levels as of the beginning of each period. There were no transfers of amounts between levels for derivative instruments for the three and six months ended June 30, 2018 and 2017.

22

Fair Value of Long-Term Debt

As of June 30, 2018 and Dec. 31, 2017, other financial instruments for which the carrying amount did not equal fair value were as follows:

	June 30, 2018				Dec. 31, 2017
(Thousands of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt, including current portion	$	4,935,068	$	5,192,385	$	4,933,018	$	5,601,919

The fair value of NSP-Minnesota’s long-term debt is estimated based on recent trades and observable spreads from benchmark interest rates for similar securities. The fair value estimates are based on information available to management as of June 30, 2018 and Dec. 31, 2017, and given the observability of the inputs to these estimates, the fair values presented for long-term debt have been assigned a Level 2.

9. Other Expense, Net

Other expense, net consisted of the following:

	Three Months Ended June 30						Six Months Ended June 30
(Thousands of Dollars)	2018			2017			2018			2017
Interest income	$	522		$	605		$	3,457		$	3,314
Other nonoperating income	697			17			698			27
Insurance policy expense	(1,537		)	(856		)	(1,195		)	(1,711		)
Benefits non-service cost	(1,916		)	(3,398		)	(4,978		)	(6,796		)
Other expense, net	$	(2,234	)	$	(3,632	)	$	(2,018	)	$	(5,166	)

10. Segment Information

Operating results from the regulated electric utility and regulated natural gas utility are each separately and regularly reviewed by NSP-Minnesota’s chief operating decision maker. NSP-Minnesota evaluates performance based on profit or loss generated from the product or service provided. These segments are managed separately because the revenue streams are dependent upon regulated rate recovery, which is separately determined for each segment.

NSP-Minnesota has the following reportable segments: regulated electric utility, regulated natural gas utility and all other.

• NSP-Minnesota’s regulated electric utility segment generates, transmits and distributes electricity primarily in portions of Minnesota, North Dakota and South Dakota. In addition, this segment includes sales for resale and provides wholesale transmission service to various entities in the United States. Regulated electric utility also includes NSP-Minnesota’s commodity trading operations.

• NSP-Minnesota’s regulated natural gas utility segment transports, stores and distributes natural gas primarily in portions of Minnesota and North Dakota.

• Revenues from operating segments not included above are below the necessary quantitative thresholds and are therefore included in the all other category. Those primarily include appliance repair services, nonutility real estate activities and revenues associated with processing solid waste into refuse-derived fuel.

Asset and capital expenditure information is not provided for NSP-Minnesota’s reportable segments because as an integrated electric and natural gas utility, NSP-Minnesota operates significant assets that are not dedicated to a specific business segment, and reporting assets and capital expenditures by business segment would require arbitrary and potentially misleading allocations which may not necessarily reflect the assets that would be required for the operation of the business segments on a stand-alone basis.

To report income from operations for regulated electric and regulated natural gas utility segments, the majority of costs are directly assigned to each segment. However, some costs, such as common depreciation, common operating and maintenance (O&M) expenses and interest expense are allocated based on cost causation allocators. A general allocator is used for certain general and administrative expenses, including office supplies, rent, property insurance and general advertising.

23

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Three Months Ended June 30, 2018
Operating revenues (a)(b)	$	1,096,408	$	83,112	$	8,215	$	—		$	1,187,735
Intersegment revenues	128		116		—		(244		)	—
Total revenues	$	1,096,536	$	83,228	$	8,215	$	(244	)	$	1,187,735
Net income	$	88,875	$	399	$	3,113	$	—		$	92,387

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas			All Other		Reconciling Eliminations			Consolidated Total
Three Months Ended June 30, 2017
Operating revenues (a)(b)	$	1,079,779	$	78,006		$	7,155	$	—		$	1,164,940
Intersegment revenues	243		177			—		(420		)	—
Total revenues	$	1,080,022	$	78,183		$	7,155	$	(420	)	$	1,164,940
Net income (loss)	$	89,477	$	(3,360	)	$	1,545	$	—		$	87,662

^(a)  Operating revenues include 117 million and 119 million of affiliate electric revenue for the three months ended June 30, 2018 and 2017.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended June 30, 2018 and 2017.

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Six Months Ended June 30, 2018
Operating revenues (a)(b)	$	2,158,671	$	324,544	$	15,271	$	—		$	2,498,486
Intersegment revenues	293		260		—		(553		)	—
Total revenues	$	2,158,964	$	324,804	$	15,271	$	(553	)	$	2,498,486
Net income	$	174,597	$	25,844	$	3,686	$	—		$	204,127

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Six Months Ended June 30, 2017
Operating revenues (a)(b)	$	2,158,809	$	299,189	$	14,082	$	—		$	2,472,080
Intersegment revenues	352		271		—		(623		)	—
Total revenues	$	2,159,161	$	299,460	$	14,082	$	(623	)	$	2,472,080
Net income	$	167,559	$	14,145	$	124	$	—		181,828

^(a)  Operating revenues include $234 million and $243 million of affiliate electric revenue for the six months ended June 30, 2018 and 2017.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the six months ended June 30, 2018 and 2017.

11. Benefit Plans and Other Postretirement Benefits

Components of Net Periodic Benefit Cost

	Three Months Ended June 30
	2018			2017			2018			2017
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	6,982		$	6,958		$	43		$	36
Interest cost (a)	8,804			10,177			769			854
Expected return on plan assets (a)	(14,542		)	(15,017		)	(96		)	(54		)
Amortization of prior service (credit) cost (a)	(28		)	265			(759		)	(759		)
Amortization of net loss (a)	9,614			9,902			595			507
Net periodic benefit cost	10,830			12,285			552			584
Costs not recognized due to the effects of regulation	(3,069		)	(4,899		)	—			—
Net benefit cost recognized for financial reporting	$	7,761		$	7,386		$	552		$	584

24

	Six Months Ended June 30
	2018			2017			2018			2017
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	13,964		$	13,916		$	86		$	72
Interest cost (a)	17,608			20,354			1,538			1,708
Expected return on plan assets (a)	(29,083		)	(30,034		)	(192		)	(108		)
Amortization of prior service (credit) cost (a)	(57		)	530			(1,518		)	(1,518		)
Amortization of net loss (a)	19,229			19,804			1,190			1,014
Net periodic benefit cost	21,661			24,570			1,104			1,168
Costs not recognized due to the effects of regulation	(5,832		)	(9,798		)	—			—
Net benefit cost recognized for financial reporting	$	15,829		$	14,772		$	1,104		$	1,168

^(a) The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the income statement or capitalized on the balance sheet as a regulatory asset.

In January 2018, contributions of $150 million were made across four of Xcel Energy’s pension plans, of which $63.0 million was attributable to NSP-Minnesota. Xcel Energy does not expect additional pension contributions during 2018.

12. Other Comprehensive Income (Loss)

Changes in accumulated other comprehensive loss, net of tax, for the three and six months ended June 30, 2018 and 2017 were as follows:

	Three Months Ended June 30, 2018
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities		Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at April 1	$	(20,723	)	$	—	$	(3,717	)	$	(24,440	)
Other comprehensive income before reclassifications	22			—		—			22
Losses reclassified from net accumulated other comprehensive loss	165			—		54			219
Net current period other comprehensive income	187			—		54			241
Accumulated other comprehensive loss at June 30	$	(20,536	)	$	—	$	(3,663	)	$	(24,199	)

	Three Months Ended June 30, 2017
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities		Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at April 1	$	(18,005	)	$	105	$	(2,645	)	$	(20,545	)
Other comprehensive income before reclassifications	26			—		—			26
Losses reclassified from net accumulated other comprehensive loss	204			—		36			240
Net current period other comprehensive income	230			—		36			266
Accumulated other comprehensive loss at June 30	$	(17,775	)	$	105	$	(2,609	)	$	(20,279	)

	Six Months Ended June 30, 2018
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities			Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at Jan. 1	$	(20,895	)	$	128		$	(3,770	)	$	(24,537	)
Other comprehensive income before reclassifications	27			—			—			27
Losses (gains) reclassified from net accumulated other comprehensive loss	332			(128		)	107			311
Net current period other comprehensive income	359			(128		)	107			338
Accumulated other comprehensive loss at June 30	$	(20,536	)	$	—		$	(3,663	)	$	(24,199	)

25

	Six Months Ended June 30, 2017
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities		Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at Jan. 1	$	(18,208	)	$	105	$	(2,680	)	$	(20,783	)
Other comprehensive income before reclassifications	26			—		—			26
Losses reclassified from net accumulated other comprehensive loss	407			—		71			478
Net current period other comprehensive income	433			—		71			504
Accumulated other comprehensive loss at June 30	$	(17,775	)	$	105	$	(2,609	)	$	(20,279	)

Reclassifications from accumulated other comprehensive loss for the three and six months ended June 30, 2018 and 2017 were as follows:

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Three Months Ended June 30, 2018				Three Months Ended June 30, 2017
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	264		(a)	$	350		(a)
Vehicle fuel derivatives	(35		)	(b)	(5		)	(b)
Total, pre-tax	229				345
Tax benefit	(64		)		(141		)
Total, net of tax	165				204
Defined benefit pension and postretirement losses:
Amortization of net loss	125			(c)	109			(c)
Prior service credit	(49		)	(c)	(51		)	(c)
Total, pre-tax	76				58
Tax benefit	(22		)		(22		)
Total, net of tax	54				36
Marketable securities:
Realization of gains	—				—
Total, pre-tax	—				—
Tax expense	—				—
Total, net of tax	—				—
Total amounts reclassified, net of tax	$	219			$	240

26

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Six Months Ended June 30, 2018				Six Months Ended June 30, 2017
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	525		(a)	$	692		(a)
Vehicle fuel derivatives	(64		)	(b)	(5		)	(b)
Total, pre-tax	461				687
Tax benefit	(129		)		(280		)
Total, net of tax	332				407
Defined benefit pension and postretirement losses:
Amortization of net loss	250			(c)	218			(c)
Prior service credit	(98		)	(c)	(100		)	(c)
Total, pre-tax	152				118
Tax benefit	(45		)		(47		)
Total, net of tax	107				71
Marketable securities:
Realization of gains	(179		)		—
Total, pre-tax	(179		)		—
Tax expense	51				—
Total, net of tax	(128		)		—
Total amounts reclassified, net of tax	$	311			$	478

^(a)  Included in interest charges.

^(b)  Included in O&M expenses.

^(c)  Included in the computation of net periodic pension and postretirement benefit costs. See Note 11 to the consolidated financial statements for details regarding these benefit plans.

13. Revenues

NSP-Minnesota principally generates revenue from the generation, transmission, distribution and sale of electricity and the transportation, distribution and sale of natural gas to wholesale and retail customers. Performance obligations related to the sale of energy are satisfied as energy is delivered to customers. NSP-Minnesota recognizes revenue in an amount that corresponds directly to the price of the energy delivered to the customer. The measurement of energy sales to customers is generally based on the reading of their meters, which occurs on a systematic basis throughout the month. At the end of each month, amounts of energy delivered to customers since the date of the last meter reading are estimated, and the corresponding unbilled revenue is recognized. Contract terms are generally short-term in nature, and as such NSP-Minnesota does not recognize a separate financing component of its collections from customers. NSP-Minnesota presents its revenues net of any excise or other fiduciary-type taxes or fees.

NSP-Minnesota participates in MISO. NSP-Minnesota recognizes sales to both native load and other end use customers on a gross basis in electric revenues and cost of sales. Revenues and charges for short term wholesale sales of excess energy transacted through RTOs are also recorded on a gross basis. Other revenues and charges related to participating and transacting in RTOs are recorded on a net basis in cost of sales.

NSP-Minnesota has various rate-adjustment mechanisms in place that provide for the recovery of natural gas, electric fuel and purchased energy costs. These cost-adjustment tariffs may increase or decrease the level of revenue collected from customers and are revised periodically for differences between the total amount collected under the clauses and the costs incurred.

When applicable, under governing regulatory commission rate orders, fuel cost over-recoveries (the excess of fuel revenue billed to customers over fuel costs incurred) are deferred as regulatory liabilities and under-recoveries (the excess of fuel costs incurred over fuel revenues billed to customers) are deferred as regulatory assets.

27

Certain rate rider mechanisms qualify as alternative revenue programs under GAAP. These mechanisms arise from costs imposed upon the utility by action of a regulator or legislative body related to an environmental, public safety or other mandate. When certain criteria are met (including collection within 24 months), revenue is recognized equal to the revenue requirement, which may include return on rate base items and incentives. The mechanisms are revised periodically for differences between the total amount collected and the revenue recognized, which may increase or decrease the level of revenue collected from customers. Alternative revenue is recorded on a gross basis and is disclosed separate from revenue from contracts with customers in the period earned.

In the following tables, revenue is classified by the type of goods/services rendered and market/customer type. The tables also reconcile revenue to the reportable segments.

	Three Months Ended June 30, 2018
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	311,086	$	42,398	$	6,710	$	360,194
Commercial and industrial (C&I)	514,710		33,417		42		548,169
Other	8,639		—		1,463		10,102
Total retail	834,435		75,815		8,215		918,465
Wholesale	42,033		—		—		42,033
Transmission	59,951		—		—		59,951
Interchange	117,417		—		—		117,417
Other	6,033		3,317		—		9,350
Total revenue from contracts with customers	1,059,869		79,132		8,215		1,147,216
Alternative revenue and other	36,539		3,980		—		40,519
Total revenues	$	1,096,408	$	83,112	$	8,215	$	1,187,735

	Three Months Ended June 30, 2017
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	288,733	$	36,860	$	6,416	$	332,009
C&I	526,867		31,382		92		558,341
Other	7,854		—		647		8,501
Total retail	823,454		68,242		7,155		898,851
Wholesale	28,841		—		—		28,841
Transmission	56,177		—		—		56,177
Interchange	119,384		—		—		119,384
Other	7,445		1,452		—		8,897
Total revenue from contracts with customers	1,035,301		69,694		7,155		1,112,150
Alternative revenue and other	44,478		8,312		—		52,790
Total revenues	$	1,079,779	$	78,006	$	7,155	$	1,164,940

28

	Six Months Ended June 30, 2018
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	622,215	$	174,057	$	13,033	$	809,305
Commercial and industrial (C&I)	982,733		130,325		85		1,113,143
Other	18,358		—		2,153		20,511
Total retail	1,623,306		304,382		15,271		1,942,959
Wholesale	88,398		—		—		88,398
Transmission	114,749		—		—		114,749
Interchange	234,389		—		—		234,389
Other	17,578		5,528		—		23,106
Total revenue from contracts with customers	2,078,420		309,910		15,271		2,403,601
Alternative revenue and other	80,251		14,634		—		94,885
Total revenues	$	2,158,671	$	324,544	$	15,271	$	2,498,486

	Six Months Ended June 30, 2017
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	593,146	$	158,273	$	12,626	$	764,045
C&I	1,011,970		119,873		130		1,131,973
Other	16,057		—		1,326		17,383
Total retail	1,621,173		278,146		14,082		1,913,401
Wholesale	74,760		—		—		74,760
Transmission	110,136		—		—		110,136
Interchange	243,073		—		—		243,073
Other	13,408		2,697		—		16,105
Total revenue from contracts with customers	2,062,550		280,843		14,082		2,357,475
Alternative revenue and other	96,259		18,346		—		114,605
Total revenues	$	2,158,809	$	299,189	$	14,082	$	2,472,080

Item 2 — MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

Discussion of financial condition and liquidity for NSP-Minnesota is omitted per conditions set forth in general instructions H (1) (a) and (b) of Form 10-Q for wholly owned subsidiaries. It is replaced with management’s narrative analysis of the results of operations set forth in general instructions H (2) (a) of Form 10-Q for wholly owned subsidiaries (reduced disclosure format).

Financial Review

The following discussion and analysis by management focuses on those factors that had a material effect on NSP-Minnesota’s financial condition, results of operations and cash flows during the periods presented, or are expected to have a material impact in the future. It should be read in conjunction with the accompanying unaudited consolidated financial statements and the related notes to consolidated financial statements. Due to the seasonality of NSP-Minnesota’s operating results, quarterly financial results are not an appropriate base from which to project annual results.

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Forward-Looking Statements

Except for the historical statements contained in this report, the matters discussed herein, are forward-looking statements that are subject to certain risks, uncertainties and assumptions. Such forward-looking statements including the TCJA’s impact to NSP-Minnesota and its customers, as well as assumptions and other statements are intended to be identified in this document by the words “anticipate,” “believe,” “could,” “estimate,” “expect,” “intend,” “may,” “objective,” “outlook,” “plan,” “project,” “possible,” “potential,” “should,” “will,” “would” and similar expressions. Actual results may vary materially. Forward-looking statements speak only as of the date they are made, and we expressly disclaim any obligation to update any forward-looking information. The following factors, in addition to those discussed elsewhere in this Quarterly Report on Form 10-Q and in other securities filings (including NSP-Minnesota’s Annual Report on Form 10-K for the fiscal year ended Dec. 31, 2017 and subsequent securities filings), could cause actual results to differ materially from management expectations as suggested by such forward-looking information: general economic conditions, including inflation rates, monetary fluctuations and their impact on capital expenditures and the ability of NSP-Minnesota and its subsidiaries to obtain financing on favorable terms; business conditions in the energy industry; including the risk of a slow down in the U.S. economy or delay in growth, recovery, trade, fiscal, taxation and environmental policies in areas where NSP-Minnesota has a financial interest; customer business conditions; actions of credit rating agencies; competitive factors including the extent and timing of the entry of additional competition in the markets served by NSP-Minnesota and its subsidiaries; unusual weather; effects of geopolitical events, including war and acts of terrorism; cyber security threats and data security breaches; state, federal and foreign legislative and regulatory initiatives that affect cost and investment recovery, have an impact on rates or have an impact on asset operation or ownership or impose environmental compliance conditions; structures that affect the speed and degree to which competition enters the electric and natural gas markets; costs and other effects of legal and administrative proceedings, settlements, investigations and claims; financial or regulatory accounting policies imposed by regulatory bodies; outcomes of regulatory proceedings; availability or cost of capital; and employee work force factors.

Non-GAAP Financial Measures

The following discussion includes financial information prepared in accordance with GAAP, as well as certain non-GAAP financial measures such as electric margin and natural gas margin.  Generally, a non-GAAP financial measure is a numerical measure of a company’s financial performance, financial position or cash flows that excludes (or includes) amounts that are adjusted from the most directly comparable measure calculated and presented in accordance with GAAP. Xcel Energy’s management uses non-GAAP measures internally for financial planning and analysis, for reporting of results to the Board of Directors and when communicating its earnings outlook to analysts and investors. Non-GAAP financial measures are intended to supplement investors’ understanding of our operating performance and should not be considered alternatives for financial measures presented in accordance with GAAP. These measures are discussed in more detail below and may not be comparable to other companies’ similarly titled non-GAAP financial measures.

Electric margin is presented as electric revenues less electric fuel and purchased power expenses and natural gas margin is presented as natural gas revenues less the cost of natural gas sold and transported. Expenses incurred for electric fuel and purchased power and the cost of natural gas sold and transported are generally recovered through various recovery mechanisms, and as a result, changes in these expenses are offset in operating revenues. Management believes electric and natural gas margins provide the most meaningful basis for evaluating our operations because they exclude the revenue impact of fluctuations in these expenses. These margins can be reconciled to operating income, a GAAP measure, by including other operating revenues, cost of sales — other, O&M expenses, conservation program expenses, depreciation and amortization and taxes (other than income taxes).

Results of Operations

NSP-Minnesota’s net income was approximately $204 million for 2018 year-to-date, compared with approximately $182 million for the same period of 2017. The increase in earnings, driven by lower O&M expenses and higher electric and natural gas margins due to favorable weather, was partially offset by higher depreciation expense due to invested capital.

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Electric Revenues and Margin

Electric revenues and fuel and purchased power expenses are impacted by fluctuations in the price of natural gas, coal and uranium used in the generation of electricity. However, these price fluctuations have minimal impact on electric margin due to fuel recovery mechanisms that recover fuel expenses. The following table details the electric revenues and margin:

	Six Months Ended June 30
(Millions of Dollars)	2018			2017
Electric revenues before impact of the TCJA	$	2,218		$	2,159
Electric fuel and purchased power	(826		)	(780		)
Electric margin before impact of the TCJA	$	1,392		$	1,379
Impact of the TCJA (offset as a reduction in income tax expense)	(57		)	—
Electric margin	$	1,335		$	1,379

The following tables summarize the components of the changes in electric revenues and electric margin for the six months endedJune 30:

Electric Revenues

(Millions of Dollars)	2018 vs. 2017
Interchange agreement billings with NSP-Wisconsin	$	(9	)
Conservation program revenue (offset by expenses)	(5		)
Conservation incentive	(5		)
Fuel and purchased power cost recovery	39
Estimated impact of weather (net of Minnesota decoupling)	11
Wholesale transmission revenue	10
Retail sales growth (including Minnesota decoupling and sales true-up)	9
Trading	7
Other, net	2
Total increase in electric revenues before impact of the TCJA	$	59
Impact of the TCJA (offset as a reduction in income tax expense)	(59		)
Total change in electric revenues	$	—

Electric Margin

(Millions of Dollars)	2018 vs. 2017
Interchange agreement billings with NSP-Wisconsin	$	(11	)
Conservation program revenue (offset by expenses)	(5		)
Conservation incentive	(5		)
Purchased capacity costs	20
Estimated impact of weather (net of Minnesota decoupling)	11
Retail sales growth (including Minnesota decoupling and sales true-up)	9
Other, net	(6		)
Total increase in electric margin before impact of the TCJA	$	13
Impact of the TCJA (offset as a reduction in income tax expense)	(57		)
Total decrease in electric margin	$	(44	)

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Natural Gas Revenues and Margin

Total natural gas expense varies with changing sales and the cost of natural gas. However, fluctuations in the cost of natural gas have minimal impact on natural gas margin due to natural gas cost recovery mechanisms. The following table details natural gas revenues and margin:

	Six Months Ended June 30
(Millions of Dollars)	2018			2017
Natural gas revenues before impact of the TCJA	$	329		$	299
Cost of natural gas sold and transported	(192		)	(178		)
Natural gas margin before impact of the TCJA	$	137		$	121
Impact of the TCJA (offset as a reduction in income tax expense)	(4		)	—
Natural gas margin	$	133		$	121

The following tables summarize the components of the changes in natural gas revenues and natural gas margin for the six months endedJune 30:

Natural Gas Revenues

(Millions of Dollars)	2018 vs. 2017
Purchased natural gas adjustment clause recovery	$	13
Estimated impact of weather	10
Conservation program revenue (offset by expenses)	2
Other, net	5
Total increase in natural gas revenues before impact of the TCJA	$	30
Impact of TCJA (offset as a reduction in income tax expense)	(4		)
Total increase in natural gas revenues	$	26

Natural Gas Margin

(Millions of Dollars)	2018 vs. 2017
Estimated impact of weather	$	10
Conservation program revenue (offset by expenses)	2
Other, net	4
Total increase in natural gas margin before impact of TCJA	$	16
Impact of the TCJA (offset as a reduction in income tax expense)	(4		)
Total increase in natural gas margin	$	12

Non-Fuel Operating Expenses and Other Items

O&M Expenses— O&M expenses decreased $12 million, or 2.0 percent, for 2018 year-to-date, largely reflecting expense timing. The significant changes are summarized in the table below:

(Millions of Dollars)	2018 vs. 2017
Nuclear plant operations and amortization	$	(16	)
Plant generation costs	7
Other, net	(3		)
Total decrease in O&M expenses	$	(12	)

• Nuclear plant operations and amortization expenses are lower largely reflecting expense timing, savings initiatives and reduced refueling outage costs; and

• Plant generation costs increased primarily due to the timing of planned maintenance and overhauls at a number of generation facilities.

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Conservation Program Expenses — Conservation program expenses decreased$2 million, or 3.7 percent, for 2018 year-to-date. The decrease was due to lower recovery rates, partially offset by additional customer participation in electric conservation programs. Conservation expenses are generally recovered concurrently through riders and base rates. Timing of recovery may not correspond to the period in which costs were incurred.

Depreciation and Amortization— Depreciation and amortization expense increased$15 million, or 4.3 percent, for 2018 year-to-date. The increase was primarily driven by capital expenditures due to planned system investments and amortization of certain regulatory assets, partially offset by lower depreciation rates in Minnesota.

Income Taxes — Income tax expense decreased$51 million for the first six months of 2018 compared with the same period in 2017. The decrease was primarily driven by a lower federal tax rate due to the TCJA, an increase in plant-related regulatory differences related to ARAM (net of deferrals), and an increase in wind PTCs. The ETR was 9.6 percent for the first six months of 2018 compared with 28.6 percent for the same period in 2017. The lower ETR in 2018 is primarily due to the items referenced above. See Note 4 to the consolidated financial statements.

Public Utility Regulation

Except to the extent noted below and in Note 5 to the consolidated financial statements the circumstances set forth in Public Utility Regulation included in Item 1 of NSP-Minnesota’s Annual Report on Form 10-K for the year ended Dec. 31, 2017 and in Item 2 of NSP-Minnesota’s Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018, appropriately represent, in all material respects, the current status of public utility regulation and are incorporated herein by reference.

Wind Development — In 2017, the MPUC approved NSP-Minnesota’s proposal to add 1,550 megawatts (MW) of new wind generation including ownership of 1,150 MW of wind generation. An order from the NDPSC is expected later in 2018.

Dakota Range — In April 2018, the MPUC approved NSP-Minnesota’s petition to build and own the Dakota Range, a 300 MW wind project in South Dakota. The project is expected to be placed into service by the end of 2021 and qualify for 80 percent of the PTC. NSP-Minnesota’s total capital investment for the Dakota Range is expected to be approximately $350 million. A NDPSC decision is expected later in 2018.

Minnesota State Right-Of-First Refusal (ROFR) Statute Complaint — In September 2017, LSP Transmission Holdings, LLC (LSP Transmission) filed a complaint in the U.S. District Court for the District of Minnesota (Minnesota District Court) against the Minnesota Attorney General, the MPUC and the DOC. The complaint was in response to MISO assigning NSP-Minnesota and ITC Midwest, LLC to jointly own a new 345 KV transmission line from near Mankato, Minn. to Winnebago, Minn. The project was estimated by MISO to cost $108 million, with the transmission line portion of the project estimated by MISO to cost $103 million. The project was assigned to NSP-Minnesota and ITC Midwest as the incumbent utilities, consistent with a Minnesota state ROFR statute. The complaint challenged the constitutionality of the state ROFR statute and is seeking declaratory judgment that the statute violates the Commerce Clause of the U.S. Constitution and should not be enforced. The Minnesota state agencies and NSP-Minnesota filed motions to dismiss. In June 2018, the Minnesota District Court granted the defendants’ motions to dismiss with prejudice. LSP Transmission filed an appeal to the 8th Circuit Court of Appeals in July 2018. It is uncertain when a decision will be rendered regarding this appeal.

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Nuclear Power Operations

NSP-Minnesota owns two nuclear generating plants: the Monticello plant and the PI plant. See Note 12 to the financial statements of NSP-Minnesota’s Annual Report on Form 10-K for the year ended Dec. 31, 2017 for further discussion regarding the nuclear generating plants. The circumstances set forth in Nuclear Power Operations and Waste Disposal included in Item 1 of NSP-Minnesota’s Annual Report on Form 10-K for the year ended Dec. 31, 2017 and Nuclear Power Operations included in Item 2 of NSP-Minnesota’s Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018, appropriately represent, in all material respects, the current status of nuclear power operations, and are incorporated herein by reference.

Nuclear Fuel Supply — NSP-Minnesota is scheduled to take delivery of approximately 58 percent of its 2018 and approximately 24 percent of its 2019 enriched nuclear material requirements from sources that could be impacted by current political/world events, including those related to Ukraine/Russia. Alternate potential sources are expected to provide the flexibility to manage NSP-Minnesota’s nuclear fuel supply to ensure that plant availability and reliability will not be negatively impacted in the near-term. Long-term, through 2024, NSP-Minnesota is scheduled to take delivery of approximately 34 percent of its average enriched nuclear material requirements from these sources. NSP-Minnesota is closely following the progression of these events and will periodically assess if further actions are required to assure a secure supply of enriched nuclear material.

Separately, NSP-Minnesota has enriched nuclear fuel materials in process with Westinghouse Electric Corporation (Westinghouse). Westinghouse filed for Chapter 11 bankruptcy protection in March 2017. NSP-Minnesota owns materials in Westinghouse’s inventory and has contracts in place under which Westinghouse will provide certain services during an upcoming outage at PI. Westinghouse will provide nuclear fuel assemblies for the upcoming PI outage under the current nuclear fuel fabrication contract. Westinghouse has indicated its intention to continue to perform under the arrangements. Based on Westinghouse’s stated intent and the interim financing secured to fund its on-going operations, NSP-Minnesota does not expect the bankruptcy to materially impact NSP-Minnesota’s operational or financial performance. Westinghouse announced on Jan. 4, 2018 it has agreed to be acquired by Brookfield Business Partners LP and other institutional partners. Brookfield’s acquisition of Westinghouse is expected to close in the third quarter of 2018, subject to bankruptcy court and regulatory approvals. NSP-Minnesota will continue to monitor the Westinghouse acquisition process.

Summary of Recent Federal Regulatory Developments

FERC

The FERC has jurisdiction over rates for electric transmission service in interstate commerce and electricity sold at wholesale, hydro facility licensing, natural gas transportation, asset transactions and mergers, accounting practices and certain other activities of NSP-Minnesota, including enforcement of North American Electric Reliability Corporation mandatory electric reliability standards. State and local agencies have jurisdiction over many of NSP-Minnesota’s activities, including regulation of retail rates and environmental matters. See additional discussion in the summary of recent federal regulatory developments and public utility regulation sections of the NSP-Minnesota Annual Report on Form 10-K for the year ended Dec. 31, 2017 and NSP-Minnesota’s Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018. In addition to the matters discussed below, see Note 5 to the financial statements for a discussion of other regulatory matters.

Xcel Energy, which includes NSP-Minnesota, attempts to mitigate the risk of regulatory penalties through formal training on

prohibited practices and a compliance function that reviews interaction with the markets under FERC and Commodity Futures Trading Commission jurisdictions. Public campaigns are conducted to raise awareness of the public safety issues of interacting with our electric systems. While programs to comply with regulatory requirements are in place, there is no guarantee the compliance programs or other measures will be sufficient to ensure against violations.

FERC Order, ROE Policy — In June 2014, the FERC adopted a two-step ROE methodology for electric utilities in an order (Opinion 531) issued in a complaint proceeding involving New England Transmission Owners (NETOs). The issue of how to apply the FERC ROE methodology has been contested in various complaint proceedings, including two ROE complaints involving the MISO TOs, which include NSP-Minnesota and NSP-Wisconsin. In April 2017, the D.C. Circuit vacated and remanded the June 2014 ROE order. The D.C. Circuit found that the FERC had not properly determined that the ROE authorized for the NETOs prior to June 2014 was unjust and unreasonable. The D.C. Circuit also found that the FERC failed to justify the new ROE methodology. The FERC has yet to act on the D.C. Circuit’s decision. See Note 5 to the consolidated financial statements for discussion of the D.C. Circuit’s decision and the impact on the MISO ROE Complaints.

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Item 4 — CONTROLS AND PROCEDURES

Disclosure Controls and Procedures

NSP-Minnesota maintains a set of disclosure controls and procedures designed to ensure that information required to be disclosed in reports that it files or submits under the Securities Exchange Act of 1934 is recorded, processed, summarized, and reported within the time periods specified in SEC rules and forms. In addition, the disclosure controls and procedures ensure that information required to be disclosed is accumulated and communicated to management, including the chief executive officer (CEO) and chief financial officer (CFO), allowing timely decisions regarding required disclosure. As of June 30, 2018, based on an evaluation carried out under the supervision and with the participation of NSP-Minnesota’s management, including the CEO and CFO, of the effectiveness of its disclosure controls and the procedures, the CEO and CFO have concluded that NSP-Minnesota’s disclosure controls and procedures were effective.

Internal Control Over Financial Reporting

No changes in NSP-Minnesota’s internal control over financial reporting occurred during the most recent fiscal quarter that materially affected, or are reasonably likely to materially affect, NSP-Minnesota’s internal control over financial reporting.

Part II — OTHER INFORMATION

Item 1 — LEGAL PROCEEDINGS

NSP-Minnesota is involved in various litigation matters that are being defended and handled in the ordinary course of business. The assessment of whether a loss is probable or is a reasonable possibility, and whether the loss or a range of loss is estimable, often involves a series of complex judgments about future events. Management maintains accruals for such losses that are probable of being incurred and subject to reasonable estimation. Management is sometimes unable to estimate an amount or range of a reasonably possible loss in certain situations, including but not limited to when (1) the damages sought are indeterminate, (2) the proceedings are in the early stages, or (3) the matters involve novel or unsettled legal theories. In such cases, there is considerable uncertainty regarding the timing or ultimate resolution of such matters, including a possible eventual loss.

Additional Information

See Note 6 to the consolidated financial statements for further discussion of legal claims and environmental proceedings. See Part I Item 2 and Note 5 to the consolidated financial statements for a discussion of proceedings involving utility rates and other regulatory matters.

Item 1A — RISK FACTORS

NSP-Minnesota’s risk factors are documented in Item 1A of Part I of its Annual Report on Form 10-K for the year ended Dec. 31,2017, which is incorporated herein by reference. There have been no material changes from the risk factors previously disclosed in the Form 10-K.

35

Item 6 — EXHIBITS

* Indicates incorporation by reference

3.01*	Articles of Incorporation and Amendments of Northern Power Corp. (renamed Northern States Power Co. (a Minnesota corporation) on Aug. 21, 2000) (Exhibit 3.01 to Form 10-12G (file no. 000-31709) dated Oct. 5, 2000).
3.02*	By-Laws of Northern States Power Co. (a Minnesota corporation) as Amended and Restated on Sept. 26, 2013 (Exhibit 3.02 to Form 10-Q/A for the quarter ended Sept. 30, 2013 (file no. 000-31387)).
10.01*	Seventh Amendment dated May 7, 2018 to the Xcel Energy Senior Executive Severance and Change-in-Control Policy (Exhibit 10.01 to Form 10-Q of Xcel Energy for the quarter ended June 30, 2018 (file no. 001-03034)).
31.01	Principal Executive Officer’s certifications pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.
31.02	Principal Financial Officer’s certifications pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.
32.01	Certification pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.
99.01	Statement pursuant to Private Securities Litigation Reform Act of 1995.
101	The following materials from NSP-Minnesota’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2018 are formatted in XBRL (eXtensible Business Reporting Language):  (i) the Consolidated Statements of Income, (ii) the Consolidated Statements of Comprehensive Income (iii) the Consolidated Statements of Cash Flows, (iv) the Consolidated Balance Sheets, (v) Notes to Consolidated Financial Statements, and (vi) document and entity information.

36

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.

		Northern States Power Company (a Minnesota corporation)
July 27, 2018	By:	/s/ JEFFREY S. SAVAGE
		Jeffrey S. Savage
		Senior Vice President, Controller
		(Principal Accounting Officer)
		/s/ ROBERT C. FRENZEL
		Robert C. Frenzel
		Executive Vice President, Chief Financial Officer and Director
		(Principal Financial Officer)

37

EX-31.01

Exhibit 31.01

CERTIFICATION

I, Ben Fowke, certify that:

1. I have reviewed this report on Form 10-Q of Northern States Power Company (a Minnesota corporation);

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: July 27, 2018

/s/ BEN FOWKE

Ben Fowke

Chairman, Chief Executive Officer and Director

(Principal Executive Officer)

1

EX-31.02

Exhibit 31.02

CERTIFICATION

I, Robert C. Frenzel, certify that:

1. I have reviewed this report on Form 10-Q of Northern States Power Company (a Minnesota corporation);

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: July 27, 2018

/s/ ROBERT C. FRENZEL

Robert C. Frenzel

Executive Vice President, Chief Financial Officer and Director

(Principal Financial Officer)

2

EX-32.01

Exhibit 32.01

OFFICER CERTIFICATION

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 Northern States Power Company, a Minnesota corporation (NSP-Minnesota) on Form 10-Q for the quarter ended June 30, 2018, as filed with the SEC on the date hereof (Form 10-Q), each of the undersigned officers of NSP-Minnesota certifies, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that, to such officer’s knowledge:

(1) The Form 10-Q 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 Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of NSP-Minnesota as of the dates and for the periods expressed in the Form 10-Q.

Date: July 27, 2018

/s/ BEN FOWKE

Ben Fowke

Chairman, Chief Executive Officer and Director

(Principal Executive Officer)

/s/ ROBERT C. FRENZEL

Robert C. Frenzel

Executive Vice President, Chief Financial Officer and Director

(Principal Financial Officer)

The foregoing certification is being furnished solely pursuant to 18 U.S.C. Section 1350 and is not being filed as part of the Report or as a separate disclosure document.

A signed original of this written statement required by Section 906, or other document authenticating, acknowledging or otherwise adopting the signature that appears in typed form within the electronic version of this written statement required by Section 906, has been provided to NSP-Minnesota and will be retained by NSP-Minnesota and furnished to the SEC or its staff upon request.

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EX-99.01

Exhibit 99.01

NSP-Minnesota Cautionary Factors

The Private Securities Litigation Reform Act provides a “safe harbor” for forward-looking statements to encourage disclosures without the threat of litigation, providing those statements are identified as forward-looking and are accompanied by meaningful, cautionary statements identifying important factors that could cause the actual results to differ materially from those projected in the statement.  Forward-looking statements are made in written documents and oral presentations of NSP-Minnesota, Xcel Energy Inc. or any of its other subsidiaries.  These statements are based on management’s beliefs as well as assumptions and information currently available to management.  Such forward-looking statements are intended to be identified in this document by the words “anticipate,” “believe,” “estimate,” “expect,” “intend,” “may,” “objective,” “outlook,” “plan,” “project,” “possible,” “potential,” “should” and similar expressions.  In addition to any assumptions and other factors referred to specifically in connection with such forward-looking statements, factors that could cause NSP-Minnesota’s actual results to differ materially from those contemplated in any forward-looking statements include, among others, the following:

• Economic conditions, including inflation rates, monetary fluctuations and their impact on capital expenditures;

• The risk of a significant slowdown in growth or decline in the U.S. economy, the risk of delay in growth recovery in the U.S. economy or the risk of increased cost for insurance premiums, security and other items as a consequence of past or future terrorist attacks;

• Trade, monetary, fiscal, taxation and environmental policies of governments, agencies and similar organizations in geographic areas where NSP-Minnesota has a financial interest;

• Customer business conditions, including demand for their products or services and supply of labor and materials used in creating their products and services;

• Financial or regulatory accounting principles or policies imposed by the FASB, the SEC, the FERC and similar entities with regulatory oversight;

• Availability of cost or capital such as changes in: interest rates; market perceptions of the utility industry, NSP-Minnesota, Xcel Energy Inc. or any of its other subsidiaries; or security ratings;

• Factors affecting utility and nonutility operations such as unusual weather conditions; catastrophic weather-related damage; unscheduled generation outages, maintenance or repairs; unanticipated changes to fossil fuel, nuclear fuel or natural gas supply costs or availability due to higher demand, shortages, transportation problems or other developments; nuclear or environmental incidents; cyber incidents; or electric transmission or natural gas pipeline constraints;

• Employee workforce factors, including loss or retirement of key executives, collective-bargaining agreements with union employees, or work stoppages;

• Increased competition in the utility industry or additional competition in the markets served by NSP-Minnesota, Xcel Energy Inc. and its other subsidiaries;

• State, federal and foreign legislative and regulatory initiatives that affect cost and investment recovery, have an impact on rate structures and affect the speed and degree to which competition enters the electric and natural gas markets; industry restructuring initiatives; transmission system operation and/or administration initiatives; recovery of investments made under traditional regulation; nature of competitors entering the industry; retail wheeling; a new pricing structure; and former customers entering the generation market;

• Environmental laws and regulations, including legislation and regulations relating to climate change, and the associated cost of compliance;

• Rate-setting policies or procedures of regulatory entities, including environmental externalities, which are values established by regulators assigning environmental costs to each method of electricity generation when evaluating generation resource options;

• Nuclear regulatory policies and procedures, including operating regulations and spent nuclear fuel storage;

• Social attitudes regarding the utility and power industries;

• Cost and other effects of legal and administrative proceedings, settlements, investigations and claims;

• Technological developments that result in competitive disadvantages and create the potential for impairment of existing assets;

• Risks associated with implementations of new technologies; and

• Other business or investment considerations that may be disclosed from time to time in SEC filings, including “Risk Factors” in Item 1A of NSP-Minnesota’s Form 10-K for the year ended Dec. 31, 2017, or in other publicly disseminated written documents.

NSP-Minnesota undertakes no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.  The foregoing review of factors should not be construed as exhaustive.

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Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 27, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	NORTHERN STATES POWER CO
Entity Central Index Key	0001123852
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		1,000,000
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018

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CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating revenues
Electric, non-affiliates	$ 978,991	$ 960,394	$ 1,924,282	$ 1,915,735
Electric, affiliates	117,417	119,385	234,389	243,074
Natural gas	83,112	78,006	324,544	299,189
Other	8,215	7,155	15,271	14,082
Total operating revenues	1,187,735	1,164,940	2,498,486	2,472,080
Operating expenses
Electric fuel and purchased power	416,502	383,947	824,274	780,068
Cost of natural gas sold and transported	36,818	35,500	192,084	178,245
Cost of sales — other	4,655	4,594	8,836	8,772
Operating and maintenance expenses	309,196	305,189	601,491	613,815
Conservation program expenses	27,518	28,065	58,328	60,564
Depreciation and amortization	178,654	173,152	360,132	345,331
Taxes (other than income taxes)	64,285	61,445	131,830	129,769
Total operating expenses	1,037,628	991,892	2,176,975	2,116,564
Operating income	150,107	173,048	321,511	355,516
Other expense, net	(2,234)	(3,632)	(2,018)	(5,166)
Allowance for funds used during construction — equity	6,903	6,425	13,651	12,708
Interest charges and financing costs
Interest charges — includes other financing costs of $1,833 $1,806, $3,648 and $3,592, respectively	56,767	57,707	114,119	114,971
Allowance for funds used during construction — debt	(3,352)	(3,298)	(6,787)	(6,526)
Total interest charges and financing costs	53,415	54,409	107,332	108,445
Income before income taxes	101,361	121,432	225,812	254,613
Income taxes	8,974	33,770	21,685	72,785
Net income	$ 92,387	$ 87,662	$ 204,127	$ 181,828

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CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest charges and financing costs
Other financing costs	$ 1,833	$ 1,806	$ 3,648	$ 3,592

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CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Comprehensive income:
Net income	$ 92,387	$ 87,662	$ 204,127	$ 181,828
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, net of tax of $22, $22, $45 and $47, respectively	54	36	107	71
Derivative instruments:
Net fair value decrease, net of tax of $9, $17, $11 and $17, respectively	22	26	27	26
Reclassification of losses to net income, net of tax of $64, $141, $129 and $280, respectively	165	204	332	407
Total derivative instruments, net of tax	187	230	359	433
Marketable securities:
Reclassification of gains to net income, net of tax of $0, $0, $(51) and $0, respectively	0	0	(128)	0
Other comprehensive income	241	266	338	504
Comprehensive income	$ 92,628	$ 87,928	$ 204,465	$ 182,332

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CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, tax	$ 22	$ 22	$ 45	$ 47
Derivative instruments:
Net fair value (decrease) increase, tax	9	17	11	17
Reclassification of losses to net income, tax	64	141	129	280
Other Comprehensive Income (Loss), Available-for-sale Securities, Tax [Abstract]
Reclassification of gains to net income, tax	$ 0	$ 0	$ (51)	$ 0

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CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities
Net income	$ 204,127	$ 181,828
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	363,310	348,442
Nuclear fuel amortization	62,294	57,003
Deferred income taxes	41,204	90,927
Amortization of Investment Tax Credits	(817)	(827)
Allowance for equity funds used during construction	(13,651)	(12,708)
Net realized and unrealized hedging and derivative transactions	(1,497)	(2,973)
Other, net	(998)	(946)
Changes in operating assets and liabilities:
Accounts receivable	(16,025)	(23,008)
Accrued unbilled revenues	31,354	45,497
Inventories	44,093	18,901
Other current assets	59,683	(56,145)
Accounts payable	(31,673)	(17,828)
Net regulatory assets and liabilities	43,782	2,613
Other current liabilities	(105,681)	(94,500)
Pension and other employee benefit obligations	(59,371)	(57,698)
Change in other noncurrent assets	1,224	(2,505)
Change in other noncurrent liabilities	(17,885)	(11,878)
Net cash provided by operating activities	603,473	464,195
Investing activities
Utility capital/construction expenditures	(439,868)	(484,172)
Allowance for equity funds used during construction	13,651	12,708
Purchases of investment securities	(367,159)	(361,881)
Proceeds from the sale of investment securities	356,973	350,446
Investments in utility money pool arrangement	(627,000)	(192,000)
Repayments from utility money pool arrangement	627,000	192,000
Other, net	(2,065)	(4,097)
Net cash used in investing activities	(438,468)	(486,996)
Financing activities
Repayments of short-term borrowings, net	(20,000)	(2,000)
Borrowings under utility money pool arrangement	131,000	465,000
Repayments under utility money pool arrangement	(154,000)	(374,000)
Repayments of long-term debt	(9)	0
Capital contributions from parent	49,622	89,487
Dividends paid to parent	(183,245)	(175,115)
Other	(68)	0
Net cash (used in) provided by financing activities	(176,700)	3,372
Net change in cash and cash equivalents	(11,695)	(19,429)
Cash and cash equivalents at beginning of period	43,781	47,595
Cash and cash equivalents at end of period	32,086	28,166
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(101,005)	(104,020)
Cash received (paid) for income taxes, net	64,212	(33,014)
Supplemental disclosure of non-cash investing transactions:
Property, plant and equipment additions in accounts payable	$ 50,370	$ 60,361

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CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 32,086	$ 43,781
Accounts receivable, net	361,144	345,110
Accounts receivable from affiliates	19,462	48,494
Accrued unbilled revenues	246,362	277,716
Inventories	294,602	337,712
Regulatory assets	300,150	276,392
Derivative instruments	31,268	25,230
Prepaid Taxes	41,763	79,145
Prepayments and other	36,717	43,682
Total current assets	1,363,554	1,477,262
Property, plant and equipment, net	13,075,676	13,033,612
Other assets
Nuclear decommissioning fund and other investments	2,195,458	2,192,344
Regulatory assets	1,343,820	1,190,429
Derivative instruments	26,790	28,102
Other	11,936	4,142
Total other assets	3,578,004	3,415,017
Total assets	18,017,234	17,925,891
Current liabilities
Current portion of long-term debt	8	7
Short-term debt	0	20,000
Borrowings under utility money pool arrangement	62,000	85,000
Accounts payable	348,475	368,342
Accounts payable to affiliates	53,790	80,070
Regulatory liabilities	135,725	83,403
Taxes accrued	193,465	229,335
Accrued interest	67,765	65,896
Dividends payable to parent	88,714	98,687
Derivative instruments	18,029	17,697
Customer deposits	66,764	95,369
Other	153,256	152,965
Total current liabilities	1,187,991	1,296,771
Deferred credits and other liabilities
Deferred income taxes	1,655,863	1,612,341
Deferred investment tax credits	21,710	22,528
Regulatory liabilities	2,013,411	1,978,527
Asset retirement obligations	2,134,741	2,083,874
Derivative instruments	92,122	102,742
Pension and employee benefit obligations	271,228	331,087
Other	178,347	89,440
Total deferred credits and other liabilities	6,367,422	6,220,539
Commitments and contingencies
Capitalization
Long-term debt	4,935,060	4,933,011
Common stock — authorized 5,000,000 shares of $0.01 par value; 1,000,000 shares outstanding at June 30, 2018 and Dec. 31, 2017, respectively	10	10
Additional paid in capital	3,600,234	3,580,234
Retained earnings	1,950,716	1,919,863
Accumulated other comprehensive loss	(24,199)	(24,537)
Total common stockholder’s equity	5,526,761	5,475,570
Total liabilities and equity	$ 18,017,234	$ 17,925,891

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CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Capitalization
Common stock, shares authorized (in shares)	5,000,000	5,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares outstanding (in shares)	1,000,000	1,000,000

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Management's Opinion

6 Months Ended

Jun. 30, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Management's Opinion

In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly, in accordance with accounting principles generally accepted in the United States of America (GAAP), the financial position of NSP-Minnesota and its subsidiaries as of June 30, 2018 and Dec. 31, 2017; the results of its operations, including the components of net income and comprehensive income, for the three and six months ended June 30, 2018 and 2017; and its cash flows for the six months endedJune 30, 2018 and 2017. All adjustments are of a normal, recurring nature, except as otherwise disclosed. Management has also evaluated the impact of events occurring after June 30, 2018 up to the date of issuance of these consolidated financial statements. These statements contain all necessary adjustments and disclosures resulting from that evaluation. The Dec. 31, 2017 balance sheet information has been derived from the audited 2017 consolidated financial statements included in the NSP-Minnesota Annual Report on Form 10-K for the year ended Dec. 31, 2017. These notes to the consolidated financial statements have been prepared pursuant to the rules and regulations of the SEC for Quarterly Reports on Form 10-Q. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP on an annual basis have been condensed or omitted pursuant to such rules and regulations. For further information, refer to the consolidated financial statements and notes thereto, included in the NSP-Minnesota Annual Report on Form 10-K for the year ended Dec. 31, 2017, filed with the SEC on Feb. 26, 2018. Due to the seasonality of NSP-Minnesota’s electric and natural gas sales, interim results are not necessarily an appropriate base from which to project annual results.

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Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

The significant accounting policies set forth in Note 1 to the consolidated financial statements in the NSP-Minnesota Annual Report on Form 10-K for the year ended Dec. 31, 2017, appropriately represent, in all material respects, the current status of accounting policies and are incorporated herein by reference.

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Accounting Pronouncements

6 Months Ended

Jun. 30, 2017

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Accounting Pronouncements

Accounting Pronouncements

Recently Issued

Leases —In February 2016, the Financial Accounting Standards Board (FASB) issued Leases, Topic 842 (Accounting Standards Update (ASU) No. 2016-02), which for lessees requires balance sheet recognition of right-of-use assets and lease liabilities for most leases. This guidance will be effective for interim and annual reporting periods beginning after Dec. 15, 2018. NSP-Minnesota has not yet fully determined the impacts of implementation. However, adoption is expected to occur on Jan. 1, 2019 utilizing the practical expedients provided by the standard and proposed in Targeted Improvements, Topic 842 (Proposed ASU 2018-200). On Jan. 1, 2019 agreements considered leases for the use of office space, equipment and natural gas storage assets, as well as certain purchased power agreements (PPAs) for fossil-fueled generating facilities are expected to be recognized on the consolidated balance sheet.

Recently Adopted

Revenue Recognition— In May 2014, the FASB issued Revenue from Contracts with Customers, Topic 606 (ASU No. 2014-09), which provides a new framework for the recognition of revenue. NSP-Minnesota implemented the guidance on a modified retrospective basis on Jan. 1, 2018. Results for reporting periods beginning after Dec. 31, 2017 are presented in accordance with Topic 606, while prior period results have not been adjusted and continue to be reported in accordance with prior accounting guidance. Other than increased disclosures regarding revenues related to contracts with customers, the implementation did not have a significant impact on NSP-Minnesota’s consolidated financial statements. For related disclosures, see Note 13 to the consolidated financial statements.

Classification and Measurement of Financial Instruments — In January 2016, the FASB issued Recognition and Measurement of Financial Assets and Financial Liabilities, Subtopic 825-10 (ASU No. 2016-01), which eliminated the available-for-sale classification for marketable equity securities and also replaced the cost method of accounting for non-marketable equity securities with a model for recognizing impairments and observable price changes. Under the new standard, other than when the consolidation or equity method of accounting is utilized, changes in the fair value of equity securities are recognized in earnings. NSP-Minnesota implemented the guidance on Jan. 1, 2018. As a result of application of accounting principles for rate regulated entities, changes in the fair value of the securities in the nuclear decommissioning fund, historically classified as available-for-sale, continue to be deferred to a regulatory asset, and the overall adoption impacts were not material.

Presentation of Net Periodic Benefit Cost —In March 2017, the FASB issued Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost, Topic 715 (ASU No. 2017-07), which establishes that only the service cost element of pension cost may be presented as a component of operating income in the income statement. Also under the guidance, only the service cost component of pension cost is eligible for capitalization. As a result of the application of accounting principles for rate regulated entities, a similar amount of pension cost, including non-service components, will be recognized consistent with the historical ratemaking treatment, and the impacts of adoption will be limited to changes in classification of non-service costs in the consolidated statement of income. NSP-Minnesota implemented the new guidance on Jan. 1, 2018, and as a result, $6.8 million of pension costs were retrospectively reclassified from operating and maintenance expenses to other income, net on the consolidated income statement for the six months ended June 30, 2017. Under a practical expedient permitted by the standard, NSP-Minnesota used benefit cost amounts disclosed for prior periods as the basis for retrospective application.

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Selected Balance Sheet Data

6 Months Ended

Jun. 30, 2018

Balance Sheet Related Disclosures [Abstract]

Selected Balance Sheet Data

Selected Balance Sheet Data

(Thousands of Dollars)	June 30, 2018			Dec. 31, 2017
Accounts receivable, net
Accounts receivable	$	380,606		$	366,388
Less allowance for bad debts	(19,462		)	(21,278		)
	$	361,144		$	345,110

(Thousands of Dollars)	June 30, 2018		Dec. 31, 2017
Inventories
Materials and supplies	$	208,596	$	209,236
Fuel	73,737		94,483
Natural gas	12,269		33,993
	$	294,602	$	337,712

(Thousands of Dollars)	June 30, 2018			Dec. 31, 2017
Property, plant and equipment, net
Electric plant	$	17,276,273		$	17,024,925
Natural gas plant	1,407,523			1,370,330
Common and other property	719,069			724,066
Construction work in progress	528,079			530,126
Total property, plant and equipment	19,930,944			19,649,447
Less accumulated depreciation	(7,210,566		)	(7,018,249		)
Nuclear fuel	2,712,590			2,697,412
Less accumulated amortization	(2,357,292		)	(2,294,998		)
	$	13,075,676		$	13,033,612

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Income Taxes

6 Months Ended

Jun. 30, 2018

Income Tax Disclosure [Abstract]

Income Taxes

Income Taxes

Except to the extent noted below, Note 6 to the consolidated financial statements included in NSP-Minnesota’s Annual Report on Form 10-K for the year ended Dec. 31, 2017 appropriately represents, in all material respects, the current status of other income tax matters, and are incorporated herein by reference.

Total income tax expense from operations differs from the amount computed by applying the statutory federal income tax rate to income before income tax expense. The following reconciles such differences:

	Six Months Ended June 30
	2018		2017
Federal statutory rate	21.0	%	35.0	%
State tax, net of federal tax effect	7.1		5.8
Increases (decreases) in tax from:
Wind production tax credits (PTCs)	(17.1	)	(11.4	)
Regulatory differences - ARAM (a)	(8.5	)	(0.2	)
Regulatory differences - ARAM deferral (b)	7.9		—
Other tax credits, net of federal income tax expense	(1.5	)	(1.0	)
Other, net	0.7		0.4
Effective income tax rate	9.6	%	28.6	%

^(a)   The average rate assumption method (ARAM); a method to flow back excess deferred taxes to customers.

^(b) As we receive direction from our regulatory commissions regarding the return of excess deferred taxes (to our customers resulting from the Tax Cuts and Jobs Act

(TCJA)), the ARAM deferral may decrease during the year, which would result in a reduction to tax expense with a corresponding reduction to revenue.

Federal Audits — NSP-Minnesota is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. The statute of limitations applicable to Xcel Energy’s federal income tax returns expire as follows:

Tax Year(s)	Expiration
2009 - 2011	December 2018
2012 - 2014	October 2019
2015	September 2019
2016	September 2020

In 2012, the Internal Revenue Service (IRS) commenced an examination of tax years 2010 and 2011, including the 2009 carryback claim. The IRS proposed an adjustment to the federal tax loss carryback claims and in 2015 the IRS forwarded the issue to the Office of Appeals (Appeals). In 2017 Xcel Energy and Appeals reached an agreement and the benefit related to the agreed upon portions was recognized. In the second quarter of 2018, the Joint Committee on Taxation completed its review and took no exception to the agreement. As a result, the remaining unrecognized tax benefit was released and recorded as a payable to the IRS.

In the third quarter of 2015, the IRS commenced an examination of tax years 2012 and 2013. In the third quarter of 2017, the IRS concluded the audit of tax years 2012 and 2013 and proposed an adjustment that would impact Xcel Energy’s net operating loss (NOL) and effective tax rate (ETR). After evaluating the proposed adjustment Xcel Energy filed a protest with the IRS. As of June 30, 2018 the case has been forwarded to Appeals and Xcel Energy has recognized its best estimate of income tax expense that will result from a final resolution of this issue; however, the outcome and timing of a resolution is unknown.

State Audits — NSP-Minnesota is a member of the Xcel Energy affiliated group that files consolidated state income tax returns. As of June 30, 2018, NSP-Minnesota’s earliest open tax year that is subject to examination by state taxing authorities under applicable statutes of limitations is 2009. In 2016, the state of Minnesota began an audit of years 2010 through 2014. As of June 30, 2018, Minnesota had not proposed any material adjustments.

Unrecognized Benefits — The unrecognized tax benefit balance includes permanent tax positions, which if recognized would affect the annual ETR. In addition, the unrecognized tax benefit balance includes temporary tax positions for which the ultimate deductibility is highly certain but for which there is uncertainty about the timing of such deductibility. A change in the period of deductibility would not affect the ETR but would accelerate the payment of cash to the taxing authority to an earlier period.

A reconciliation of the amount of unrecognized tax benefit is as follows:

(Millions of Dollars)	June 30, 2018		Dec. 31, 2017
Unrecognized tax benefit — Permanent tax positions	$	10.2	$	10.2
Unrecognized tax benefit — Temporary tax positions	5.5		7.9
Total unrecognized tax benefit	$	15.7	$	18.1

The unrecognized tax benefit amounts were reduced by the tax benefits associated with NOL and tax credit carryforwards. The amounts of tax benefits associated with NOL and tax credit carryforwards are as follows:

(Millions of Dollars)	June 30, 2018			Dec. 31, 2017
NOL and tax credit carryforwards	$	(15.0	)	$	(12.8	)

It is reasonably possible that NSP-Minnesota’s amount of unrecognized tax benefits could significantly change in the next 12 months as the IRS Appeals progresses and audit resumes, the Minnesota audit progresses, and other state audits resume. As the IRS Appeals and Minnesota audit progress and the IRS audit resumes, it is reasonably possible that the amount of unrecognized tax benefit could decrease up to approximately $13 million.

The payable for interest related to unrecognized tax benefits is partially offset by the interest benefit associated with NOL and tax credit carryforwards. A reconciliation of the beginning and ending amount of the payable for interest related to unrecognized tax benefits are as follows:

(Millions of Dollars)	June 30, 2018			Dec. 31, 2017
Payable for interest related to unrecognized tax benefits at beginning of period	$	(0.9	)	$	(2.0	)
Interest (expense) income related to unrecognized tax benefits recorded during the period	(1.0		)	1.1
Payable for interest related to unrecognized tax benefits at end of period	$	(1.9	)	$	(0.9	)

No amounts were accrued for penalties related to unrecognized tax benefits as of June 30, 2018 or Dec. 31, 2017.

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Rate Matters

6 Months Ended

Jun. 30, 2018

Public Utilities, General Disclosures [Abstract]

Rate Matters

Rate Matters

Except to the extent noted below, the circumstances set forth in Note 10 to the consolidated financial statements included in NSP-Minnesota’s Annual Report on Form 10-K for the year ended Dec. 31, 2017 and in Note 5 to the consolidated financial statements to NSP-Minnesota’s Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018, appropriately represent, in all material respects, the current status of other rate matters, and are incorporated herein by reference.

Tax Reform — Regulatory Proceedings

The specific impacts of the TCJA on customer rates are subject to regulatory approval. Each of the states in NSP-Minnesota’s service areas have opened dockets to address the impacts of the TCJA.

In April 2018, NSP-Minnesota updated the estimated impact of the TCJA, which reflected an overall reduction in 2018 revenue requirements of approximately $136 million for electric and $7 million for natural gas, and made recommendations regarding the sharing of those benefits with ratepayers. The proposed electric options included: customer refunds and rider impacts of $68 million, deferral of $44 million to allow for a rate case stay-out for 2020, acceleration of depreciation for the King coal plant of $22 million and low income program funding of $2 million. The proposed natural gas options included customer refunds and rider impacts of $3 million, with the remaining TCJA benefits deferred to mitigate increased costs in the next natural gas rate case.

In June 2018, the Minnesota Department of Commerce (DOC) recommended to implement refunds for the current tax impacts (approximately $90 million), and incorporate the deferred tax impacts (approximately $53 million) in NSP-Minnesota’s next electric and gas rate cases. A decision from the Minnesota Public Utilities Commission (MPUC) is expected in 2018.

North and South Dakota — In February 2018, NSP-Minnesota proposed using the reduced revenue requirements from the TCJA to defer planned future rate filings in North Dakota and South Dakota. In July 2018, the South Dakota Public Utilities Commission (SDPUC) approved a settlement which proposed a one-time customer refund of $11 million for the 2018 impact of the TCJA and a 2-year rate case moratorium.

Dockets have also been opened in North Dakota and South Dakota. In February 2018, NSP-Minnesota proposed using the reduced revenue requirements from the TCJA to defer planned future rate filings in both jurisdictions.

Recently Concluded Regulatory Proceedings — MPUC and the North Dakota Public Service Commission (NDPSC)

PPA Terminations and Amendments — In June 2018, NSP-Minnesota executed the terminations of the Benson and Laurentian PPAs, and purchased the Benson biomass facility. As a result, a $103 million regulatory asset was recognized for the costs of the Benson transaction, including payments to Benson of $93 million, as well as other transaction costs and future estimated facility removal costs. For Laurentian, a regulatory asset of $109 million was recognized for annual termination payments over 6 years. The regulatory approvals provide for recovery of the Benson regulatory asset over approximately 10 years, and for recovery of the Laurentian termination payments as they occur, through fuel and purchased energy recovery mechanisms.

Pending Regulatory Proceeding — Federal Energy Regulatory Commission (FERC)

Midcontinent Independent System Operator, Inc. (MISO) Return on Equity (ROE) Complaints — In November 2013, a group of customers filed a complaint at the FERC against MISO transmission owners (TOs), including NSP-Minnesota and NSP-Wisconsin. The complaint argued for a reduction in the ROE in transmission formula rates in the MISO region from 12.38 percent to 9.15 percent, and the removal of ROE adders (including those for Regional Transmission Organization (RTO) membership), effective Nov. 12, 2013.

In September 2016, the FERC approved an Administrative Law Judge (ALJ) recommendation that MISO TOs be granted a 10.32 percent base ROE using the methodology adopted by FERC in June 2014 (Opinion 531). This ROE would be applicable for the 15-month refund period from Nov. 12, 2013 to Feb. 11, 2015, and prospectively from the date of the FERC order. The total prospective ROE would be 10.82 percent, including a 50 basis point adder for RTO membership. The requests are pending FERC action.

In February 2015, a second complaint seeking to reduce the MISO ROE from 12.38 percent to 8.67 percent prior to any RTO adder was filed, resulting in a second period of potential refunds from Feb. 12, 2015 to May 11, 2016. In June 2016, an ALJ recommended a base ROE of 9.7 percent, applying the FERC Opinion 531 methodology. FERC action is pending. In April 2017, the United States Court of Appeals for the District of Columbia Circuit (D.C. Circuit) vacated and remanded Opinion 531. It is unclear how the D.C. Circuit’s opinion to vacate and remand Opinion 531 will affect the September 2016 FERC order or the timing and outcome of the second ROE complaint.

NSP-Minnesota has recognized a current refund liability consistent with the best estimate of the final ROE.

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Commitments and Contingencies

6 Months Ended

Jun. 30, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

6. Commitments and Contingencies

Except to the extent noted below and in Note 5 to the consolidated financial statements, the circumstances set forth in Notes 10, 11 and 12 to the consolidated financial statements included in the NSP-Minnesota Annual Report on Form 10-K for the year ended Dec. 31, 2017 and in Notes 5 and 6 to NSP-Minnesota’s Quarterly Report of Form 10-Q for the quarterly period ended March 31, 2018, appropriately represent, in all material respects, the current status of commitments and contingent liabilities and are incorporated herein by reference. The following include commitments, contingencies and unresolved contingencies that are material to NSP-Minnesota’s financial position.

PPAs

NSP-Minnesota purchases power from independent power producing entities for which NSP-Minnesota is required to reimburse natural gas or biomass fuel costs, or to participate in tolling arrangements under which NSP-Minnesota procures the natural gas required to produce the energy that it purchases. These specific PPAs create a variable interest in the associated independent power producing entity.

NSP-Minnesota had approximately 1,002 Megawatts (MW) of capacity under long-term PPAs as of June 30, 2018 and 1,069 MW as of Dec. 31, 2017, with entities that have been determined to be variable interest entities. NSP-Minnesota has concluded that these entities are not required to be consolidated in its consolidated financial statements because it does not have the power to direct the activities that most significantly impact the entities’ economic performance. These agreements have various expiration dates through 2027.

Guarantees

Under NSP-Minnesota’s railcar lease agreement, accounted for as an operating lease, NSP-Minnesota guarantees the lessor proceeds from sale of the leased assets at the end of the lease term will at least equal the guaranteed residual value. The guarantee issued by NSP-Minnesota has a stated maximum amount; however, NSP-Minnesota expects sale proceeds to exceed the guaranteed amount. This agreement expires in 2019.

The following table presents the guarantee issued and outstanding for NSP-Minnesota:

(Millions of Dollars)	June 30, 2018		Dec. 31, 2017
Guarantee issued and outstanding	$	4.8	$	4.8

Environmental Loss Contingency Disclosure [Text Block]

Environmental Contingencies

Fargo, N.D. Manufactured Gas Plant (MGP) Site — In May 2015, underground pipes, tars and impacted soils were discovered in a right-of-way in Fargo, N.D. that appeared to be associated with a former MGP operated by NSP-Minnesota or prior companies. NSP-Minnesota removed impacted soils and other materials and commenced an investigation of the historic MGP and adjacent properties (the Fargo MGP Site). The North Dakota Department of Health approved NSP-Minnesota’s proposed cleanup plan in January 2017, which involves targeted source removal of impacted soils and historic MGP infrastructure. Remediation activities commenced in June 2018. NSP-Minnesota has also initiated insurance recovery litigation in North Dakota. The U.S. District Court for the District of North Dakota has set a trial date for Spring of 2020.

NSP-Minnesota recorded an estimated liability of $10 million as of June 30, 2018 and $16 million as of Dec. 31, 2017, for the Fargo MGP Site. The current cost estimate for the remediation of the site is approximately $22 million, of which approximately $12 million has been spent. NSP-Minnesota has deferred Fargo MGP Site costs allocable to the North Dakota jurisdiction, or approximately 88 percent of all remediation costs, as approved by the NDPSC. In December 2017, NSP-Minnesota filed a request with the MPUC to defer post-2017 MGP remediation expenditures allocable to the Minnesota jurisdiction, including the Fargo MGP Site. In March 2018, the DOC recommended that the MPUC deny NSP-Minnesota’s deferral request. A MPUC decision is expected in the third quarter of 2018.

Other MGP, Landfill or Disposal Sites — NSP-Minnesota is currently involved in investigating and/or remediating several MGP, landfill or other disposal sites. NSP-Minnesota has identified five sites, in addition to the Fargo MGP Site, where contamination is present and where investigation and/or remediation activities are currently underway. Other parties may have responsibility for some portion of the investigation and/or remediation activities. NSP-Minnesota anticipates that these investigation or remediation activities will continue through at least 2018. NSP-Minnesota accrued $3 million as of June 30, 2018 and Dec. 31, 2017 for all of these sites. There may be insurance recovery and/or recovery from other PRPs that will offset any costs incurred. Xcel Energy anticipates that any amounts spent will be fully recovered from customers.

Legal Matters and Contingencies

Legal Contingencies

NSP-Minnesota is involved in various litigation matters that are being defended and handled in the ordinary course of business. The assessment of whether a loss is probable or is a reasonable possibility, and whether the loss or a range of loss is estimable, often involves a series of complex judgments about future events. Management maintains accruals for such losses that are probable of being incurred and subject to reasonable estimation. Management is sometimes unable to estimate an amount or range of a reasonably possible loss in certain situations, including but not limited to when (1) the damages sought are indeterminate, (2) the proceedings are in the early stages, or (3) the matters involve novel or unsettled legal theories. In such cases, there is considerable uncertainty regarding the timing or ultimate resolution of such matters, including a possible eventual loss. For current proceedings not specifically reported herein, management does not anticipate that the ultimate liabilities, if any, arising from such current proceedings would have a material effect on NSP-Minnesota’s financial statements. Unless otherwise required by GAAP, legal fees are expensed as incurred.

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Borrowings and Other Financing Instruments

6 Months Ended

Jun. 30, 2018

Debt Disclosure [Abstract]

Borrowings and Other Financing Instruments

Borrowings and Other Financing Instruments

Short-Term Borrowings

Money Pool — Xcel Energy Inc. and its utility subsidiaries have established a money pool arrangement that allows for short-term investments in and borrowings between the utility subsidiaries. Xcel Energy Inc. may make investments in the utility subsidiaries at market-based interest rates; however, the money pool arrangement does not allow the utility subsidiaries to make investments in Xcel Energy Inc. Money pool borrowings for NSP-Minnesota were as follows:

(Amounts in Millions, Except Interest Rates)	Three Months Ended June 30, 2018			Year Ended Dec. 31, 2017
Borrowing limit	$	250		$	250
Amount outstanding at period end	62			85
Average amount outstanding	1			25
Maximum amount outstanding	62			142
Weighted average interest rate, computed on a daily basis	1.85		%	1.14		%
Weighted average interest rate at period end	1.85			1.18

Commercial Paper — NSP-Minnesota meets its short-term liquidity requirements primarily through the issuance of commercial paper and borrowings under its credit facility and the money pool. Commercial paper outstanding for NSP-Minnesota was as follows:

(Amounts in Millions, Except Interest Rates)	Three Months Ended June 30, 2018		Year Ended Dec. 31, 2017
Borrowing limit	$	500	$	500
Amount outstanding at period end	—		20
Average amount outstanding	—		62
Maximum amount outstanding	—		237
Weighted average interest rate, computed on a daily basis	N/A		1.10		%
Weighted average interest rate at period end	N/A		1.93

Letters of Credit — NSP-Minnesota uses letters of credit, generally with terms of one year, to provide financial guarantees for certain operating obligations. At June 30, 2018 and Dec. 31, 2017, there were $36 million and $24 million, respectively, of letters of credit outstanding under the credit facility. The contract amounts of these letters of credit approximate their fair value and are subject to fees.

Credit Facility — In order to use its commercial paper program to fulfill short-term funding needs, NSP-Minnesota must have a revolving credit facility in place at least equal to the amount of its commercial paper borrowing limit and cannot issue commercial paper in an amount exceeding available capacity under this credit facility. The line of credit provides short-term financing in the form of notes payable to banks, letters of credit and back-up support for commercial paper borrowings.

At June 30, 2018, NSP-Minnesota had the following committed credit facility available (in millions of dollars):

Credit Facility (a)		Drawn(b)		Available
$	500	$	36	$	464

^(a)  This credit facility expires in June 2021.

^(b)  Includes outstanding letters of credit.

All credit facility bank borrowings, outstanding letters of credit and outstanding commercial paper reduce the available capacity under the credit facility. NSP-Minnesota had no direct advances on the credit facility outstanding at June 30, 2018 and Dec. 31, 2017.

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Fair Value of Financial Assets and Liabilities

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets and Liabilities

Fair Value of Financial Assets and Liabilities

Fair Value Measurements

The accounting guidance for fair value measurements and disclosuresprovides a single definition of fair value and requires certain disclosures about assets and liabilities measured at fair value. A hierarchical framework for disclosing the observability of the inputs utilized in measuring assets and liabilities at fair value is established by this guidance. The three levels in the hierarchy are as follows:

Level 1 — Quoted prices are available in active markets for identical assets or liabilities as of the reporting date. The types of assets and liabilities included in Level 1 are highly liquid and actively traded instruments with quoted prices.

Level 2 — Pricing inputs are other than quoted prices in active markets, but are either directly or indirectly observable as of the reporting date. The types of assets and liabilities included in Level 2 are typically either comparable to actively traded securities or contracts, or priced with models using highly observable inputs.

Level 3 — Significant inputs to pricing have little or no observability as of the reporting date. The types of assets and liabilities included in Level 3 are those valued with models requiring significant management judgment or estimation.

Specific valuation methods include the following:

Cash equivalents— The fair values of cash equivalents are generally based on cost plus accrued interest; money market funds are measured using quoted net asset value (NAV).

Investments in equity securities and other funds— Equity securities are valued using quoted prices in active markets. The fair values for commingled funds are measured using NAVs, which take into consideration the value of underlying fund investments, as well as the other accrued assets and liabilities of a fund, in order to determine a per-share market value. The investments in commingled funds may be redeemed for NAV with proper notice. Proper notice varies by fund and can range from daily with one or two days notice to annually with 90 days notice. Private equity investments require approval of the fund for any unscheduled redemption, and such redemptions may be approved or denied by the fund at its sole discretion. Unscheduled distributions from real estate investments may be redeemed with proper notice, which is typically quarterly with 45-90 days notice; however, withdrawals from real estate investments may be delayed or discounted as a result of fund illiquidity.

Investments in debt securities— Fair values for debt securities are determined by a third party pricing service using recent trades and observable spreads from benchmark interest rates for similar securities.

Interest rate derivatives— The fair values of interest rate derivatives are based on broker quotes that utilize current market interest rate forecasts.

Commodity derivatives— The methods used to measure the fair value of commodity derivative forwards and options utilize forward prices and volatilities, as well as pricing adjustments for specific delivery locations, and are generally assigned a Level 2 classification. When contractual settlements extend to periods beyond those readily observable on active exchanges or quoted by brokers, the significance of the use of less observable forecasts of long-term forward prices and volatilities on a valuation is evaluated, and may result in Level 3 classification.

Electric commodity derivatives held by NSP-Minnesota include transmission congestion instruments, generally referred to as financial transmission rights (FTRs), purchased from MISO. FTRs purchased from a RTO are financial instruments that entitle or obligate the holder to monthly revenues or charges based on transmission congestion across a given transmission path. The value of an FTR is derived from, and designed to offset, the cost of transmission congestion. In addition to overall transmission load, congestion is also influenced by the operating schedules of power plants and the consumption of electricity pertinent to a given transmission path. Unplanned plant outages, scheduled plant maintenance, changes in the relative costs of fuels used in generation, weather and overall changes in demand for electricity can each impact the operating schedules of the power plants on the transmission grid and the value of an FTR. NSP-Minnesota’s valuation process for FTRs utilizes the cleared prices for each FTR for the most recent auction.

If forecasted costs of electric transmission congestion increase or decrease for a given FTR path, the value of that particular FTR instrument will likewise increase or decrease. Given the limited transparency in the auction process, fair value measurements for FTRs have been assigned a Level 3. Non-trading monthly FTR settlements are included in fuel and purchased energy cost recovery mechanisms, and therefore changes in the fair value of the yet to be settled portions of most FTRs are deferred as a regulatory asset or liability. Given this regulatory treatment and the limited magnitude of NSP-Minnesota’s FTRs, the limited transparency associated with the valuation of FTRs are insignificant to the consolidated financial statements of NSP-Minnesota.

Non-Derivative Instruments Fair Value Measurements

Nuclear Decommissioning Fund

The Nuclear Regulatory Commission requires NSP-Minnesota to maintain a portfolio of investments to fund the costs of decommissioning its nuclear generating plants. Together with all accumulated earnings or losses, the assets of the nuclear decommissioning fund are legally restricted for the decommissioning the Monticello and Prairie Island (PI) nuclear generating plants. The fund contains cash equivalents, debt securities, equity securities and other investments. NSP-Minnesota plans to reinvest matured securities until decommissioning begins. NSP-Minnesota uses the asset class target allocations approved by the MPUC for the qualified trust.

NSP-Minnesota recognizes the costs of funding the decommissioning of its nuclear generating plants over the lives of the plants, assuming rate recovery of all costs. Given the purpose and legal restrictions on the use of nuclear decommissioning fund assets, realized and unrealized gains on fund investments over the life of the fund are deferred as an offset of NSP-Minnesota’s regulatory asset for nuclear decommissioning costs. Consequently, any realized and unrealized gains and losses on securities in the nuclear decommissioning fund, including any impairments, are deferred as a component of the regulatory asset for nuclear decommissioning.

Unrealized gains for the nuclear decommissioning fund were $547 million and $560 million as of June 30, 2018 and Dec. 31, 2017, respectively, and unrealized losses and amounts recorded as other-than-temporary impairments were $23 million and $7 million as of June 30, 2018 and Dec. 31, 2017, respectively.

The following tables present the cost and fair value of NSP-Minnesota’s non-derivative instruments with recurring fair value measurements in the nuclear decommissioning fund as of June 30, 2018 and Dec. 31, 2017:

	June 30, 2018
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Investments Measured at NAV (b)		Total
Nuclear decommissioning fund (a)
Cash equivalents	$	30,868	$	30,868	$	—	$	—	$	—	$	30,868
Commingled funds:
Non U.S. equities	262,468		197,545		—		—		90,402		287,947
Emerging market debt funds	158,296		—		—		—		158,075		158,075
Private equity investments	150,565		—		—		—		220,460		220,460
Real estate	128,115		—		—		—		197,032		197,032
Debt securities:
Government securities	75,806		—		75,477		—		—		75,477
U.S. corporate bonds	330,170		—		322,689		—		—		322,689
Non U.S. corporate bonds	57,902		—		56,422		—		—		56,422
Equity securities:
U.S. equities	269,483		568,134		—		—		—		568,134
Non U.S. equities	156,756		227,226		—		—		—		227,226
Total	$	1,620,429	$	1,023,773	$	454,588	$	—	$	665,969	$	2,144,330

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $51 million of rabbi trust assets and miscellaneous investments.

^(b)  Due to limited availability of published pricing and a lack of immediate redeemability, certain fund investments measured at NAV are not required to be categorized within the fair value hierarchy.

	Dec. 31, 2017
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Investments Measured at NAV (b)		Total
Nuclear decommissioning fund (a)
Cash equivalents	$	28,741	$	28,741	$	—	$	—	$	—	$	28,741
Commingled funds:
Non U.S. equities	263,694		216,551		—		—		89,857		306,408
Emerging market debt funds	156,057		—		—		—		166,375		166,375
Private equity investments	141,413		—		—		—		198,037		198,037
Real estate	130,787		—		—		—		201,842		201,842
Other commingled funds	9,340		6,286		—		—		2,975		9,261
Debt securities:
Government securities	67,760		—		69,413		—		—		69,413
U.S. corporate bonds	319,809		—		322,129		—		—		322,129
Non U.S. corporate bonds	50,121		—		50,102		—		—		50,102
Equity securities:
U.S. equities	271,166		556,974		—		—		—		556,974
Non U.S. equities	151,961		233,999		—		—		—		233,999
Total	$	1,590,849	$	1,042,551	$	441,644	$	—	$	659,086	$	2,143,281

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $49 million of rabbi trust assets and miscellaneous investments.

^(b)  Due to limited availability of published pricing and a lack of immediate redeemability, certain fund investments measured at NAV are not required to be categorized within the fair value hierarchy.

For the three and six months ended June 30, 2018 and 2017 there were no Level 3 nuclear decommissioning fund investments and no transfers of amounts between levels.

The following table summarizes the final contractual maturity dates of the debt securities in the nuclear decommissioning fund, by asset class, as of June 30, 2018:

	Final Contractual Maturity
(Thousands of Dollars)	Due in 1Year or Less		Due in 1 to 5 Years		Due in 5 to 10 Years		Due after 10 Years		Total
Government securities	$	—	$	3,930	$	2,300	$	69,247	$	75,477
U.S. corporate bonds	4,919		89,594		172,423		55,753		322,689
Non U.S. corporate bonds	2,007		19,925		30,316		4,174		56,422
Debt securities	$	6,926	$	113,449	$	205,039	$	129,174	$	454,588

Rabbi Trusts

In 2016, NSP-Minnesota established a rabbi trust to provide partial funding for future deferred compensation plan distributions. The following tables present the cost and fair value of the assets held in rabbi trust at June 30, 2018 and Dec. 31, 2017:

	June 30, 2018
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trust (a)
Cash equivalents	$	394	$	394	$	—	$	—	$	394
Mutual funds	10,423		11,374		—		—		11,374
Total	$	10,817	$	11,768	$	—	$	—	$	11,768

	Dec. 31, 2017
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trusts (a)
Cash equivalents	$	783	$	783	$	—	$	—	$	783
Mutual funds	10,332		11,283		—		—		11,283
Total	$	11,115	$	12,066	$	—	$	—	$	12,066

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet.

Derivative Instruments Fair Value Measurements

NSP-Minnesota enters into derivative instruments, including forward contracts, futures, swaps and options, for trading purposes and to manage risk in connection with changes in interest rates, utility commodity prices and vehicle fuel prices.

Interest Rate Derivatives — NSP-Minnesota enters into various instruments that effectively fix the interest payments on certain floating rate debt obligations or effectively fix the yield or price on a specified benchmark interest rate for an anticipated debt issuance for a specific period. These derivative instruments are generally designated as cash flow hedges for accounting purposes.

At June 30, 2018, accumulated other comprehensive losses related to interest rate derivatives included $0.8 million of net losses expected to be reclassified into earnings during the next 12 months as the related hedged interest rate transactions impact earnings, including forecasted amounts for unsettled hedges, as applicable.

Wholesale and Commodity Trading Risk — NSP-Minnesota conducts various wholesale and commodity trading activities, including the purchase and sale of electric capacity, energy, energy-related instruments and natural gas related instruments, including derivatives. NSP-Minnesota’s risk management policy allows management to conduct these activities within guidelines and limitations as approved by its risk management committee, which is made up of management personnel not directly involved in the activities governed by this policy.

Commodity Derivatives — NSP-Minnesota enters into derivative instruments to manage variability of future cash flows from changes in commodity prices in its electric and natural gas operations, as well as for trading purposes. This could include the purchase or sale of energy or energy-related products, natural gas to generate electric energy, natural gas for resale, FTRs, vehicle fuel, and weather derivatives.

At June 30, 2018, NSP-Minnesota had various vehicle fuel contracts designated as cash flow hedges extending through December 2018. NSP-Minnesota enters into derivative instruments that mitigate commodity price risk on behalf of electric and natural gas customers, but may not be designated as qualifying hedging transactions. Changes in the fair value of non-trading commodity derivative instruments are recorded in other comprehensive income or deferred as a regulatory asset or liability. The classification as a regulatory asset or liability is based on commission approved regulatory recovery mechanisms. NSP-Minnesota recorded immaterial amounts to income related to the ineffectiveness of cash flow hedges for the three and six months ended June 30, 2018 and 2017.

At June 30, 2018, net gains related to commodity derivative cash flow hedges recorded as a component of accumulated other comprehensive losses included $0.1 million of net gains expected to be reclassified into earnings during the next 12 months as the hedged transactions occur.

Additionally, NSP-Minnesota enters into commodity derivative instruments for trading purposes not directly related to commodity price risks associated with serving its electric and natural gas customers. Changes in the fair value of these commodity derivatives are recorded in electric operating revenues, net of amounts credited to customers under margin-sharing mechanisms.

The following table details the gross notional amounts of commodity forwards, options and FTRs at June 30, 2018 and Dec. 31, 2017:

(Amounts in Thousands)(a)(b)	June 30, 2018	Dec. 31, 2017
Megawatt hours of electricity	73,771	41,711
Million British thermal units of natural gas	7,403	23,829
Gallons of vehicle fuel	120	240

^(a)  Amounts are not reflective of net positions in the underlying commodities.

^(b)  Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.

The following tables detail the impact of derivative activity during the three and six months ended June 30, 2018 and 2017 on accumulated other comprehensive loss, regulatory assets and liabilities and income:

	Three Months Ended June 30, 2018
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:							Pre-Tax Gains Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	264		(a)	$	—		$	—
Vehicle fuel and other commodity	31		—			(35		)	(b)	—			—
Total	$	31	$	—		$	229			$	—		$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—		$	2,263	(c)
Electric commodity	—		24,262			—				1,142		(d)	—
Natural gas commodity	—		(18		)	—				—			—
Total	$	—	$	24,244		$	—			$	1,142		$	2,263

	Six Months Ended June 30, 2018
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:								Pre-Tax Gains (Losses) Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	525		(a)	$	—			$	—
Vehicle fuel and other commodity	38		—			(64		)	(b)	—				—
Total	$	38	$	—		$	461			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	8,981		(c)
Electric commodity	—		(5,615		)	—				3,311			(d)	—
Natural gas commodity	—		830			—				(521		)	(e)	(404		)	(e)
Total	$	—	$	(4,785	)	$	—			$	2,790			$	8,577

	Three Months Ended June 30, 2017
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:								Pre-Tax Gains Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	350		(a)	$	—			$	—
Vehicle fuel and other commodity	43		—			(5		)	(b)	—				—
Total	$	43	$	—		$	345			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	5,977	(c)
Electric commodity	—		(1,526		)	—				(1,149		)	(d)	—
Natural gas commodity	—		(51		)	—				—				—
Total	$	—	$	(1,577	)	$	—			$	(1,149	)		$	5,977

	Six Months Ended June 30, 2017
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:								Pre-Tax Gains (Losses) Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	692		(a)	$	—			$	—
Vehicle fuel and other commodity	43		—			(5		)	(b)	—				—
Total	$	43	$	—		$	687			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	6,599		(c)
Electric commodity	—		(2,772		)	—				(3,937		)	(d)	—
Natural gas commodity	—		(717		)	—				698			(e)	(945		)	(e)
Total	$	—	$	(3,489	)	$	—			$	(3,239	)		$	5,654

^(a)  Amounts are recorded to interest charges.

^(b)  Amounts are recorded to operating and maintenance (O&M) expenses.

^(c)  Amounts are recorded to electric operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue, as appropriate.

^(d)  Amounts are recorded to electric fuel and purchased power. These derivative settlement gains and losses are shared with electric customers through fuel and purchased energy cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.

(e) Amounts are recorded to cost of natural gas sold and transported. These derivative settlement gains and losses are shared with natural gas customers through purchased natural gas cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.

NSP-Minnesota had no derivative instruments designated as fair value hedges during the three and six months ended June 30, 2018 and 2017. Therefore, no gains or losses from fair value hedges or related hedged transactions were recognized for these periods.

Consideration of Credit Risk and Concentrations — NSP-Minnesota continuously monitors the creditworthiness of the counterparties to its interest rate derivatives and commodity derivative contracts prior to settlement, and assesses each counterparty’s ability to perform on the transactions set forth in the contracts. Given this assessment, as well as an assessment of the impact of NSP-Minnesota’s own credit risk when determining the fair value of derivative liabilities, the impact of credit risk was immaterial to the fair value of unsettled commodity derivatives presented in the consolidated balance sheets.

NSP-Minnesota employs additional credit risk control mechanisms when appropriate, such as letters of credit, parental guarantees, standardized master netting agreements and termination provisions that allow for offsetting of positive and negative exposures. Credit exposure is monitored and, when necessary, the activity with a specific counterparty is limited until credit enhancement is provided.

NSP-Minnesota’s most significant concentrations of credit risk with particular entities or industries are contracts with counterparties to its wholesale, trading and non-trading commodity activities. At June 30, 2018, five of NSP-Minnesota’s 10 most significant counterparties for these activities, comprising $39.7 million or 48 percent of this credit exposure, had investment grade credit ratings from Standard & Poor’s, Moody’s or Fitch Ratings. Five of the 10 most significant counterparties, comprising $20.1 million or 24 percent of this credit exposure, were not rated by these external agencies, but based on NSP-Minnesota’s internal analysis, had credit quality consistent with investment grade. All ten of these significant counterparties are municipal or cooperative electric entities, or other utilities.

Credit Related Contingent Features — Contract provisions for derivative instruments that NSP-Minnesota enters into, including those accounted for as normal purchase-normal sale contracts and therefore not reflected on the balance sheet, may require the posting of collateral or settlement of the contracts for various reasons, including if NSP-Minnesota’s credit ratings are downgraded below its investment grade credit rating by any of the major credit rating agencies or for cross-default contractual provisions that could result in the settlement of such contracts if there was a failure under other financing arrangements related to payment terms or other covenants. At June 30, 2018 and Dec. 31, 2017, there were no derivative instruments in a material liability position with such underlying contract provisions.

Certain derivative instruments are also subject to contract provisions that contain adequate assurance clauses. These provisions allow counterparties to seek performance assurance, including cash collateral, in the event that NSP-Minnesota’s ability to fulfill its contractual obligations is reasonably expected to be impaired. NSP-Minnesota had no collateral posted related to adequate assurance clauses in derivative contracts as of June 30, 2018 and Dec. 31, 2017.

Recurring Fair Value Measurements — The following table presents for each of the fair value hierarchy levels, NSP-Minnesota’s derivative assets and liabilities measured at fair value on a recurring basis at June 30, 2018:

	June 30, 2018
	Fair Value						Fair Value Total		Counterparty Netting(b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative assets
Derivatives designated as cash flow hedges:
Vehicle fuel and other commodity	$	—	$	81	$	—	$	81	$	—		$	81
Other derivative instruments:
Commodity trading	480		14,737		1,661		16,878		(8,601		)	8,277
Electric commodity	—		—		22,896		22,896		(177		)	22,719
Natural gas commodity	—		167		—		167		—			167
Total current derivative assets	$	480	$	14,985	$	24,557	$	40,022	$	(8,778	)	31,244
PPAs (a)												24
Current derivative instruments												$	31,268
Noncurrent derivative assets
Other derivative instruments:
Commodity trading	$	—	$	33,171	$	5,596	$	38,767	$	(12,085	)	$	26,682
Total noncurrent derivative assets	$	—	$	33,171	$	5,596	$	38,767	$	(12,085	)	26,682
PPAs (a)												108
Noncurrent derivative instruments												$	26,790

	June 30, 2018
	Fair Value						Fair Value Total		Counterparty Netting(b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative liabilities
Other derivative instruments:
Commodity trading	$	286	$	12,147	$	1,550	$	13,983	$	(9,805	)	$	4,178
Electric commodity	—		—		177		177		(177		)	—
Total current derivative liabilities	$	286	$	12,147	$	1,727	$	14,160	$	(9,982	)	4,178
PPAs (a)												13,851
Current derivative instruments												$	18,029
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	—	$	24,476	$	397	$	24,873	$	(15,738	)	$	9,135
Total noncurrent derivative liabilities	$	—	$	24,476	$	397	$	24,873	$	(15,738	)	9,135
PPAs (a)												82,987
Noncurrent derivative instruments												$	92,122

^(a)  During 2006, NSP-Minnesota qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts is being amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

^(b)  NSP-Minnesota nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at June 30, 2018. At June 30, 2018, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $4.9 million. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

The following table presents for each of the fair value hierarchy levels, NSP-Minnesota’s derivative assets and liabilities measured at fair value on a recurring basis at Dec. 31, 2017:

	Dec. 31, 2017
	Fair Value						Fair Value Total		Counterparty Netting (b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative assets
Derivatives designated as cash flow hedges:
Vehicle fuel and other commodity	$	—	$	107	$	—	$	107	$	—		$	107
Other derivative instruments:
Commodity trading	1,691		17,144		142		18,977		(11,744		)	7,233
Electric commodity	—		—		17,581		17,581		(425		)	17,156
Natural gas commodity	—		77		—		77		—			77
Total current derivative assets	$	1,691	$	17,328	$	17,723	$	36,742	$	(12,169	)	24,573
PPAs (a)												657
Current derivative instruments												$	25,230
Noncurrent derivative assets
Other derivative instruments:
Commodity trading	$	—	$	29,121	$	5,363	$	34,484	$	(6,502	)	$	27,982
Total noncurrent derivative assets	$	—	$	29,121	$	5,363	$	34,484	$	(6,502	)	27,982
PPAs (a)												120
Noncurrent derivative instruments												$	28,102

	Dec. 31, 2017
	Fair Value						Fair Value Total		Counterparty Netting (b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative liabilities
Other derivative instruments:
Commodity trading	$	1,713	$	13,853	$	—	$	15,566	$	(11,974	)	$	3,592
Electric commodity	—		—		425		425		(425		)	—
Total current derivative liabilities	$	1,713	$	13,853	$	425	$	15,991	$	(12,399	)	3,592
PPAs (a)												14,105
Current derivative instruments												$	17,697
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	—	$	22,163	$	—	$	22,163	$	(9,334	)	$	12,829
Total noncurrent derivative liabilities	$	—	$	22,163	$	—	$	22,163	$	(9,334	)	12,829
PPAs (a)												89,913
Noncurrent derivative instruments												$	102,742

^(a)  During 2006, NSP-Minnesota qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts is being amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

^(b)  NSP-Minnesota nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2017. At Dec. 31, 2017, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $3.1 million. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

The following table presents the changes in Level 3 commodity derivatives for the three and six months ended June 30, 2018 and 2017:

	Three Months Ended June 30
(Thousands of Dollars)	2018			2017
Balance at April 1	$	13,516		$	4,643
Purchases	26,395			40,460
Settlements	(5,170		)	(8,166		)
Net transactions recorded during the period:
(Losses) gains recognized in earnings (a)	(2,654		)	6,007
Net losses recognized as regulatory assets and liabilities	(4,058		)	(2,372		)
Balance at June 30	$	28,029		$	40,572
	Six Months Ended June 30
(Thousands of Dollars)	2018			2017
Balance at Jan. 1	$	22,662		$	15,320
Purchases	26,397			40,740
Settlements	(7,104		)	(11,592		)
Net transactions recorded during the period:
(Losses) gains recognized in earnings (a)	(374		)	5,215
Net gains recognized as regulatory assets and liabilities	(13,552		)	(9,111		)
Balance at June 30	$	28,029		$	40,572

^(a)  These amounts relate to commodity derivatives held at the end of the period.

NSP-Minnesota recognizes transfers between levels as of the beginning of each period. There were no transfers of amounts between levels for derivative instruments for the three and six months ended June 30, 2018 and 2017.

Fair Value of Long-Term Debt

As of June 30, 2018 and Dec. 31, 2017, other financial instruments for which the carrying amount did not equal fair value were as follows:

	June 30, 2018				Dec. 31, 2017
(Thousands of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt, including current portion	$	4,935,068	$	5,192,385	$	4,933,018	$	5,601,919

The fair value of NSP-Minnesota’s long-term debt is estimated based on recent trades and observable spreads from benchmark interest rates for similar securities. The fair value estimates are based on information available to management as of June 30, 2018 and Dec. 31, 2017, and given the observability of the inputs to these estimates, the fair values presented for long-term debt have been assigned a Level 2.

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Other (Expense) Income, Net

6 Months Ended

Jun. 30, 2018

Other Income and Expenses [Abstract]

Other (Expense) Income, Net

Other Expense, Net

Other expense, net consisted of the following:

	Three Months Ended June 30						Six Months Ended June 30
(Thousands of Dollars)	2018			2017			2018			2017
Interest income	$	522		$	605		$	3,457		$	3,314
Other nonoperating income	697			17			698			27
Insurance policy expense	(1,537		)	(856		)	(1,195		)	(1,711		)
Benefits non-service cost	(1,916		)	(3,398		)	(4,978		)	(6,796		)
Other expense, net	$	(2,234	)	$	(3,632	)	$	(2,018	)	$	(5,166	)

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Segment Information

6 Months Ended

Jun. 30, 2018

Segment Reporting [Abstract]

Segment Information

Segment Information

Operating results from the regulated electric utility and regulated natural gas utility are each separately and regularly reviewed by NSP-Minnesota’s chief operating decision maker. NSP-Minnesota evaluates performance based on profit or loss generated from the product or service provided. These segments are managed separately because the revenue streams are dependent upon regulated rate recovery, which is separately determined for each segment.

NSP-Minnesota has the following reportable segments: regulated electric utility, regulated natural gas utility and all other.

• NSP-Minnesota’s regulated electric utility segment generates, transmits and distributes electricity primarily in portions of Minnesota, North Dakota and South Dakota. In addition, this segment includes sales for resale and provides wholesale transmission service to various entities in the United States. Regulated electric utility also includes NSP-Minnesota’s commodity trading operations.

• NSP-Minnesota’s regulated natural gas utility segment transports, stores and distributes natural gas primarily in portions of Minnesota and North Dakota.

• Revenues from operating segments not included above are below the necessary quantitative thresholds and are therefore included in the all other category. Those primarily include appliance repair services, nonutility real estate activities and revenues associated with processing solid waste into refuse-derived fuel.

Asset and capital expenditure information is not provided for NSP-Minnesota’s reportable segments because as an integrated electric and natural gas utility, NSP-Minnesota operates significant assets that are not dedicated to a specific business segment, and reporting assets and capital expenditures by business segment would require arbitrary and potentially misleading allocations which may not necessarily reflect the assets that would be required for the operation of the business segments on a stand-alone basis.

To report income from operations for regulated electric and regulated natural gas utility segments, the majority of costs are directly assigned to each segment. However, some costs, such as common depreciation, common operating and maintenance (O&M) expenses and interest expense are allocated based on cost causation allocators. A general allocator is used for certain general and administrative expenses, including office supplies, rent, property insurance and general advertising.

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Three Months Ended June 30, 2018
Operating revenues (a)(b)	$	1,096,408	$	83,112	$	8,215	$	—		$	1,187,735
Intersegment revenues	128		116		—		(244		)	—
Total revenues	$	1,096,536	$	83,228	$	8,215	$	(244	)	$	1,187,735
Net income	$	88,875	$	399	$	3,113	$	—		$	92,387

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas			All Other		Reconciling Eliminations			Consolidated Total
Three Months Ended June 30, 2017
Operating revenues (a)(b)	$	1,079,779	$	78,006		$	7,155	$	—		$	1,164,940
Intersegment revenues	243		177			—		(420		)	—
Total revenues	$	1,080,022	$	78,183		$	7,155	$	(420	)	$	1,164,940
Net income (loss)	$	89,477	$	(3,360	)	$	1,545	$	—		$	87,662

^(a)  Operating revenues include 117 million and 119 million of affiliate electric revenue for the three months ended June 30, 2018 and 2017.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended June 30, 2018 and 2017.

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Six Months Ended June 30, 2018
Operating revenues (a)(b)	$	2,158,671	$	324,544	$	15,271	$	—		$	2,498,486
Intersegment revenues	293		260		—		(553		)	—
Total revenues	$	2,158,964	$	324,804	$	15,271	$	(553	)	$	2,498,486
Net income	$	174,597	$	25,844	$	3,686	$	—		$	204,127

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Six Months Ended June 30, 2017
Operating revenues (a)(b)	$	2,158,809	$	299,189	$	14,082	$	—		$	2,472,080
Intersegment revenues	352		271		—		(623		)	—
Total revenues	$	2,159,161	$	299,460	$	14,082	$	(623	)	$	2,472,080
Net income	$	167,559	$	14,145	$	124	$	—		181,828

^(a)  Operating revenues include $234 million and $243 million of affiliate electric revenue for the six months ended June 30, 2018 and 2017.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the six months ended June 30, 2018 and 2017.

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Benefit Plans and Other Postretirement Benefits

6 Months Ended

Jun. 30, 2018

Retirement Benefits [Abstract]

Benefit Plans and Other Postretirement Benefits

Benefit Plans and Other Postretirement Benefits

Components of Net Periodic Benefit Cost

	Three Months Ended June 30
	2018			2017			2018			2017
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	6,982		$	6,958		$	43		$	36
Interest cost (a)	8,804			10,177			769			854
Expected return on plan assets (a)	(14,542		)	(15,017		)	(96		)	(54		)
Amortization of prior service (credit) cost (a)	(28		)	265			(759		)	(759		)
Amortization of net loss (a)	9,614			9,902			595			507
Net periodic benefit cost	10,830			12,285			552			584
Costs not recognized due to the effects of regulation	(3,069		)	(4,899		)	—			—
Net benefit cost recognized for financial reporting	$	7,761		$	7,386		$	552		$	584

	Six Months Ended June 30
	2018			2017			2018			2017
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	13,964		$	13,916		$	86		$	72
Interest cost (a)	17,608			20,354			1,538			1,708
Expected return on plan assets (a)	(29,083		)	(30,034		)	(192		)	(108		)
Amortization of prior service (credit) cost (a)	(57		)	530			(1,518		)	(1,518		)
Amortization of net loss (a)	19,229			19,804			1,190			1,014
Net periodic benefit cost	21,661			24,570			1,104			1,168
Costs not recognized due to the effects of regulation	(5,832		)	(9,798		)	—			—
Net benefit cost recognized for financial reporting	$	15,829		$	14,772		$	1,104		$	1,168

^(a) The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the income statement or capitalized on the balance sheet as a regulatory asset.

In January 2018, contributions of $150 million were made across four of Xcel Energy’s pension plans, of which $63.0 million was attributable to NSP-Minnesota. Xcel Energy does not expect additional pension contributions during 2018.

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Other Comprehensive Income

6 Months Ended

Jun. 30, 2018

Stockholders' Equity Note [Abstract]

Other Comprehensive Income

Other Comprehensive Income (Loss)

Changes in accumulated other comprehensive loss, net of tax, for the three and six months ended June 30, 2018 and 2017 were as follows:

	Three Months Ended June 30, 2018
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities		Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at April 1	$	(20,723	)	$	—	$	(3,717	)	$	(24,440	)
Other comprehensive income before reclassifications	22			—		—			22
Losses reclassified from net accumulated other comprehensive loss	165			—		54			219
Net current period other comprehensive income	187			—		54			241
Accumulated other comprehensive loss at June 30	$	(20,536	)	$	—	$	(3,663	)	$	(24,199	)

	Three Months Ended June 30, 2017
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities		Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at April 1	$	(18,005	)	$	105	$	(2,645	)	$	(20,545	)
Other comprehensive income before reclassifications	26			—		—			26
Losses reclassified from net accumulated other comprehensive loss	204			—		36			240
Net current period other comprehensive income	230			—		36			266
Accumulated other comprehensive loss at June 30	$	(17,775	)	$	105	$	(2,609	)	$	(20,279	)

	Six Months Ended June 30, 2018
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities			Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at Jan. 1	$	(20,895	)	$	128		$	(3,770	)	$	(24,537	)
Other comprehensive income before reclassifications	27			—			—			27
Losses (gains) reclassified from net accumulated other comprehensive loss	332			(128		)	107			311
Net current period other comprehensive income	359			(128		)	107			338
Accumulated other comprehensive loss at June 30	$	(20,536	)	$	—		$	(3,663	)	$	(24,199	)

	Six Months Ended June 30, 2017
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities		Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at Jan. 1	$	(18,208	)	$	105	$	(2,680	)	$	(20,783	)
Other comprehensive income before reclassifications	26			—		—			26
Losses reclassified from net accumulated other comprehensive loss	407			—		71			478
Net current period other comprehensive income	433			—		71			504
Accumulated other comprehensive loss at June 30	$	(17,775	)	$	105	$	(2,609	)	$	(20,279	)

Reclassifications from accumulated other comprehensive loss for the three and six months ended June 30, 2018 and 2017 were as follows:

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Three Months Ended June 30, 2018				Three Months Ended June 30, 2017
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	264		(a)	$	350		(a)
Vehicle fuel derivatives	(35		)	(b)	(5		)	(b)
Total, pre-tax	229				345
Tax benefit	(64		)		(141		)
Total, net of tax	165				204
Defined benefit pension and postretirement losses:
Amortization of net loss	125			(c)	109			(c)
Prior service credit	(49		)	(c)	(51		)	(c)
Total, pre-tax	76				58
Tax benefit	(22		)		(22		)
Total, net of tax	54				36
Marketable securities:
Realization of gains	—				—
Total, pre-tax	—				—
Tax expense	—				—
Total, net of tax	—				—
Total amounts reclassified, net of tax	$	219			$	240

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Six Months Ended June 30, 2018				Six Months Ended June 30, 2017
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	525		(a)	$	692		(a)
Vehicle fuel derivatives	(64		)	(b)	(5		)	(b)
Total, pre-tax	461				687
Tax benefit	(129		)		(280		)
Total, net of tax	332				407
Defined benefit pension and postretirement losses:
Amortization of net loss	250			(c)	218			(c)
Prior service credit	(98		)	(c)	(100		)	(c)
Total, pre-tax	152				118
Tax benefit	(45		)		(47		)
Total, net of tax	107				71
Marketable securities:
Realization of gains	(179		)		—
Total, pre-tax	(179		)		—
Tax expense	51				—
Total, net of tax	(128		)		—
Total amounts reclassified, net of tax	$	311			$	478

^(a)  Included in interest charges.

^(b)  Included in O&M expenses.

^(c)  Included in the computation of net periodic pension and postretirement benefit costs. See Note 11 to the consolidated financial statements for details regarding these benefit plans.

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Revenues

6 Months Ended

Jun. 30, 2018

Revenue from Contract with Customer [Abstract]

Revenues

Revenues

NSP-Minnesota principally generates revenue from the generation, transmission, distribution and sale of electricity and the transportation, distribution and sale of natural gas to wholesale and retail customers. Performance obligations related to the sale of energy are satisfied as energy is delivered to customers. NSP-Minnesota recognizes revenue in an amount that corresponds directly to the price of the energy delivered to the customer. The measurement of energy sales to customers is generally based on the reading of their meters, which occurs on a systematic basis throughout the month. At the end of each month, amounts of energy delivered to customers since the date of the last meter reading are estimated, and the corresponding unbilled revenue is recognized. Contract terms are generally short-term in nature, and as such NSP-Minnesota does not recognize a separate financing component of its collections from customers. NSP-Minnesota presents its revenues net of any excise or other fiduciary-type taxes or fees.

NSP-Minnesota participates in MISO. NSP-Minnesota recognizes sales to both native load and other end use customers on a gross basis in electric revenues and cost of sales. Revenues and charges for short term wholesale sales of excess energy transacted through RTOs are also recorded on a gross basis. Other revenues and charges related to participating and transacting in RTOs are recorded on a net basis in cost of sales.

NSP-Minnesota has various rate-adjustment mechanisms in place that provide for the recovery of natural gas, electric fuel and purchased energy costs. These cost-adjustment tariffs may increase or decrease the level of revenue collected from customers and are revised periodically for differences between the total amount collected under the clauses and the costs incurred.

When applicable, under governing regulatory commission rate orders, fuel cost over-recoveries (the excess of fuel revenue billed to customers over fuel costs incurred) are deferred as regulatory liabilities and under-recoveries (the excess of fuel costs incurred over fuel revenues billed to customers) are deferred as regulatory assets.

Certain rate rider mechanisms qualify as alternative revenue programs under GAAP. These mechanisms arise from costs imposed upon the utility by action of a regulator or legislative body related to an environmental, public safety or other mandate. When certain criteria are met (including collection within 24 months), revenue is recognized equal to the revenue requirement, which may include return on rate base items and incentives. The mechanisms are revised periodically for differences between the total amount collected and the revenue recognized, which may increase or decrease the level of revenue collected from customers. Alternative revenue is recorded on a gross basis and is disclosed separate from revenue from contracts with customers in the period earned.

In the following tables, revenue is classified by the type of goods/services rendered and market/customer type. The tables also reconcile revenue to the reportable segments.

	Three Months Ended June 30, 2018
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	311,086	$	42,398	$	6,710	$	360,194
Commercial and industrial (C&I)	514,710		33,417		42		548,169
Other	8,639		—		1,463		10,102
Total retail	834,435		75,815		8,215		918,465
Wholesale	42,033		—		—		42,033
Transmission	59,951		—		—		59,951
Interchange	117,417		—		—		117,417
Other	6,033		3,317		—		9,350
Total revenue from contracts with customers	1,059,869		79,132		8,215		1,147,216
Alternative revenue and other	36,539		3,980		—		40,519
Total revenues	$	1,096,408	$	83,112	$	8,215	$	1,187,735

	Three Months Ended June 30, 2017
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	288,733	$	36,860	$	6,416	$	332,009
C&I	526,867		31,382		92		558,341
Other	7,854		—		647		8,501
Total retail	823,454		68,242		7,155		898,851
Wholesale	28,841		—		—		28,841
Transmission	56,177		—		—		56,177
Interchange	119,384		—		—		119,384
Other	7,445		1,452		—		8,897
Total revenue from contracts with customers	1,035,301		69,694		7,155		1,112,150
Alternative revenue and other	44,478		8,312		—		52,790
Total revenues	$	1,079,779	$	78,006	$	7,155	$	1,164,940

	Six Months Ended June 30, 2018
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	622,215	$	174,057	$	13,033	$	809,305
Commercial and industrial (C&I)	982,733		130,325		85		1,113,143
Other	18,358		—		2,153		20,511
Total retail	1,623,306		304,382		15,271		1,942,959
Wholesale	88,398		—		—		88,398
Transmission	114,749		—		—		114,749
Interchange	234,389		—		—		234,389
Other	17,578		5,528		—		23,106
Total revenue from contracts with customers	2,078,420		309,910		15,271		2,403,601
Alternative revenue and other	80,251		14,634		—		94,885
Total revenues	$	2,158,671	$	324,544	$	15,271	$	2,498,486

	Six Months Ended June 30, 2017
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	593,146	$	158,273	$	12,626	$	764,045
C&I	1,011,970		119,873		130		1,131,973
Other	16,057		—		1,326		17,383
Total retail	1,621,173		278,146		14,082		1,913,401
Wholesale	74,760		—		—		74,760
Transmission	110,136		—		—		110,136
Interchange	243,073		—		—		243,073
Other	13,408		2,697		—		16,105
Total revenue from contracts with customers	2,062,550		280,843		14,082		2,357,475
Alternative revenue and other	96,259		18,346		—		114,605
Total revenues	$	2,158,809	$	299,189	$	14,082	$	2,472,080

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Selected Balance Sheet Data (Tables)

6 Months Ended

Jun. 30, 2018

Balance Sheet Related Disclosures [Abstract]

Accounts receivable, net

(Thousands of Dollars)	June 30, 2018			Dec. 31, 2017
Accounts receivable, net
Accounts receivable	$	380,606		$	366,388
Less allowance for bad debts	(19,462		)	(21,278		)
	$	361,144		$	345,110

Inventories

(Thousands of Dollars)	June 30, 2018		Dec. 31, 2017
Inventories
Materials and supplies	$	208,596	$	209,236
Fuel	73,737		94,483
Natural gas	12,269		33,993
	$	294,602	$	337,712

Property, plant and equipment, net

(Thousands of Dollars)	June 30, 2018			Dec. 31, 2017
Property, plant and equipment, net
Electric plant	$	17,276,273		$	17,024,925
Natural gas plant	1,407,523			1,370,330
Common and other property	719,069			724,066
Construction work in progress	528,079			530,126
Total property, plant and equipment	19,930,944			19,649,447
Less accumulated depreciation	(7,210,566		)	(7,018,249		)
Nuclear fuel	2,712,590			2,697,412
Less accumulated amortization	(2,357,292		)	(2,294,998		)
	$	13,075,676		$	13,033,612

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Income Taxes (Tables)

6 Months Ended

Jun. 30, 2018

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

Total income tax expense from operations differs from the amount computed by applying the statutory federal income tax rate to income before income tax expense. The following reconciles such differences:

	Six Months Ended June 30
	2018		2017
Federal statutory rate	21.0	%	35.0	%
State tax, net of federal tax effect	7.1		5.8
Increases (decreases) in tax from:
Wind production tax credits (PTCs)	(17.1	)	(11.4	)
Regulatory differences - ARAM (a)	(8.5	)	(0.2	)
Regulatory differences - ARAM deferral (b)	7.9		—
Other tax credits, net of federal income tax expense	(1.5	)	(1.0	)
Other, net	0.7		0.4
Effective income tax rate	9.6	%	28.6	%

^(a)   The average rate assumption method (ARAM); a method to flow back excess deferred taxes to customers.

^(b) As we receive direction from our regulatory commissions regarding the return of excess deferred taxes (to our customers resulting from the Tax Cuts and Jobs Act

(TCJA)), the ARAM deferral may decrease during the year, which would result in a reduction to tax expense with a corresponding reduction to revenue.

Summary of Statute of Limitations Applicable to Open Tax Years [Table Text Block]

NSP-Minnesota is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. The statute of limitations applicable to Xcel Energy’s federal income tax returns expire as follows:

Tax Year(s)	Expiration
2009 - 2011	December 2018
2012 - 2014	October 2019
2015	September 2019
2016	September 2020

Reconciliation of Unrecognized Tax Benefits

A reconciliation of the amount of unrecognized tax benefit is as follows:

(Millions of Dollars)	June 30, 2018		Dec. 31, 2017
Unrecognized tax benefit — Permanent tax positions	$	10.2	$	10.2
Unrecognized tax benefit — Temporary tax positions	5.5		7.9
Total unrecognized tax benefit	$	15.7	$	18.1

Tax Benefits Associated with NOL and Tax Credit Carryforwards

The unrecognized tax benefit amounts were reduced by the tax benefits associated with NOL and tax credit carryforwards. The amounts of tax benefits associated with NOL and tax credit carryforwards are as follows:

(Millions of Dollars)	June 30, 2018			Dec. 31, 2017
NOL and tax credit carryforwards	$	(15.0	)	$	(12.8	)

Interest Payable related to Unrecognized Tax Benefits [Table Text Block]

(Millions of Dollars)	June 30, 2018			Dec. 31, 2017
Payable for interest related to unrecognized tax benefits at beginning of period	$	(0.9	)	$	(2.0	)
Interest (expense) income related to unrecognized tax benefits recorded during the period	(1.0		)	1.1
Payable for interest related to unrecognized tax benefits at end of period	$	(1.9	)	$	(0.9	)

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Commitments and Contingencies Schedule of Guarantor Obligations (Tables)

6 Months Ended

Jun. 30, 2018

Commitments and Contingencies Disclosure [Abstract]

Schedule of Guarantor Obligations [Table Text Block]

The following table presents the guarantee issued and outstanding for NSP-Minnesota:

(Millions of Dollars)	June 30, 2018		Dec. 31, 2017
Guarantee issued and outstanding	$	4.8	$	4.8

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Borrowings and Other Financing Instruments (Tables)

6 Months Ended

Jun. 30, 2018

Borrowings and Other Financing Instruments [Abstract]

Credit Facilities

At June 30, 2018, NSP-Minnesota had the following committed credit facility available (in millions of dollars):

Credit Facility (a)		Drawn(b)		Available
$	500	$	36	$	464

^(a)  This credit facility expires in June 2021.

^(b)  Includes outstanding letters of credit.

Money Pool

Borrowings and Other Financing Instruments [Abstract]

Short-Term Borrowings

Money pool borrowings for NSP-Minnesota were as follows:

(Amounts in Millions, Except Interest Rates)	Three Months Ended June 30, 2018			Year Ended Dec. 31, 2017
Borrowing limit	$	250		$	250
Amount outstanding at period end	62			85
Average amount outstanding	1			25
Maximum amount outstanding	62			142
Weighted average interest rate, computed on a daily basis	1.85		%	1.14		%
Weighted average interest rate at period end	1.85			1.18

Commercial Paper

Borrowings and Other Financing Instruments [Abstract]

Short-Term Borrowings

Commercial paper outstanding for NSP-Minnesota was as follows:

(Amounts in Millions, Except Interest Rates)	Three Months Ended June 30, 2018		Year Ended Dec. 31, 2017
Borrowing limit	$	500	$	500
Amount outstanding at period end	—		20
Average amount outstanding	—		62
Maximum amount outstanding	—		237
Weighted average interest rate, computed on a daily basis	N/A		1.10		%
Weighted average interest rate at period end	N/A		1.93

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Fair Value of Financial Assets and Liabilities (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Cost and Fair Value of Nuclear Decommissioning Fund Investments

The following tables present the cost and fair value of NSP-Minnesota’s non-derivative instruments with recurring fair value measurements in the nuclear decommissioning fund as of June 30, 2018 and Dec. 31, 2017:

	June 30, 2018
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Investments Measured at NAV (b)		Total
Nuclear decommissioning fund (a)
Cash equivalents	$	30,868	$	30,868	$	—	$	—	$	—	$	30,868
Commingled funds:
Non U.S. equities	262,468		197,545		—		—		90,402		287,947
Emerging market debt funds	158,296		—		—		—		158,075		158,075
Private equity investments	150,565		—		—		—		220,460		220,460
Real estate	128,115		—		—		—		197,032		197,032
Debt securities:
Government securities	75,806		—		75,477		—		—		75,477
U.S. corporate bonds	330,170		—		322,689		—		—		322,689
Non U.S. corporate bonds	57,902		—		56,422		—		—		56,422
Equity securities:
U.S. equities	269,483		568,134		—		—		—		568,134
Non U.S. equities	156,756		227,226		—		—		—		227,226
Total	$	1,620,429	$	1,023,773	$	454,588	$	—	$	665,969	$	2,144,330

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $51 million of rabbi trust assets and miscellaneous investments.

^(b)  Due to limited availability of published pricing and a lack of immediate redeemability, certain fund investments measured at NAV are not required to be categorized within the fair value hierarchy.

	Dec. 31, 2017
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Investments Measured at NAV (b)		Total
Nuclear decommissioning fund (a)
Cash equivalents	$	28,741	$	28,741	$	—	$	—	$	—	$	28,741
Commingled funds:
Non U.S. equities	263,694		216,551		—		—		89,857		306,408
Emerging market debt funds	156,057		—		—		—		166,375		166,375
Private equity investments	141,413		—		—		—		198,037		198,037
Real estate	130,787		—		—		—		201,842		201,842
Other commingled funds	9,340		6,286		—		—		2,975		9,261
Debt securities:
Government securities	67,760		—		69,413		—		—		69,413
U.S. corporate bonds	319,809		—		322,129		—		—		322,129
Non U.S. corporate bonds	50,121		—		50,102		—		—		50,102
Equity securities:
U.S. equities	271,166		556,974		—		—		—		556,974
Non U.S. equities	151,961		233,999		—		—		—		233,999
Total	$	1,590,849	$	1,042,551	$	441,644	$	—	$	659,086	$	2,143,281

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $49 million of rabbi trust assets and miscellaneous investments.

^(b)  Due to limited availability of published pricing and a lack of immediate redeemability, certain fund investments measured at NAV are not required to be categorized within the fair value hierarchy.

Final Contractual Maturity Dates of Debt Securities in the Nuclear Decommissioning Fund by Asset Class

The following table summarizes the final contractual maturity dates of the debt securities in the nuclear decommissioning fund, by asset class, as of June 30, 2018:

	Final Contractual Maturity
(Thousands of Dollars)	Due in 1Year or Less		Due in 1 to 5 Years		Due in 5 to 10 Years		Due after 10 Years		Total
Government securities	$	—	$	3,930	$	2,300	$	69,247	$	75,477
U.S. corporate bonds	4,919		89,594		172,423		55,753		322,689
Non U.S. corporate bonds	2,007		19,925		30,316		4,174		56,422
Debt securities	$	6,926	$	113,449	$	205,039	$	129,174	$	454,588

Rabbi Trust Securities Amortized Cost and Fair Value Measured on Recurrring Basis [Table Text Block]

In 2016, NSP-Minnesota established a rabbi trust to provide partial funding for future deferred compensation plan distributions. The following tables present the cost and fair value of the assets held in rabbi trust at June 30, 2018 and Dec. 31, 2017:

	June 30, 2018
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trust (a)
Cash equivalents	$	394	$	394	$	—	$	—	$	394
Mutual funds	10,423		11,374		—		—		11,374
Total	$	10,817	$	11,768	$	—	$	—	$	11,768

	Dec. 31, 2017
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trusts (a)
Cash equivalents	$	783	$	783	$	—	$	—	$	783
Mutual funds	10,332		11,283		—		—		11,283
Total	$	11,115	$	12,066	$	—	$	—	$	12,066

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet.

Gross Notional Amounts of Commodity Forwards, Options, and FTRs

The following table details the gross notional amounts of commodity forwards, options and FTRs at June 30, 2018 and Dec. 31, 2017:

(Amounts in Thousands)(a)(b)	June 30, 2018	Dec. 31, 2017
Megawatt hours of electricity	73,771	41,711
Million British thermal units of natural gas	7,403	23,829
Gallons of vehicle fuel	120	240

^(a)  Amounts are not reflective of net positions in the underlying commodities.

^(b)  Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.

Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income

The following tables detail the impact of derivative activity during the three and six months ended June 30, 2018 and 2017 on accumulated other comprehensive loss, regulatory assets and liabilities and income:

	Three Months Ended June 30, 2018
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:							Pre-Tax Gains Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	264		(a)	$	—		$	—
Vehicle fuel and other commodity	31		—			(35		)	(b)	—			—
Total	$	31	$	—		$	229			$	—		$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—		$	2,263	(c)
Electric commodity	—		24,262			—				1,142		(d)	—
Natural gas commodity	—		(18		)	—				—			—
Total	$	—	$	24,244		$	—			$	1,142		$	2,263

	Six Months Ended June 30, 2018
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:								Pre-Tax Gains (Losses) Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	525		(a)	$	—			$	—
Vehicle fuel and other commodity	38		—			(64		)	(b)	—				—
Total	$	38	$	—		$	461			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	8,981		(c)
Electric commodity	—		(5,615		)	—				3,311			(d)	—
Natural gas commodity	—		830			—				(521		)	(e)	(404		)	(e)
Total	$	—	$	(4,785	)	$	—			$	2,790			$	8,577

	Three Months Ended June 30, 2017
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:								Pre-Tax Gains Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	350		(a)	$	—			$	—
Vehicle fuel and other commodity	43		—			(5		)	(b)	—				—
Total	$	43	$	—		$	345			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	5,977	(c)
Electric commodity	—		(1,526		)	—				(1,149		)	(d)	—
Natural gas commodity	—		(51		)	—				—				—
Total	$	—	$	(1,577	)	$	—			$	(1,149	)		$	5,977

	Six Months Ended June 30, 2017
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax (Gains) Losses Reclassified into Income During the Period from:								Pre-Tax Gains (Losses) Recognized During the Period in Income
(Thousands of Dollars)	Accumulated Other Comprehensive Loss		Regulatory (Assets) and Liabilities			Accumulated Other Comprehensive Loss				Regulatory Assets and (Liabilities)
Derivatives designated as cash flow hedges
Interest rate	$	—	$	—		$	692		(a)	$	—			$	—
Vehicle fuel and other commodity	43		—			(5		)	(b)	—				—
Total	$	43	$	—		$	687			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	6,599		(c)
Electric commodity	—		(2,772		)	—				(3,937		)	(d)	—
Natural gas commodity	—		(717		)	—				698			(e)	(945		)	(e)
Total	$	—	$	(3,489	)	$	—			$	(3,239	)		$	5,654

^(a)  Amounts are recorded to interest charges.

^(b)  Amounts are recorded to operating and maintenance (O&M) expenses.

^(c)  Amounts are recorded to electric operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue, as appropriate.

^(d)  Amounts are recorded to electric fuel and purchased power. These derivative settlement gains and losses are shared with electric customers through fuel and purchased energy cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.

(e) Amounts are recorded to cost of natural gas sold and transported. These derivative settlement gains and losses are shared with natural gas customers through purchased natural gas cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.

Derivative Assets and Liabilities Measured at Fair Value on a Recurring Basis by Hierarchy Level

Recurring Fair Value Measurements — The following table presents for each of the fair value hierarchy levels, NSP-Minnesota’s derivative assets and liabilities measured at fair value on a recurring basis at June 30, 2018:

	June 30, 2018
	Fair Value						Fair Value Total		Counterparty Netting(b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative assets
Derivatives designated as cash flow hedges:
Vehicle fuel and other commodity	$	—	$	81	$	—	$	81	$	—		$	81
Other derivative instruments:
Commodity trading	480		14,737		1,661		16,878		(8,601		)	8,277
Electric commodity	—		—		22,896		22,896		(177		)	22,719
Natural gas commodity	—		167		—		167		—			167
Total current derivative assets	$	480	$	14,985	$	24,557	$	40,022	$	(8,778	)	31,244
PPAs (a)												24
Current derivative instruments												$	31,268
Noncurrent derivative assets
Other derivative instruments:
Commodity trading	$	—	$	33,171	$	5,596	$	38,767	$	(12,085	)	$	26,682
Total noncurrent derivative assets	$	—	$	33,171	$	5,596	$	38,767	$	(12,085	)	26,682
PPAs (a)												108
Noncurrent derivative instruments												$	26,790

	June 30, 2018
	Fair Value						Fair Value Total		Counterparty Netting(b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative liabilities
Other derivative instruments:
Commodity trading	$	286	$	12,147	$	1,550	$	13,983	$	(9,805	)	$	4,178
Electric commodity	—		—		177		177		(177		)	—
Total current derivative liabilities	$	286	$	12,147	$	1,727	$	14,160	$	(9,982	)	4,178
PPAs (a)												13,851
Current derivative instruments												$	18,029
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	—	$	24,476	$	397	$	24,873	$	(15,738	)	$	9,135
Total noncurrent derivative liabilities	$	—	$	24,476	$	397	$	24,873	$	(15,738	)	9,135
PPAs (a)												82,987
Noncurrent derivative instruments												$	92,122

^(a)  During 2006, NSP-Minnesota qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts is being amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

^(b)  NSP-Minnesota nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at June 30, 2018. At June 30, 2018, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $4.9 million. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

The following table presents for each of the fair value hierarchy levels, NSP-Minnesota’s derivative assets and liabilities measured at fair value on a recurring basis at Dec. 31, 2017:

	Dec. 31, 2017
	Fair Value						Fair Value Total		Counterparty Netting (b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative assets
Derivatives designated as cash flow hedges:
Vehicle fuel and other commodity	$	—	$	107	$	—	$	107	$	—		$	107
Other derivative instruments:
Commodity trading	1,691		17,144		142		18,977		(11,744		)	7,233
Electric commodity	—		—		17,581		17,581		(425		)	17,156
Natural gas commodity	—		77		—		77		—			77
Total current derivative assets	$	1,691	$	17,328	$	17,723	$	36,742	$	(12,169	)	24,573
PPAs (a)												657
Current derivative instruments												$	25,230
Noncurrent derivative assets
Other derivative instruments:
Commodity trading	$	—	$	29,121	$	5,363	$	34,484	$	(6,502	)	$	27,982
Total noncurrent derivative assets	$	—	$	29,121	$	5,363	$	34,484	$	(6,502	)	27,982
PPAs (a)												120
Noncurrent derivative instruments												$	28,102

	Dec. 31, 2017
	Fair Value						Fair Value Total		Counterparty Netting (b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative liabilities
Other derivative instruments:
Commodity trading	$	1,713	$	13,853	$	—	$	15,566	$	(11,974	)	$	3,592
Electric commodity	—		—		425		425		(425		)	—
Total current derivative liabilities	$	1,713	$	13,853	$	425	$	15,991	$	(12,399	)	3,592
PPAs (a)												14,105
Current derivative instruments												$	17,697
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	—	$	22,163	$	—	$	22,163	$	(9,334	)	$	12,829
Total noncurrent derivative liabilities	$	—	$	22,163	$	—	$	22,163	$	(9,334	)	12,829
PPAs (a)												89,913
Noncurrent derivative instruments												$	102,742

^(a)  During 2006, NSP-Minnesota qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts is being amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

^(b)  NSP-Minnesota nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2017. At Dec. 31, 2017, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $3.1 million. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

Changes in Level 3 Commodity Derivatives

The following table presents the changes in Level 3 commodity derivatives for the three and six months ended June 30, 2018 and 2017:

	Three Months Ended June 30
(Thousands of Dollars)	2018			2017
Balance at April 1	$	13,516		$	4,643
Purchases	26,395			40,460
Settlements	(5,170		)	(8,166		)
Net transactions recorded during the period:
(Losses) gains recognized in earnings (a)	(2,654		)	6,007
Net losses recognized as regulatory assets and liabilities	(4,058		)	(2,372		)
Balance at June 30	$	28,029		$	40,572
	Six Months Ended June 30
(Thousands of Dollars)	2018			2017
Balance at Jan. 1	$	22,662		$	15,320
Purchases	26,397			40,740
Settlements	(7,104		)	(11,592		)
Net transactions recorded during the period:
(Losses) gains recognized in earnings (a)	(374		)	5,215
Net gains recognized as regulatory assets and liabilities	(13,552		)	(9,111		)
Balance at June 30	$	28,029		$	40,572

^(a)  These amounts relate to commodity derivatives held at the end of the period.

Carrying Amount and Fair Value of Long-term Debt

As of June 30, 2018 and Dec. 31, 2017, other financial instruments for which the carrying amount did not equal fair value were as follows:

	June 30, 2018				Dec. 31, 2017
(Thousands of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt, including current portion	$	4,935,068	$	5,192,385	$	4,933,018	$	5,601,919

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Other (Expense) Income, Net (Tables)

6 Months Ended

Jun. 30, 2018

Other Income and Expenses [Abstract]

Other (Expense) Income, Net

Other expense, net consisted of the following:

	Three Months Ended June 30						Six Months Ended June 30
(Thousands of Dollars)	2018			2017			2018			2017
Interest income	$	522		$	605		$	3,457		$	3,314
Other nonoperating income	697			17			698			27
Insurance policy expense	(1,537		)	(856		)	(1,195		)	(1,711		)
Benefits non-service cost	(1,916		)	(3,398		)	(4,978		)	(6,796		)
Other expense, net	$	(2,234	)	$	(3,632	)	$	(2,018	)	$	(5,166	)

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Segment Information (Tables)

6 Months Ended

Jun. 30, 2018

Segment Reporting [Abstract]

Results from Operations by Reportable Segment

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Three Months Ended June 30, 2018
Operating revenues (a)(b)	$	1,096,408	$	83,112	$	8,215	$	—		$	1,187,735
Intersegment revenues	128		116		—		(244		)	—
Total revenues	$	1,096,536	$	83,228	$	8,215	$	(244	)	$	1,187,735
Net income	$	88,875	$	399	$	3,113	$	—		$	92,387

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas			All Other		Reconciling Eliminations			Consolidated Total
Three Months Ended June 30, 2017
Operating revenues (a)(b)	$	1,079,779	$	78,006		$	7,155	$	—		$	1,164,940
Intersegment revenues	243		177			—		(420		)	—
Total revenues	$	1,080,022	$	78,183		$	7,155	$	(420	)	$	1,164,940
Net income (loss)	$	89,477	$	(3,360	)	$	1,545	$	—		$	87,662

^(a)  Operating revenues include 117 million and 119 million of affiliate electric revenue for the three months ended June 30, 2018 and 2017.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended June 30, 2018 and 2017.

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Six Months Ended June 30, 2018
Operating revenues (a)(b)	$	2,158,671	$	324,544	$	15,271	$	—		$	2,498,486
Intersegment revenues	293		260		—		(553		)	—
Total revenues	$	2,158,964	$	324,804	$	15,271	$	(553	)	$	2,498,486
Net income	$	174,597	$	25,844	$	3,686	$	—		$	204,127

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Six Months Ended June 30, 2017
Operating revenues (a)(b)	$	2,158,809	$	299,189	$	14,082	$	—		$	2,472,080
Intersegment revenues	352		271		—		(623		)	—
Total revenues	$	2,159,161	$	299,460	$	14,082	$	(623	)	$	2,472,080
Net income	$	167,559	$	14,145	$	124	$	—		181,828

^(a)  Operating revenues include $234 million and $243 million of affiliate electric revenue for the six months ended June 30, 2018 and 2017.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the six months ended June 30, 2018 and 2017.

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Benefit Plans and Other Postretirement Benefits (Tables)

6 Months Ended

Jun. 30, 2018

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost (Credit)

Components of Net Periodic Benefit Cost

	Three Months Ended June 30
	2018			2017			2018			2017
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	6,982		$	6,958		$	43		$	36
Interest cost (a)	8,804			10,177			769			854
Expected return on plan assets (a)	(14,542		)	(15,017		)	(96		)	(54		)
Amortization of prior service (credit) cost (a)	(28		)	265			(759		)	(759		)
Amortization of net loss (a)	9,614			9,902			595			507
Net periodic benefit cost	10,830			12,285			552			584
Costs not recognized due to the effects of regulation	(3,069		)	(4,899		)	—			—
Net benefit cost recognized for financial reporting	$	7,761		$	7,386		$	552		$	584

	Six Months Ended June 30
	2018			2017			2018			2017
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	13,964		$	13,916		$	86		$	72
Interest cost (a)	17,608			20,354			1,538			1,708
Expected return on plan assets (a)	(29,083		)	(30,034		)	(192		)	(108		)
Amortization of prior service (credit) cost (a)	(57		)	530			(1,518		)	(1,518		)
Amortization of net loss (a)	19,229			19,804			1,190			1,014
Net periodic benefit cost	21,661			24,570			1,104			1,168
Costs not recognized due to the effects of regulation	(5,832		)	(9,798		)	—			—
Net benefit cost recognized for financial reporting	$	15,829		$	14,772		$	1,104		$	1,168

^(a) The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the income statement or capitalized on the balance sheet as a regulatory asset.

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Other Comprehensive Income (Tables)

6 Months Ended

Jun. 30, 2018

Stockholders' Equity Note [Abstract]

Changes in Accumulated Other Comprehensive Income (Loss), Net of Tax

Changes in accumulated other comprehensive loss, net of tax, for the three and six months ended June 30, 2018 and 2017 were as follows:

	Three Months Ended June 30, 2018
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities		Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at April 1	$	(20,723	)	$	—	$	(3,717	)	$	(24,440	)
Other comprehensive income before reclassifications	22			—		—			22
Losses reclassified from net accumulated other comprehensive loss	165			—		54			219
Net current period other comprehensive income	187			—		54			241
Accumulated other comprehensive loss at June 30	$	(20,536	)	$	—	$	(3,663	)	$	(24,199	)

	Three Months Ended June 30, 2017
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities		Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at April 1	$	(18,005	)	$	105	$	(2,645	)	$	(20,545	)
Other comprehensive income before reclassifications	26			—		—			26
Losses reclassified from net accumulated other comprehensive loss	204			—		36			240
Net current period other comprehensive income	230			—		36			266
Accumulated other comprehensive loss at June 30	$	(17,775	)	$	105	$	(2,609	)	$	(20,279	)

	Six Months Ended June 30, 2018
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities			Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at Jan. 1	$	(20,895	)	$	128		$	(3,770	)	$	(24,537	)
Other comprehensive income before reclassifications	27			—			—			27
Losses (gains) reclassified from net accumulated other comprehensive loss	332			(128		)	107			311
Net current period other comprehensive income	359			(128		)	107			338
Accumulated other comprehensive loss at June 30	$	(20,536	)	$	—		$	(3,663	)	$	(24,199	)

	Six Months Ended June 30, 2017
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Unrealized Gains on Marketable Securities		Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at Jan. 1	$	(18,208	)	$	105	$	(2,680	)	$	(20,783	)
Other comprehensive income before reclassifications	26			—		—			26
Losses reclassified from net accumulated other comprehensive loss	407			—		71			478
Net current period other comprehensive income	433			—		71			504
Accumulated other comprehensive loss at June 30	$	(17,775	)	$	105	$	(2,609	)	$	(20,279	)

Reclassifications out of Accumulated Other Comprehensive Loss

Reclassifications from accumulated other comprehensive loss for the three and six months ended June 30, 2018 and 2017 were as follows:

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Three Months Ended June 30, 2018				Three Months Ended June 30, 2017
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	264		(a)	$	350		(a)
Vehicle fuel derivatives	(35		)	(b)	(5		)	(b)
Total, pre-tax	229				345
Tax benefit	(64		)		(141		)
Total, net of tax	165				204
Defined benefit pension and postretirement losses:
Amortization of net loss	125			(c)	109			(c)
Prior service credit	(49		)	(c)	(51		)	(c)
Total, pre-tax	76				58
Tax benefit	(22		)		(22		)
Total, net of tax	54				36
Marketable securities:
Realization of gains	—				—
Total, pre-tax	—				—
Tax expense	—				—
Total, net of tax	—				—
Total amounts reclassified, net of tax	$	219			$	240

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Six Months Ended June 30, 2018				Six Months Ended June 30, 2017
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	525		(a)	$	692		(a)
Vehicle fuel derivatives	(64		)	(b)	(5		)	(b)
Total, pre-tax	461				687
Tax benefit	(129		)		(280		)
Total, net of tax	332				407
Defined benefit pension and postretirement losses:
Amortization of net loss	250			(c)	218			(c)
Prior service credit	(98		)	(c)	(100		)	(c)
Total, pre-tax	152				118
Tax benefit	(45		)		(47		)
Total, net of tax	107				71
Marketable securities:
Realization of gains	(179		)		—
Total, pre-tax	(179		)		—
Tax expense	51				—
Total, net of tax	(128		)		—
Total amounts reclassified, net of tax	$	311			$	478

^(a)  Included in interest charges.

^(b)  Included in O&M expenses.

^(c)  Included in the computation of net periodic pension and postretirement benefit costs. See Note 11 to the consolidated financial statements for details regarding these benefit plans.

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Revenues Revenues (Tables)

6 Months Ended

Jun. 30, 2018

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue [Table Text Block]

In the following tables, revenue is classified by the type of goods/services rendered and market/customer type. The tables also reconcile revenue to the reportable segments.

	Three Months Ended June 30, 2018
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	311,086	$	42,398	$	6,710	$	360,194
Commercial and industrial (C&I)	514,710		33,417		42		548,169
Other	8,639		—		1,463		10,102
Total retail	834,435		75,815		8,215		918,465
Wholesale	42,033		—		—		42,033
Transmission	59,951		—		—		59,951
Interchange	117,417		—		—		117,417
Other	6,033		3,317		—		9,350
Total revenue from contracts with customers	1,059,869		79,132		8,215		1,147,216
Alternative revenue and other	36,539		3,980		—		40,519
Total revenues	$	1,096,408	$	83,112	$	8,215	$	1,187,735

	Three Months Ended June 30, 2017
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	288,733	$	36,860	$	6,416	$	332,009
C&I	526,867		31,382		92		558,341
Other	7,854		—		647		8,501
Total retail	823,454		68,242		7,155		898,851
Wholesale	28,841		—		—		28,841
Transmission	56,177		—		—		56,177
Interchange	119,384		—		—		119,384
Other	7,445		1,452		—		8,897
Total revenue from contracts with customers	1,035,301		69,694		7,155		1,112,150
Alternative revenue and other	44,478		8,312		—		52,790
Total revenues	$	1,079,779	$	78,006	$	7,155	$	1,164,940

	Six Months Ended June 30, 2018
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	622,215	$	174,057	$	13,033	$	809,305
Commercial and industrial (C&I)	982,733		130,325		85		1,113,143
Other	18,358		—		2,153		20,511
Total retail	1,623,306		304,382		15,271		1,942,959
Wholesale	88,398		—		—		88,398
Transmission	114,749		—		—		114,749
Interchange	234,389		—		—		234,389
Other	17,578		5,528		—		23,106
Total revenue from contracts with customers	2,078,420		309,910		15,271		2,403,601
Alternative revenue and other	80,251		14,634		—		94,885
Total revenues	$	2,158,671	$	324,544	$	15,271	$	2,498,486

	Six Months Ended June 30, 2017
(Thousands of Dollars)	Electric		Natural Gas		All Other		Total
Major revenue types
Revenue from contracts with customers:
Residential	$	593,146	$	158,273	$	12,626	$	764,045
C&I	1,011,970		119,873		130		1,131,973
Other	16,057		—		1,326		17,383
Total retail	1,621,173		278,146		14,082		1,913,401
Wholesale	74,760		—		—		74,760
Transmission	110,136		—		—		110,136
Interchange	243,073		—		—		243,073
Other	13,408		2,697		—		16,105
Total revenue from contracts with customers	2,062,550		280,843		14,082		2,357,475
Alternative revenue and other	96,259		18,346		—		114,605
Total revenues	$	2,158,809	$	299,189	$	14,082	$	2,472,080

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Accounting Pronouncements (Details) - Accounting Standards Update 2017-07 $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Operating and Maintenance Expense
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net benefit cost recognized for financial reporting	$ 6.8
Other Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net benefit cost recognized for financial reporting	$ (6.8)

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Selected Balance Sheet Data, Accounts Receivable (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts receivable, net
Accounts receivable	$ 380,606	$ 366,388
Less allowance for bad debts	(19,462)	(21,278)
Accounts receivable, net	$ 361,144	$ 345,110

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Selected Balance Sheet Data, Inventories (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Public Utilities, Inventory [Line Items]
Inventories	$ 294,602	$ 337,712
Materials and supplies
Public Utilities, Inventory [Line Items]
Inventories	208,596	209,236
Fuel
Public Utilities, Inventory [Line Items]
Inventories	73,737	94,483
Natural gas
Public Utilities, Inventory [Line Items]
Inventories	$ 12,269	$ 33,993

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Selected Balance Sheet Data, Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 19,930,944	$ 19,649,447
Less accumulated depreciation	(7,210,566)	(7,018,249)
Property, plant and equipment, net	13,075,676	13,033,612
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	17,276,273	17,024,925
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,407,523	1,370,330
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	719,069	724,066
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	528,079	530,126
Nuclear fuel
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,712,590	2,697,412
Less accumulated depreciation	$ (2,357,292)	$ (2,294,998)

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Income Taxes (Details) - USD ($)	6 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2012
Income Tax Examination [Line Items]
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	$ (1,900,000)			$ (900,000)	$ (2,000,000)
Interest Expense related to unrecognized tax benefits	$ (1,000,000)			1,100,000
Tax Audits [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	35.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent	7.10%	5.80%
Effective Income Tax Rate Reconciliation, Tax Credit, Percent	(17.10%)	(11.40%)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	(8.50%)	(0.20%)
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Percent	7.90%	0.00%
Effective Income Tax Rate Reconciliation Regulatory Differences Utility Plant Items	(1.50%)	(1.00%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	0.70%	0.40%
Effective Income Tax Rate Reconciliation, Percent	9.60%	28.60%
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions	$ 10,200,000			10,200,000
Unrecognized tax benefit — Temporary tax positions	5,500,000			7,900,000
Total unrecognized tax benefit	15,700,000			18,100,000
NOL and tax credit carryforwards	(15,000,000)			(12,800,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible	13,000,000
Amounts accrued for penalties related to unrecognized tax benefits	$ 0			$ 0
Internal Revenue Service (IRS)
Tax Audits [Abstract]
Year(s) under examination			2012 and 2013			2010 and 2011
Year of carryback claim under examination						2009
State Jurisdiction (Minnesota)
Tax Audits [Abstract]
Year(s) under examination					2010 through 2014
Earliest year subject to examination	2009

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Rate Matters (Details) - USD ($) $ in Millions	1 Months Ended							6 Months Ended
	Jul. 31, 2018	Jun. 30, 2018	Apr. 30, 2018	Sep. 30, 2016	Jun. 30, 2016	Feb. 28, 2015	Nov. 30, 2013	Jun. 30, 2018
FERC Proceeding, MISO ROE Complaint
Rate Matters [Abstract]
Public Utilities, Base Return On Equity Charged To Customers Through Transmission Formula Rates						12.38%	12.38%
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Recommended By Third Parties						8.67%	9.15%
Benson purchase power agreement termination [Member]
Rate Matters [Abstract]
Regulatory Assets		$ 103						$ 103
Public Utilities, Purchase Power Agreement Termination Payments		$ 93						93
Regulatory Asset, Amortization Period		10 years
Laurentian purchase power agreement termination [Member]
Rate Matters [Abstract]
Regulatory Assets		$ 109						$ 109
Regulatory Asset, Amortization Period		6 years
Minnesota Public Utilities Commission | MPUC Proceeding - Tax Cuts and Jobs Act of 2017 [Member]
Rate Matters [Abstract]
Tax Cuts and Jobs Act of 2017, Estimated 2018 Electric Rate Reduction			$ 136
Tax Cuts and Jobs Act of 2017, Estimated 2018 Natural Gas Rate Reduction			7
Tax Cuts and Jobs Act of 2017, Proposed 2018 Electric Refund of TCJA Benefits			68
Tax Cuts and Jobs Act of 2017, Proposed Electric Deferral of TCJA Benefits			44
Tax Cuts and Jobs Act of 2017, Proposed Amount of Accelerated Depreciation			22
Tax Cuts and Jobs Act of 2017, Proposed Low Income Program Funding from TCJA Benefits			2
Tax Cuts and Jobs Act of 2017, Proposed 2018 Natural Gas Refund of TCJA Benefits			$ 3
Federal Energy Regulatory Commission (FERC) | FERC Proceeding, MISO ROE Complaint
Rate Matters [Abstract]
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Approved				10.32%
Public Utilities, Length of Refund Period, In Months				15 months
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, with RTO Adder, Approved								10.82%
Public Utilities, ROE Basis Point Adder, Approved								50
Administrative Law Judge | FERC Proceeding, MISO ROE Complaint
Rate Matters [Abstract]
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Recommended By Third Parties					9.70%
Minnesota Department of Commerce [Member] | MPUC Proceeding - Tax Cuts and Jobs Act of 2017 [Member]
Rate Matters [Abstract]
Tax Cuts and Jobs Act of 2017, Proposed 2018 Total Refund of TCJA Benefits		$ 90
Tax Cuts and Jobs Act of 2017, Proposed Total Deferral of TCJA Benefits		$ 53
Subsequent Event [Member] | South Dakota Public Utilities Commission [Member] | SDPUC Proceeding - Tax Cuts and Jobs Act of 2017 [Member]
Rate Matters [Abstract]
Tax Cuts and Jobs Act of 2017, Approved Refund of 2018 TCJA Benefits	$ 11
Public Utilities, Length of Stay-out Provision, In Years	2 years

XML

Commitments and Contingencies, Purchased Power Agreements (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($) MW	Dec. 31, 2017 USD ($) MW
Independent Power Producing Entities
Purchased Power Agreements [Abstract]
Generating capacity under long term purchased power agreements (in MW) | MW	1,002	1,069
Purchase Power Agreement Expiration (year)	2027
Payment or Performance Guarantee
Purchased Power Agreements [Abstract]
Lease Guarantee Expiration (year)	2019
Other MGP Sites [Member]
Purchased Power Agreements [Abstract]
Accrual for Environmental Loss Contingencies, Gross | $	$ 3	$ 3

XML

Commitments and Contingencies Commitments and Contingencies, Guarantees and Indemnifications (Details) - Payment or Performance Guarantee - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Guarantor Obligations [Line Items]
Lease Guarantee Expiration (year)	2019
Guarantees issued and outstanding	$ 4.8	$ 4.8

XML

Commitments and Contingencies, Environmental Contingencies (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fargo MGP Site
Environmental Requirements [Abstract]
Accrual for Environmental Loss Contingencies, Gross	$ 10	$ 16
Current Cost Estimate for Site Remediation	22
Estimated amount spent on cleanup	$ 12
Percentage of Response Costs Allocable to the Minnesota Jurisdiction	88.00%
Other MGP Sites [Member]
Environmental Requirements [Abstract]
Accrual for Environmental Loss Contingencies, Gross	$ 3	$ 3
Number of identified MGP sites under current investigation and/or remediation in addition to those separately disclosed	5

XML

Borrowings and Other Financing Instruments, Short-Term Borrowings (Details) - USD ($)	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
Amount outstanding at period end	$ 0	$ 20,000,000
Money Pool
Short-term Debt [Line Items]
Borrowing limit	250,000,000	250,000,000
Amount outstanding at period end	62,000,000	85,000,000
Average amount outstanding	1,000,000	25,000,000
Maximum amount outstanding	$ 62,000,000	$ 142,000,000
Weighted average interest rate, computed on a daily basis (percentage)	1.85%	1.14%
Weighted average interest rate at period end (percentage)	1.85%	1.18%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 500,000,000	$ 500,000,000
Amount outstanding at period end	0	20,000,000
Average amount outstanding	0	62,000,000
Maximum amount outstanding	$ 0	$ 237,000,000
Weighted average interest rate, computed on a daily basis (percentage)		1.10%
Weighted average interest rate at period end (percentage)		1.93%

XML

Borrowings and Other Financing Instruments, Letters of Credit (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 0	$ 20,000
Letter of Credit
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 36,000	$ 24,000
Letter of Credit | Letter of Credit
Line of Credit Facility [Line Items]
Term of letters of credit (in years)	1 year

XML

Borrowings and Other Financing Instruments, Credit Facility (Details) - Credit Facility - USD ($)		6 Months Ended
		Jun. 30, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Credit Facility	[1]	$ 500,000,000
Drawn	[2]	36,000,000
Available		$ 464,000,000
Maturity Date		Jun. 30, 2021
Direct advances on the credit facility outstanding		$ 0	$ 0

[1] This credit facility expires in June 2021.

[2] Includes outstanding letters of credit.

XML

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities (Details)	6 Months Ended
	Jun. 30, 2018
Minimum | Commingled and international equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Notice period for investment redemption (in days)	1 day
Minimum | Real Estate Funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Notice period for investment redemption (in days)	45 days
Maximum | Commingled and international equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Notice period for investment redemption (in days)	90 days
Maximum | Real Estate Funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Notice period for investment redemption (in days)	90 days

XML

Fair Value of Financial Assets and Liabilities, Cost and Fair Value of Nuclear Decommissioning Fund (Details) - USD ($) $ in Thousands		6 Months Ended		12 Months Ended
		Jun. 30, 2018		Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Gain on Securities		$ 547,000		$ 560,000
Unrealized Loss on Securities		23,000		7,000
Investments [Abstract]
Miscellaneous investments		51,000		49,000
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		30,868	[1]	28,741	[2]
Investments [Abstract]
Equity Securities		1,620,429	[1]	1,590,849	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Non U.S. equities
Investments [Abstract]
Equity Securities		262,468	[1]	263,694	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Emerging market debt funds
Investments [Abstract]
Equity Securities		158,296	[1]	156,057	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Private equity investments
Investments [Abstract]
Equity Securities		150,565	[1]	141,413	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Real estate
Investments [Abstract]
Equity Securities		128,115	[1]	130,787	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Other commingled funds
Investments [Abstract]
Equity Securities	[2]			9,340
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Government securities
Investments [Abstract]
Available-for-sale Securities, Debt Securities		75,806	[1]	67,760	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | U.S. corporate bonds
Investments [Abstract]
Available-for-sale Securities, Debt Securities		330,170	[1]	319,809	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Non U.S. corporate bonds
Investments [Abstract]
Available-for-sale Securities, Debt Securities		57,902	[1]	50,121	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | U.S. equities
Investments [Abstract]
Equity Securities		269,483	[1]	271,166	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Non U.S. equities
Investments [Abstract]
Equity Securities		156,756	[1]	151,961	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		30,868	[1]	28,741	[2]
Alternative Investment, Fair Value Disclosure		665,969	[1],[3]	659,086	[2],[4]
Investments [Abstract]
Equity Securities		2,144,330	[1]	2,143,281	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Non U.S. equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure		90,402	[1],[3]	89,857	[2],[4]
Investments [Abstract]
Equity Securities		287,947	[1]	306,408	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Emerging market debt funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure		158,075	[1],[3]	166,375	[2],[4]
Investments [Abstract]
Equity Securities		158,075	[1]	166,375	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure		220,460	[1],[3]	198,037	[2],[4]
Investments [Abstract]
Equity Securities		220,460	[1]	198,037	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure		197,032	[1],[3]	201,842	[2],[4]
Investments [Abstract]
Equity Securities		197,032	[1]	201,842	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Other commingled funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure	[2],[4]			2,975
Investments [Abstract]
Equity Securities	[2]			9,261
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Investments [Abstract]
Available-for-sale Securities, Debt Securities		75,477	[1]	69,413	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | U.S. corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Investments [Abstract]
Available-for-sale Securities, Debt Securities		322,689	[1]	322,129	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Non U.S. corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Investments [Abstract]
Available-for-sale Securities, Debt Securities		56,422	[1]	50,102	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | U.S. equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Investments [Abstract]
Equity Securities		568,134	[1]	556,974	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Non U.S. equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Investments [Abstract]
Equity Securities		227,226	[1]	233,999	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		30,868	[1]	28,741	[2]
Investments [Abstract]
Equity Securities		1,023,773	[1]	1,042,551	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Non U.S. equities
Investments [Abstract]
Equity Securities		197,545	[1]	216,551	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Emerging market debt funds
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Private equity investments
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Real estate
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Other commingled funds
Investments [Abstract]
Equity Securities	[2]			6,286
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Government securities
Investments [Abstract]
Available-for-sale Securities, Debt Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | U.S. corporate bonds
Investments [Abstract]
Available-for-sale Securities, Debt Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Non U.S. corporate bonds
Investments [Abstract]
Available-for-sale Securities, Debt Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | U.S. equities
Investments [Abstract]
Equity Securities		568,134	[1]	556,974	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Non U.S. equities
Investments [Abstract]
Equity Securities		227,226	[1]	233,999	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		0	[1]	0	[2]
Investments [Abstract]
Equity Securities		454,588	[1]	441,644	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Non U.S. equities
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Emerging market debt funds
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Private equity investments
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Real estate
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Other commingled funds
Investments [Abstract]
Equity Securities	[2]			0
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Government securities
Investments [Abstract]
Available-for-sale Securities, Debt Securities		75,477	[1]	69,413	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | U.S. corporate bonds
Investments [Abstract]
Available-for-sale Securities, Debt Securities		322,689	[1]	322,129	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Non U.S. corporate bonds
Investments [Abstract]
Available-for-sale Securities, Debt Securities		56,422	[1]	50,102	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | U.S. equities
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Non U.S. equities
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		0	[1]	0	[2]
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Non U.S. equities
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Emerging market debt funds
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Private equity investments
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Real estate
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Other commingled funds
Investments [Abstract]
Equity Securities	[2]			0
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Government securities
Investments [Abstract]
Available-for-sale Securities, Debt Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | U.S. corporate bonds
Investments [Abstract]
Available-for-sale Securities, Debt Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Non U.S. corporate bonds
Investments [Abstract]
Available-for-sale Securities, Debt Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | U.S. equities
Investments [Abstract]
Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Non U.S. equities
Investments [Abstract]
Equity Securities		$ 0	[1]	$ 0	[2]

[1] Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $51 million of rabbi trust assets and miscellaneous investments.

[2] Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $49 million of rabbi trust assets and miscellaneous investments.

[3] Due to limited availability of published pricing and a lack of immediate redeemability, certain fund investments measured at NAV are not required to be categorized within the fair value hierarchy.

[4] Due to limited availability of published pricing and a lack of immediate redeemability, certain fund investments measured at NAV are not required to be categorized within the fair value hierarchy.

XML

Fair Value of Financial Assets and Liabilities, Final Contractual Maturity Dates of Debt Securities in Nuclear Decommissioning Fund (Details) $ in Thousands	Jun. 30, 2018 USD ($)
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	$ 6,926
Due in 1 to 5 Years	113,449
Due in 5 to 10 Years	205,039
Due after 10 Years	129,174
Total	454,588
Government securities
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0
Due in 1 to 5 Years	3,930
Due in 5 to 10 Years	2,300
Due after 10 Years	69,247
Total	75,477
U.S. corporate bonds
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	4,919
Due in 1 to 5 Years	89,594
Due in 5 to 10 Years	172,423
Due after 10 Years	55,753
Total	322,689
Non U.S. corporate bonds
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	2,007
Due in 1 to 5 Years	19,925
Due in 5 to 10 Years	30,316
Due after 10 Years	4,174
Total	$ 56,422

XML

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities, Cost and Fair Value of Rabbi Trust (Details) - Fair Value Measured on a Recurring Basis - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	$ 10,817	$ 11,115
Cost | Rabbi Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	394	783
Cost | Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	10,423	10,332
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	11,768	12,066
Fair Value | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	11,768	12,066
Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	0	0
Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	0	0
Fair Value | Rabbi Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	394	783
Fair Value | Rabbi Trust [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	394	783
Fair Value | Rabbi Trust [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	0	0
Fair Value | Rabbi Trust [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	0	0
Fair Value | Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	11,374	11,283
Fair Value | Mutual Funds [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	11,374	11,283
Fair Value | Mutual Funds [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	0	0
Fair Value | Mutual Funds [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	$ 0	$ 0

[1] Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet.

XML

Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details) gal in Thousands, MWh in Thousands, MMBTU in Thousands, $ in Millions		6 Months Ended
		Jun. 30, 2018 USD ($) MMBTU gal MWh Counterparty	Dec. 31, 2017 MMBTU gal MWh
Credit Concentration Risk
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty		10
Credit Concentration Risk | Municipal or Cooperative Entities or Other Utilities [Member]
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty		10
Credit Concentration Risk | External Credit Rating, Investment Grade [Member]
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty		5
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $		$ 39.7
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		48.00%
Credit Concentration Risk | No Investment Grade Ratings from External Credit Rating Agencies [Member]
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty		5
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $		$ 20.1
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		24.00%
Interest Rate Derivatives
Interest Rate Derivatives [Abstract]
Amount of accumulated other comprehensive gains (losses) related to interest rate derivatives expected to be reclassified into earnings within the next twelve months | $		$ (0.8)
Electric Commodity (in megawatt hours)
Gross Notional Amounts of Commodity Forwards, Options and FTRs [Abstract]
Derivative, Nonmonetary Notional amount | MWh	[1],[2]	73,771	41,711
Natural Gas Commodity (in million British thermal units)
Gross Notional Amounts of Commodity Forwards, Options and FTRs [Abstract]
Derivative, Nonmonetary Notional amount | MMBTU	[1],[2]	7,403	23,829
Vehicle Fuel Commodity (in gallons)
Gross Notional Amounts of Commodity Forwards, Options and FTRs [Abstract]
Derivative, Nonmonetary Notional amount | gal	[1],[2]	120	240
Commodity Derivative
Reclassification of Cash Flow Hedge Gain (Loss) [Abstract]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months | $		$ 0.1

[1] Amounts are not reflective of net positions in the underlying commodities.

[2] Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.

XML

Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017
Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract]
Derivative instruments designated as fair value hedges		$ 0	$ 0	$ 0		$ 0
Recognized gains (losses) from fair value hedges or related hedged transactions		0	0	0		0
Designated as Hedging Instrument | Cash Flow Hedges
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss		31,000	43,000	38,000		43,000
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		0	0	0		0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		229,000	345,000	461,000		687,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0	0		0
Pre-tax gains (losses) recognized during the period in income		0	0	0		0
Designated as Hedging Instrument | Cash Flow Hedges | Interest Rate
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss		0	0	0		0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		0	0	0		0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	[1]	264,000	350,000	525,000		692,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0	0		0
Pre-tax gains (losses) recognized during the period in income		0	0	0		0
Designated as Hedging Instrument | Cash Flow Hedges | Vehicle Fuel And Other Commodity
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss		31,000	43,000	38,000		43,000
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		0	0	0		0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	[2]	(35,000)	(5,000)	(64,000)		(5,000)
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0	0		0
Pre-tax gains (losses) recognized during the period in income		0	0	0		0
Other Derivative Instruments
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss		0	0	0		0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		24,244,000	(1,577,000)	(4,785,000)		(3,489,000)
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		0	0	0		0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		1,142,000	(1,149,000)	2,790,000		(3,239,000)
Pre-tax gains (losses) recognized during the period in income		2,263,000	5,977,000	8,577,000		5,654,000
Other Derivative Instruments | Commodity Trading
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss		0	0	0		0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		0	0	0		0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		0	0	0		0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0	0		0
Pre-tax gains (losses) recognized during the period in income	[3]	2,263,000	5,977,000	8,981,000		6,599,000
Other Derivative Instruments | Electric Commodity
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss		0	0	0		0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		24,262,000	(1,526,000)	(5,615,000)		(2,772,000)
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		0	0	0		0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	[4]	1,142,000	(1,149,000)	3,311,000		(3,937,000)
Pre-tax gains (losses) recognized during the period in income		0	0	0		0
Other Derivative Instruments | Natural Gas Commodity
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss		0	0	0		0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		(18,000)	(51,000)	830,000		(717,000)
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		0	0	0		0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0	(521,000)	[5]	698,000	[5]
Pre-tax gains (losses) recognized during the period in income		$ 0	$ 0	$ (404,000)	[5]	$ (945,000)	[5]

[1] Amounts are recorded to interest charges.

[2] Amounts are recorded to operating and maintenance (O&M) expenses.

[3] Amounts are recorded to electric operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue, as appropriate.

[4] Amounts are recorded to electric fuel and purchased power. These derivative settlement gains and losses are shared with electric customers through fuel and purchased energy cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.

[5] Amounts are recorded to cost of natural gas sold and transported. These derivative settlement gains and losses are shared with natural gas customers through purchased natural gas cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.

XML

Fair Value of Financial Assets and Liabilities, Credit Related Contingent Features (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Derivative instruments in a gross liability position	$ 0	$ 0
Collateral posted on derivative instruments	0	0
Collateral posted related to adequate assurance clauses in derivative contracts	$ 0	$ 0

XML

Fair Value of Financial Assets and Liabilities, Derivative Assets and Liabilities at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2018		Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative Asset, Collateral, Obligation to Return Cash, Offset	$ 0		$ 0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	4,900		3,100
Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	31,268		25,230
Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	26,790		28,102
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	18,029		17,697
Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	92,122		102,742
Fair Value Measured on a Recurring Basis | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	31,244		24,573
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(8,778)	[1]	(12,169)	[2]
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	8,277		7,233
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(8,601)	[1]	(11,744)	[2]
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	22,719		17,156
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(177)	[1]	(425)	[2]
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	167		77
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	0	[1]	0	[2]
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	26,682		27,982
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(12,085)	[1]	(6,502)	[2]
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	26,682		27,982
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(12,085)	[1]	(6,502)	[2]
Fair Value Measured on a Recurring Basis | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	4,178		3,592
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(9,982)	[1]	(12,399)	[2]
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	4,178		3,592
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(9,805)	[1]	(11,974)	[2]
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0		0
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(177)	[1]	(425)	[2]
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	9,135		12,829
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(15,738)	[1]	(9,334)	[2]
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	9,135		12,829
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(15,738)	[1]	(9,334)	[2]
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	480		1,691
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	480		1,691
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0		0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0		0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0		0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0		0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	286		1,713
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	286		1,713
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0		0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0		0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0		0
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	14,985		17,328
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	14,737		17,144
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0		0
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	167		77
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	33,171		29,121
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	33,171		29,121
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	12,147		13,853
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	12,147		13,853
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0		0
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	24,476		22,163
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	24,476		22,163
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	24,557		17,723
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,661		142
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	22,896		17,581
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0		0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	5,596		5,363
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	5,596		5,363
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	1,727		425
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	1,550		0
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	177		425
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	397		0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	397		0
Fair Value, Measurements, Nonrecurring | Other Current Assets | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	24	[3]	657	[4]
Fair Value, Measurements, Nonrecurring | Other Noncurrent Assets | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	108	[3]	120	[4]
Fair Value, Measurements, Nonrecurring | Other Current Liabilities | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	13,851	[3]	14,105	[4]
Fair Value, Measurements, Nonrecurring | Other Noncurrent Liabilities | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	82,987	[3]	89,913	[4]
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	40,022		36,742
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	16,878		18,977
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	22,896		17,581
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	167		77
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	38,767		34,484
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	38,767		34,484
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	14,160		15,991
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	13,983		15,566
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	177		425
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	24,873		22,163
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	24,873		22,163
Cash Flow Hedges | Fair Value Measured on a Recurring Basis | Other Current Assets | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	81		107
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	0	[1]	0
Cash Flow Hedges | Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0		0
Cash Flow Hedges | Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	81		107
Cash Flow Hedges | Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0		0
Cash Flow Hedges | Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 81		$ 107

[1] NSP-Minnesota nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at June 30, 2018. At June 30, 2018, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $4.9 million. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

[2] NSP-Minnesota nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2017. At Dec. 31, 2017, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $3.1 million. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

[3] During 2006, NSP-Minnesota qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts is being amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

[4] During 2006, NSP-Minnesota qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts is being amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

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Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) - Commodity Contract - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period		$ 13,516,000	$ 4,643,000	$ 22,662,000	$ 15,320,000
Purchases		26,395,000	40,460,000	26,397,000	40,740,000
Settlements		(5,170,000)	(8,166,000)	(7,104,000)	(11,592,000)
Gains (losses) recognized in earnings	[1]	(2,654,000)	6,007,000	(374,000)	5,215,000
Net losses recognized as regulatory assets and liabilities		(4,058,000)	(2,372,000)	(13,552,000)	(9,111,000)
Balance at end of period		28,029,000	40,572,000	28,029,000	40,572,000
Transfers into Level 3		0	0	0	0
Transfers out of Level 3		$ 0	$ 0	$ 0	$ 0

[1] (a) These amounts relate to commodity derivatives held at the end of the period.

XML

Fair Value of Financial Assets and Liabilities, Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Carrying Amount
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	$ 4,935,068	$ 4,933,018
Fair Value
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	$ 5,192,385	$ 5,601,919

XML

Other (Expense) Income, Net (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other Income and Expenses [Abstract]
Interest income	$ 522	$ 605	$ 3,457	$ 3,314
Other nonoperating income	697	17	698	27
Insurance policy expense	(1,537)	(856)	(1,195)	(1,711)
Defined Benefit Plan, Non-service Costs	(1,916)	(3,398)	(4,978)	(6,796)
Other expense, net	$ (2,234)	$ (3,632)	$ (2,018)	$ (5,166)

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Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
Segment Reporting Information [Line Items]
Operating revenues	$ 1,187,735		$ 1,164,940		$ 2,498,486		$ 2,472,080
Net income (loss)	92,387		87,662		204,127		181,828
Affiliate electric revenue	117,417		119,385		234,389		243,074
Regulated Electric
Segment Reporting Information [Line Items]
Operating revenues	1,096,536		1,080,022		2,158,964		2,159,161
Net income (loss)	88,875		89,477		174,597		167,559
Regulated Natural Gas
Segment Reporting Information [Line Items]
Operating revenues	83,228		78,183		324,804		299,460
Net income (loss)	399		(3,360)		25,844		14,145
All Other
Segment Reporting Information [Line Items]
Operating revenues	8,215		7,155		15,271		14,082
Net income (loss)	3,113		1,545		3,686		124
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	1,187,735	[1],[2]	1,164,940	[1],[2]	2,498,486	[3],[4]	2,472,080	[3],[4]
Operating Segments | Regulated Electric
Segment Reporting Information [Line Items]
Operating revenues	1,096,408	[1]	1,079,779	[1]	2,158,671	[3]	2,158,809	[3]
Operating Segments | Regulated Natural Gas
Segment Reporting Information [Line Items]
Operating revenues	83,112	[2]	78,006	[2]	324,544	[4]	299,189	[4]
Operating Segments | All Other
Segment Reporting Information [Line Items]
Operating revenues	8,215		7,155		15,271		14,082
Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(244)		(420)		(553)		(623)
Net income (loss)	0		0		0		0
Intersegment Eliminations | Regulated Electric
Segment Reporting Information [Line Items]
Operating revenues	128		243		293		352
Intersegment Eliminations | Regulated Natural Gas
Segment Reporting Information [Line Items]
Operating revenues	116		177		260		271
Intersegment Eliminations | All Other
Segment Reporting Information [Line Items]
Operating revenues	$ 0		$ 0		$ 0		$ 0

[1] Operating revenues include 117 million and 119 million of affiliate electric revenue for the three months ended June 30, 2018 and 2017.

[2] Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended June 30, 2018 and 2017.

[3] Operating revenues include $234 million and $243 million of affiliate electric revenue for the six months ended June 30, 2018 and 2017.

[4] Operating revenues include an immaterial amount of affiliate gas revenue for the six months ended June 30, 2018 and 2017.

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Benefit Plans and Other Postretirement Benefits (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2018 USD ($) Plan	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Pension Plan [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost		$ 6,982	$ 6,958	$ 13,964	$ 13,916
Interest cost (a)		8,804	10,177	17,608	20,354
Expected return on plan assets (a)		(14,542)	(15,017)	(29,083)	(30,034)
Amortization of prior service (credit) cost (a)		(28)	265	(57)	530
Amortization of net loss (a)		9,614	9,902	19,229	19,804
Net periodic benefit cost		10,830	12,285	21,661	24,570
Costs not recognized due to the effects of regulation		(3,069)	(4,899)	(5,832)	(9,798)
Net benefit cost recognized for financial reporting		7,761	7,386	15,829	14,772
Total contributions to the pension plans during the period	$ 63,000
Pension Plan [Member] | Xcel Energy Inc.
Components of Net Periodic Benefit Cost [Abstract]
Total contributions to the pension plans during the period	$ 150,000
Number of Xcel Energy's pension plans to which contributions were made | Plan	4
Other Postretirement Benefits Plan [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost		43	36	86	72
Interest cost (a)		769	854	1,538	1,708
Expected return on plan assets (a)		(96)	(54)	(192)	(108)
Amortization of prior service (credit) cost (a)		(759)	(759)	(1,518)	(1,518)
Amortization of net loss (a)		595	507	1,190	1,014
Net periodic benefit cost		552	584	1,104	1,168
Costs not recognized due to the effects of regulation		0	0	0	0
Net benefit cost recognized for financial reporting		$ 552	$ 584	$ 1,104	$ 1,168

XML

Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income at beginning of period			$ 5,475,570
(Gains) losses reclassified from net accumulated other comprehensive loss	$ 219	$ 240	311	$ 478
Accumulated other comprehensive (loss) income at end of period	5,526,761		5,526,761
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income at beginning of period	(20,723)	(18,005)	(20,895)	(18,208)
Other comprehensive income (loss) before reclassifications	22	26	27	26
(Gains) losses reclassified from net accumulated other comprehensive loss	165	204	332	407
Net current period other comprehensive income (loss)	187	230	359	433
Accumulated other comprehensive (loss) income at end of period	(20,536)	(17,775)	(20,536)	(17,775)
Unrealized Gains and Losses on Marketable Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income at beginning of period	0	105	128	105
Other comprehensive income (loss) before reclassifications	0	0	0	0
(Gains) losses reclassified from net accumulated other comprehensive loss	0	0	(128)	0
Net current period other comprehensive income (loss)	0	0	(128)	0
Accumulated other comprehensive (loss) income at end of period	0	105	0	105
Defined Benefit Pension and Postretirement Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income at beginning of period	(3,717)	(2,645)	(3,770)	(2,680)
Other comprehensive income (loss) before reclassifications	0	0	0	0
(Gains) losses reclassified from net accumulated other comprehensive loss	54	36	107	71
Net current period other comprehensive income (loss)	54	36	107	71
Accumulated other comprehensive (loss) income at end of period	(3,663)	(2,609)	(3,663)	(2,609)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income at beginning of period	(24,440)	(20,545)	(24,537)	(20,783)
Other comprehensive income (loss) before reclassifications	22	26	27	26
(Gains) losses reclassified from net accumulated other comprehensive loss	219	240	311	478
Net current period other comprehensive income (loss)	241	266	338	504
Accumulated other comprehensive (loss) income at end of period	$ (24,199)	$ (20,279)	$ (24,199)	$ (20,279)

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Other Comprehensive Income (Reclassification from AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating and maintenance expenses	$ 309,196	$ 305,189	$ 601,491	$ 613,815
Total, pre-tax	(101,361)	(121,432)	(225,812)	(254,613)
Tax benefit	8,974	33,770	21,685	72,785
Total amounts reclassified, net of tax	219	240	311	478
Gains and Losses on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amounts reclassified, net of tax	165	204	332	407
Gains and Losses on Cash Flow Hedges | Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total, pre-tax	229	345	461	687
Tax benefit	(64)	(141)	(129)	(280)
Total, net of tax	165	204	332	407
Gains and Losses on Cash Flow Hedges | Interest Rate Derivatives | Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	264	350	525	692
Gains and Losses on Cash Flow Hedges | Vehicle Fuel Derivatives | Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating and maintenance expenses	(35)	(5)	(64)	(5)
Amortization of net loss | Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total, pre-tax	125	109	250	218
Prior service credit | Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total, pre-tax	(49)	(51)	(98)	(100)
Defined Benefit Pension and Postretirement Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amounts reclassified, net of tax	54	36	107	71
Defined Benefit Pension and Postretirement Items | Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total, pre-tax	76	58	152	118
Tax (benefit) expense	(22)	(22)	(45)	(47)
Total amounts reclassified, net of tax	54	36	107	71
Marketable securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amounts reclassified, net of tax	0	0	(128)	0
Marketable securities | Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realization of gains	0	0	(179)	0
Total, pre-tax	0	0	(179)	0
Tax benefit	0	0	51	0
Total, net of tax	$ 0	$ 0	$ (128)	$ 0

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Revenues Revenues (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 1,147,216		$ 1,112,150		$ 2,403,601		$ 2,357,475
Alternative revenue and other	40,519		52,790		94,885		114,605
Total operating revenues	1,187,735		1,164,940		$ 2,498,486		2,472,080
Maximum number of months following end of annual period in which revenues are earned to be included in incentive programs					24 months
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	1,187,735	[1],[2]	1,164,940	[1],[2]	$ 2,498,486	[3],[4]	2,472,080	[3],[4]
Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	918,465		898,851		1,942,959		1,913,401
Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	360,194		332,009		809,305		764,045
Retail | Commercial and Industrial (C&I)
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	548,169		558,341		1,113,143		1,131,973
Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	10,102		8,501		20,511		17,383
Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	42,033		28,841		88,398		74,760
Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	59,951		56,177		114,749		110,136
Interchange
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	117,417		119,384		234,389		243,073
Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	9,350		8,897		23,106		16,105
Regulated Electric
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,059,869		1,035,301		2,078,420		2,062,550
Alternative revenue and other	36,539		44,478		80,251		96,259
Total operating revenues	1,096,536		1,080,022		2,158,964		2,159,161
Regulated Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	1,096,408	[1]	1,079,779	[1]	2,158,671	[3]	2,158,809	[3]
Regulated Electric | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	834,435		823,454		1,623,306		1,621,173
Regulated Electric | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	311,086		288,733		622,215		593,146
Regulated Electric | Retail | Commercial and Industrial (C&I)
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	514,710		526,867		982,733		1,011,970
Regulated Electric | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	8,639		7,854		18,358		16,057
Regulated Electric | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	42,033		28,841		88,398		74,760
Regulated Electric | Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	59,951		56,177		114,749		110,136
Regulated Electric | Interchange
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	117,417		119,384		234,389		243,073
Regulated Electric | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	6,033		7,445		17,578		13,408
Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	79,132		69,694		309,910		280,843
Alternative revenue and other	3,980		8,312		14,634		18,346
Total operating revenues	83,228		78,183		324,804		299,460
Regulated Natural Gas | Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	83,112	[2]	78,006	[2]	324,544	[4]	299,189	[4]
Regulated Natural Gas | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	75,815		68,242		304,382		278,146
Regulated Natural Gas | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	42,398		36,860		174,057		158,273
Regulated Natural Gas | Retail | Commercial and Industrial (C&I)
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	33,417		31,382		130,325		119,873
Regulated Natural Gas | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0		0		0		0
Regulated Natural Gas | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0		0		0		0
Regulated Natural Gas | Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0		0		0		0
Regulated Natural Gas | Interchange
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0		0		0		0
Regulated Natural Gas | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	3,317		1,452		5,528		2,697
All Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	8,215		7,155		15,271		14,082
Alternative revenue and other	0		0		0		0
Total operating revenues	8,215		7,155		15,271		14,082
All Other | Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues	8,215		7,155		15,271		14,082
All Other | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	8,215		7,155		15,271		14,082
All Other | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	6,710		6,416		13,033		12,626
All Other | Retail | Commercial and Industrial (C&I)
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	42		92		85		130
All Other | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,463		647		2,153		1,326
All Other | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0		0		0		0
All Other | Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0		0		0		0
All Other | Interchange
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0		0		0		0
All Other | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 0		$ 0		$ 0		$ 0

[1] Operating revenues include 117 million and 119 million of affiliate electric revenue for the three months ended June 30, 2018 and 2017.

[2] Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended June 30, 2018 and 2017.

[3] Operating revenues include $234 million and $243 million of affiliate electric revenue for the six months ended June 30, 2018 and 2017.

[4] Operating revenues include an immaterial amount of affiliate gas revenue for the six months ended June 30, 2018 and 2017.