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 Sept. 30, 2017

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 Oct. 27, 2017
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	27
Item 4 —	Controls and Procedures	34
PART II —	OTHER INFORMATION
Item 1 —	Legal Proceedings	34
Item 1A —	Risk Factors	35
Item 6 —	Exhibits	35
SIGNATURES		36
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 Sept. 30						Nine Months Ended Sept. 30
	2017			2016			2017			2016
Operating revenues
Electric, non-affiliates	$	1,167,447		$	1,161,259		$	3,083,182		$	2,973,350
Electric, affiliates	123,524			121,315			366,598			359,338
Natural gas	57,442			55,519			356,631			314,020
Other	7,366			7,286			21,448			21,404
Total operating revenues	1,355,779			1,345,379			3,827,859			3,668,112
Operating expenses
Electric fuel and purchased power	435,003			435,560			1,215,071			1,148,818
Cost of natural gas sold and transported	20,723			19,105			198,968			163,608
Cost of sales — other	4,313			4,898			13,085			14,185
Operating and maintenance expenses	288,770			315,298			909,381			954,334
Conservation program expenses	31,674			23,926			92,238			67,424
Depreciation and amortization	176,739			149,408			522,070			442,649
Taxes (other than income taxes)	62,220			49,763			191,989			186,100
Total operating expenses	1,019,442			997,958			3,142,802			2,977,118
Operating income	336,337			347,421			685,057			690,994
Other income (expense), net	2,120			(439		)	3,750			1,834
Allowance for funds used during construction — equity	10,683			7,983			23,391			21,011
Interest charges and financing costs
Interest charges — includes other financing costs of  $1,845, $1,822, $5,437 and $5,325, respectively	57,577			57,859			172,548			168,010
Allowance for funds used during construction — debt	(5,383		)	(3,591		)	(11,909		)	(9,575		)
Total interest charges and financing costs	52,194			54,268			160,639			158,435
Income before income taxes	296,946			300,697			551,559			555,404
Income taxes	67,943			94,145			140,728			176,047
Net income	$	229,003		$	206,552		$	410,831		$	379,357

See Notes to Consolidated Financial Statements

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NSP-MINNESOTA AND SUBSIDIARIES

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED)

(amounts in thousands)

	Three Months Ended Sept. 30					Nine Months Ended Sept. 30
	2017		2016			2017		2016
Net income	$	229,003	$	206,552		$	410,831	$	379,357
Other comprehensive income
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, net of tax of $21, $15, $70 and $45, respectively	39		19			110		57
Derivative instruments:
Net fair value increase (decrease), net of tax of $16, $(1), $33 and $3, respectively	22		(1		)	48		5
Reclassification of losses to net income, net of tax of $222, $162, $502 and $467, respectively	379		213			786		657
	401		212			834		662
Other comprehensive income	440		231			944		719
Comprehensive income	$	229,443	$	206,783		$	411,775	$	380,076

See Notes to Consolidated Financial Statements

4

NSP-MINNESOTA AND SUBSIDIARIES

CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED)

(amounts in thousands)

	Nine Months Ended Sept. 30,
	2017			2016
Operating activities
Net income	$	410,831		$	379,357
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	526,784			447,284
Nuclear fuel amortization	87,654			89,475
Deferred income taxes	98,125			129,410
Amortization of investment tax credits	(1,241		)	(1,260		)
Allowance for equity funds used during construction	(23,391		)	(21,011		)
Net realized and unrealized hedging and derivative transactions	(2,703		)	2,873
Other, net	(1,072		)	—
Changes in operating assets and liabilities:
Accounts receivable	(14,677		)	(46,294		)
Accrued unbilled revenues	33,465			26,660
Inventories	(4,265		)	5,709
Other current assets	35,591			24,431
Accounts payable	(34,275		)	19,736
Net regulatory assets and liabilities	(15,467		)	57,452
Other current liabilities	(73,898		)	(3,947		)
Pension and other employee benefit obligations	(55,548		)	(42,447		)
Change in other noncurrent assets	(3,585		)	(8,862		)
Change in other noncurrent liabilities	(30,704		)	(17,084		)
Net cash provided by operating activities	931,624			1,041,482
Investing activities
Utility capital/construction expenditures	(696,857		)	(833,845		)
Allowance for equity funds used during construction	23,391			21,011
Purchases investment securities	(965,086		)	(349,717		)
Proceeds from the sale of investment securities	948,558			327,378
Investments in utility money pool arrangement	(122,000		)	(492,000		)
Repayments from utility money pool arrangement	122,000			441,000
Other, net	(3,463		)	(1,262		)
Net cash used in investing activities	(693,457		)	(887,435		)
Financing activities
Repayments of short-term borrowings, net	(85,000		)	(223,000		)
Borrowings under utility money pool arrangement	516,000			424,000
Repayments under utility money pool arrangement	(466,000		)	(424,000		)
Proceeds from issuance of long-term debt	586,264			342,570
Repayments of long-term debt, including reacquisition premiums	(507,865		)	(11		)
Capital contributions from parent	123,247			96,628
Dividends paid to parent	(418,133		)	(306,209		)
Net cash used in financing activities	(251,487		)	(90,022		)
Net change in cash and cash equivalents	(13,320		)	64,025
Cash and cash equivalents at beginning of period	47,595			42,605
Cash and cash equivalents at end of period	$	34,275		$	106,630
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	$	(177,336	)	$	(169,382	)
Cash paid for income taxes, net	(60,911		)	(14,279		)
Supplemental disclosure of non-cash investing transactions:
Property, plant and equipment additions in accounts payable	$	47,261		$	72,889

See Notes to Consolidated Financial Statements

5

NSP-MINNESOTA AND SUBSIDIARIES

CONSOLIDATED BALANCE SHEETS (UNAUDITED)

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

	Sept. 30, 2017			Dec. 31, 2016
Assets
Current assets
Cash and cash equivalents	$	34,275		$	47,595
Accounts receivable, net	344,528			329,481
Accounts receivable from affiliates	19,989			49,355
Accrued unbilled revenues	226,125			259,590
Inventories	349,578			345,192
Regulatory assets	253,876			186,266
Derivative instruments	47,177			22,028
Prepayments and other	65,292			98,006
Total current assets	1,340,840			1,337,513
Property, plant and equipment, net	13,360,494			13,300,793
Other assets
Nuclear decommissioning fund and other investments	2,105,741			1,905,059
Regulatory assets	1,187,195			1,245,151
Derivative instruments	28,520			24,678
Other	13,217			9,086
Total other assets	3,334,673			3,183,974
Total assets	$	18,036,007		$	17,822,280
Liabilities and Equity
Current liabilities
Current portion of long-term debt	$	7		$	10
Short-term debt	—			85,000
Borrowings under utility money pool arrangement	50,000			—
Accounts payable	292,970			371,589
Accounts payable to affiliates	50,745			59,216
Regulatory liabilities	98,587			60,779
Taxes accrued	235,999			241,100
Accrued interest	52,115			71,012
Dividends payable to parent	88,461			89,428
Derivative instruments	18,045			16,606
Customer deposits	103,549			110,244
Other	152,919			150,244
Total current liabilities	1,143,397			1,255,228
Deferred credits and other liabilities
Deferred income taxes	2,947,022			2,788,752
Deferred investment tax credits	22,935			24,175
Regulatory liabilities	491,385			489,825
Asset retirement obligations	2,543,497			2,452,567
Derivative instruments	105,963			116,804
Pension and employee benefit obligations	313,772			368,922
Other	94,372			127,283
Total deferred credits and other liabilities	6,518,946			6,368,328
Commitments and contingencies
Capitalization
Long-term debt	4,932,970			4,843,155
Common stock — authorized 5,000,000 shares of $0.01 par value; 1,000,000 shares outstanding at Sept. 30, 2017 and Dec. 31, 2016, respectively	10			10
Additional paid in capital	3,525,612			3,435,096
Retained earnings	1,934,911			1,941,246
Accumulated other comprehensive loss	(19,839		)	(20,783		)
Total common stockholder’s equity	5,440,694			5,355,569
Total liabilities and equity	$	18,036,007		$	17,822,280

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 Sept. 30, 2017 and Dec. 31, 2016; the results of its operations, including the components of net income and comprehensive income, for the three and nine months ended Sept. 30, 2017 and 2016; and its cash flows for the nine months endedSept. 30, 2017 and 2016. All adjustments are of a normal, recurring nature, except as otherwise disclosed. Management has also evaluated the impact of events occurring after Sept. 30, 2017 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, 2016 balance sheet information has been derived from the audited 2016 consolidated financial statements included in the NSP-Minnesota Annual Report on Form 10-K for the year ended Dec. 31, 2016. 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, 2016, filed with the SEC on Feb. 24, 2017. 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, 2016, appropriately represent, in all material respects, the current status of accounting policies and are incorporated herein by reference.

2. Accounting Pronouncements

Recently Issued

Revenue Recognition— In May 2014, the Financial Accounting Standards Board (FASB) issued Revenue from Contracts with Customers, Topic 606 (Accounting Standards Update (ASU) No. 2014-09), which provides a new framework for the recognition of revenue. NSP-Minnesota expects its adoption will primarily result in increased disclosures regarding revenue related to arrangements with customers, as well as separate presentation of alternative revenue programs. NSP-Minnesota currently expects to implement the standard on a modified retrospective basis, which requires application to contracts with customers effective Jan. 1, 2018, with the cumulative impact on contracts not yet completed as of Dec. 31, 2017 recognized as an adjustment to the opening balance of retained earnings.

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 eliminates the available-for-sale classification for marketable equity securities and also replaces 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 to be recognized in earnings. This guidance will be effective for interim and annual reporting periods beginning after Dec. 15, 2017. NSP-Minnesota expects that 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, currently classified as available-for-sale, will continue to be deferred to a regulatory asset, and that the overall impacts of the Jan. 1, 2018 adoption will not be material.

Leases —In February 2016, the FASB issued Leases, Topic 842 (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. As such, agreements entered prior to Jan. 1, 2017 that are currently considered leases are expected to be recognized on the consolidated balance sheet, including contracts for use of office space, equipment and natural gas storage assets, as well as certain purchased power agreements (PPAs) for natural gas-fueled generating facilities. NSP-Minnesota expects that similar agreements entered after Dec. 31, 2016 will generally qualify as leases under the new standard, but has not yet completed its evaluation of certain other contracts, including arrangements for the secondary use of assets, such as land easements.

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. NSP-Minnesota expects that as a result of application of accounting principles for rate regulated entities, a similar amount of pension cost, including non-service components, will be recognized consistent with the current ratemaking treatment and that the impacts of adoption will be limited to changes in classification of non-service costs in the consolidated statement of income. This guidance will be effective for interim and annual reporting periods beginning after Dec. 15, 2017.

3. Selected Balance Sheet Data

(Thousands of Dollars)	Sept. 30, 2017			Dec. 31, 2016
Accounts receivable, net
Accounts receivable	$	364,970		$	349,449
Less allowance for bad debts	(20,442		)	(19,968		)
	$	344,528		$	329,481

(Thousands of Dollars)	Sept. 30, 2017		Dec. 31, 2016
Inventories
Materials and supplies	$	216,850	$	214,234
Fuel	91,555		97,527
Natural gas	41,173		33,431
	$	349,578	$	345,192

(Thousands of Dollars)	Sept. 30, 2017			Dec. 31, 2016
Property, plant and equipment, net
Electric plant	$	17,323,127		$	17,059,993
Natural gas plant	1,340,688			1,311,235
Common and other property	803,599			710,958
Construction work in progress	508,306			509,891
Total property, plant and equipment	19,975,720			19,592,077
Less accumulated depreciation	(7,015,522		)	(6,682,418		)
Nuclear fuel	2,668,586			2,571,770
Less accumulated amortization	(2,268,290		)	(2,180,636		)
	$	13,360,494		$	13,300,793

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, 2016 appropriately represents, in all material respects, the current status of other income tax matters, and are incorporated herein by reference.

Federal Loss Carryback Claims — In 2012-2015, NSP-Minnesota identified certain expenses related to 2009, 2010, 2011, 2013, 2014 and 2015 that qualify for an extended carryback beyond the typical two-year carryback period. As a result of a higher tax rate in prior years, NSP-Minnesota recognized a tax benefit of approximately $5 million in 2015, $17 million in 2014, $12 million in 2013 and $15 million in 2012.

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 2009 through 2011 and 2012 through 2013 federal income tax returns, following extensions, expires in June 2018 and October 2018, respectively.

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 that would have resulted in $14 million of income tax expense for the 2009 through 2011 claims, and the 2013 through 2015 claims. In the fourth quarter of 2015, the IRS forwarded the issue to the Office of Appeals (Appeals). In the third quarter of 2017, Xcel Energy and Appeals reached an agreement and the benefit related to the agreed upon portions was recognized.

8

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. Xcel Energy anticipates the issue will be forwarded to Appeals. As of Sept. 30, 2017, 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 Sept. 30, 2017, 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 Sept. 30, 2017, Minnesota had not proposed any material adjustments, and there were no other state income tax audits in progress.

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)	Sept. 30, 2017		Dec. 31, 2016
Unrecognized tax benefit — Permanent tax positions	$	9.8	$	21.5
Unrecognized tax benefit — Temporary tax positions	8.1		39.3
Total unrecognized tax benefit	$	17.9	$	60.8

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)	Sept. 30, 2017			Dec. 31, 2016
NOL and tax credit carryforwards	$	(12.5	)	$	(19.3	)

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 audits progress, it is reasonably possible that the amount of unrecognized tax benefit could decrease up to approximately $7 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)	Sept. 30, 2017			Dec. 31, 2016
Payable for interest related to unrecognized tax benefits at beginning of period	$	(2.0	)	$	(0.2	)
Interest income (expense) related to unrecognized tax benefits recorded during the period	1.1			(1.8		)
Payable for interest related to unrecognized tax benefits at end of period	$	(0.9	)	$	(2.0	)

No amounts were accrued for penalties related to unrecognized tax benefits as of Sept. 30, 2017 or Dec. 31, 2016.

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, 2016 and in Note 5 to NSP-Minnesota’s Quarterly Report on Form 10-Q for the quarterly periods ended March 31, 2017 and June 30, 2017, appropriately represent, in all material respects, the current status of other rate matters, and are incorporated herein by reference.

Pending and Recently Concluded Regulatory Proceedings — Minnesota Public Utilities Commission (MPUC)

Minnesota 2016 Multi-Year Electric Rate Case — In June 2017, the MPUC issued a written order. NSP-Minnesota estimated the total rate increase to be approximately $245 million over the four-year period covering 2016-2019.

9

Key terms:

• Four-year period covering 2016-2019;

• Annual sales true-up with decoupling subject to a 3 percent cap;

• Return on equity (ROE) of 9.2 percent and an equity ratio of 52.5 percent;

• Nuclear related costs will not be considered provisional;

• Continued use of all existing riders, however no new riders may be utilized during the four-year term;

• Deferral of incremental 2016 property tax expense above a fixed threshold to 2018 and 2019;

• Four-year stay-out provision for rate cases;

• Property tax true-up mechanism for 2017-2019; and

• Capital expenditure true-up mechanism for 2016-2019.

(Millions of Dollars, Incremental)	2016		2017		2018		2019			Total
Revenues	$	74.99	$	59.86	$	—	$	50.12		$	184.97
NSP-Minnesota’s sales true-up	59.95		—		—		(0.20		)	59.75
Total rate impact	$	134.94	$	59.86	$	—	$	49.92		$	244.72

In September 2017, the MPUC ordered NSP-Minnesota to collect final rates beginning March 1, 2017 (requested date was Jan. 1, 2017). As a result, NSP-Minnesota estimates the adjusted total rate increase to be approximately $240 million over the four-year period covering 2016-2019.

Annual Automatic Adjustment of Fuel Clause Charges — In May 2017, the MPUC voted to disallow approximately $4.4 million of replacement energy costs for the Prairie Island (PI) nuclear facility outages allocated to the Minnesota jurisdiction in 2015. This disallowance was recognized in the second quarter of 2017. In September 2017, the Minnesota Department of Commerce (DOC) recommended the MPUC should hold utilities responsible for incremental costs of replacement power incurred due to unplanned outages under certain circumstances. In addition, the DOC is continuing its review of nuclear costs and operations focusing on PI under the initial rate case and resource plan orders as well as the recently finalized rate case.

Pending Regulatory Proceeding — Federal Energy Regulatory Commission (FERC)

Midcontinent Independent System Operator, Inc. (MISO) 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 December 2015, an administrative law judge (ALJ) recommended the FERC approve a base ROE of 10.32 percent for the MISO TOs. The ALJ found the existing 12.38 percent ROE to be unjust and unreasonable. The recommended 10.32 percent ROE applied a FERC ROE policy adopted in a June 2014 order (Opinion 531). The FERC approved the ALJ recommended 10.32 percent base ROE in an order issued in September 2016. 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. Various parties requested rehearing of the September 2016 order. 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 adder was filed with the FERC, resulting in a second period of potential refund from Feb. 12, 2015 to May 11, 2016. In June 2016, the ALJ recommended a ROE of 9.7 percent, applying the methodology adopted by the FERC in Opinion 531. A final FERC decision on the second ROE complaint was expected later in 2017, but in April 2017, the United States Court of Appeals for the District of Columbia Circuit (D.C. Circuit) by opinion, 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. The MISO TOs are evaluating the impact of the D.C. Circuit ruling on the November 2013 and February 2015 ROE complaints. In September 2017, certain MISO TOs (not including NSP-Minnesota and NSP-Wisconsin) filed a motion to dismiss the second ROE complaint. The motion to dismiss is pending FERC action.

As of Sept. 30, 2017, NSP-Minnesota has processed the refunds for the Nov. 12, 2013 to Feb. 11, 2015 complaint period based on the 10.32 percent ROE provided in the September 2016 FERC order. NSP-Minnesota has also recognized a current refund liability consistent with the best estimate of the final ROE for the Feb. 12, 2015 to May 11, 2016 complaint period.

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6. Commitments and Contingencies

Except to the extent noted below and in Note 5 above, 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, 2016 and in Notes 5 and 6 to the consolidated financial statements included in NSP-Minnesota’s Quarterly Report on Form 10-Q for the quarterly periods ended March 31, 2017 and June 30, 2017, 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

Under certain 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 1,069 megawatts (MW) of capacity under long-term PPAs as of Sept. 30, 2017 and Dec. 31, 2016, 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 expiration dates through 2028.

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 lease agreement expires in 2019.

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

(Millions of Dollars)	Sept. 30, 2017		Dec. 31, 2016
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 from the right-of-way and commenced an investigation of the historic MGP and adjacent properties (the Fargo MGP Site). NSP-Minnesota has recommended that targeted source removal of impacted soils and historic MGP infrastructure should be performed. The North Dakota Department of Health approved NSP-Minnesota’s proposed cleanup plan in January 2017. It is anticipated that remediation activities will be performed in 2018, although the timing and final scope of remediation is dependent on whether reasonable access is provided to NSP-Minnesota to perform and implement the approved cleanup plan. Access agreements have been reached with a majority of the property owners in the area to perform the work. NSP-Minnesota has also initiated insurance recovery litigation in North Dakota. The U.S. District Court for the District of North Dakota agreed to the parties’ request for a stay of the litigation until January 2018.

As of Sept. 30, 2017 and Dec. 31, 2016, NSP-Minnesota had recorded a liability of $16.2 million and $11.3 million, respectively, for the Fargo MGP Site. The current cost estimate for the remediation of the site is approximately $23.0 million, of which approximately $6.8 million has been spent. In December 2015, the North Dakota Public Service Commission (NDPSC) approved NSP-Minnesota’s request to defer costs associated with the Fargo MGP Site, resulting in deferral of all investigation and response costs with the exception of approximately 12 percent allocable to the Minnesota jurisdiction. Uncertainties related to the liability recognized include obtaining access to perform the approved remediation (including the prospective purchase of the historic MGP property), and the potential for contributions from entities that may be identified as potentially responsible parties (PRPs).

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Other MGP and Landfill Sites — NSP-Minnesota is currently involved in investigating and/or remediating several other MGP and landfill sites. NSP-Minnesota has identified six sites, in addition to the site in Fargo, N.D., where former MGP or landfill disposal activities have or may have resulted in site contamination and are under current investigation and/or remediation. At some or all of these sites, there are other parties that may have responsibility for some portion of any remediation. NSP-Minnesota anticipates that the majority of the investigation or remediation at these sites will continue through at least 2018. NSP-Minnesota had accrued $1.1 million and $0.2 million for these sites as of Sept. 30, 2017 and Dec. 31, 2016, respectively. There may be insurance recovery and/or recovery from other PRPs to offset any costs incurred. NSP-Minnesota anticipates that any significant amounts incurred will be recovered from customers.

Environmental Requirements

Water and Waste

Federal Clean Water Act (CWA) Waters of the United States Rule —In 2015, the United States Environmental Protection Agency (EPA) and the U.S. Army Corps of Engineers (Corps) published a final rule that significantly expanded the types of water bodies regulated under the CWA and broadened the scope of waters subject to federal jurisdiction. In October 2015, the U.S. Court of Appeals for the Sixth Circuit issued a nationwide stay of the final rule and subsequently ruled that it, rather than the federal district courts, had jurisdiction over challenges to the rule.  In January 2017, the U.S. Supreme Court agreed to resolve the dispute as to which court should hear challenges to the rule. A ruling is expected in the first quarter of 2018.

In February 2017, President Trump issued an executive order requiring the EPA and the Corps to review and revise the final rule. On June 27, 2017, the agencies issued a proposed rule that rescinds the 2015 final rule and reinstates the prior 1986 definition of “Water of the U.S.” The agencies are also undertaking a rulemaking to develop a new definition of “Waters of the U.S.”

Federal CWA Effluent Limitations Guidelines (ELG) —In 2015, the EPA issued a final ELG rule for power plants that use coal, natural gas, oil or nuclear materials as fuel and discharge treated effluent to surface waters as well as utility-owned landfills that receive coal combustion residuals. In September 2017, the EPA delayed the compliance date for flue gas desulfurization wastewater and bottom ash transport water until November 2020 while the agency conducts a rulemaking process to potentially revise the effluent limitations and pretreatment standards for these waste streams.

Air

Greenhouse Gas (GHG) Emission Standard for Existing Sources (Clean Power Plan or CPP) — In 2015, the EPA issued its final rule for existing power plants.  Among other things, the rule requires that state plans include enforceable measures to ensure emissions from existing power plants achieve the EPA’s state-specific interim (2022-2029) and final (2030 and thereafter) emission performance targets. 

The CPP was challenged by multiple parties in the D.C. Circuit Court.  In February 2016, the U.S. Supreme Court issued an order staying the final CPP rule. In September 2016, the D.C. Circuit Court heard oral arguments in the consolidated challenges to the CPP. The stay will remain in effect until the D.C. Circuit Court reaches its decision and the U.S. Supreme Court either declines to review the lower court’s decision or reaches a decision of its own.

In March 2017, President Trump signed an executive order requiring the EPA Administrator to review the CPP rule and if appropriate, publish proposed rules suspending, revising or rescinding it. Accordingly, the EPA has requested that the D.C. Circuit Court hold the litigation in abeyance until the EPA completes its work under the executive order. The D.C. Circuit granted the EPA’s request and is holding the litigation in abeyance, while considering briefs by the parties on whether the court should remand the challenges to the EPA rather than holding them in abeyance, determining whether and how the court continues or ends the stay that currently applies to the CPP.

In October 2017, the EPA published a proposed rule to repeal the CPP, based on an analysis that the CPP exceeds the EPA’s statutory authority under the Clean Air Act (CAA). The EPA will take public comment on the proposal for 60 days. The EPA stated it has not yet determined whether it will promulgate a new rule to regulate GHG emissions from existing electric generating units.

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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.

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 Sept. 30, 2017			Year Ended Dec. 31, 2016
Borrowing limit	$	250		$	250
Amount outstanding at period end	50			—
Average amount outstanding	50			16
Maximum amount outstanding	116			225
Weighted average interest rate, computed on a daily basis	1.11		%	0.69		%
Weighted average interest rate at period end	1.11			N/A

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 Sept. 30, 2017			Year Ended Dec. 31, 2016
Borrowing limit	$	500		$	500
Amount outstanding at period end	—			85
Average amount outstanding	51			73
Maximum amount outstanding	204			353
Weighted average interest rate, computed on a daily basis	1.33		%	0.65		%
Weighted average interest rate at period end	N/A			0.94

Letters of Credit — NSP-Minnesota uses letters of credit, generally with terms of one year, to provide financial guarantees for certain operating obligations. At Sept. 30, 2017 and Dec. 31, 2016, there were $21 million and $11 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.

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At Sept. 30, 2017, NSP-Minnesota had the following committed credit facility available (in millions of dollars):

Credit Facility (a)		Drawn(b)		Available
$	500	$	21	$	479

^(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 Sept. 30, 2017 and Dec. 31, 2016.

Long-Term Borrowings

In September 2017, NSP-Minnesota issued $600 million of 3.60 percent first mortgage bonds due Sept. 15, 2047.

Debt Redemption

On Sept. 29, 2017, NSP-Minnesota reacquired $500 million of debt with a coupon rate of 5.25 percent and an original maturity date of March 1, 2018. The redemption resulted in payment of an early redemption premium of $7.9 million which was deferred as a regulatory asset.

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.

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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 PI nuclear generating plants. The fund contains cash equivalents, debt securities, equity securities and other investments – all classified as available-for-sale. NSP-Minnesota plans to reinvest matured securities until decommissioning begins. NSP-Minnesota uses the MPUC approved asset allocation for the escrow and investment targets by asset class for both the escrow and 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 other-than-temporary impairments, are deferred as a component of the regulatory asset for nuclear decommissioning.

Unrealized gains for the nuclear decommissioning fund were $511.7 million and $378.6 million at Sept. 30, 2017 and Dec. 31, 2016, respectively, and unrealized losses and amounts recorded as other-than-temporary impairments were $10.3 million and $46.9 million at Sept. 30, 2017 and Dec. 31, 2016, respectively.

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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 at Sept. 30, 2017 and Dec. 31, 2016:

	Sept. 30, 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	$	32,727	$	32,727	$	—	$	—	$	—	$	32,727
Commingled funds:
Non U.S. equities	257,487		204,502		—		—		86,654		291,156
Emerging market debt funds	97,285		—		—		—		106,842		106,842
Private equity investments	139,185		—		—		—		192,098		192,098
Real estate	129,219		—		—		—		195,506		195,506
Other commingled funds	146,179		14,964		—		—		145,313		160,277
Debt securities:
Government securities	45,310		—		44,944		—		—		44,944
U.S. corporate bonds	251,138		—		252,868		—		—		252,868
Non U.S. corporate bonds	46,245		—		46,611		—		—		46,611
Equity securities:
U.S. equities	258,075		509,564		—		—		—		509,564
Non U.S. equities	152,575		224,139		—		—		—		224,139
Total	$	1,555,425	$	985,896	$	344,423	$	—	$	726,413	$	2,056,732

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $49.0 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, 2016
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Investments Measured at NAV (b)		Total
Nuclear decommissioning fund (a)
Cash equivalents	$	20,379	$	20,379	$	—	$	—	$	—	$	20,379
Commingled funds:
Non U.S. equities	260,877		133,126		—		—		112,233		245,359
Emerging market debt funds	93,597		—		—		—		97,543		97,543
Commodity funds	106,571		—		—		—		92,091		92,091
Private equity investments	132,190		—		—		—		190,462		190,462
Real estate	128,630		—		—		—		187,647		187,647
Other commingled funds	151,048		—		—		—		159,489		159,489
Debt securities:
Government securities	32,764		—		31,965		—		—		31,965
U.S. corporate bonds	104,913		—		105,772		—		—		105,772
Non U.S. corporate bonds	21,751		—		21,672		—		—		21,672
Municipal bonds	13,609		—		13,786		—		—		13,786
Mortgage-backed securities	2,785		—		2,816		—		—		2,816
Equity securities:
U.S. equities	270,779		473,400		—		—		—		473,400
Non U.S. equities	189,100		218,381		—		—		—		218,381
Total	$	1,528,993	$	845,286	$	176,011	$	—	$	839,465	$	1,860,762

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $44.3 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 nine months ended Sept. 30, 2017 and 2016 there were no Level 3 nuclear decommissioning fund investments and no transfers of amounts between levels.

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The following table summarizes the final contractual maturity dates of the debt securities in the nuclear decommissioning fund, by asset class, at Sept. 30, 2017:

	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	$	—	$	1,275	$	2,303	$	41,366	$	44,944
U.S. corporate bonds	3,834		64,119		150,741		34,174		252,868
Non U.S. corporate bonds	—		13,793		26,651		6,167		46,611
Debt securities	$	3,834	$	79,187	$	179,695	$	81,707	$	344,423

Rabbi Trusts

In June 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 Sept. 30, 2017 and Dec. 31, 2016:

	Sept. 30, 2017
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trust (a)
Cash equivalents	$	391	$	391	$	—	$	—	$	391
Mutual funds	10,075		10,963		—		—		10,963
Total	$	10,466	$	11,354	$	—	$	—	$	11,354

	Dec. 31, 2016
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trusts (a)
Cash equivalents	$	7,459	$	7,459	$	—	$	—	$	7,459
Mutual funds	1,663		1,901		—		—		1,901
Total	$	9,122	$	9,360	$	—	$	—	$	9,360

^(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.

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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 Sept. 30, 2017, accumulated other comprehensive losses related to interest rate derivatives included $0.6 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 Sept. 30, 2017, 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 nine months ended Sept. 30, 2017 and 2016.

At Sept. 30, 2017, 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 Sept. 30, 2017 and Dec. 31, 2016:

(Amounts in Thousands)(a)(b)	Sept. 30, 2017	Dec. 31, 2016
Megawatt hours of electricity	58,582	37,805
Million British thermal units of natural gas	47,329	79,520
Gallons of vehicle fuel	300	—

^(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.

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The following tables detail the impact of derivative activity during the three and nine months ended Sept. 30, 2017 and 2016 on accumulated other comprehensive loss, regulatory assets and liabilities and income:

	Three Months Ended Sept. 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	$	—	$	—		$	612		(a)	$	—			$	—
Vehicle fuel and other commodity	38		—			(11		)	(b)	—				—
Total	$	38	$	—		$	601			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	1,493	(c)
Electric commodity	—		20,216			—				(5,356		)	(d)	—
Natural gas commodity	—		(383		)	—				—				—
Total	$	—	$	19,833		$	—			$	(5,356	)		$	1,493

	Nine Months Ended Sept. 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	$	—	$	—		$	1,304		(a)	$	—			$	—
Vehicle fuel and other commodity	81		—			(16		)	(b)	—				—
Total	$	81	$	—		$	1,288			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	8,092		(c)
Electric commodity	—		17,444			—				(9,293		)	(d)	—
Natural gas commodity	—		(1,010		)	—				698			(e)	(945		)	(e)
Total	$	—	$	16,434		$	—			$	(8,595	)		$	7,147

	Three Months Ended Sept. 30, 2016
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:						Pre-Tax 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	(2		)	—			25		(b)	—			—
Total	$	(2	)	$	—		$	375		$	—		$	—
Other derivative instruments
Commodity trading	$	—		$	—		$	—		$	—		$	1,808	(c)
Electric commodity	—			15,301			—			2,044		(d)	—
Natural gas commodity	—			(792		)	—			—			—
Total	$	—		$	14,509		$	—		$	2,044		$	1,808

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	Nine Months Ended Sept. 30, 2016
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax 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	$	—	$	—		$	1,042	(a)	$	—		$	—
Vehicle fuel and other commodity	8		—			82		(b)	—			—
Total	$	8	$	—		$	1,124		$	—		$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—		$	—		$	3,069		(c)
Electric commodity	—		12,550			—			26,328		(d)	—
Natural gas commodity	—		(1,045		)	—			3,460		(e)	(1,595		)	(e)
Total	$	—	$	11,505		$	—		$	29,788		$	1,474

^(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 nine months ended Sept. 30, 2017 and 2016. 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 Sept. 30, 2017, five of NSP-Minnesota’s 10 most significant counterparties for these activities, comprising $23.9 million or 33 percent of this credit exposure, had investment grade credit ratings from Standard & Poor’s, Moody’s or Fitch Ratings. Four of the 10 most significant counterparties, comprising $28.0 million or 38 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. The one remaining significant counterparty, comprising $0.9 million or 1 percent of this credit exposure, had credit quality less than investment grade, based on ratings from internal analysis. 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 Sept. 30, 2017 and Dec. 31, 2016, there were no derivative instruments in a material liability position with such underlying contract provisions.

20

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 Sept. 30, 2017 and Dec. 31, 2016.

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 Sept. 30, 2017:

	Sept. 30, 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	$	—	$	56	$	—	$	56	$	—		$	56
Other derivative instruments:
Commodity trading	1,297		8,933		81		10,311		(4,040		)	6,271
Electric commodity	—		—		39,932		39,932		(261		)	39,671
Natural gas commodity	—		427		—		427		—			427
Total current derivative assets	$	1,297	$	9,416	$	40,013	$	50,726	$	(4,301	)	46,425
PPAs (a)												752
Current derivative instruments												$	47,177
Noncurrent derivative assets
Derivatives designated as cash flow hedges:
Vehicle fuel and other commodity	$	—	$	11	$	—	$	11	$	—		$	11
Other derivative instruments:
Commodity trading	84		30,103		5,661		35,848		(7,465		)	28,383
Total noncurrent derivative assets	$	84	$	30,114	$	5,661	$	35,859	$	(7,465	)	28,394
PPAs (a)												126
Noncurrent derivative instruments												$	28,520

	Sept. 30, 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	$	1,146	$	7,100	$	—	$	8,246	$	(4,307	)	$	3,939
Electric commodity	—		—		261		261		(261		)	—
Total current derivative liabilities	$	1,146	$	7,100	$	261	$	8,507	$	(4,568	)	3,939
PPAs (a)												14,106
Current derivative instruments												$	18,045
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	52	$	22,666	$	—	$	22,718	$	(10,130	)	$	12,588
Total noncurrent derivative liabilities	$	52	$	22,666	$	—	$	22,718	$	(10,130	)	12,588
PPAs (a)												93,375
Noncurrent derivative instruments												$	105,963

^(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 will be 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 Sept. 30, 2017. At Sept. 30, 2017, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $2.9 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.

21

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, 2016:

	Dec. 31, 2016
	Fair Value						Fair Value Total		Counterparty Netting (b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative assets
Other derivative instruments:
Commodity trading	$	12,053	$	8,651	$	—	$	20,704	$	(15,500	)	$	5,204
Electric commodity	—		—		15,997		15,997		(677		)	15,320
Natural gas commodity	—		912		—		912		—			912
Total current derivative assets	$	12,053	$	9,563	$	15,997	$	37,613	$	(16,177	)	21,436
PPAs (a)												592
Current derivative instruments												$	22,028
Noncurrent derivative assets
Other derivative instruments:
Commodity trading	$	100	$	31,029	$	—	$	31,129	$	(7,323	)	$	23,806
Total noncurrent derivative assets	$	100	$	31,029	$	—	$	31,129	$	(7,323	)	23,806
PPAs (a)												872
Noncurrent derivative instruments												$	24,678

	Dec. 31, 2016
	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	$	12,397	$	5,964	$	—	$	18,361	$	(15,837	)	$	2,524
Electric commodity	—		—		677		677		(677		)	—
Total current derivative liabilities	$	12,397	$	5,964	$	677	$	19,038	$	(16,514	)	2,524
PPAs (a)												14,082
Current derivative instruments												$	16,606
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	89	$	23,424	$	—	$	23,513	$	(10,727	)	$	12,786
Total noncurrent derivative liabilities	$	89	$	23,424	$	—	$	23,513	$	(10,727	)	12,786
PPAs (a)												104,018
Noncurrent derivative instruments												$	116,804

^(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 will be 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, 2016. At Dec. 31, 2016, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $3.7 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.

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The following table presents the changes in Level 3 commodity derivatives for the three and nine months ended Sept. 30, 2017 and 2016:

	Three Months Ended Sept. 30
(Thousands of Dollars)	2017			2016
Balance at July 1	$	40,572		$	23,488
Settlements	(23,186		)	(26,192		)
Net transactions recorded during the period:
Gains recognized in earnings (a)	527			—
Net gains recognized as regulatory assets and liabilities	27,500			27,163
Balance at Sept. 30	$	45,413		$	24,459
	Nine Months Ended Sept. 30
(Thousands of Dollars)	2017			2016
Balance at Jan. 1	$	15,320		$	12,969
Purchases	40,740			27,870
Settlements	(34,681		)	(38,300		)
Net transactions recorded during the period:
Gains (losses) recognized in earnings (a)	5,742			(2		)
Net gains recognized as regulatory assets and liabilities	18,292			21,922
Balance at Sept. 30	$	45,413		$	24,459

^(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 nine months ended Sept. 30, 2017 and 2016.

Fair Value of Long-Term Debt

As of Sept. 30, 2017 and Dec. 31, 2016, other financial instruments for which the carrying amount did not equal fair value were as follows:

	Sept. 30, 2017				Dec. 31, 2016
(Thousands of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt, including current portion	$	4,932,977	$	5,501,602	$	4,843,165	$	5,310,925

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 Sept. 30, 2017 and Dec. 31, 2016, 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 Income (Expense), Net

Other income (expense), net consisted of the following:

	Three Months Ended Sept. 30						Nine Months Ended Sept. 30
(Thousands of Dollars)	2017			2016			2017			2016
Interest income	$	2,936		$	510		$	6,250		$	3,975
Other nonoperating income	—			—			—			248
Insurance policy expense	(387		)	(926		)	(2,098		)	(2,389		)
Other nonoperating expense	(429		)	(23		)	(402		)	—
Other income (expense), net	$	2,120		$	(439	)	$	3,750		$	1,834

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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 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 Sept. 30, 2017
Operating revenues (a)(b)	$	1,290,971	$	57,442		$	7,366	$	—		$	1,355,779
Intersegment revenues	160		100			—		(260		)	—
Total revenues	$	1,291,131	$	57,542		$	7,366	$	(260	)	$	1,355,779
Net income (loss)	$	232,078	$	(6,242	)	$	3,167	$	—		$	229,003

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas			All Other		Reconciling Eliminations			Consolidated Total
Three Months Ended Sept. 30, 2016
Operating revenues (a)(b)	$	1,282,574	$	55,519		$	7,286	$	—		$	1,345,379
Intersegment revenues	118		189			—		(307		)	—
Total revenues	$	1,282,692	$	55,708		$	7,286	$	(307	)	$	1,345,379
Net income (loss)	$	217,674	$	(14,900	)	$	3,778	$	—		$	206,552

^(a)  Operating revenues include $124 million and $121 million of affiliate electric revenue for the three months ended Sept. 30, 2017 and 2016.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended Sept. 30, 2017 and 2016.

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Nine Months Ended Sept. 30, 2017
Operating revenues (a)(b)	$	3,449,780	$	356,631	$	21,448	$	—		$	3,827,859
Intersegment revenues	512		371		—		(883		)	—
Total revenues	$	3,450,292	$	357,002	$	21,448	$	(883	)	$	3,827,859
Net income	$	399,637	$	7,903	$	3,291	$	—		$	410,831

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(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Nine Months Ended Sept. 30, 2016
Operating revenues (a)(b)	$	3,332,688	$	314,020	$	21,404	$	—		$	3,668,112
Intersegment revenues	525		437		—		(962		)	—
Total revenues	$	3,333,213	$	314,457	$	21,404	$	(962	)	$	3,668,112
Net income (loss)	$	367,776	$	8,700	$	2,881	$	—		$	379,357

^(a)  Operating revenues include $367 million and $359 million of affiliate electric revenue for the nine months ended Sept. 30, 2017 and 2016.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the nine months ended Sept. 30, 2017 and 2016.

11. Benefit Plans and Other Postretirement Benefits

Components of Net Periodic Benefit Cost

	Three Months Ended Sept. 30
	2017			2016			2017			2016
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	6,958		$	7,077		$	36		$	31
Interest cost	10,177			11,358			854			981
Expected return on plan assets	(15,016		)	(15,236		)	(53		)	(43		)
Amortization of prior service cost (credit)	265			234			(759		)	(759		)
Amortization of net loss	9,902			9,194			506			401
Net periodic benefit cost	12,286			12,627			584			611
Costs not recognized due to the effects of regulation	(4,899		)	(5,295		)	—			—
Net benefit cost recognized for financial reporting	$	7,387		$	7,332		$	584		$	611

	Nine Months Ended Sept. 30
	2017			2016			2017			2016
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	20,874		$	21,231		$	108		$	93
Interest cost	30,531			34,074			2,562			2,943
Expected return on plan assets	(45,050		)	(45,708		)	(161		)	(129		)
Amortization of prior service cost (credit)	795			702			(2,277		)	(2,277		)
Amortization of net loss	29,706			27,582			1,520			1,203
Net periodic benefit cost	36,856			37,881			1,752			1,833
Costs not recognized due to the effects of regulation	(14,696		)	(15,887		)	—			—
Net benefit cost recognized for financial reporting	$	22,160		$	21,994		$	1,752		$	1,833

In January 2017, contributions of $150.0 million were made across four of Xcel Energy’s pension plans, of which $59.4 million was attributable to NSP-Minnesota. Xcel Energy does not expect additional pension contributions during 2017.

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12. Other Comprehensive Income (Loss)

Changes in accumulated other comprehensive (loss) income, net of tax, for the three and nine months ended Sept. 30, 2017 and 2016 were as follows:

	Three Months Ended Sept. 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) income at July 1	$	(17,775	)	$	105	$	(2,609	)	$	(20,279	)
Other comprehensive income before reclassifications	22			—		—			22
Losses reclassified from net accumulated other comprehensive loss	379			—		39			418
Net current period other comprehensive income	401			—		39			440
Accumulated other comprehensive (loss) income at Sept. 30	$	(17,374	)	$	105	$	(2,570	)	$	(19,839	)

	Three Months Ended Sept. 30, 2016
(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) income at July 1	$	(18,640	)	$	105	$	(2,058	)	$	(20,593	)
Other comprehensive loss before reclassifications	(1		)	—		—			(1		)
Losses reclassified from net accumulated other comprehensive loss	213			—		19			232
Net current period other comprehensive income	212			—		19			231
Accumulated other comprehensive (loss) income at Sept. 30	$	(18,428	)	$	105	$	(2,039	)	$	(20,362	)

	Nine Months Ended Sept. 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) income at Jan. 1	$	(18,208	)	$	105	$	(2,680	)	$	(20,783	)
Other comprehensive income before reclassifications	48			—		—			48
Losses reclassified from net accumulated other comprehensive loss	786			—		110			896
Net current period other comprehensive income	834			—		110			944
Accumulated other comprehensive (loss) income at Sept. 30	$	(17,374	)	$	105	$	(2,570	)	$	(19,839	)

	Nine Months Ended Sept. 30, 2016
(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) income at Jan. 1	$	(19,090	)	$	105	$	(2,096	)	$	(21,081	)
Other comprehensive income before reclassifications	5			—		—			5
Losses reclassified from net accumulated other comprehensive loss	657			—		57			714
Net current period other comprehensive income	662			—		57			719
Accumulated other comprehensive (loss) income at Sept. 30	$	(18,428	)	$	105	$	(2,039	)	$	(20,362	)

26

Reclassifications from accumulated other comprehensive loss for the three and nine months ended Sept. 30, 2017 and 2016 were as follows:

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Three Months Ended Sept. 30, 2017				Three Months Ended Sept. 30, 2016
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	612		(a)	$	350		(a)
Vehicle fuel derivatives	(11		)	(b)	25			(b)
Total, pre-tax	601				375
Tax benefit	(222		)		(162		)
Total, net of tax	379				213
Defined benefit pension and postretirement losses:
Amortization of net loss	109			(c)	83			(c)
Prior service credit	(49		)	(c)	(49		)	(c)
Total, pre-tax	60				34
Tax benefit	(21		)		(15		)
Total, net of tax	39				19
Total amounts reclassified, net of tax	$	418			$	232

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Nine Months Ended Sept. 30, 2017				Nine Months Ended Sept. 30, 2016
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	1,304		(a)	$	1,042		(a)
Vehicle fuel derivatives	(16		)	(b)	82			(b)
Total, pre-tax	1,288				1,124
Tax benefit	(502		)		(467		)
Total, net of tax	786				657
Defined benefit pension and postretirement losses:
Amortization of net loss	327			(c)	249			(c)
Prior service credit	(147		)	(c)	(147		)	(c)
Total, pre-tax	180				102
Tax benefit	(70		)		(45		)
Total, net of tax	110				57
Total amounts reclassified, net of tax	$	896			$	714

^(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 for details regarding these benefit plans.

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).

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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.

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 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. 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, 2016 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.

Results of Operations

NSP-Minnesota’s net income was approximately $410.8 million for 2017 year-to-date, compared with approximately $379.4 million for the same period of 2016. The year-to-date increase in earnings reflects electric rate increases, lower ETR and reduced O&M expenses. These positive factors were partially offset by depreciation expense and higher property taxes.

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:

	Nine Months Ended Sept. 30
(Millions of Dollars)	2017			2016
Electric revenues	$	3,450		$	3,333
Electric fuel and purchased power	(1,215		)	(1,149		)
Electric margin	$	2,235		$	2,184

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The following tables summarize the components of the changes in electric revenues and electric margin for the nine months endedSept. 30:

Electric Revenues

(Millions of Dollars)	2017 vs. 2016
Retail rate increases (Minnesota)	$	39
Trading	34
Non-fuel riders	30
Decoupling (weather portion - Minnesota)	24
Conservation program revenue, offset by expenses	20
Estimated impact of weather	(24		)
Wholesale transmission revenue	(14		)
Conservation incentive	(10		)
Other, net	18
Total increase in electric revenues	$	117

Electric Margin

(Millions of Dollars)	2017 vs. 2016
Retail rate increases (Minnesota)	$	39
Non-fuel riders	30
Decoupling (weather portion - Minnesota)	24
Conservation program revenue, offset by expenses	20
Wholesale transmission revenue, net of costs	(28		)
Estimated impact of weather	(24		)
Conservation incentive	(10		)
Total increase in electric margin	$	51

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:

	Nine Months Ended Sept. 30
(Millions of Dollars)	2017			2016
Natural gas revenues	$	357		$	314
Cost of natural gas sold and transported	(199		)	(164		)
Natural gas margin	$	158		$	150

The following tables summarize the components of the changes in natural gas revenues and natural gas margin for the nine months endedSept. 30:

Natural Gas Revenues

(Millions of Dollars)	2017 vs. 2016
Purchased natural gas adjustment clause recovery	$	34
Conservation program revenue, offset by expenses	4
Retail sales growth, excluding weather impact	3
Infrastructure and integrity riders	3
Other, net	(1		)
Total increase in natural gas revenues	$	43

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Natural Gas Margin

(Millions of Dollars)	2017 vs. 2016
Conservation program revenue, offset by expenses	$	4
Retail sales growth, excluding weather impact	3
Infrastructure and integrity riders	3
Other, net	(2		)
Total increase in natural gas margin	$	8

Non-Fuel Operating Expenses and Other Items

O&M Expenses— O&M expenses decreased $45.0 million, or 4.7 percent, for 2017 year-to-date. The decrease primarily relates to the timing of maintenance activities and the overhauls at various generation facilities and reduced expense for nuclear refueling outages, as summarized in the table below:

(Millions of Dollars)	2017 vs. 2016
Plant generation costs	$	(19	)
Nuclear plant operations and amortization	(17		)
Transmission costs	(6		)
Electric distribution costs	(3		)
Employee benefits expense	4
Other, net	(4		)
Total decrease in O&M expenses	$	(45	)

Conservation Program Expenses — Conservation program expenses increased$24.8 million, for 2017 year-to-date. The increase was due to higher recovery rates and additional customer participation in electric conservation programs. Conservation expenses are generally recovered in major jurisdictions 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$79.4 million, or 17.9 percent, for 2017 year-to-date. The increase was primarily due to capital investments, including the Courtenay Wind Farm and prior year amortization of the excess depreciation reserve.

Taxes (Other than Income Taxes) — Taxes (other than income taxes) increased$5.9 million, or 3.2 percent for 2017 year-to-date. The increase was primarily due to higher property taxes.

Interest Charges — Interest charges increased$4.5 million, or 2.7 percent, for 2017 year-to-date. The increase was related to higher debt levels to fund capital investments, partially offset by refinancings at lower interest rates.

Income Taxes — Income tax expense decreased$35.3 million for the first nine months of 2017. The decrease was primarily due to net tax benefits related to an increase in wind production tax credits (PTCs) and the resolution of IRS appeals/audits. The ETR was 25.5 percent for 2017 year-to-date, compared with 31.7 percent for the same period in 2016. The lower ETR in 2017 was primarily due to the adjustments referenced above.

The wind PTCs largely flow back to customers through electric margin.

Public Utility Regulation

Except to the extent noted below, 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, 2016 and Public Utility Regulation included in Item 2 of NSP-Minnesota’s Quarterly Report on Form 10-Q for the quarterly periods ended March 31, 2017 and June 30, 2017, appropriately represent, in all material respects, the current status of public utility regulation and are incorporated herein by reference.

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Wind Development — In July 2017, the MPUC approved NSP-Minnesota’s proposal to add 1,550 MW of new wind generation, including ownership of 1,150 MW of wind generation by NSP-Minnesota. In September 2017, NSP-Minnesota filed with the MPUC seeking approval to build and own the Dakota Range project, a 300 MW wind project in South Dakota. The project is projected to be placed into service by the end of 2021 to qualify for 80 percent of the PTC. NSP-Minnesota has requested that the MPUC approve the proposed wind project by March 2018.

These wind projects (with the exception of the Dakota Range project) would qualify for 100 percent of the PTC and are expected to provide billions of dollars of savings to NSP-Minnesota’s customers and substantial environmental benefits. Projected savings/benefits assume fuel costs and generation mix consistent with various commission approved resource plans.

The following table details these wind projects:

Project Name	Capacity (MW)	State	Estimated Year of Completion	Ownership/PPA	Regulatory Status
Freeborn	200	MN/IA	2020	NSP-Minnesota	Approved by MPUC
Blazing Star 1	200	MN	2019	NSP-Minnesota	Approved by MPUC
Blazing Star 2	200	MN	2020	NSP-Minnesota	Approved by MPUC
Lake Benton	100	MN	2019	NSP-Minnesota	Approved by MPUC
Foxtail	150	ND	2019	NSP-Minnesota	Approved by MPUC
Crowned Ridge	300	SD	2019	NSP-Minnesota	Approved by MPUC
Dakota Range	300	SD	2021	NSP-Minnesota	Pending MPUC Approval
Total Ownership	1,450
Crowned Ridge	300	SD	2019	PPA	Approved by MPUC
Clean Energy 1	100	ND	2019	PPA	Approved by MPUC
Total PPA	400
Total Wind Capacity	1,850

PPA Terminations and Amendments — In June and July 2017, NSP-Minnesota filed requests with the MPUC and/or the NDPSC for several initiatives including changes to four PPAs to reduce future costs for customers. These actions include the following:

• The termination of a PPA with Benson Power LLC (Benson) for its 55 MW biomass facility in Benson, Minn., including the purchase and closure of the facility. The purchase of the Benson biomass facility requires FERC approval, which was requested in August 2017. The transaction would result in payments of $95 million to terminate the PPA and acquire the facility, as well as additional expenditures of approximately $26 million to temporarily operate then close the facility.

• The termination of a PPA with Laurentian Energy Authority I, LLC (Laurentian) for its 35 MW of biomass facilities in Hibbing and Virginia, Minn. The termination of the Laurentian PPA would result in $108.5 million of contract cancellation payments over six years.

• The remaining two requested PPA changes involve a PPA extension for a 34 MW waste-to-energy facility at a price reflective of current market conditions and termination of another 12 MW waste-to-energy PPA.

NSP-Minnesota has requested recovery of all costs associated with these changes through the Fuel Clause Adjustment (FCA), including a return on NSP-Minnesota’s total investment in the Benson transaction over the remaining life of the current PPA through 2028. NSP-Minnesota and NSP-Wisconsin will jointly request FERC approval to modify the Interchange Agreement to share a portion of the cost with NSP-Wisconsin. If approved, these actions together are intended to provide approximately $653 million in net cost savings to NSP System customers over the next 10 years.

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Jurisdictional Cost Recovery Allocation — In December 2016, NSP-Minnesota filed a resource treatment framework with the NDPSC and MPUC. The filing proposed a framework to allow NSP-Minnesota’s operations in North Dakota and Minnesota to gradually become more independent of one another with respect to future generation resource selection while also identifying a path for cost sharing of current resources. NSP-Minnesota’s filing identified two options: a legal separation, creating a separate North Dakota operating company; or a pseudo-separation, which maintains the current corporate structure but directly assigns the costs and benefits of each resource to the jurisdiction that supports it. The annual costs for a legal separation and pseudo-separation are estimated to be approximately $3 million and $1 million, respectively. A one-time cost of approximately $10 million would also be incurred to establish a North Dakota operating company under legal separation. Costs are not expected to be incurred until 2020 and are anticipated to be recoverable through rates. The filing proposed a procedural schedule that considers an order in mid-2018. In October 2017, NDPSC staff filed testimony recommending no change to the current system of proxy pricing and policy-based disallowances claiming there is a likelihood of overall increased costs and potential loss of resource diversity. NSP-Minnesota’s rebuttal testimony is due Nov. 15, 2017 and hearings are scheduled in January 2018.

CapX2020 — The estimated cost of the five major CapX2020 transmission projects listed below was approximately $2 billion.  NSP-Minnesota and NSP-Wisconsin were responsible for approximately $1.04 billion of the total investment and the majority of this investment has occurred. The projects are as follows:

• Hampton, Minn. to Rochester, Minn. to La Crosse, Wis. 161/345 kilovolt (KV) transmission lines— The final 161 KV and 345 KV segments of the project went into service in January 2016 and September 2016, respectively;

• Brookings County, S.D. to Hampton, Minn. 345 KV transmission line— The project was placed in service in March 2015;

• Bemidji, Minn. to Grand Rapids, Minn. 230 KV transmission line — The project was placed in service in September 2012;

• Monticello, Minn. to Fargo, N.D. 345 KV transmission line— The final portion of the project was placed in service in April 2015; and

• Big Stone South to Brookings County, S.D. 345 KV transmission line — The project was placed in service in September 2017.

Minnesota FCA — In October 2017, the MPUC voted to change the process in which utilities seek fuel cost recovery under the FCA in Minnesota.  Each month, utilities collect amounts equal to the baseline cost of energy set at the start of the plan year, as well as issue refunds or billings for the difference relative to the baseline costs. Under the new process, monthly variations to the baseline costs will be tracked and netted over a 12-month period. Subsequently, utilities can seek recovery of any overage.  The MPUC has requested additional compliance filings from all utilities outlining the details and timing of the proposed process.  

Nuclear Power Operations

NSP-Minnesota owns two nuclear generating plants: the Monticello plant and the PI plant. NSP-Minnesota’s next triennial nuclear decommissioning filing is expected to be submitted in the fourth quarter of 2017. See Note 12 of NSP-Minnesota’s Annual Report on Form 10-K for the year ended Dec. 31, 2016 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, 2016 and Nuclear Power Operations included in Item 2 of NSP-Minnesota’s Quarterly Report

on Form 10-Q for the quarterly periods ended March 31, 2017 and June 30, 2017, 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 12 percent of its 2017 and approximately 59 percent of its 2018 enriched nuclear material requirements from sources that could be impacted by events in Ukraine and sanctions against 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 31 percent of its average enriched nuclear material requirements from sources that could be impacted by events in Ukraine and extended sanctions against Russia. 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 provided 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.

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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, 2016 and Quarterly Report on Form 10-Q for the quarterly periods ended March 31, 2017 and June 30, 2017. In addition to the matters discussed below, see Note 5 to the consolidated financial statements for a discussion of other regulatory matters.

FERC ROE Policy — In June 2014, the FERC adopted a two-step ROE methodology for electric utilities in an order 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 includes 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.

Department of Energy (DOE) Grid Resiliency Notice of Proposed Rule (NOPR) — In September 2017, the DOE requested the FERC consider and adopt a Grid Resiliency and Pricing Rule to address threats to the U.S. electrical grid. The proposed DOE rule expands upon an August 2017 DOE grid study on the resiliency of the grid. Under the proposed rule, coal and nuclear generation facilities would qualify for full recovery of their costs, which includes a fair rate of return, if they meet the following criteria:

• Are located within a FERC-approved organized wholesale market operated by an RTO or Independent System Operator;

• Have 90 days of on-site fuel storage;

• Provide essential energy and ancillary reliability services to the grid;

• Are in compliance with all environmental mandates; and

• Are not subject to cost-of-service regulation by any state or local authority.

If implemented as written, the coal and nuclear generation owned by NSP-Minnesota and NSP-Wisconsin are not expected to be eligible for wholesale cost recovery from MISO because the generation is subject to state cost-of-service regulation. This rule could impact utilities in MISO subject to cost-of-service regulation if they have to compensate other generation facilities who qualify for full recovery of their costs under the rule. Xcel Energy is evaluating the DOE proposal and plans to engage in the FERC stakeholder process. The FERC has indicated that they plan to take action within 60 days, as requested by the DOE. It is unclear how the FERC will respond to the DOE’s NOPR.

Minnesota State Right-Of-First Refusal (ROFR) Statute Complaint —In September 2017, LSP Transmission Holdings, LLC filed a complaint in the U.S. District Court in Minnesota against the Minnesota Attorney General, the MPUC and the DOC. The complaint was in response to NSP-Minnesota and ITC Midwest, LLC being assigned by MISO to jointly own a new 345 kilovolt transmission line that is planned to run from NSP-Minnesota’s Wilmarth Substation near Mankato, Minn. to ITC Midwest’s Huntley Substation in Minnesota south of Winnebago, Minn. The line is estimated to cost $108 million. The project was assigned to NSP-Minnesota and ITC Midwest as the incumbent utilities, consistent with a Minnesota state ROFR statute. The complaint challenges 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 are expected to answer the complaint in November 2017. NSP-Minnesota expects to intervene in the case. The timing and outcome of the litigation is uncertain.

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North American Electric Reliability Corporation (NERC) Supply Chain Standards — In September 2017, NERC filed supply chain cyber security reliability standards with the FERC. These standards consider the FERC’s directives to address supply chain cyber security risk management for industrial control system hardware, software, computing and network services associated with electric grid operations. The proposed reliability standards focus on security objectives including software integrity and authenticity, vendor remote access protections, information system planning and vendor risk management. It is uncertain when the FERC will take action to approve or remand the proposed reliability standards. If approved by the FERC, the proposed reliability standards will become effective on the first calendar quarter that is 18 months after the effective date of the approval. NSP-Minnesota is in the process of developing plans in accordance with the requirements of the standards. The additional cost for compliance is anticipated to be recoverable through wholesale and retail rates.

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 Sept. 30, 2017, 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

In 2016, NSP-Minnesota implemented the general ledger modules, as well as initiated deployment of work management systems modules, of a new enterprise resource planning system to improve certain financial and related transaction processes. NSP-Minnesota is continuing to implement additional modules including the conversion of existing work management systems to this same system during 2017. In connection with this ongoing implementation, NSP-Minnesota is updating its internal control over financial reporting, as necessary, to accommodate modifications to its business processes and accounting systems. NSP-Minnesota does not believe that this implementation will have an adverse effect on its 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.

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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. 31,2016, which is incorporated herein by reference. There have been no material changes from the risk factors previously disclosed in the Form 10-K.

Item 6 — EXHIBITS

* Indicates incorporation by reference

+ Executive Compensation Arrangements and Benefit Plans Covering Executive Officers and Directors

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)).
4.01*	Supplemental Indenture dated as of Sept. 1, 2017 between NSP-Minnesota and The Bank of New York Mellon Trust Company, N.A., as successor trustee, creating $600 million principal amount of 3.60 percent First Mortgage Bonds, Series due Sept. 15, 2047 (Exhibit 4.01 to Form 8-K dated Sept. 13, 2017 (file no. 001-31387)).
10.1*+	Fourth Amendment to the Xcel Energy Inc. Nonqualified Deferred Compensation Plan (2009 Restatement) (Exhibit 10.1 to Form 10-Q of Xcel Energy for the quarter ended Sept. 30, 2017 (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 Sept. 30, 2017 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.

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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)
Oct. 27, 2017	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)

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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: Oct. 27, 2017

/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: Oct. 27, 2017

/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 Sept. 30, 2017, 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: Oct. 27, 2017

/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.

1

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, 2016, 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.

1

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Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 27, 2017
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	2017
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017

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CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating revenues
Electric, non-affiliates	$ 1,167,447	$ 1,161,259	$ 3,083,182	$ 2,973,350
Electric, affiliates	123,524	121,315	366,598	359,338
Natural gas	57,442	55,519	356,631	314,020
Other	7,366	7,286	21,448	21,404
Total operating revenues	1,355,779	1,345,379	3,827,859	3,668,112
Operating expenses
Electric fuel and purchased power	435,003	435,560	1,215,071	1,148,818
Cost of natural gas sold and transported	20,723	19,105	198,968	163,608
Cost of sales — other	4,313	4,898	13,085	14,185
Operating and maintenance expenses	288,770	315,298	909,381	954,334
Conservation program expenses	31,674	23,926	92,238	67,424
Depreciation and amortization	176,739	149,408	522,070	442,649
Taxes (other than income taxes)	62,220	49,763	191,989	186,100
Total operating expenses	1,019,442	997,958	3,142,802	2,977,118
Operating income	336,337	347,421	685,057	690,994
Other income (expense), net	2,120	(439)	3,750	1,834
Allowance for funds used during construction — equity	10,683	7,983	23,391	21,011
Interest charges and financing costs
Interest charges — includes other financing costs of $1,845, $1,822, $5,437 and $5,325, respectively	57,577	57,859	172,548	168,010
Allowance for funds used during construction — debt	(5,383)	(3,591)	(11,909)	(9,575)
Total interest charges and financing costs	52,194	54,268	160,639	158,435
Income before income taxes	296,946	300,697	551,559	555,404
Income taxes	67,943	94,145	140,728	176,047
Net income	$ 229,003	$ 206,552	$ 410,831	$ 379,357

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CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Interest charges and financing costs
Other financing costs	$ 1,845	$ 1,822	$ 5,437	$ 5,325

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CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Comprehensive income:
Net income	$ 229,003	$ 206,552	$ 410,831	$ 379,357
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, net of tax of $21, $15, $70 and $45, respectively	39	19	110	57
Derivative instruments:
Net fair value increase (decrease), net of tax of $16, $(1), $33 and $3, respectively	22	(1)	48	5
Reclassification of losses to net income, net of tax of $222, $162, $502 and $467, respectively	379	213	786	657
Total derivative instruments, net of tax	401	212	834	662
Other comprehensive income	440	231	944	719
Comprehensive income	$ 229,443	$ 206,783	$ 411,775	$ 380,076

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CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, tax	$ 21	$ 15	$ 70	$ 45
Derivative instruments:
Net fair value (decrease) increase, tax	16	(1)	33	3
Reclassification of losses to net income, tax	$ 222	$ 162	$ 502	$ 467

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CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net income	$ 410,831	$ 379,357
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	526,784	447,284
Nuclear fuel amortization	87,654	89,475
Deferred income taxes	98,125	129,410
Amortization of Investment Tax Credits	(1,241)	(1,260)
Allowance for equity funds used during construction	(23,391)	(21,011)
Net realized and unrealized hedging and derivative transactions	(2,703)	2,873
Other, net	(1,072)	0
Changes in operating assets and liabilities:
Accounts receivable	(14,677)	(46,294)
Accrued unbilled revenues	33,465	26,660
Inventories	(4,265)	5,709
Other current assets	35,591	24,431
Accounts payable	(34,275)	19,736
Net regulatory assets and liabilities	(15,467)	57,452
Other current liabilities	(73,898)	(3,947)
Pension and other employee benefit obligations	(55,548)	(42,447)
Change in other noncurrent assets	(3,585)	(8,862)
Change in other noncurrent liabilities	(30,704)	(17,084)
Net cash provided by operating activities	931,624	1,041,482
Investing activities
Utility capital/construction expenditures	(696,857)	(833,845)
Allowance for equity funds used during construction	23,391	21,011
Purchases of investment securities	(965,086)	(349,717)
Proceeds from the sale of investment securities	948,558	327,378
Investments in utility money pool arrangement	(122,000)	(492,000)
Repayments from utility money pool arrangement	122,000	441,000
Other, net	(3,463)	(1,262)
Net cash used in investing activities	(693,457)	(887,435)
Financing activities
Repayments of short-term borrowings, net	(85,000)	(223,000)
Borrowings under utility money pool arrangement	516,000	424,000
Repayments under utility money pool arrangement	(466,000)	(424,000)
Proceeds from issuance of long-term debt	586,264	342,570
Repayments of long-term debt, including reacquisition premiums	(507,865)	(11)
Capital contributions from parent	123,247	96,628
Dividends paid to parent	(418,133)	(306,209)
Net cash used in financing activities	(251,487)	(90,022)
Net change in cash and cash equivalents	(13,320)	64,025
Cash and cash equivalents at beginning of period	47,595	42,605
Cash and cash equivalents at end of period	34,275	106,630
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(177,336)	(169,382)
Cash paid for income taxes, net	(60,911)	(14,279)
Supplemental disclosure of non-cash investing transactions:
Property, plant and equipment additions in accounts payable	$ 47,261	$ 72,889

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CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 34,275	$ 47,595
Accounts receivable, net	344,528	329,481
Accounts receivable from affiliates	19,989	49,355
Accrued unbilled revenues	226,125	259,590
Inventories	349,578	345,192
Regulatory assets	253,876	186,266
Derivative instruments	47,177	22,028
Prepayments and other	65,292	98,006
Total current assets	1,340,840	1,337,513
Property, plant and equipment, net	13,360,494	13,300,793
Other assets
Nuclear decommissioning fund and other investments	2,105,741	1,905,059
Regulatory assets	1,187,195	1,245,151
Derivative instruments	28,520	24,678
Other	13,217	9,086
Total other assets	3,334,673	3,183,974
Total assets	18,036,007	17,822,280
Current liabilities
Current portion of long-term debt	7	10
Short-term debt	0	85,000
Borrowings under utility money pool arrangement	50,000	0
Accounts payable	292,970	371,589
Accounts payable to affiliates	50,745	59,216
Regulatory liabilities	98,587	60,779
Taxes accrued	235,999	241,100
Accrued interest	52,115	71,012
Dividends payable to parent	88,461	89,428
Derivative instruments	18,045	16,606
Customer deposits	103,549	110,244
Other	152,919	150,244
Total current liabilities	1,143,397	1,255,228
Deferred credits and other liabilities
Deferred income taxes	2,947,022	2,788,752
Deferred investment tax credits	22,935	24,175
Regulatory liabilities	491,385	489,825
Asset retirement obligations	2,543,497	2,452,567
Derivative instruments	105,963	116,804
Pension and employee benefit obligations	313,772	368,922
Other	94,372	127,283
Total deferred credits and other liabilities	6,518,946	6,368,328
Commitments and contingencies
Capitalization
Long-term debt	4,932,970	4,843,155
Common stock — authorized 5,000,000 shares of $0.01 par value; 1,000,000 shares outstanding at Sept. 30, 2017 and Dec. 31, 2016, respectively	10	10
Additional paid in capital	3,525,612	3,435,096
Retained earnings	1,934,911	1,941,246
Accumulated other comprehensive loss	(19,839)	(20,783)
Total common stockholder’s equity	5,440,694	5,355,569
Total liabilities and equity	$ 18,036,007	$ 17,822,280

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CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
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

9 Months Ended

Sep. 30, 2017

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 Sept. 30, 2017 and Dec. 31, 2016; the results of its operations, including the components of net income and comprehensive income, for the three and nine months ended Sept. 30, 2017 and 2016; and its cash flows for the nine months endedSept. 30, 2017 and 2016. All adjustments are of a normal, recurring nature, except as otherwise disclosed. Management has also evaluated the impact of events occurring after Sept. 30, 2017 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, 2016 balance sheet information has been derived from the audited 2016 consolidated financial statements included in the NSP-Minnesota Annual Report on Form 10-K for the year ended Dec. 31, 2016. 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, 2016, filed with the SEC on Feb. 24, 2017. 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

9 Months Ended

Sep. 30, 2017

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, 2016, appropriately represent, in all material respects, the current status of accounting policies and are incorporated herein by reference.

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Accounting Pronouncements

9 Months Ended

Sep. 30, 2017

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Accounting Pronouncements

Accounting Pronouncements

Recently Issued

Revenue Recognition— In May 2014, the Financial Accounting Standards Board (FASB) issued Revenue from Contracts with Customers, Topic 606 (Accounting Standards Update (ASU) No. 2014-09), which provides a new framework for the recognition of revenue. NSP-Minnesota expects its adoption will primarily result in increased disclosures regarding revenue related to arrangements with customers, as well as separate presentation of alternative revenue programs. NSP-Minnesota currently expects to implement the standard on a modified retrospective basis, which requires application to contracts with customers effective Jan. 1, 2018, with the cumulative impact on contracts not yet completed as of Dec. 31, 2017 recognized as an adjustment to the opening balance of retained earnings.

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 eliminates the available-for-sale classification for marketable equity securities and also replaces 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 to be recognized in earnings. This guidance will be effective for interim and annual reporting periods beginning after Dec. 15, 2017. NSP-Minnesota expects that 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, currently classified as available-for-sale, will continue to be deferred to a regulatory asset, and that the overall impacts of the Jan. 1, 2018 adoption will not be material.

Leases —In February 2016, the FASB issued Leases, Topic 842 (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. As such, agreements entered prior to Jan. 1, 2017 that are currently considered leases are expected to be recognized on the consolidated balance sheet, including contracts for use of office space, equipment and natural gas storage assets, as well as certain purchased power agreements (PPAs) for natural gas-fueled generating facilities. NSP-Minnesota expects that similar agreements entered after Dec. 31, 2016 will generally qualify as leases under the new standard, but has not yet completed its evaluation of certain other contracts, including arrangements for the secondary use of assets, such as land easements.

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. NSP-Minnesota expects that as a result of application of accounting principles for rate regulated entities, a similar amount of pension cost, including non-service components, will be recognized consistent with the current ratemaking treatment and that the impacts of adoption will be limited to changes in classification of non-service costs in the consolidated statement of income. This guidance will be effective for interim and annual reporting periods beginning after Dec. 15, 2017.

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Selected Balance Sheet Data

9 Months Ended

Sep. 30, 2017

Balance Sheet Related Disclosures [Abstract]

Selected Balance Sheet Data

Selected Balance Sheet Data

(Thousands of Dollars)	Sept. 30, 2017			Dec. 31, 2016
Accounts receivable, net
Accounts receivable	$	364,970		$	349,449
Less allowance for bad debts	(20,442		)	(19,968		)
	$	344,528		$	329,481

(Thousands of Dollars)	Sept. 30, 2017		Dec. 31, 2016
Inventories
Materials and supplies	$	216,850	$	214,234
Fuel	91,555		97,527
Natural gas	41,173		33,431
	$	349,578	$	345,192

(Thousands of Dollars)	Sept. 30, 2017			Dec. 31, 2016
Property, plant and equipment, net
Electric plant	$	17,323,127		$	17,059,993
Natural gas plant	1,340,688			1,311,235
Common and other property	803,599			710,958
Construction work in progress	508,306			509,891
Total property, plant and equipment	19,975,720			19,592,077
Less accumulated depreciation	(7,015,522		)	(6,682,418		)
Nuclear fuel	2,668,586			2,571,770
Less accumulated amortization	(2,268,290		)	(2,180,636		)
	$	13,360,494		$	13,300,793

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Income Taxes

9 Months Ended

Sep. 30, 2017

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, 2016 appropriately represents, in all material respects, the current status of other income tax matters, and are incorporated herein by reference.

Federal Loss Carryback Claims — In 2012-2015, NSP-Minnesota identified certain expenses related to 2009, 2010, 2011, 2013, 2014 and 2015 that qualify for an extended carryback beyond the typical two-year carryback period. As a result of a higher tax rate in prior years, NSP-Minnesota recognized a tax benefit of approximately $5 million in 2015, $17 million in 2014, $12 million in 2013 and $15 million in 2012.

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 2009 through 2011 and 2012 through 2013 federal income tax returns, following extensions, expires in June 2018 and October 2018, respectively.

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 that would have resulted in $14 million of income tax expense for the 2009 through 2011 claims, and the 2013 through 2015 claims. In the fourth quarter of 2015, the IRS forwarded the issue to the Office of Appeals (Appeals). In the third quarter of 2017, Xcel Energy and Appeals reached an agreement and the benefit related to the agreed upon portions was recognized.

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. Xcel Energy anticipates the issue will be forwarded to Appeals. As of Sept. 30, 2017, 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 Sept. 30, 2017, 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 Sept. 30, 2017, Minnesota had not proposed any material adjustments, and there were no other state income tax audits in progress.

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)	Sept. 30, 2017		Dec. 31, 2016
Unrecognized tax benefit — Permanent tax positions	$	9.8	$	21.5
Unrecognized tax benefit — Temporary tax positions	8.1		39.3
Total unrecognized tax benefit	$	17.9	$	60.8

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)	Sept. 30, 2017			Dec. 31, 2016
NOL and tax credit carryforwards	$	(12.5	)	$	(19.3	)

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 audits progress, it is reasonably possible that the amount of unrecognized tax benefit could decrease up to approximately $7 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)	Sept. 30, 2017			Dec. 31, 2016
Payable for interest related to unrecognized tax benefits at beginning of period	$	(2.0	)	$	(0.2	)
Interest income (expense) related to unrecognized tax benefits recorded during the period	1.1			(1.8		)
Payable for interest related to unrecognized tax benefits at end of period	$	(0.9	)	$	(2.0	)

No amounts were accrued for penalties related to unrecognized tax benefits as of Sept. 30, 2017 or Dec. 31, 2016.

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Rate Matters

9 Months Ended

Sep. 30, 2017

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, 2016 and in Note 5 to NSP-Minnesota’s Quarterly Report on Form 10-Q for the quarterly periods ended March 31, 2017 and June 30, 2017, appropriately represent, in all material respects, the current status of other rate matters, and are incorporated herein by reference.

Pending and Recently Concluded Regulatory Proceedings — Minnesota Public Utilities Commission (MPUC)

Minnesota 2016 Multi-Year Electric Rate Case — In June 2017, the MPUC issued a written order. NSP-Minnesota estimated the total rate increase to be approximately $245 million over the four-year period covering 2016-2019.

Key terms:

• Four-year period covering 2016-2019;

• Annual sales true-up with decoupling subject to a 3 percent cap;

• Return on equity (ROE) of 9.2 percent and an equity ratio of 52.5 percent;

• Nuclear related costs will not be considered provisional;

• Continued use of all existing riders, however no new riders may be utilized during the four-year term;

• Deferral of incremental 2016 property tax expense above a fixed threshold to 2018 and 2019;

• Four-year stay-out provision for rate cases;

• Property tax true-up mechanism for 2017-2019; and

• Capital expenditure true-up mechanism for 2016-2019.

(Millions of Dollars, Incremental)	2016		2017		2018		2019			Total
Revenues	$	74.99	$	59.86	$	—	$	50.12		$	184.97
NSP-Minnesota’s sales true-up	59.95		—		—		(0.20		)	59.75
Total rate impact	$	134.94	$	59.86	$	—	$	49.92		$	244.72

In September 2017, the MPUC ordered NSP-Minnesota to collect final rates beginning March 1, 2017 (requested date was Jan. 1, 2017). As a result, NSP-Minnesota estimates the adjusted total rate increase to be approximately $240 million over the four-year period covering 2016-2019.

Annual Automatic Adjustment of Fuel Clause Charges — In May 2017, the MPUC voted to disallow approximately $4.4 million of replacement energy costs for the Prairie Island (PI) nuclear facility outages allocated to the Minnesota jurisdiction in 2015. This disallowance was recognized in the second quarter of 2017. In September 2017, the Minnesota Department of Commerce (DOC) recommended the MPUC should hold utilities responsible for incremental costs of replacement power incurred due to unplanned outages under certain circumstances. In addition, the DOC is continuing its review of nuclear costs and operations focusing on PI under the initial rate case and resource plan orders as well as the recently finalized rate case.

Pending Regulatory Proceeding — Federal Energy Regulatory Commission (FERC)

Midcontinent Independent System Operator, Inc. (MISO) 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 December 2015, an administrative law judge (ALJ) recommended the FERC approve a base ROE of 10.32 percent for the MISO TOs. The ALJ found the existing 12.38 percent ROE to be unjust and unreasonable. The recommended 10.32 percent ROE applied a FERC ROE policy adopted in a June 2014 order (Opinion 531). The FERC approved the ALJ recommended 10.32 percent base ROE in an order issued in September 2016. 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. Various parties requested rehearing of the September 2016 order. 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 adder was filed with the FERC, resulting in a second period of potential refund from Feb. 12, 2015 to May 11, 2016. In June 2016, the ALJ recommended a ROE of 9.7 percent, applying the methodology adopted by the FERC in Opinion 531. A final FERC decision on the second ROE complaint was expected later in 2017, but in April 2017, the United States Court of Appeals for the District of Columbia Circuit (D.C. Circuit) by opinion, 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. The MISO TOs are evaluating the impact of the D.C. Circuit ruling on the November 2013 and February 2015 ROE complaints. In September 2017, certain MISO TOs (not including NSP-Minnesota and NSP-Wisconsin) filed a motion to dismiss the second ROE complaint. The motion to dismiss is pending FERC action.

As of Sept. 30, 2017, NSP-Minnesota has processed the refunds for the Nov. 12, 2013 to Feb. 11, 2015 complaint period based on the 10.32 percent ROE provided in the September 2016 FERC order. NSP-Minnesota has also recognized a current refund liability consistent with the best estimate of the final ROE for the Feb. 12, 2015 to May 11, 2016 complaint period.

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Commitments and Contingencies

9 Months Ended

Sep. 30, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

6. Commitments and Contingencies

Except to the extent noted below and in Note 5 above, 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, 2016 and in Notes 5 and 6 to the consolidated financial statements included in NSP-Minnesota’s Quarterly Report on Form 10-Q for the quarterly periods ended March 31, 2017 and June 30, 2017, 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

Under certain 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 1,069 megawatts (MW) of capacity under long-term PPAs as of Sept. 30, 2017 and Dec. 31, 2016, 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 expiration dates through 2028.

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 lease agreement expires in 2019.

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

(Millions of Dollars)	Sept. 30, 2017		Dec. 31, 2016
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 from the right-of-way and commenced an investigation of the historic MGP and adjacent properties (the Fargo MGP Site). NSP-Minnesota has recommended that targeted source removal of impacted soils and historic MGP infrastructure should be performed. The North Dakota Department of Health approved NSP-Minnesota’s proposed cleanup plan in January 2017. It is anticipated that remediation activities will be performed in 2018, although the timing and final scope of remediation is dependent on whether reasonable access is provided to NSP-Minnesota to perform and implement the approved cleanup plan. Access agreements have been reached with a majority of the property owners in the area to perform the work. NSP-Minnesota has also initiated insurance recovery litigation in North Dakota. The U.S. District Court for the District of North Dakota agreed to the parties’ request for a stay of the litigation until January 2018.

As of Sept. 30, 2017 and Dec. 31, 2016, NSP-Minnesota had recorded a liability of $16.2 million and $11.3 million, respectively, for the Fargo MGP Site. The current cost estimate for the remediation of the site is approximately $23.0 million, of which approximately $6.8 million has been spent. In December 2015, the North Dakota Public Service Commission (NDPSC) approved NSP-Minnesota’s request to defer costs associated with the Fargo MGP Site, resulting in deferral of all investigation and response costs with the exception of approximately 12 percent allocable to the Minnesota jurisdiction. Uncertainties related to the liability recognized include obtaining access to perform the approved remediation (including the prospective purchase of the historic MGP property), and the potential for contributions from entities that may be identified as potentially responsible parties (PRPs).

Other MGP and Landfill Sites — NSP-Minnesota is currently involved in investigating and/or remediating several other MGP and landfill sites. NSP-Minnesota has identified six sites, in addition to the site in Fargo, N.D., where former MGP or landfill disposal activities have or may have resulted in site contamination and are under current investigation and/or remediation. At some or all of these sites, there are other parties that may have responsibility for some portion of any remediation. NSP-Minnesota anticipates that the majority of the investigation or remediation at these sites will continue through at least 2018. NSP-Minnesota had accrued $1.1 million and $0.2 million for these sites as of Sept. 30, 2017 and Dec. 31, 2016, respectively. There may be insurance recovery and/or recovery from other PRPs to offset any costs incurred. NSP-Minnesota anticipates that any significant amounts incurred will be recovered from customers.

Environmental Requirements

Water and Waste

Federal Clean Water Act (CWA) Waters of the United States Rule —In 2015, the United States Environmental Protection Agency (EPA) and the U.S. Army Corps of Engineers (Corps) published a final rule that significantly expanded the types of water bodies regulated under the CWA and broadened the scope of waters subject to federal jurisdiction. In October 2015, the U.S. Court of Appeals for the Sixth Circuit issued a nationwide stay of the final rule and subsequently ruled that it, rather than the federal district courts, had jurisdiction over challenges to the rule.  In January 2017, the U.S. Supreme Court agreed to resolve the dispute as to which court should hear challenges to the rule. A ruling is expected in the first quarter of 2018.

In February 2017, President Trump issued an executive order requiring the EPA and the Corps to review and revise the final rule. On June 27, 2017, the agencies issued a proposed rule that rescinds the 2015 final rule and reinstates the prior 1986 definition of “Water of the U.S.” The agencies are also undertaking a rulemaking to develop a new definition of “Waters of the U.S.”

Federal CWA Effluent Limitations Guidelines (ELG) —In 2015, the EPA issued a final ELG rule for power plants that use coal, natural gas, oil or nuclear materials as fuel and discharge treated effluent to surface waters as well as utility-owned landfills that receive coal combustion residuals. In September 2017, the EPA delayed the compliance date for flue gas desulfurization wastewater and bottom ash transport water until November 2020 while the agency conducts a rulemaking process to potentially revise the effluent limitations and pretreatment standards for these waste streams.

Air

Greenhouse Gas (GHG) Emission Standard for Existing Sources (Clean Power Plan or CPP) — In 2015, the EPA issued its final rule for existing power plants.  Among other things, the rule requires that state plans include enforceable measures to ensure emissions from existing power plants achieve the EPA’s state-specific interim (2022-2029) and final (2030 and thereafter) emission performance targets. 

The CPP was challenged by multiple parties in the D.C. Circuit Court.  In February 2016, the U.S. Supreme Court issued an order staying the final CPP rule. In September 2016, the D.C. Circuit Court heard oral arguments in the consolidated challenges to the CPP. The stay will remain in effect until the D.C. Circuit Court reaches its decision and the U.S. Supreme Court either declines to review the lower court’s decision or reaches a decision of its own.

In March 2017, President Trump signed an executive order requiring the EPA Administrator to review the CPP rule and if appropriate, publish proposed rules suspending, revising or rescinding it. Accordingly, the EPA has requested that the D.C. Circuit Court hold the litigation in abeyance until the EPA completes its work under the executive order. The D.C. Circuit granted the EPA’s request and is holding the litigation in abeyance, while considering briefs by the parties on whether the court should remand the challenges to the EPA rather than holding them in abeyance, determining whether and how the court continues or ends the stay that currently applies to the CPP.

In October 2017, the EPA published a proposed rule to repeal the CPP, based on an analysis that the CPP exceeds the EPA’s statutory authority under the Clean Air Act (CAA). The EPA will take public comment on the proposal for 60 days. The EPA stated it has not yet determined whether it will promulgate a new rule to regulate GHG emissions from existing electric generating units.

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

9 Months Ended

Sep. 30, 2017

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 Sept. 30, 2017			Year Ended Dec. 31, 2016
Borrowing limit	$	250		$	250
Amount outstanding at period end	50			—
Average amount outstanding	50			16
Maximum amount outstanding	116			225
Weighted average interest rate, computed on a daily basis	1.11		%	0.69		%
Weighted average interest rate at period end	1.11			N/A

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 Sept. 30, 2017			Year Ended Dec. 31, 2016
Borrowing limit	$	500		$	500
Amount outstanding at period end	—			85
Average amount outstanding	51			73
Maximum amount outstanding	204			353
Weighted average interest rate, computed on a daily basis	1.33		%	0.65		%
Weighted average interest rate at period end	N/A			0.94

Letters of Credit — NSP-Minnesota uses letters of credit, generally with terms of one year, to provide financial guarantees for certain operating obligations. At Sept. 30, 2017 and Dec. 31, 2016, there were $21 million and $11 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 Sept. 30, 2017, NSP-Minnesota had the following committed credit facility available (in millions of dollars):

Credit Facility (a)		Drawn(b)		Available
$	500	$	21	$	479

^(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 Sept. 30, 2017 and Dec. 31, 2016.

Long-Term Borrowings

In September 2017, NSP-Minnesota issued $600 million of 3.60 percent first mortgage bonds due Sept. 15, 2047.

Debt Redemption

On Sept. 29, 2017, NSP-Minnesota reacquired $500 million of debt with a coupon rate of 5.25 percent and an original maturity date of March 1, 2018. The redemption resulted in payment of an early redemption premium of $7.9 million which was deferred as a regulatory asset.

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Fair Value of Financial Assets and Liabilities

9 Months Ended

Sep. 30, 2017

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 PI nuclear generating plants. The fund contains cash equivalents, debt securities, equity securities and other investments – all classified as available-for-sale. NSP-Minnesota plans to reinvest matured securities until decommissioning begins. NSP-Minnesota uses the MPUC approved asset allocation for the escrow and investment targets by asset class for both the escrow and 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 other-than-temporary impairments, are deferred as a component of the regulatory asset for nuclear decommissioning.

Unrealized gains for the nuclear decommissioning fund were $511.7 million and $378.6 million at Sept. 30, 2017 and Dec. 31, 2016, respectively, and unrealized losses and amounts recorded as other-than-temporary impairments were $10.3 million and $46.9 million at Sept. 30, 2017 and Dec. 31, 2016, 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 at Sept. 30, 2017 and Dec. 31, 2016:

	Sept. 30, 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	$	32,727	$	32,727	$	—	$	—	$	—	$	32,727
Commingled funds:
Non U.S. equities	257,487		204,502		—		—		86,654		291,156
Emerging market debt funds	97,285		—		—		—		106,842		106,842
Private equity investments	139,185		—		—		—		192,098		192,098
Real estate	129,219		—		—		—		195,506		195,506
Other commingled funds	146,179		14,964		—		—		145,313		160,277
Debt securities:
Government securities	45,310		—		44,944		—		—		44,944
U.S. corporate bonds	251,138		—		252,868		—		—		252,868
Non U.S. corporate bonds	46,245		—		46,611		—		—		46,611
Equity securities:
U.S. equities	258,075		509,564		—		—		—		509,564
Non U.S. equities	152,575		224,139		—		—		—		224,139
Total	$	1,555,425	$	985,896	$	344,423	$	—	$	726,413	$	2,056,732

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $49.0 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, 2016
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Investments Measured at NAV (b)		Total
Nuclear decommissioning fund (a)
Cash equivalents	$	20,379	$	20,379	$	—	$	—	$	—	$	20,379
Commingled funds:
Non U.S. equities	260,877		133,126		—		—		112,233		245,359
Emerging market debt funds	93,597		—		—		—		97,543		97,543
Commodity funds	106,571		—		—		—		92,091		92,091
Private equity investments	132,190		—		—		—		190,462		190,462
Real estate	128,630		—		—		—		187,647		187,647
Other commingled funds	151,048		—		—		—		159,489		159,489
Debt securities:
Government securities	32,764		—		31,965		—		—		31,965
U.S. corporate bonds	104,913		—		105,772		—		—		105,772
Non U.S. corporate bonds	21,751		—		21,672		—		—		21,672
Municipal bonds	13,609		—		13,786		—		—		13,786
Mortgage-backed securities	2,785		—		2,816		—		—		2,816
Equity securities:
U.S. equities	270,779		473,400		—		—		—		473,400
Non U.S. equities	189,100		218,381		—		—		—		218,381
Total	$	1,528,993	$	845,286	$	176,011	$	—	$	839,465	$	1,860,762

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $44.3 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 nine months ended Sept. 30, 2017 and 2016 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, at Sept. 30, 2017:

	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	$	—	$	1,275	$	2,303	$	41,366	$	44,944
U.S. corporate bonds	3,834		64,119		150,741		34,174		252,868
Non U.S. corporate bonds	—		13,793		26,651		6,167		46,611
Debt securities	$	3,834	$	79,187	$	179,695	$	81,707	$	344,423

Rabbi Trusts

In June 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 Sept. 30, 2017 and Dec. 31, 2016:

	Sept. 30, 2017
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trust (a)
Cash equivalents	$	391	$	391	$	—	$	—	$	391
Mutual funds	10,075		10,963		—		—		10,963
Total	$	10,466	$	11,354	$	—	$	—	$	11,354

	Dec. 31, 2016
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trusts (a)
Cash equivalents	$	7,459	$	7,459	$	—	$	—	$	7,459
Mutual funds	1,663		1,901		—		—		1,901
Total	$	9,122	$	9,360	$	—	$	—	$	9,360

^(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 Sept. 30, 2017, accumulated other comprehensive losses related to interest rate derivatives included $0.6 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 Sept. 30, 2017, 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 nine months ended Sept. 30, 2017 and 2016.

At Sept. 30, 2017, 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 Sept. 30, 2017 and Dec. 31, 2016:

(Amounts in Thousands)(a)(b)	Sept. 30, 2017	Dec. 31, 2016
Megawatt hours of electricity	58,582	37,805
Million British thermal units of natural gas	47,329	79,520
Gallons of vehicle fuel	300	—

^(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 nine months ended Sept. 30, 2017 and 2016 on accumulated other comprehensive loss, regulatory assets and liabilities and income:

	Three Months Ended Sept. 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	$	—	$	—		$	612		(a)	$	—			$	—
Vehicle fuel and other commodity	38		—			(11		)	(b)	—				—
Total	$	38	$	—		$	601			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	1,493	(c)
Electric commodity	—		20,216			—				(5,356		)	(d)	—
Natural gas commodity	—		(383		)	—				—				—
Total	$	—	$	19,833		$	—			$	(5,356	)		$	1,493

	Nine Months Ended Sept. 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	$	—	$	—		$	1,304		(a)	$	—			$	—
Vehicle fuel and other commodity	81		—			(16		)	(b)	—				—
Total	$	81	$	—		$	1,288			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	8,092		(c)
Electric commodity	—		17,444			—				(9,293		)	(d)	—
Natural gas commodity	—		(1,010		)	—				698			(e)	(945		)	(e)
Total	$	—	$	16,434		$	—			$	(8,595	)		$	7,147

	Three Months Ended Sept. 30, 2016
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:						Pre-Tax 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	(2		)	—			25		(b)	—			—
Total	$	(2	)	$	—		$	375		$	—		$	—
Other derivative instruments
Commodity trading	$	—		$	—		$	—		$	—		$	1,808	(c)
Electric commodity	—			15,301			—			2,044		(d)	—
Natural gas commodity	—			(792		)	—			—			—
Total	$	—		$	14,509		$	—		$	2,044		$	1,808

	Nine Months Ended Sept. 30, 2016
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax 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	$	—	$	—		$	1,042	(a)	$	—		$	—
Vehicle fuel and other commodity	8		—			82		(b)	—			—
Total	$	8	$	—		$	1,124		$	—		$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—		$	—		$	3,069		(c)
Electric commodity	—		12,550			—			26,328		(d)	—
Natural gas commodity	—		(1,045		)	—			3,460		(e)	(1,595		)	(e)
Total	$	—	$	11,505		$	—		$	29,788		$	1,474

^(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 nine months ended Sept. 30, 2017 and 2016. 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 Sept. 30, 2017, five of NSP-Minnesota’s 10 most significant counterparties for these activities, comprising $23.9 million or 33 percent of this credit exposure, had investment grade credit ratings from Standard & Poor’s, Moody’s or Fitch Ratings. Four of the 10 most significant counterparties, comprising $28.0 million or 38 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. The one remaining significant counterparty, comprising $0.9 million or 1 percent of this credit exposure, had credit quality less than investment grade, based on ratings from internal analysis. 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 Sept. 30, 2017 and Dec. 31, 2016, 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 Sept. 30, 2017 and Dec. 31, 2016.

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 Sept. 30, 2017:

	Sept. 30, 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	$	—	$	56	$	—	$	56	$	—		$	56
Other derivative instruments:
Commodity trading	1,297		8,933		81		10,311		(4,040		)	6,271
Electric commodity	—		—		39,932		39,932		(261		)	39,671
Natural gas commodity	—		427		—		427		—			427
Total current derivative assets	$	1,297	$	9,416	$	40,013	$	50,726	$	(4,301	)	46,425
PPAs (a)												752
Current derivative instruments												$	47,177
Noncurrent derivative assets
Derivatives designated as cash flow hedges:
Vehicle fuel and other commodity	$	—	$	11	$	—	$	11	$	—		$	11
Other derivative instruments:
Commodity trading	84		30,103		5,661		35,848		(7,465		)	28,383
Total noncurrent derivative assets	$	84	$	30,114	$	5,661	$	35,859	$	(7,465	)	28,394
PPAs (a)												126
Noncurrent derivative instruments												$	28,520

	Sept. 30, 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	$	1,146	$	7,100	$	—	$	8,246	$	(4,307	)	$	3,939
Electric commodity	—		—		261		261		(261		)	—
Total current derivative liabilities	$	1,146	$	7,100	$	261	$	8,507	$	(4,568	)	3,939
PPAs (a)												14,106
Current derivative instruments												$	18,045
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	52	$	22,666	$	—	$	22,718	$	(10,130	)	$	12,588
Total noncurrent derivative liabilities	$	52	$	22,666	$	—	$	22,718	$	(10,130	)	12,588
PPAs (a)												93,375
Noncurrent derivative instruments												$	105,963

^(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 will be 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 Sept. 30, 2017. At Sept. 30, 2017, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $2.9 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, 2016:

	Dec. 31, 2016
	Fair Value						Fair Value Total		Counterparty Netting (b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative assets
Other derivative instruments:
Commodity trading	$	12,053	$	8,651	$	—	$	20,704	$	(15,500	)	$	5,204
Electric commodity	—		—		15,997		15,997		(677		)	15,320
Natural gas commodity	—		912		—		912		—			912
Total current derivative assets	$	12,053	$	9,563	$	15,997	$	37,613	$	(16,177	)	21,436
PPAs (a)												592
Current derivative instruments												$	22,028
Noncurrent derivative assets
Other derivative instruments:
Commodity trading	$	100	$	31,029	$	—	$	31,129	$	(7,323	)	$	23,806
Total noncurrent derivative assets	$	100	$	31,029	$	—	$	31,129	$	(7,323	)	23,806
PPAs (a)												872
Noncurrent derivative instruments												$	24,678

	Dec. 31, 2016
	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	$	12,397	$	5,964	$	—	$	18,361	$	(15,837	)	$	2,524
Electric commodity	—		—		677		677		(677		)	—
Total current derivative liabilities	$	12,397	$	5,964	$	677	$	19,038	$	(16,514	)	2,524
PPAs (a)												14,082
Current derivative instruments												$	16,606
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	89	$	23,424	$	—	$	23,513	$	(10,727	)	$	12,786
Total noncurrent derivative liabilities	$	89	$	23,424	$	—	$	23,513	$	(10,727	)	12,786
PPAs (a)												104,018
Noncurrent derivative instruments												$	116,804

^(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 will be 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, 2016. At Dec. 31, 2016, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $3.7 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 nine months ended Sept. 30, 2017 and 2016:

	Three Months Ended Sept. 30
(Thousands of Dollars)	2017			2016
Balance at July 1	$	40,572		$	23,488
Settlements	(23,186		)	(26,192		)
Net transactions recorded during the period:
Gains recognized in earnings (a)	527			—
Net gains recognized as regulatory assets and liabilities	27,500			27,163
Balance at Sept. 30	$	45,413		$	24,459
	Nine Months Ended Sept. 30
(Thousands of Dollars)	2017			2016
Balance at Jan. 1	$	15,320		$	12,969
Purchases	40,740			27,870
Settlements	(34,681		)	(38,300		)
Net transactions recorded during the period:
Gains (losses) recognized in earnings (a)	5,742			(2		)
Net gains recognized as regulatory assets and liabilities	18,292			21,922
Balance at Sept. 30	$	45,413		$	24,459

^(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 nine months ended Sept. 30, 2017 and 2016.

Fair Value of Long-Term Debt

As of Sept. 30, 2017 and Dec. 31, 2016, other financial instruments for which the carrying amount did not equal fair value were as follows:

	Sept. 30, 2017				Dec. 31, 2016
(Thousands of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt, including current portion	$	4,932,977	$	5,501,602	$	4,843,165	$	5,310,925

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 Sept. 30, 2017 and Dec. 31, 2016, 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

9 Months Ended

Sep. 30, 2017

Other Income and Expenses [Abstract]

Other (Expense) Income, Net

Other Income (Expense), Net

Other income (expense), net consisted of the following:

	Three Months Ended Sept. 30						Nine Months Ended Sept. 30
(Thousands of Dollars)	2017			2016			2017			2016
Interest income	$	2,936		$	510		$	6,250		$	3,975
Other nonoperating income	—			—			—			248
Insurance policy expense	(387		)	(926		)	(2,098		)	(2,389		)
Other nonoperating expense	(429		)	(23		)	(402		)	—
Other income (expense), net	$	2,120		$	(439	)	$	3,750		$	1,834

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Segment Information

9 Months Ended

Sep. 30, 2017

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 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 Sept. 30, 2017
Operating revenues (a)(b)	$	1,290,971	$	57,442		$	7,366	$	—		$	1,355,779
Intersegment revenues	160		100			—		(260		)	—
Total revenues	$	1,291,131	$	57,542		$	7,366	$	(260	)	$	1,355,779
Net income (loss)	$	232,078	$	(6,242	)	$	3,167	$	—		$	229,003

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas			All Other		Reconciling Eliminations			Consolidated Total
Three Months Ended Sept. 30, 2016
Operating revenues (a)(b)	$	1,282,574	$	55,519		$	7,286	$	—		$	1,345,379
Intersegment revenues	118		189			—		(307		)	—
Total revenues	$	1,282,692	$	55,708		$	7,286	$	(307	)	$	1,345,379
Net income (loss)	$	217,674	$	(14,900	)	$	3,778	$	—		$	206,552

^(a)  Operating revenues include $124 million and $121 million of affiliate electric revenue for the three months ended Sept. 30, 2017 and 2016.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended Sept. 30, 2017 and 2016.

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Nine Months Ended Sept. 30, 2017
Operating revenues (a)(b)	$	3,449,780	$	356,631	$	21,448	$	—		$	3,827,859
Intersegment revenues	512		371		—		(883		)	—
Total revenues	$	3,450,292	$	357,002	$	21,448	$	(883	)	$	3,827,859
Net income	$	399,637	$	7,903	$	3,291	$	—		$	410,831

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Nine Months Ended Sept. 30, 2016
Operating revenues (a)(b)	$	3,332,688	$	314,020	$	21,404	$	—		$	3,668,112
Intersegment revenues	525		437		—		(962		)	—
Total revenues	$	3,333,213	$	314,457	$	21,404	$	(962	)	$	3,668,112
Net income (loss)	$	367,776	$	8,700	$	2,881	$	—		$	379,357

^(a)  Operating revenues include $367 million and $359 million of affiliate electric revenue for the nine months ended Sept. 30, 2017 and 2016.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the nine months ended Sept. 30, 2017 and 2016.

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Benefit Plans and Other Postretirement Benefits

9 Months Ended

Sep. 30, 2017

Retirement Benefits [Abstract]

Benefit Plans and Other Postretirement Benefits

Benefit Plans and Other Postretirement Benefits

Components of Net Periodic Benefit Cost

	Three Months Ended Sept. 30
	2017			2016			2017			2016
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	6,958		$	7,077		$	36		$	31
Interest cost	10,177			11,358			854			981
Expected return on plan assets	(15,016		)	(15,236		)	(53		)	(43		)
Amortization of prior service cost (credit)	265			234			(759		)	(759		)
Amortization of net loss	9,902			9,194			506			401
Net periodic benefit cost	12,286			12,627			584			611
Costs not recognized due to the effects of regulation	(4,899		)	(5,295		)	—			—
Net benefit cost recognized for financial reporting	$	7,387		$	7,332		$	584		$	611

	Nine Months Ended Sept. 30
	2017			2016			2017			2016
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	20,874		$	21,231		$	108		$	93
Interest cost	30,531			34,074			2,562			2,943
Expected return on plan assets	(45,050		)	(45,708		)	(161		)	(129		)
Amortization of prior service cost (credit)	795			702			(2,277		)	(2,277		)
Amortization of net loss	29,706			27,582			1,520			1,203
Net periodic benefit cost	36,856			37,881			1,752			1,833
Costs not recognized due to the effects of regulation	(14,696		)	(15,887		)	—			—
Net benefit cost recognized for financial reporting	$	22,160		$	21,994		$	1,752		$	1,833

In January 2017, contributions of $150.0 million were made across four of Xcel Energy’s pension plans, of which $59.4 million was attributable to NSP-Minnesota. Xcel Energy does not expect additional pension contributions during 2017.

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Other Comprehensive Income

9 Months Ended

Sep. 30, 2017

Stockholders' Equity Note [Abstract]

Other Comprehensive Income

Other Comprehensive Income (Loss)

Changes in accumulated other comprehensive (loss) income, net of tax, for the three and nine months ended Sept. 30, 2017 and 2016 were as follows:

	Three Months Ended Sept. 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) income at July 1	$	(17,775	)	$	105	$	(2,609	)	$	(20,279	)
Other comprehensive income before reclassifications	22			—		—			22
Losses reclassified from net accumulated other comprehensive loss	379			—		39			418
Net current period other comprehensive income	401			—		39			440
Accumulated other comprehensive (loss) income at Sept. 30	$	(17,374	)	$	105	$	(2,570	)	$	(19,839	)

	Three Months Ended Sept. 30, 2016
(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) income at July 1	$	(18,640	)	$	105	$	(2,058	)	$	(20,593	)
Other comprehensive loss before reclassifications	(1		)	—		—			(1		)
Losses reclassified from net accumulated other comprehensive loss	213			—		19			232
Net current period other comprehensive income	212			—		19			231
Accumulated other comprehensive (loss) income at Sept. 30	$	(18,428	)	$	105	$	(2,039	)	$	(20,362	)

	Nine Months Ended Sept. 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) income at Jan. 1	$	(18,208	)	$	105	$	(2,680	)	$	(20,783	)
Other comprehensive income before reclassifications	48			—		—			48
Losses reclassified from net accumulated other comprehensive loss	786			—		110			896
Net current period other comprehensive income	834			—		110			944
Accumulated other comprehensive (loss) income at Sept. 30	$	(17,374	)	$	105	$	(2,570	)	$	(19,839	)

	Nine Months Ended Sept. 30, 2016
(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) income at Jan. 1	$	(19,090	)	$	105	$	(2,096	)	$	(21,081	)
Other comprehensive income before reclassifications	5			—		—			5
Losses reclassified from net accumulated other comprehensive loss	657			—		57			714
Net current period other comprehensive income	662			—		57			719
Accumulated other comprehensive (loss) income at Sept. 30	$	(18,428	)	$	105	$	(2,039	)	$	(20,362	)

Reclassifications from accumulated other comprehensive loss for the three and nine months ended Sept. 30, 2017 and 2016 were as follows:

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Three Months Ended Sept. 30, 2017				Three Months Ended Sept. 30, 2016
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	612		(a)	$	350		(a)
Vehicle fuel derivatives	(11		)	(b)	25			(b)
Total, pre-tax	601				375
Tax benefit	(222		)		(162		)
Total, net of tax	379				213
Defined benefit pension and postretirement losses:
Amortization of net loss	109			(c)	83			(c)
Prior service credit	(49		)	(c)	(49		)	(c)
Total, pre-tax	60				34
Tax benefit	(21		)		(15		)
Total, net of tax	39				19
Total amounts reclassified, net of tax	$	418			$	232

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Nine Months Ended Sept. 30, 2017				Nine Months Ended Sept. 30, 2016
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	1,304		(a)	$	1,042		(a)
Vehicle fuel derivatives	(16		)	(b)	82			(b)
Total, pre-tax	1,288				1,124
Tax benefit	(502		)		(467		)
Total, net of tax	786				657
Defined benefit pension and postretirement losses:
Amortization of net loss	327			(c)	249			(c)
Prior service credit	(147		)	(c)	(147		)	(c)
Total, pre-tax	180				102
Tax benefit	(70		)		(45		)
Total, net of tax	110				57
Total amounts reclassified, net of tax	$	896			$	714

^(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 for details regarding these benefit plans.

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Selected Balance Sheet Data (Tables)

9 Months Ended

Sep. 30, 2017

Balance Sheet Related Disclosures [Abstract]

Accounts receivable, net

(Thousands of Dollars)	Sept. 30, 2017			Dec. 31, 2016
Accounts receivable, net
Accounts receivable	$	364,970		$	349,449
Less allowance for bad debts	(20,442		)	(19,968		)
	$	344,528		$	329,481

Inventories

(Thousands of Dollars)	Sept. 30, 2017		Dec. 31, 2016
Inventories
Materials and supplies	$	216,850	$	214,234
Fuel	91,555		97,527
Natural gas	41,173		33,431
	$	349,578	$	345,192

Property, plant and equipment, net

(Thousands of Dollars)	Sept. 30, 2017			Dec. 31, 2016
Property, plant and equipment, net
Electric plant	$	17,323,127		$	17,059,993
Natural gas plant	1,340,688			1,311,235
Common and other property	803,599			710,958
Construction work in progress	508,306			509,891
Total property, plant and equipment	19,975,720			19,592,077
Less accumulated depreciation	(7,015,522		)	(6,682,418		)
Nuclear fuel	2,668,586			2,571,770
Less accumulated amortization	(2,268,290		)	(2,180,636		)
	$	13,360,494		$	13,300,793

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Income Taxes (Tables)

9 Months Ended

Sep. 30, 2017

Income Tax Disclosure [Abstract]

Reconciliation of Unrecognized Tax Benefits

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

(Millions of Dollars)	Sept. 30, 2017		Dec. 31, 2016
Unrecognized tax benefit — Permanent tax positions	$	9.8	$	21.5
Unrecognized tax benefit — Temporary tax positions	8.1		39.3
Total unrecognized tax benefit	$	17.9	$	60.8

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)	Sept. 30, 2017			Dec. 31, 2016
NOL and tax credit carryforwards	$	(12.5	)	$	(19.3	)

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

:

(Millions of Dollars)	Sept. 30, 2017			Dec. 31, 2016
Payable for interest related to unrecognized tax benefits at beginning of period	$	(2.0	)	$	(0.2	)
Interest income (expense) related to unrecognized tax benefits recorded during the period	1.1			(1.8		)
Payable for interest related to unrecognized tax benefits at end of period	$	(0.9	)	$	(2.0	)

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Rate Matters (Tables)

9 Months Ended

Sep. 30, 2017

Public Utilities, General Disclosures [Abstract]

NSP-Minnesota 2016 Rate Case Final Order

(Millions of Dollars, Incremental)	2016		2017		2018		2019			Total
Revenues	$	74.99	$	59.86	$	—	$	50.12		$	184.97
NSP-Minnesota’s sales true-up	59.95		—		—		(0.20		)	59.75
Total rate impact	$	134.94	$	59.86	$	—	$	49.92		$	244.72

XML

Commitments and Contingencies Schedule of Guarantor Obligations (Tables)

9 Months Ended

Sep. 30, 2017

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)	Sept. 30, 2017		Dec. 31, 2016
Guarantee issued and outstanding	$	4.8	$	4.8

XML

Borrowings and Other Financing Instruments (Tables)

9 Months Ended

Sep. 30, 2017

Borrowings and Other Financing Instruments [Abstract]

Credit Facilities

At Sept. 30, 2017, NSP-Minnesota had the following committed credit facility available (in millions of dollars):

Credit Facility (a)		Drawn(b)		Available
$	500	$	21	$	479

^(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 Sept. 30, 2017			Year Ended Dec. 31, 2016
Borrowing limit	$	250		$	250
Amount outstanding at period end	50			—
Average amount outstanding	50			16
Maximum amount outstanding	116			225
Weighted average interest rate, computed on a daily basis	1.11		%	0.69		%
Weighted average interest rate at period end	1.11			N/A

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 Sept. 30, 2017			Year Ended Dec. 31, 2016
Borrowing limit	$	500		$	500
Amount outstanding at period end	—			85
Average amount outstanding	51			73
Maximum amount outstanding	204			353
Weighted average interest rate, computed on a daily basis	1.33		%	0.65		%
Weighted average interest rate at period end	N/A			0.94

XML

Fair Value of Financial Assets and Liabilities (Tables)

9 Months Ended

Sep. 30, 2017

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 at Sept. 30, 2017 and Dec. 31, 2016:

	Sept. 30, 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	$	32,727	$	32,727	$	—	$	—	$	—	$	32,727
Commingled funds:
Non U.S. equities	257,487		204,502		—		—		86,654		291,156
Emerging market debt funds	97,285		—		—		—		106,842		106,842
Private equity investments	139,185		—		—		—		192,098		192,098
Real estate	129,219		—		—		—		195,506		195,506
Other commingled funds	146,179		14,964		—		—		145,313		160,277
Debt securities:
Government securities	45,310		—		44,944		—		—		44,944
U.S. corporate bonds	251,138		—		252,868		—		—		252,868
Non U.S. corporate bonds	46,245		—		46,611		—		—		46,611
Equity securities:
U.S. equities	258,075		509,564		—		—		—		509,564
Non U.S. equities	152,575		224,139		—		—		—		224,139
Total	$	1,555,425	$	985,896	$	344,423	$	—	$	726,413	$	2,056,732

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $49.0 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, 2016
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Investments Measured at NAV (b)		Total
Nuclear decommissioning fund (a)
Cash equivalents	$	20,379	$	20,379	$	—	$	—	$	—	$	20,379
Commingled funds:
Non U.S. equities	260,877		133,126		—		—		112,233		245,359
Emerging market debt funds	93,597		—		—		—		97,543		97,543
Commodity funds	106,571		—		—		—		92,091		92,091
Private equity investments	132,190		—		—		—		190,462		190,462
Real estate	128,630		—		—		—		187,647		187,647
Other commingled funds	151,048		—		—		—		159,489		159,489
Debt securities:
Government securities	32,764		—		31,965		—		—		31,965
U.S. corporate bonds	104,913		—		105,772		—		—		105,772
Non U.S. corporate bonds	21,751		—		21,672		—		—		21,672
Municipal bonds	13,609		—		13,786		—		—		13,786
Mortgage-backed securities	2,785		—		2,816		—		—		2,816
Equity securities:
U.S. equities	270,779		473,400		—		—		—		473,400
Non U.S. equities	189,100		218,381		—		—		—		218,381
Total	$	1,528,993	$	845,286	$	176,011	$	—	$	839,465	$	1,860,762

^(a)  Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $44.3 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, at Sept. 30, 2017:

	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	$	—	$	1,275	$	2,303	$	41,366	$	44,944
U.S. corporate bonds	3,834		64,119		150,741		34,174		252,868
Non U.S. corporate bonds	—		13,793		26,651		6,167		46,611
Debt securities	$	3,834	$	79,187	$	179,695	$	81,707	$	344,423

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

In June 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 Sept. 30, 2017 and Dec. 31, 2016:

	Sept. 30, 2017
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trust (a)
Cash equivalents	$	391	$	391	$	—	$	—	$	391
Mutual funds	10,075		10,963		—		—		10,963
Total	$	10,466	$	11,354	$	—	$	—	$	11,354

	Dec. 31, 2016
			Fair Value
(Thousands of Dollars)	Cost		Level 1		Level 2		Level 3		Total
Rabbi Trusts (a)
Cash equivalents	$	7,459	$	7,459	$	—	$	—	$	7,459
Mutual funds	1,663		1,901		—		—		1,901
Total	$	9,122	$	9,360	$	—	$	—	$	9,360

^(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 Sept. 30, 2017 and Dec. 31, 2016:

(Amounts in Thousands)(a)(b)	Sept. 30, 2017	Dec. 31, 2016
Megawatt hours of electricity	58,582	37,805
Million British thermal units of natural gas	47,329	79,520
Gallons of vehicle fuel	300	—

^(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 nine months ended Sept. 30, 2017 and 2016 on accumulated other comprehensive loss, regulatory assets and liabilities and income:

	Three Months Ended Sept. 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	$	—	$	—		$	612		(a)	$	—			$	—
Vehicle fuel and other commodity	38		—			(11		)	(b)	—				—
Total	$	38	$	—		$	601			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	1,493	(c)
Electric commodity	—		20,216			—				(5,356		)	(d)	—
Natural gas commodity	—		(383		)	—				—				—
Total	$	—	$	19,833		$	—			$	(5,356	)		$	1,493

	Nine Months Ended Sept. 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	$	—	$	—		$	1,304		(a)	$	—			$	—
Vehicle fuel and other commodity	81		—			(16		)	(b)	—				—
Total	$	81	$	—		$	1,288			$	—			$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—			$	—			$	8,092		(c)
Electric commodity	—		17,444			—				(9,293		)	(d)	—
Natural gas commodity	—		(1,010		)	—				698			(e)	(945		)	(e)
Total	$	—	$	16,434		$	—			$	(8,595	)		$	7,147

	Three Months Ended Sept. 30, 2016
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:						Pre-Tax 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	(2		)	—			25		(b)	—			—
Total	$	(2	)	$	—		$	375		$	—		$	—
Other derivative instruments
Commodity trading	$	—		$	—		$	—		$	—		$	1,808	(c)
Electric commodity	—			15,301			—			2,044		(d)	—
Natural gas commodity	—			(792		)	—			—			—
Total	$	—		$	14,509		$	—		$	2,044		$	1,808

	Nine Months Ended Sept. 30, 2016
	Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:					Pre-Tax 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	$	—	$	—		$	1,042	(a)	$	—		$	—
Vehicle fuel and other commodity	8		—			82		(b)	—			—
Total	$	8	$	—		$	1,124		$	—		$	—
Other derivative instruments
Commodity trading	$	—	$	—		$	—		$	—		$	3,069		(c)
Electric commodity	—		12,550			—			26,328		(d)	—
Natural gas commodity	—		(1,045		)	—			3,460		(e)	(1,595		)	(e)
Total	$	—	$	11,505		$	—		$	29,788		$	1,474

^(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 Sept. 30, 2017:

	Sept. 30, 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	$	—	$	56	$	—	$	56	$	—		$	56
Other derivative instruments:
Commodity trading	1,297		8,933		81		10,311		(4,040		)	6,271
Electric commodity	—		—		39,932		39,932		(261		)	39,671
Natural gas commodity	—		427		—		427		—			427
Total current derivative assets	$	1,297	$	9,416	$	40,013	$	50,726	$	(4,301	)	46,425
PPAs (a)												752
Current derivative instruments												$	47,177
Noncurrent derivative assets
Derivatives designated as cash flow hedges:
Vehicle fuel and other commodity	$	—	$	11	$	—	$	11	$	—		$	11
Other derivative instruments:
Commodity trading	84		30,103		5,661		35,848		(7,465		)	28,383
Total noncurrent derivative assets	$	84	$	30,114	$	5,661	$	35,859	$	(7,465	)	28,394
PPAs (a)												126
Noncurrent derivative instruments												$	28,520

	Sept. 30, 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	$	1,146	$	7,100	$	—	$	8,246	$	(4,307	)	$	3,939
Electric commodity	—		—		261		261		(261		)	—
Total current derivative liabilities	$	1,146	$	7,100	$	261	$	8,507	$	(4,568	)	3,939
PPAs (a)												14,106
Current derivative instruments												$	18,045
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	52	$	22,666	$	—	$	22,718	$	(10,130	)	$	12,588
Total noncurrent derivative liabilities	$	52	$	22,666	$	—	$	22,718	$	(10,130	)	12,588
PPAs (a)												93,375
Noncurrent derivative instruments												$	105,963

^(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 will be 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 Sept. 30, 2017. At Sept. 30, 2017, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $2.9 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, 2016:

	Dec. 31, 2016
	Fair Value						Fair Value Total		Counterparty Netting (b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative assets
Other derivative instruments:
Commodity trading	$	12,053	$	8,651	$	—	$	20,704	$	(15,500	)	$	5,204
Electric commodity	—		—		15,997		15,997		(677		)	15,320
Natural gas commodity	—		912		—		912		—			912
Total current derivative assets	$	12,053	$	9,563	$	15,997	$	37,613	$	(16,177	)	21,436
PPAs (a)												592
Current derivative instruments												$	22,028
Noncurrent derivative assets
Other derivative instruments:
Commodity trading	$	100	$	31,029	$	—	$	31,129	$	(7,323	)	$	23,806
Total noncurrent derivative assets	$	100	$	31,029	$	—	$	31,129	$	(7,323	)	23,806
PPAs (a)												872
Noncurrent derivative instruments												$	24,678

	Dec. 31, 2016
	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	$	12,397	$	5,964	$	—	$	18,361	$	(15,837	)	$	2,524
Electric commodity	—		—		677		677		(677		)	—
Total current derivative liabilities	$	12,397	$	5,964	$	677	$	19,038	$	(16,514	)	2,524
PPAs (a)												14,082
Current derivative instruments												$	16,606
Noncurrent derivative liabilities
Other derivative instruments:
Commodity trading	$	89	$	23,424	$	—	$	23,513	$	(10,727	)	$	12,786
Total noncurrent derivative liabilities	$	89	$	23,424	$	—	$	23,513	$	(10,727	)	12,786
PPAs (a)												104,018
Noncurrent derivative instruments												$	116,804

^(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 will be 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, 2016. At Dec. 31, 2016, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $3.7 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 nine months ended Sept. 30, 2017 and 2016:

	Three Months Ended Sept. 30
(Thousands of Dollars)	2017			2016
Balance at July 1	$	40,572		$	23,488
Settlements	(23,186		)	(26,192		)
Net transactions recorded during the period:
Gains recognized in earnings (a)	527			—
Net gains recognized as regulatory assets and liabilities	27,500			27,163
Balance at Sept. 30	$	45,413		$	24,459
	Nine Months Ended Sept. 30
(Thousands of Dollars)	2017			2016
Balance at Jan. 1	$	15,320		$	12,969
Purchases	40,740			27,870
Settlements	(34,681		)	(38,300		)
Net transactions recorded during the period:
Gains (losses) recognized in earnings (a)	5,742			(2		)
Net gains recognized as regulatory assets and liabilities	18,292			21,922
Balance at Sept. 30	$	45,413		$	24,459

^(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 Sept. 30, 2017 and Dec. 31, 2016, other financial instruments for which the carrying amount did not equal fair value were as follows:

	Sept. 30, 2017				Dec. 31, 2016
(Thousands of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt, including current portion	$	4,932,977	$	5,501,602	$	4,843,165	$	5,310,925

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Other (Expense) Income, Net (Tables)

9 Months Ended

Sep. 30, 2017

Other Income and Expenses [Abstract]

Other (Expense) Income, Net

Other income (expense), net consisted of the following:

	Three Months Ended Sept. 30						Nine Months Ended Sept. 30
(Thousands of Dollars)	2017			2016			2017			2016
Interest income	$	2,936		$	510		$	6,250		$	3,975
Other nonoperating income	—			—			—			248
Insurance policy expense	(387		)	(926		)	(2,098		)	(2,389		)
Other nonoperating expense	(429		)	(23		)	(402		)	—
Other income (expense), net	$	2,120		$	(439	)	$	3,750		$	1,834

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Segment Information (Tables)

9 Months Ended

Sep. 30, 2017

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 Sept. 30, 2017
Operating revenues (a)(b)	$	1,290,971	$	57,442		$	7,366	$	—		$	1,355,779
Intersegment revenues	160		100			—		(260		)	—
Total revenues	$	1,291,131	$	57,542		$	7,366	$	(260	)	$	1,355,779
Net income (loss)	$	232,078	$	(6,242	)	$	3,167	$	—		$	229,003

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas			All Other		Reconciling Eliminations			Consolidated Total
Three Months Ended Sept. 30, 2016
Operating revenues (a)(b)	$	1,282,574	$	55,519		$	7,286	$	—		$	1,345,379
Intersegment revenues	118		189			—		(307		)	—
Total revenues	$	1,282,692	$	55,708		$	7,286	$	(307	)	$	1,345,379
Net income (loss)	$	217,674	$	(14,900	)	$	3,778	$	—		$	206,552

^(a)  Operating revenues include $124 million and $121 million of affiliate electric revenue for the three months ended Sept. 30, 2017 and 2016.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended Sept. 30, 2017 and 2016.

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Nine Months Ended Sept. 30, 2017
Operating revenues (a)(b)	$	3,449,780	$	356,631	$	21,448	$	—		$	3,827,859
Intersegment revenues	512		371		—		(883		)	—
Total revenues	$	3,450,292	$	357,002	$	21,448	$	(883	)	$	3,827,859
Net income	$	399,637	$	7,903	$	3,291	$	—		$	410,831

(Thousands of Dollars)	Regulated Electric		Regulated Natural Gas		All Other		Reconciling Eliminations			Consolidated Total
Nine Months Ended Sept. 30, 2016
Operating revenues (a)(b)	$	3,332,688	$	314,020	$	21,404	$	—		$	3,668,112
Intersegment revenues	525		437		—		(962		)	—
Total revenues	$	3,333,213	$	314,457	$	21,404	$	(962	)	$	3,668,112
Net income (loss)	$	367,776	$	8,700	$	2,881	$	—		$	379,357

^(a)  Operating revenues include $367 million and $359 million of affiliate electric revenue for the nine months ended Sept. 30, 2017 and 2016.

^(b)  Operating revenues include an immaterial amount of affiliate gas revenue for the nine months ended Sept. 30, 2017 and 2016.

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Benefit Plans and Other Postretirement Benefits (Tables)

9 Months Ended

Sep. 30, 2017

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost (Credit)

Components of Net Periodic Benefit Cost

	Three Months Ended Sept. 30
	2017			2016			2017			2016
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	6,958		$	7,077		$	36		$	31
Interest cost	10,177			11,358			854			981
Expected return on plan assets	(15,016		)	(15,236		)	(53		)	(43		)
Amortization of prior service cost (credit)	265			234			(759		)	(759		)
Amortization of net loss	9,902			9,194			506			401
Net periodic benefit cost	12,286			12,627			584			611
Costs not recognized due to the effects of regulation	(4,899		)	(5,295		)	—			—
Net benefit cost recognized for financial reporting	$	7,387		$	7,332		$	584		$	611

	Nine Months Ended Sept. 30
	2017			2016			2017			2016
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	20,874		$	21,231		$	108		$	93
Interest cost	30,531			34,074			2,562			2,943
Expected return on plan assets	(45,050		)	(45,708		)	(161		)	(129		)
Amortization of prior service cost (credit)	795			702			(2,277		)	(2,277		)
Amortization of net loss	29,706			27,582			1,520			1,203
Net periodic benefit cost	36,856			37,881			1,752			1,833
Costs not recognized due to the effects of regulation	(14,696		)	(15,887		)	—			—
Net benefit cost recognized for financial reporting	$	22,160		$	21,994		$	1,752		$	1,833

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Other Comprehensive Income (Tables)

9 Months Ended

Sep. 30, 2017

Stockholders' Equity Note [Abstract]

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

Changes in accumulated other comprehensive (loss) income, net of tax, for the three and nine months ended Sept. 30, 2017 and 2016 were as follows:

	Three Months Ended Sept. 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) income at July 1	$	(17,775	)	$	105	$	(2,609	)	$	(20,279	)
Other comprehensive income before reclassifications	22			—		—			22
Losses reclassified from net accumulated other comprehensive loss	379			—		39			418
Net current period other comprehensive income	401			—		39			440
Accumulated other comprehensive (loss) income at Sept. 30	$	(17,374	)	$	105	$	(2,570	)	$	(19,839	)

	Three Months Ended Sept. 30, 2016
(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) income at July 1	$	(18,640	)	$	105	$	(2,058	)	$	(20,593	)
Other comprehensive loss before reclassifications	(1		)	—		—			(1		)
Losses reclassified from net accumulated other comprehensive loss	213			—		19			232
Net current period other comprehensive income	212			—		19			231
Accumulated other comprehensive (loss) income at Sept. 30	$	(18,428	)	$	105	$	(2,039	)	$	(20,362	)

	Nine Months Ended Sept. 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) income at Jan. 1	$	(18,208	)	$	105	$	(2,680	)	$	(20,783	)
Other comprehensive income before reclassifications	48			—		—			48
Losses reclassified from net accumulated other comprehensive loss	786			—		110			896
Net current period other comprehensive income	834			—		110			944
Accumulated other comprehensive (loss) income at Sept. 30	$	(17,374	)	$	105	$	(2,570	)	$	(19,839	)

	Nine Months Ended Sept. 30, 2016
(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) income at Jan. 1	$	(19,090	)	$	105	$	(2,096	)	$	(21,081	)
Other comprehensive income before reclassifications	5			—		—			5
Losses reclassified from net accumulated other comprehensive loss	657			—		57			714
Net current period other comprehensive income	662			—		57			719
Accumulated other comprehensive (loss) income at Sept. 30	$	(18,428	)	$	105	$	(2,039	)	$	(20,362	)

Reclassifications out of Accumulated Other Comprehensive Loss

Reclassifications from accumulated other comprehensive loss for the three and nine months ended Sept. 30, 2017 and 2016 were as follows:

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Three Months Ended Sept. 30, 2017				Three Months Ended Sept. 30, 2016
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	612		(a)	$	350		(a)
Vehicle fuel derivatives	(11		)	(b)	25			(b)
Total, pre-tax	601				375
Tax benefit	(222		)		(162		)
Total, net of tax	379				213
Defined benefit pension and postretirement losses:
Amortization of net loss	109			(c)	83			(c)
Prior service credit	(49		)	(c)	(49		)	(c)
Total, pre-tax	60				34
Tax benefit	(21		)		(15		)
Total, net of tax	39				19
Total amounts reclassified, net of tax	$	418			$	232

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Nine Months Ended Sept. 30, 2017				Nine Months Ended Sept. 30, 2016
Losses (gains) on cash flow hedges:
Interest rate derivatives	$	1,304		(a)	$	1,042		(a)
Vehicle fuel derivatives	(16		)	(b)	82			(b)
Total, pre-tax	1,288				1,124
Tax benefit	(502		)		(467		)
Total, net of tax	786				657
Defined benefit pension and postretirement losses:
Amortization of net loss	327			(c)	249			(c)
Prior service credit	(147		)	(c)	(147		)	(c)
Total, pre-tax	180				102
Tax benefit	(70		)		(45		)
Total, net of tax	110				57
Total amounts reclassified, net of tax	$	896			$	714

^(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 for details regarding these benefit plans.

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Selected Balance Sheet Data, Accounts Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts receivable, net
Accounts receivable	$ 364,970	$ 349,449
Less allowance for bad debts	(20,442)	(19,968)
Accounts receivable, net	$ 344,528	$ 329,481

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Selected Balance Sheet Data, Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Public Utilities, Inventory [Line Items]
Inventories	$ 349,578	$ 345,192
Materials and supplies
Public Utilities, Inventory [Line Items]
Inventories	216,850	214,234
Fuel
Public Utilities, Inventory [Line Items]
Inventories	91,555	97,527
Natural gas
Public Utilities, Inventory [Line Items]
Inventories	$ 41,173	$ 33,431

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Selected Balance Sheet Data, Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 19,975,720	$ 19,592,077
Less accumulated depreciation	(7,015,522)	(6,682,418)
Property, plant and equipment, net	13,360,494	13,300,793
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	17,323,127	17,059,993
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,340,688	1,311,235
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	803,599	710,958
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	508,306	509,891
Nuclear fuel
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,668,586	2,571,770
Less accumulated depreciation	$ (2,268,290)	$ (2,180,636)

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Income Taxes (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Examination [Line Items]
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	$ (900,000)		$ (2,000,000)	$ (200,000)
Interest Expense related to unrecognized tax benefits	1,100,000		(1,800,000)
Number Of Years Of Tax Loss Carryback Period				2 years
Tax Adjustments, Settlements, and Unusual Provisions				$ 5,000,000	$ 17,000,000	$ 12,000,000	$ 15,000,000
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions	9,800,000		21,500,000
Unrecognized tax benefit — Temporary tax positions	8,100,000		39,300,000
Total unrecognized tax benefit	17,900,000		60,800,000
NOL and tax credit carryforwards	(12,500,000)		(19,300,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible	7,000,000
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
Potential Tax Adjustments	$ 14,000,000
Earliest year subject to 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 Thousands	1 Months Ended								9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	May 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Feb. 28, 2015	Nov. 30, 2013	Sep. 30, 2017
Minnesota Public Utilities Commission | Annual Automatic Adjustment of Charges
Rate Matters [Abstract]
Public Utilities; Approved Decrease Related To Disallowance Of Replacement Energy Costs			$ 4,400
NSP-Minnesota | 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%
NSP-Minnesota | Minnesota Public Utilities Commission | MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case
Rate Matters [Abstract]
Public Utilities, Number Of Years Rate Case Is Applicable For	4 years	4 years
Public Utilities, Cap on Annual True-Up for Decoupled Classes, Percentage		3.00%
Public Utilities, Approved Return on Equity, Percentage		9.20%
Public Utilities, Approved Equity Capital Structure, Percentage		52.50%
Public Utilities, Length of Stay-out Provision, In Years		4 years
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 184,970
Public Utilities, Increase (Decrease) Related to Sales True-up		59,750
Public Utilities, Rate Impact	$ 240,000	244,720
NSP-Minnesota | Minnesota Public Utilities Commission | MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2016
Rate Matters [Abstract]
Public Utilities, Approved Rate Increase (Decrease), Amount		74,990
Public Utilities, Increase (Decrease) Related to Sales True-up		59,950
Public Utilities, Rate Impact		134,940
NSP-Minnesota | Minnesota Public Utilities Commission | MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2017
Rate Matters [Abstract]
Public Utilities, Approved Rate Increase (Decrease), Amount		59,860
Public Utilities, Increase (Decrease) Related to Sales True-up		0
Public Utilities, Rate Impact		59,860
NSP-Minnesota | Minnesota Public Utilities Commission | MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2018
Rate Matters [Abstract]
Public Utilities, Approved Rate Increase (Decrease), Amount		0
Public Utilities, Increase (Decrease) Related to Sales True-up		0
Public Utilities, Rate Impact		0
NSP-Minnesota | Minnesota Public Utilities Commission | MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2019
Rate Matters [Abstract]
Public Utilities, Approved Rate Increase (Decrease), Amount		50,120
Public Utilities, Increase (Decrease) Related to Sales True-up		(200)
Public Utilities, Rate Impact		$ 49,920
NSP-Minnesota | 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%		10.32%
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Recommended						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
NSP-Minnesota | 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%

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Commitments and Contingencies, Purchased Power Agreements (Details) - MW	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Independent Power Producing Entities
Purchased Power Agreements [Abstract]
Generating capacity under long term purchased power agreements (in MW)	1,069	1,069
Purchase Power Agreement Expiration (year)	2028
Payment or Performance Guarantee
Purchased Power Agreements [Abstract]
Lease Guarantee Expiration (year)	2019

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Commitments and Contingencies Commitments and Contingencies, Guarantees and Indemnifications (Details) - Payment or Performance Guarantee - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Lease Guarantee Expiration (year)	2019
Guarantees issued and outstanding	$ 4.8	$ 4.8

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Commitments and Contingencies, Environmental Contingencies (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Fargo MGP Site
Environmental Requirements [Abstract]
Accrual for Environmental Loss Contingencies, Gross	$ 16.2	$ 11.3
Current Cost Estimate for Site Remediation	23.0
Estimated amount spent on cleanup	$ 6.8
Percentage of Response Costs Allocable to the Minnesota Jurisdiction	12.00%
Other MGP Sites [Member]
Environmental Requirements [Abstract]
Accrual for Environmental Loss Contingencies, Gross	$ 1.1	$ 0.2
Number of identified MGP sites under current investigation and/or remediation in addition to those separately disclosed	6
Clean Power Plan [Member]
Environmental Requirements [Abstract]
Length of Public Comment Period	60 days

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Borrowings and Other Financing Instruments, Short-Term Borrowings (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Amount outstanding at period end	$ 0	$ 85,000,000
Money Pool
Short-term Debt [Line Items]
Borrowing limit	250,000,000	250,000,000
Amount outstanding at period end	50,000,000	0
Average amount outstanding	50,000,000	16,000,000
Maximum amount outstanding	$ 116,000,000	$ 225,000,000
Weighted average interest rate, computed on a daily basis (percentage)	1.11%	0.69%
Weighted average interest rate at period end (percentage)	1.11%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 500,000,000	$ 500,000,000
Amount outstanding at period end	0	85,000,000
Average amount outstanding	51,000,000	73,000,000
Maximum amount outstanding	$ 204,000,000	$ 353,000,000
Weighted average interest rate, computed on a daily basis (percentage)	1.33%	0.65%
Weighted average interest rate at period end (percentage)		0.94%

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Borrowings and Other Financing Instruments, Letters of Credit (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 0	$ 85,000
Letter of Credit
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 21,000	$ 11,000
Letter of Credit | Letter of Credit
Line of Credit Facility [Line Items]
Term of letters of credit (in years)	1 year

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Borrowings and Other Financing Instruments, Credit Facility (Details) - Credit Facility - USD ($)		9 Months Ended
		Sep. 30, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Credit Facility	[1]	$ 500,000,000
Drawn	[2]	21,000,000
Available		$ 479,000,000
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.

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Borrowings and Other Financing Instruments Borrowings and Other Financing Instruments, Long-Term Borrowings (Details) - NSP-Minnesota - USD ($)		9 Months Ended
	Sep. 29, 2017	Sep. 30, 2017
Series Due March 1, 2018 | Bonds
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.25%
Maturity Date	Mar. 01, 2018
Debt Repayment, Amount	$ 500,000,000
Redemption Premium	$ 7,900,000
Bonds | Series Due September 15, 2047
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 600,000,000
Debt Instrument, Interest Rate, Stated Percentage		3.60%
Maturity Date		Sep. 15, 2047

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Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities (Details)	9 Months Ended
	Sep. 30, 2017
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

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Fair Value of Financial Assets and Liabilities, Cost and Fair Value of Nuclear Decommissioning Fund (Details) - USD ($) $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 30, 2017		Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Gross Unrealized Gain		$ 511,700		$ 378,600
Available-for-sale Securities, Gross Unrealized Loss		10,300		46,900
Investments [Abstract]
Miscellaneous investments		49,000		44,300
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		32,727	[1]	20,379	[2]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		1,555,425	[1]	1,528,993	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Non U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities		257,487	[1]	260,877	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Emerging market debt funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities		97,285	[1]	93,597	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Commodity funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities	[2]			106,571
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Private equity investments
Available-for-sale Securities [Abstract]
Available-for-sale Securities		139,185	[1]	132,190	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Real estate
Available-for-sale Securities [Abstract]
Available-for-sale Securities		129,219	[1]	128,630	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Other commingled funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities		146,179	[1]	151,048	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Government securities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		45,310	[1]	32,764	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | U.S. corporate bonds
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		251,138	[1]	104,913	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Non U.S. corporate bonds
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		46,245	[1]	21,751	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Municipal bonds
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities	[2]			13,609
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Mortgage-backed securities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities	[2]			2,785
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Equity Securities		258,075	[1]	270,779	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Non U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Equity Securities		152,575	[1]	189,100	[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		32,727	[1]	20,379	[2]
Alternative Investment, Fair Value Disclosure		726,413	[1],[3]	839,465	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		2,056,732	[1]	1,860,762	[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		86,654	[1],[3]	112,233	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		291,156	[1]	245,359	[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		106,842	[1],[3]	97,543	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		106,842	[1]	97,543	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Commodity funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure	[2],[4]			92,091
Available-for-sale Securities [Abstract]
Available-for-sale Securities	[2]			92,091
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		192,098	[1],[3]	190,462	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		192,098	[1]	190,462	[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		195,506	[1],[3]	187,647	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		195,506	[1]	187,647	[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		145,313	[1],[3]	159,489	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		160,277	[1]	159,489	[2]
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]
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		44,944	[1]	31,965	[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]
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		252,868	[1]	105,772	[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]
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		46,611	[1]	21,672	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure	[2],[4]			0
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities	[2]			13,786
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment, Fair Value Disclosure	[2],[4]			0
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities	[2]			2,816
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]
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Equity Securities		509,564	[1]	473,400	[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]
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Equity Securities		224,139	[1]	218,381	[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		32,727	[1]	20,379	[2]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		985,896	[1]	845,286	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Non U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities		204,502	[1]	133,126	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Emerging market debt funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Commodity funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities	[2]			0
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Private equity investments
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Real estate
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Other commingled funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities		14,964	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Government securities
Available-for-sale Securities [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
Available-for-sale Securities [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
Available-for-sale Securities [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 | Municipal bonds
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities	[2]			0
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Mortgage-backed securities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities	[2]			0
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Equity Securities		509,564	[1]	473,400	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Non U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Equity Securities		224,139	[1]	218,381	[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]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		344,423	[1]	176,011	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Non U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Emerging market debt funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Commodity funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities	[2]			0
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Private equity investments
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Real estate
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Other commingled funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Government securities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		44,944	[1]	31,965	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | U.S. corporate bonds
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		252,868	[1]	105,772	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Non U.S. corporate bonds
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		46,611	[1]	21,672	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Municipal bonds
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities	[2]			13,786
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Mortgage-backed securities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities	[2]			2,816
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Non U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, 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]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Non U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Emerging market debt funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Commodity funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities	[2]			0
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Private equity investments
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Real estate
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Other commingled funds
Available-for-sale Securities [Abstract]
Available-for-sale Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Government securities
Available-for-sale Securities [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
Available-for-sale Securities [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
Available-for-sale Securities [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 | Municipal bonds
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities	[2]			0
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Mortgage-backed securities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities	[2]			0
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Equity Securities		0	[1]	0	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Non U.S. equities
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Equity Securities		$ 0	[1]	$ 0	[2]

[1] Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $49.0 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 $44.3 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.

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Fair Value of Financial Assets and Liabilities, Final Contractual Maturity Dates of Debt Securities in Nuclear Decommissioning Fund (Details) $ in Thousands	Sep. 30, 2017 USD ($)
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	$ 3,834
Due in 1 to 5 Years	79,187
Due in 5 to 10 Years	179,695
Due after 10 Years	81,707
Total	344,423
Government securities
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0
Due in 1 to 5 Years	1,275
Due in 5 to 10 Years	2,303
Due after 10 Years	41,366
Total	44,944
U.S. corporate bonds
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	3,834
Due in 1 to 5 Years	64,119
Due in 5 to 10 Years	150,741
Due after 10 Years	34,174
Total	252,868
Non U.S. corporate bonds
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0
Due in 1 to 5 Years	13,793
Due in 5 to 10 Years	26,651
Due after 10 Years	6,167
Total	$ 46,611

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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		Sep. 30, 2017	Dec. 31, 2016
Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	$ 10,466	$ 9,122
Cost | Rabbi Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	391	7,459
Cost | Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	10,075	1,663
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	11,354	9,360
Fair Value | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	11,354	9,360
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]	391	7,459
Fair Value | Rabbi Trust [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	391	7,459
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]	10,963	1,901
Fair Value | Mutual Funds [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	10,963	1,901
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.

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Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details) gal in Thousands, MWh in Thousands, MMBTU in Thousands, $ in Millions		Sep. 30, 2017 USD ($) MMBTU gal MWh Counterparty	Dec. 31, 2016 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 | $		$ 23.9
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		33.00%
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		4
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $		$ 28.0
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		38.00%
Credit Concentration Risk | Internal Noninvestment 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		1
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $		$ 0.9
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		1.00%
Interest Rate Swap
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 | $		$ (0.6)
Electric Commodity (in megawatt hours)
Gross Notional Amounts of Commodity Forwards, Options and FTRs [Abstract]
Derivative, Nonmonetary Notional amount | MWh	[1],[2]	58,582	37,805
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]	47,329	79,520
Vehicle Fuel Commodity (in gallons)
Gross Notional Amounts of Commodity Forwards, Options and FTRs [Abstract]
Derivative, Nonmonetary Notional amount | gal	[1],[2]	300	0

[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.

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Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017		Sep. 30, 2016
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		38,000	(2,000)	81,000		8,000
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		601,000	375,000	1,288,000		1,124,000
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]	612,000	350,000	1,304,000		1,042,000
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		38,000	(2,000)	81,000		8,000
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]	(11,000)	25,000	(16,000)		82,000
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		19,833,000	14,509,000	16,434,000		11,505,000
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)		(5,356,000)	2,044,000	(8,595,000)		29,788,000
Pre-tax gains (losses) recognized during the period in income		1,493,000	1,808,000	7,147,000		1,474,000
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]	1,493,000	1,808,000	8,092,000		3,069,000
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		20,216,000	15,301,000	17,444,000		12,550,000
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]	(5,356,000)	2,044,000	(9,293,000)		26,328,000
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		(383,000)	(792,000)	(1,010,000)		(1,045,000)
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	698,000	[5]	3,460,000	[5]
Pre-tax gains (losses) recognized during the period in income		$ 0	$ 0	$ (945,000)	[5]	$ (1,595,000)	[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 ($)	Sep. 30, 2017	Dec. 31, 2016
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		Sep. 30, 2017		Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative Asset, Collateral, Obligation to Return Cash, Offset		$ 0		$ 0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		2,900		3,700
Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		47,177		22,028
Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		28,520		24,678
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		18,045		16,606
Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		105,963		116,804
Fair Value Measured on a Recurring Basis | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		46,425		21,436
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(4,301)	[1]	(16,177)	[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		6,271		5,204
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(4,040)	[1]	(15,500)	[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		39,671		15,320
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(261)	[1]	(677)	[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		427		912
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		28,394		23,806
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(7,465)	[1]	(7,323)	[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		28,383		23,806
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(7,465)	[1]	(7,323)	[2]
Fair Value Measured on a Recurring Basis | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		3,939		2,524
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		(4,568)	[1]	(16,514)	[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		3,939		2,524
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		(4,307)	[1]	(15,837)	[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		(261)	[1]	(677)	[2]
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		12,588		12,786
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		(10,130)	[1]	(10,727)	[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		12,588		12,786
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		(10,130)	[1]	(10,727)	[2]
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		1,297		12,053
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		1,297		12,053
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		84		100
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		84		100
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		1,146		12,397
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		1,146		12,397
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		52		89
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		52		89
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		9,416		9,563
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		8,933		8,651
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		427		912
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		30,114		31,029
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		30,103		31,029
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		7,100		5,964
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		7,100		5,964
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		22,666		23,424
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		22,666		23,424
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		40,013		15,997
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		81		0
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		39,932		15,997
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		5,661		0
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		5,661		0
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		261		677
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		0		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		261		677
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0		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		0		0
Fair Value, Measurements, Nonrecurring | Other Current Assets | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		752	[3]	592	[4]
Fair Value, Measurements, Nonrecurring | Other Noncurrent Assets | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		126	[3]	872	[4]
Fair Value, Measurements, Nonrecurring | Other Current Liabilities | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		14,106	[3]	14,082	[4]
Fair Value, Measurements, Nonrecurring | Other Noncurrent Liabilities | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		93,375	[3]	104,018	[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		50,726		37,613
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		10,311		20,704
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		39,932		15,997
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		427		912
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		35,859		31,129
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		35,848		31,129
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		8,507		19,038
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		8,246		18,361
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		261		677
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		22,718		23,513
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		22,718		$ 23,513
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		56
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[1]	0
Cash Flow Hedges | Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		11
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[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
Cash Flow Hedges | Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Assets | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		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		56
Cash Flow Hedges | Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Assets | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		11
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
Cash Flow Hedges | Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Assets | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		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		56
Cash Flow Hedges | Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 11

[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 Sept. 30, 2017. At Sept. 30, 2017, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $2.9 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, 2016. At Dec. 31, 2016, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $3.7 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 will be 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 will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

XML

Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) - Commodity Contract - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period		$ 40,572,000	$ 23,488,000	$ 15,320,000	$ 12,969,000
Purchases				40,740,000	27,870,000
Settlements		(23,186,000)	(26,192,000)	(34,681,000)	(38,300,000)
Gains (losses) recognized in earnings	[1]	527,000	0	5,742,000	(2,000)
Net losses recognized as regulatory assets and liabilities		27,500,000	27,163,000	18,292,000	21,922,000
Balance at end of period		45,413,000	24,459,000	45,413,000	24,459,000
Transfers into Level 3		0	0	0	0
Transfers out of Level 3		$ 0	$ 0	$ 0	$ 0

[1] 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	Sep. 30, 2017	Dec. 31, 2016
Carrying Amount
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	$ 4,932,977	$ 4,843,165
Fair Value
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	$ 5,501,602	$ 5,310,925

XML

Other (Expense) Income, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Income and Expenses [Abstract]
Interest income	$ 2,936	$ 510	$ 6,250	$ 3,975
Other nonoperating income	0	0	0	248
Insurance policy expense	(387)	(926)	(2,098)	(2,389)
Other nonoperating expense	(429)	(23)	(402)	0
Other income (expense), net	$ 2,120	$ (439)	$ 3,750	$ 1,834

XML

Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016
Segment Reporting Information [Line Items]
Operating revenues	$ 1,355,779		$ 1,345,379		$ 3,827,859		$ 3,668,112
Net income (loss)	229,003		206,552		410,831		379,357
Affiliate electric revenue	123,524		121,315		366,598		359,338
Regulated Electric
Segment Reporting Information [Line Items]
Operating revenues	1,291,131		1,282,692		3,450,292		3,333,213
Net income (loss)	232,078		217,674		399,637		367,776
Regulated Natural Gas
Segment Reporting Information [Line Items]
Operating revenues	57,542		55,708		357,002		314,457
Net income (loss)	(6,242)		(14,900)		7,903		8,700
All Other
Segment Reporting Information [Line Items]
Operating revenues	7,366		7,286		21,448		21,404
Net income (loss)	3,167		3,778		3,291		2,881
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	1,355,779	[1],[2]	1,345,379	[1],[2]	3,827,859	[3],[4]	3,668,112	[3],[4]
Operating Segments | Regulated Electric
Segment Reporting Information [Line Items]
Operating revenues	1,290,971	[1]	1,282,574	[1]	3,449,780	[3]	3,332,688	[3]
Operating Segments | Regulated Natural Gas
Segment Reporting Information [Line Items]
Operating revenues	57,442	[2]	55,519	[2]	356,631	[4]	314,020	[4]
Operating Segments | All Other
Segment Reporting Information [Line Items]
Operating revenues	7,366		7,286		21,448		21,404
Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(260)		(307)		(883)		(962)
Net income (loss)	0		0		0		0
Intersegment Eliminations | Regulated Electric
Segment Reporting Information [Line Items]
Operating revenues	160		118		512		525
Intersegment Eliminations | Regulated Natural Gas
Segment Reporting Information [Line Items]
Operating revenues	100		189		371		437
Intersegment Eliminations | All Other
Segment Reporting Information [Line Items]
Operating revenues	$ 0		$ 0		$ 0		$ 0

[1] Operating revenues include $124 million and $121 million of affiliate electric revenue for the three months ended Sept. 30, 2017 and 2016.

[2] Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended Sept. 30, 2017 and 2016.

[3] Operating revenues include $367 million and $359 million of affiliate electric revenue for the nine months ended Sept. 30, 2017 and 2016.

[4] Operating revenues include an immaterial amount of affiliate gas revenue for the nine months ended Sept. 30, 2017 and 2016.

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Benefit Plans and Other Postretirement Benefits (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2017 USD ($) Plan	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Pension Plan [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost		$ 6,958	$ 7,077	$ 20,874	$ 21,231
Interest cost		10,177	11,358	30,531	34,074
Expected return on plan assets		(15,016)	(15,236)	(45,050)	(45,708)
Amortization of prior service cost (credit)		265	234	795	702
Amortization of net loss		9,902	9,194	29,706	27,582
Net periodic benefit cost		12,286	12,627	36,856	37,881
Costs not recognized due to the effects of regulation		(4,899)	(5,295)	(14,696)	(15,887)
Net benefit cost recognized for financial reporting		7,387	7,332	22,160	21,994
Total contributions to the pension plans during the period	$ 59,400
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		36	31	108	93
Interest cost		854	981	2,562	2,943
Expected return on plan assets		(53)	(43)	(161)	(129)
Amortization of prior service cost (credit)		(759)	(759)	(2,277)	(2,277)
Amortization of net loss		506	401	1,520	1,203
Net periodic benefit cost		584	611	1,752	1,833
Costs not recognized due to the effects of regulation		0	0	0	0
Net benefit cost recognized for financial reporting		$ 584	$ 611	$ 1,752	$ 1,833

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Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income at beginning of period			$ 5,355,569
(Gains) losses reclassified from net accumulated other comprehensive loss	$ 418	$ 232	896	$ 714
Accumulated other comprehensive (loss) income at end of period	5,440,694		5,440,694
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	(17,775)	(18,640)	(18,208)	(19,090)
Other comprehensive income (loss) before reclassifications	22	(1)	48	5
(Gains) losses reclassified from net accumulated other comprehensive loss	379	213	786	657
Net current period other comprehensive income (loss)	401	212	834	662
Accumulated other comprehensive (loss) income at end of period	(17,374)	(18,428)	(17,374)	(18,428)
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	105	105	105	105
Other comprehensive income (loss) before reclassifications	0	0	0	0
(Gains) losses reclassified from net accumulated other comprehensive loss	0	0	0	0
Net current period other comprehensive income (loss)	0	0	0	0
Accumulated other comprehensive (loss) income at end of period	105	105	105	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	(2,609)	(2,058)	(2,680)	(2,096)
Other comprehensive income (loss) before reclassifications	0	0	0	0
(Gains) losses reclassified from net accumulated other comprehensive loss	39	19	110	57
Net current period other comprehensive income (loss)	39	19	110	57
Accumulated other comprehensive (loss) income at end of period	(2,570)	(2,039)	(2,570)	(2,039)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income at beginning of period	(20,279)	(20,593)	(20,783)	(21,081)
Other comprehensive income (loss) before reclassifications	22	(1)	48	5
(Gains) losses reclassified from net accumulated other comprehensive loss	418	232	896	714
Net current period other comprehensive income (loss)	440	231	944	719
Accumulated other comprehensive (loss) income at end of period	$ (19,839)	$ (20,362)	$ (19,839)	$ (20,362)

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Other Comprehensive Income (Reclassification from AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating and maintenance expenses	$ 288,770	$ 315,298	$ 909,381	$ 954,334
Total, pre-tax	(296,946)	(300,697)	(551,559)	(555,404)
Tax benefit	67,943	94,145	140,728	176,047
Total amounts reclassified, net of tax	418	232	896	714
Gains and Losses on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amounts reclassified, net of tax	379	213	786	657
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	601	375	1,288	1,124
Tax benefit	(222)	(162)	(502)	(467)
Total, net of tax	379	213	786	657
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	612	350	1,304	1,042
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	(11)	25	(16)	82
Amortization of net loss | Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total, pre-tax	109	83	327	249
Prior service credit | Amounts Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total, pre-tax	(49)	(49)	(147)	(147)
Defined Benefit Pension and Postretirement Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amounts reclassified, net of tax	39	19	110	57
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	60	34	180	102
Tax (benefit) expense	(21)	(15)	(70)	(45)
Total amounts reclassified, net of tax	$ 39	$ 19	$ 110	$ 57