Northern States Power 10-Q 28 Apr 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	Apr. 28, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	NORTHERN STATES POWER CO
Entity Central Index Key	1,123,852
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	2,017
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating revenues
Electric, non-affiliates	$ 955,341	$ 908,747
Electric, affiliates	123,689	124,896
Natural gas	221,183	194,130
Other	6,927	6,860
Total operating revenues	1,307,140	1,234,633
Operating expenses
Electric fuel and purchased power	396,121	366,166
Cost of natural gas sold and transported	142,745	120,223
Cost of sales — other	4,178	4,432
Operating and maintenance expenses	312,024	320,496
Conservation program expenses	32,499	23,269
Depreciation and amortization	172,179	145,797
Taxes (other than income taxes)	68,324	70,352
Total operating expenses	1,128,070	1,050,735
Operating income	179,070	183,898
Other income, net	1,864	2,860
Allowance for funds used during construction — equity	6,283	5,648
Interest charges and financing costs
Interest charges — includes other financing costs of $1,786, and $1,742, respectively	57,264	54,015
Allowance for funds used during construction — debt	(3,228)	(2,706)
Total interest charges and financing costs	54,036	51,309
Income before income taxes	133,181	141,097
Income taxes	39,015	46,468
Net income	$ 94,166	$ 94,629

CONSOLIDATED STATEMENTS OF INC3

CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Interest charges and financing costs
Other financing costs	$ 1,786	$ 1,742

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Comprehensive income:
Net income	$ 94,166	$ 94,629
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, net of tax of $25 and $15 respectively	35	19
Derivative instruments:
Net fair value decrease, net of tax of $0 and $(1), respectively	0	(1)
Reclassification of losses to net income, net of tax of $139 and $154, respectively	203	223
Total derivative instruments, net of tax	203	222
Other comprehensive income	238	241
Comprehensive income	$ 94,404	$ 94,870

CONSOLIDATED STATEMENTS OF COM5

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, tax	$ 25	$ 15
Derivative instruments:
Net fair value (decrease) increase, tax	0	(1)
Reclassification of losses to net income, tax	$ 139	$ 154

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating activities
Net income	$ 94,166	$ 94,629
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	173,726	147,310
Nuclear fuel amortization	30,852	25,750
Deferred income taxes	52,411	47,018
Amortization of Investment Tax Credits	(414)	(420)
Allowance for equity funds used during construction	(6,283)	(5,648)
Net realized and unrealized hedging and derivative transactions	1,744	1,890
Changes in operating assets and liabilities:
Accounts receivable	(25,483)	(45,382)
Accrued unbilled revenues	69,893	40,322
Inventories	32,678	35,378
Other current assets	(6,397)	(14,146)
Accounts payable	(22,007)	(4,057)
Net regulatory assets and liabilities	1,513	51,517
Other current liabilities	(16,016)	(12,118)
Pension and other employee benefit obligations	(58,004)	(48,074)
Change in other noncurrent assets	849	(43)
Change in other noncurrent liabilities	(11,593)	(1,112)
Net cash provided by operating activities	311,635	312,814
Investing activities
Utility capital/construction expenditures	(277,125)	(259,570)
Allowance for equity funds used during construction	6,283	5,648
Purchases of investment securities	(172,751)	(109,373)
Proceeds from the sale of investment securities	167,658	104,280
Investments in utility money pool arrangement	(87,000)	0
Repayments from utility money pool arrangement	87,000	0
Other, net	(4,565)	(2,084)
Net cash used in investing activities	(280,500)	(261,099)
Financing activities
Repayments of short-term borrowings, net	(46,000)	(150,000)
Borrowings under utility money pool arrangement	25,000	310,000
Repayments under utility money pool arrangement	(25,000)	(217,000)
Repayments of long-term debt	(10)	0
Capital contributions from parent	89,487	89,874
Dividends paid to parent	(89,428)	(73,498)
Net cash used in financing activities	(45,951)	(40,624)
Net change in cash and cash equivalents	(14,816)	11,091
Cash and cash equivalents at beginning of period	47,595	42,605
Cash and cash equivalents at end of period	32,779	53,696
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(68,511)	(69,643)
Cash received (paid) for income taxes, net	10,080	(7,558)
Supplemental disclosure of non-cash investing transactions:
Property, plant and equipment additions in accounts payable	$ 48,551	$ 56,605

CONSOLIDATED BALANCE SHEETS (UN

CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 32,779	$ 47,595
Accounts receivable, net	328,368	329,481
Accounts receivable from affiliates	46,955	49,355
Accrued unbilled revenues	189,697	259,590
Inventories	312,554	345,192
Regulatory assets	190,644	186,266
Derivative instruments	11,117	22,028
Prepaid Taxes	60,915	56,083
Prepayments and other	43,534	41,923
Total current assets	1,216,563	1,337,513
Property, plant and equipment, net	13,339,095	13,300,793
Other assets
Nuclear decommissioning fund and other investments	2,001,318	1,905,059
Regulatory assets	1,194,192	1,245,151
Derivative instruments	26,041	24,678
Other	8,237	9,086
Total other assets	3,229,788	3,183,974
Total assets	17,785,446	17,822,280
Current liabilities
Current portion of long-term debt	500,004	10
Short-term debt	39,000	85,000
Accounts payable	297,098	371,589
Accounts payable to affiliates	60,706	59,216
Regulatory liabilities	34,460	60,779
Taxes accrued	296,092	241,100
Accrued interest	54,790	71,012
Dividends payable to parent	85,687	89,428
Derivative instruments	17,136	16,606
Customer deposits	100,267	110,244
Other	103,493	150,244
Total current liabilities	1,588,733	1,255,228
Deferred credits and other liabilities
Deferred income taxes	2,859,965	2,788,752
Deferred investment tax credits	23,762	24,175
Regulatory liabilities	496,905	489,825
Asset retirement obligations	2,482,507	2,452,567
Derivative instruments	114,524	116,804
Pension and employee benefit obligations	311,435	368,922
Other	139,106	127,283
Total deferred credits and other liabilities	6,428,204	6,368,328
Commitments and contingencies
Capitalization
Long-term debt	4,344,223	4,843,155
Common stock — authorized 5,000,000 shares of $0.01 par value; 1,000,000 shares outstanding at March 31, 2017 and Dec. 31, 2016, respectively	10	10
Additional paid in capital	3,495,096	3,435,096
Retained earnings	1,949,725	1,941,246
Accumulated other comprehensive loss	(20,545)	(20,783)
Total common stockholder’s equity	5,424,286	5,355,569
Total liabilities and equity	$ 17,785,446	$ 17,822,280

CONSOLIDATED BALANCE SHEETS (U8

CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Mar. 31, 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

Management's Opinion

Management's Opinion	3 Months Ended
	Mar. 31, 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 March 31, 2017 and Dec. 31, 2016 ; the results of its operations, including the components of net income and comprehensive income, for the three months ended March 31, 2017 and 2016 ; and its cash flows for the three months ended March 31, 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 March 31, 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.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 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.

Accounting Pronouncements

Accounting Pronouncements	3 Months Ended
	Mar. 31, 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 result in increased disclosures regarding revenue, cash flows and obligations related to arrangements with customers, as well as separate presentation of alternative revenue programs. NSP-Minnesota has not yet fully determined the impacts of adoption for several aspects of the standard, including a determination whether and how much an evaluation of the collectability of regulated electric and gas revenues will impact the amounts of revenue recognized upon delivery. 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 — I n 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 has not yet fully determined the impacts of adoption of the standard, but 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.

Selected Balance Sheet Data

Selected Balance Sheet Data	3 Months Ended
	Mar. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Selected Balance Sheet Data	Selected Balance Sheet Data (Thousands of Dollars) March 31, 2017 Dec. 31, 2016 Accounts receivable, net Accounts receivable $ 348,348 $ 349,449 Less allowance for bad debts (19,980 ) (19,968 ) $ 328,368 $ 329,481 (Thousands of Dollars) March 31, 2017 Dec. 31, 2016 Inventories Materials and supplies $ 217,287 $ 214,234 Fuel 85,069 97,527 Natural gas 10,198 33,431 $ 312,554 $ 345,192 (Thousands of Dollars) March 31, 2017 Dec. 31, 2016 Property, plant and equipment, net Electric plant $ 17,085,453 $ 17,059,993 Natural gas plant 1,316,661 1,311,235 Common and other property 702,387 710,958 Construction work in progress 565,146 509,891 Total property, plant and equipment 19,669,647 19,592,077 Less accumulated depreciation (6,771,090 ) (6,682,418 ) Nuclear fuel 2,652,026 2,571,770 Less accumulated amortization (2,211,488 ) (2,180,636 ) $ 13,339,095 $ 13,300,793

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 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 Tax Loss Carryback Claims — In 2012-2016, 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 Audit — NSP-Minnesota is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. In 2012, the Internal Revenue Service (IRS) commenced an examination of tax years 2010 and 2011 , including the 2009 carryback claim. As of March 31, 2017 , the IRS had proposed an adjustment to the federal tax loss carryback claims that would result 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 2016 the IRS audit team and Xcel Energy presented their case to Appeals; however, the outcome and timing of a resolution is uncertain. The statute of limitations applicable to Xcel Energy’s 2009 through 2011 federal income tax returns, following extensions, expires in December 2017. Xcel Energy has recognized its best estimate of income tax expense that will result from a final resolution of the IRS’s proposed adjustment of the carryback claims. In the third quarter of 2015, the IRS commenced an examination of tax years 2012 and 2013 . In the first quarter of 2017, the IRS proposed an adjustment to tax years 2012 and 2013 that could have impacted Xcel Energy’s net operating loss (NOL) and tax credit carryforwards and effective tax rate (ETR). After additional review, the IRS withdrew their proposed adjustment. As of March 31, 2017, the IRS had not proposed any other material adjustments to tax years 2012 and 2013. State Audits — NSP-Minnesota is a member of the Xcel Energy affiliated group that files consolidated state income tax returns. As of March 31, 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 March 31, 2017, Minnesota had not proposed any adjustments, and there were no other state income tax audits in progress. Unrecognized Tax 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 impact the timing of cash payment to the taxing authority. A reconciliation of the amount of unrecognized tax benefit is as follows: (Millions of Dollars) March 31, 2017 Dec. 31, 2016 Unrecognized tax benefit — Permanent tax positions $ 21.8 $ 21.5 Unrecognized tax benefit — Temporary tax positions 39.8 39.3 Total unrecognized tax benefit $ 61.6 $ 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) March 31, 2017 Dec. 31, 2016 NOL and tax credit carryforwards $ (19.5 ) $ (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 and audit progress, the Minnesota audit progresses, and other state audits resume. As the IRS Appeals and IRS and Minnesota audits progress, it is reasonably possible that the amount of unrecognized tax benefit could decrease up to approximately $32 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 amount of the payable for interest related to unrecognized tax benefits reported are as follows: (Millions of Dollars) March 31, 2017 Dec. 31, 2016 Payable for interest related to unrecognized tax benefits at beginning of period $ (2.0 ) $ (0.2 ) Interest expense related to unrecognized tax benefits recorded during the period (0.3 ) (1.8 ) Payable for interest related to unrecognized tax benefits at end of period $ (2.3 ) $ (2.0 ) No amounts were accrued for penalties related to unrecognized tax benefits as of March 31, 2017 or Dec. 31, 2016.

Rate Matters

Rate Matters	3 Months Ended
	Mar. 31, 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 , appropriately represent, in all material respects, the current status of other rate matters, and are incorporated herein by reference. Pending Regulatory Proceeding — Minnesota Public Utilities Commission (MPUC) Minnesota 2016 Multi-Year Electric Rate Case — In November 2015, NSP-Minnesota filed a three -year electric rate case with the MPUC. The rate case is based on a requested return on equity (ROE) of 10.0 percent and a 52.50 percent equity ratio. In December 2015, the MPUC approved interim rates for 2016. The request is detailed in the table below: Request (Millions of Dollars) 2016 2017 2018 Rate request $ 194.6 $ 52.1 $ 50.4 Increase percentage 6.4 % 1.7 % 1.7 % Interim request $ 163.7 $ 44.9 N/A Rate base $ 7,800 $ 7,700 $ 7,700 Settlement Agreement In August 2016, NSP-Minnesota and various parties reached a settlement which resolves all revenue requirement issues in dispute. The settlement agreement requires the approval of the MPUC. Key terms of the settlement are listed below: • Four -year period covering 2016-2019; • Annual sales true-up; • 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 Settlement 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 March 2017, the Administrative Law Judge (ALJ) recommended that the MPUC approve the settlement as it will contribute to just and reasonable rates and that no objections to the settlement are sufficient to merit rejection. The ALJ also provided recommendations for a majority of the revenue requirement issues in the event the MPUC decides to reject the settlement. The MPUC is anticipated to hold deliberations on the rate case in May 2017 and issue an order in June 2017. Pending Regulatory Proceeding — Federal Energy Regulatory Commission (FERC) Midcontinent Independent System Operator, Inc. (MISO) ROE Complaints/ROE Adder — 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 , a prohibition on capital structures in excess of 50 percent equity, and the removal of ROE adders (including those for Regional Transmission Organization (RTO) membership and for being an independent transmission company), effective Nov. 12, 2013. In December 2015, an ALJ recommended the FERC approve a ROE of 10.32 percent using a FERC ROE methodology adopted in June 2014, which the FERC upheld in an order issued in September 2016. This ROE is 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 is 10.82 percent , which includes a 50 basis point adder for RTO membership. 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. The MPUC, the North Dakota Public Service Commission (NDPSC), the South Dakota Public Utilities Commission and the Minnesota Department of Commerce joined a joint complainant/intervenor initial brief recommending an ROE of approximately 8.81 percent . FERC staff recommended a ROE of 8.78 percent . The MISO TOs recommended a ROE of 10.92 percent . In June 2016, the ALJ recommended a ROE of 9.7 percent , the midpoint of the upper half of the discounted cash flow (DCF) range, applying the June 2014 FERC ROE methodology. A decision was expected later in 2017, but could be delayed by the lack of a quorum at the FERC. On April 14, 2017 the D.C. Circuit Court of Appeals vacated and remanded the June 2014 FERC decision, previously made in a New England ROE case. The court decision found that the FERC in that case had not established that the prior ROE was unjust and unreasonable, and that the FERC also failed to adequately support the newly approved ROE. The New England ROE ruling was then the basis for the ROE methodology used in the MISO complaint cases. The court found that the ROE methodology used in the New England ROE case was inadequate because it relied on approaches other than the DCF model. The impact of this court decision on the pending MISO complaint cases is uncertain. As of March 2017, NSP-Minnesota has recognized a current liability for the Nov. 12, 2013 to Feb. 11, 2015 complaint period based on the 10.32 percent ROE provided in the FERC order. This liability is net of refunds processed during the first quarter of 2017. NSP-Minnesota has also recognized a current liability representing the best estimate of the final ROE for the Feb. 12, 2015 to May 11, 2016 complaint period.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	. 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 , 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 March 31, 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) March 31, 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. The timing and final scope of remediation is dependent on whether current property owners will agree to provide reasonable access to NSP-Minnesota to perform and implement the approved cleanup plan. NSP-Minnesota has 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 May 2017. As of March 31, 2017 and Dec. 31, 2016, NSP-Minnesota had recorded a liability of $11.1 million and $11.3 million , respectively, for the Fargo MGP Site. In December 2015, the 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, final designs that will be developed to implement the approved cleanup plan 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 at March 31, 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 expands the types of water bodies regulated under the CWA and broadens the scope of waters subject to federal jurisdiction. The final rule will subject more utility projects to federal CWA jurisdiction, thereby potentially delaying the siting of new generation projects, pipelines, transmission lines and distribution lines, as well as increasing project costs and expanding permitting and reporting requirements. 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 by the end of 2017. In February 2017, President Trump issued an executive order requiring the EPA and the Corps to review and revise the final rule. The executive order directs the agencies to consider interpreting the term “Waters of the U.S.” in a manner that is more narrow than the final rule. In March 2017, the EPA and the Corps published formal notice of the agencies’ intent to review the final rule and engage in further rulemaking. 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. • The estimated compliance cost for NSP-Minnesota’s Allen S. King Plant is approximately $10 million ; and • NSP-Minnesota continues to evaluate the cost of compliance at its other facilities potentially affected by this rule. NSP-Minnesota believes that compliance costs would be recoverable through regulatory mechanisms. Consolidated challenges to the rule are being heard by the Fifth Circuit Court of Appeals. On April 12, 2017, the EPA issued an administrative stay to delay the ELG rule’s compliance deadlines during the pendency of the ongoing litigation in order to give the agency the opportunity to reconsider and review the rule. 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. Parties in the litigation, who support the CPP have filed briefs opposing the EPA’s motion. A court ruling on the EPA’s motion is expected in the second quarter of 2017. NSP-Minnesota has undertaken a number of initiatives that reduce GHG emissions and respond to state renewable and energy efficiency goals. The CPP could require additional emission reductions in states in which NSP-Minnesota operates. If state plans do not provide credit for the investments NSP-Minnesota has already made to reduce GHG emissions, or if they require additional initiatives or emission reductions, then their requirements would potentially impose additional substantial costs. NSP-Minnesota cannot predict the costs of compliance with the final rule once it takes effect due to the uncertainty about what, if anything, the final rules may require. NSP-Minnesota believes compliance costs will be recoverable through regulatory mechanisms. If NSP-Minnesota’s regulators do not allow recovery of all or a part of the cost of capital investment or the operating and maintenance (O&M) costs incurred to comply with the CPP or cost recovery is not provided in a timely manner, it could have a material impact on results of operations, financial position or cash flows.
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.

Borrowings and Other Financing

Borrowings and Other Financing Instruments	3 Months Ended
	Mar. 31, 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 March 31, 2017 Year Ended Dec. 31, 2016 Borrowing limit $ 250 $ 250 Amount outstanding at period end — — Average amount outstanding — 16 Maximum amount outstanding 21 225 Weighted average interest rate, computed on a daily basis 0.93 % 0.69 % Weighted average interest rate at period end N/A 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 March 31, 2017 Year Ended Dec. 31, 2016 Borrowing limit $ 500 $ 500 Amount outstanding at period end 39 85 Average amount outstanding 95 73 Maximum amount outstanding 237 353 Weighted average interest rate, computed on a daily basis 0.91 % 0.65 % Weighted average interest rate at period end 1.10 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 March 31, 2017 and Dec. 31, 2016 , there were $8 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 March 31, 2017 , NSP-Minnesota had the following committed credit facility available (in millions of dollars): Credit Facility (a) Drawn (b) Available $ 500 $ 47 $ 453 (a) This credit facility matures in June 2021 . (b) Includes outstanding commercial paper and 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 March 31, 2017 and Dec. 31, 2016 .

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	3 Months Ended
	Mar. 31, 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 disclosures provides 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. 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 complex iterative modeling to predict the impacts of forecasted changes in these drivers of transmission system congestion on the historical pricing of FTR purchases. 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. Fair value measurements for FTRs have been assigned a Level 3 given the limited observability of management’s forecasts for several of the inputs to this complex valuation model. 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 numerous unobservable quantitative inputs to the complex model used for 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 purpose of decommissioning the Monticello and Prairie Island (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 $428.2 million and $378.6 million at March 31, 2017 and Dec. 31, 2016 , respectively, and unrealized losses and amounts recorded as other-than-temporary impairments were $31.7 million and $46.9 million at March 31, 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 March 31, 2017 and Dec. 31, 2016 : March 31, 2017 Fair Value (Thousands of Dollars) Cost Level 1 Level 2 Level 3 Investments Measured at NAV (b) Total Nuclear decommissioning fund (a) Cash equivalents $ 24,161 $ 24,161 $ — $ — $ — $ 24,161 Commingled funds: Non U.S. equities 272,437 178,990 — — 98,876 277,866 Emerging market debt funds 94,772 — — — 101,269 101,269 Commodity funds 106,571 — — — 88,749 88,749 Private equity investments 137,176 — — — 194,912 194,912 Real estate 125,410 — — — 187,609 187,609 Other commingled funds 151,048 — — — 161,936 161,936 Debt securities: Government securities 27,369 — 27,199 — — 27,199 U.S. corporate bonds 127,841 — 128,799 — — 128,799 Non U.S. corporate bonds 25,345 — 25,556 — — 25,556 Municipal bonds 5 — 5 — — 5 Equity securities: U.S. equities 275,101 501,543 — — — 501,543 Non U.S. equities 188,763 232,851 — — — 232,851 Total $ 1,555,999 $ 937,545 $ 181,559 $ — $ 833,351 $ 1,952,455 (a) Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $48.9 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 months ended March 31, 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 March 31, 2017 : Final Contractual Maturity (Thousands of Dollars) Due in 1 Year or Less Due in 1 to 5 Years Due in 5 to 10 Years Due after 10 Years Total Government securities $ — $ 1,100 $ 3,017 $ 23,082 $ 27,199 U.S. corporate bonds 354 38,741 74,617 15,087 128,799 International corporate bonds — 8,085 13,443 4,028 25,556 Municipal bonds — — 5 — 5 Debt securities $ 354 $ 47,926 $ 91,082 $ 42,197 $ 181,559 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 March 31, 2017 and Dec. 31, 2016 : March 31, 2017 Fair Value (Thousands of Dollars) Cost Level 1 Level 2 Level 3 Total Rabbi Trust (a) Cash equivalents $ 392 $ 392 $ — $ — $ 392 Mutual funds 8,745 9,089 — — 9,089 Total $ 9,137 $ 9,481 $ — $ — $ 9,481 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 March 31, 2017 , accumulated other comprehensive losses related to interest rate derivatives included $0.9 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. 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 months ended March 31, 2016 . 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 March 31, 2017 and Dec. 31, 2016 : (Amounts in Thousands) (a)(b) March 31, 2017 Dec. 31, 2016 Megawatt hours of electricity 21,044 37,805 Million British thermal units of natural gas 77,728 79,520 (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 months ended March 31, 2017 and 2016 on accumulated other comprehensive loss, regulatory assets and liabilities and income: Three Months Ended March 31, 2017 Pre-Tax Fair Value Pre-Tax (Gains) Losses Pre-Tax Gains (Losses) Recognized (Thousands of Dollars) Accumulated Regulatory Accumulated Regulatory Derivatives designated as cash flow hedges Interest rate $ — $ — $ 342 (a) $ — $ — Total $ — $ — $ 342 $ — $ — Other derivative instruments Commodity trading $ — $ — $ — $ — $ 622 (c) Electric commodity — (1,247 ) — (2,788 ) (d) — Natural gas commodity — (665 ) — 698 (e) (945 ) (e) Total $ — $ (1,912 ) $ — $ (2,090 ) $ (323 ) Three Months Ended March 31, 2016 Pre-Tax Fair Value Pre-Tax Losses Pre-Tax Gains (Losses) (Thousands of Dollars) Accumulated Regulatory Accumulated Regulatory Derivatives designated as cash flow hedges Interest rate $ — $ — $ 346 (a) $ — $ — Vehicle fuel and other commodity (2 ) — 31 (b) — — Total $ (2 ) $ — $ 377 $ — $ — Other derivative instruments Commodity trading $ — $ — $ — $ — $ 992 (c) Electric commodity — (1,558 ) — 10,712 (d) — Natural gas commodity — (631 ) — 3,460 (e) (1,595 ) (e) Total $ — $ (2,189 ) $ — $ 14,172 $ (603 ) (a) Amounts are recorded to interest charges. (b) Amounts are recorded to 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 months ended March 31, 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 considering 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 March 31, 2017 , five of NSP-Minnesota’s 10 most significant counterparties for these activities, comprising $30.1 million or 38 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 $17.1 million or 22 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. Another of these significant counterparties, 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 recorded to the consolidated balance sheet at fair value, as well as 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 is unable to maintain its credit ratings. At March 31, 2017 and Dec. 31, 2016 , there were no derivative instruments in a liability position with underlying contract provisions that required the posting of collateral or settlement of outstanding contracts if the credit ratings of NSP-Minnesota were downgraded below investment grade. 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 March 31, 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 March 31, 2017 : March 31, 2017 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 $ 4,015 $ 7,307 $ — $ 11,322 $ (6,258 ) $ 5,064 Electric commodity — — 5,659 5,659 (223 ) 5,436 Total current derivative assets $ 4,015 $ 7,307 $ 5,659 $ 16,981 $ (6,481 ) 10,500 PPAs (a) 617 Current derivative instruments $ 11,117 Noncurrent derivative assets Other derivative instruments: Commodity trading $ 198 $ 32,272 $ — $ 32,470 $ (7,295 ) $ 25,175 Total noncurrent derivative assets $ 198 $ 32,272 $ — $ 32,470 $ (7,295 ) 25,175 PPAs (a) 866 Noncurrent derivative instruments $ 26,041 March 31, 2017 Fair Value Fair Value Total Counterparty Netting (b) (Thousands of Dollars) Level 1 Level 2 Level 3 Total Current derivative liabilities Other derivative instruments: Commodity trading $ 4,777 $ 5,026 $ — $ 9,803 $ (6,777 ) $ 3,026 Electric commodity — — 223 223 (223 ) — Total current derivative liabilities $ 4,777 $ 5,026 $ 223 $ 10,026 $ (7,000 ) 3,026 PPAs (a) 14,110 Current derivative instruments $ 17,136 Noncurrent derivative liabilities Other derivative instruments: Commodity trading $ 204 $ 23,434 $ 793 $ 24,431 $ (10,463 ) $ 13,968 Total noncurrent derivative liabilities $ 204 $ 23,434 $ 793 $ 24,431 $ (10,463 ) 13,968 PPAs (a) 100,556 Noncurrent derivative instruments $ 114,524 (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 March 31, 2017 . At March 31, 2017 , 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 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 months ended March 31, 2017 and 2016 : Three Months Ended March 31 (Thousands of Dollars) 2017 2016 Balance at Jan. 1 $ 15,320 $ 12,970 Purchases 280 — Settlements (3,426 ) (5,038 ) Net transactions recorded during the period: Losses recognized in earnings (a) (792 ) (24 ) Net losses recognized as regulatory assets and liabilities (6,739 ) (2,784 ) Balance at March 31 $ 4,643 $ 5,124 (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 months ended March 31, 2017 and 2016. Fair Value of Long-Term Debt As of March 31, 2017 and Dec. 31, 2016 , other financial instruments for which the carrying amount did not equal fair value were as follows: March 31, 2017 Dec. 31, 2016 (Thousands of Dollars) Carrying Amount Fair Value Carrying Fair Value Long-term debt, including current portion $ 4,844,227 $ 5,304,592 $ 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 March 31, 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.

Other (Expense) Income, Net

Other (Expense) Income, Net	3 Months Ended
	Mar. 31, 2017
Other Income and Expenses [Abstract]
Other (Expense) Income, Net	Other Income, Net Other income, net consisted of the following: Three Months Ended March 31 (Thousands of Dollars) 2017 2016 Interest income $ 2,709 $ 3,336 Other nonoperating income 10 164 Insurance policy expense (855 ) (640 ) Other income, net $ 1,864 $ 2,860

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 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 March 31, 2017 Operating revenues (a)(b) $ 1,079,030 $ 221,183 $ 6,927 $ — $ 1,307,140 Intersegment revenues 109 94 — (203 ) — Total revenues $ 1,079,139 $ 221,277 $ 6,927 $ (203 ) $ 1,307,140 Net income (loss) $ 78,082 $ 17,505 $ (1,421 ) $ — $ 94,166 (Thousands of Dollars) Regulated Electric Regulated Natural Gas All Other Reconciling Eliminations Consolidated Total Three Months Ended March 31, 2016 Operating revenues (a)(b) $ 1,033,643 $ 194,130 $ 6,860 $ — $ 1,234,633 Intersegment revenues 145 162 — (307 ) — Total revenues $ 1,033,788 $ 194,292 $ 6,860 $ (307 ) $ 1,234,633 Net income $ 71,321 $ 23,142 $ 166 $ — $ 94,629 (a) Operating revenues include $124 million and $125 million of affiliate electric revenue for the three months ended March 31, 2017 and 2016 . (b) Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended March 31, 2017 and 2016 .

Benefit Plans and Other Postret

Benefit Plans and Other Postretirement Benefits	3 Months Ended
	Mar. 31, 2017
Compensation and Retirement Disclosure [Abstract]
Benefit Plans and Other Postretirement Benefits	Benefit Plans and Other Postretirement Benefits Components of Net Periodic Benefit Cost Three Months Ended March 31 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 (15,017 ) (15,236 ) (54 ) (43 ) Amortization of prior service cost (credit) 265 234 (759 ) (759 ) Amortization of net loss 9,902 9,194 507 401 Net periodic benefit cost 12,285 12,627 584 611 Costs not recognized due to the effects of regulation (4,899 ) (5,296 ) — — Net benefit cost recognized for financial reporting $ 7,386 $ 7,331 $ 584 $ 611 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.

Other Comprehensive Income

Other Comprehensive Income	3 Months Ended
	Mar. 31, 2017
Stockholders' Equity Note [Abstract]
Other Comprehensive Income	Other Comprehensive Income Changes in accumulated other comprehensive (loss) income, net of tax, for the three months ended March 31, 2017 and 2016 were as follows: Three Months Ended March 31, 2017 (Thousands of Dollars) Gains and Unrealized Defined Benefit Total Accumulated other comprehensive (loss) income at Jan. 1 $ (18,208 ) $ 105 $ (2,680 ) $ (20,783 ) Losses reclassified from net accumulated other comprehensive loss 203 — 35 238 Net current period other comprehensive income 203 — 35 238 Accumulated other comprehensive (loss) income at March 31 $ (18,005 ) $ 105 $ (2,645 ) $ (20,545 ) Three Months Ended March 31, 2016 (Thousands of Dollars) Gains and Unrealized Defined Benefit Total Accumulated other comprehensive (loss) income at Jan. 1 $ (19,090 ) $ 105 $ (2,096 ) $ (21,081 ) Other comprehensive loss before reclassifications (1 ) — — (1 ) Losses reclassified from net accumulated other comprehensive loss 223 — 19 242 Net current period other comprehensive income 222 — 19 241 Accumulated other comprehensive (loss) income at March 31 $ (18,868 ) $ 105 $ (2,077 ) $ (20,840 ) Reclassifications from accumulated other comprehensive loss for the three months ended March 31, 2017 and 2016 were as follows: Amounts Reclassified from (Thousands of Dollars) Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 Losses on cash flow hedges: Interest rate derivatives $ 342 (a) $ 346 (a) Vehicle fuel derivatives — (b) 31 (b) Total, pre-tax 342 377 Tax benefit (139 ) (154 ) Total, net of tax 203 223 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 (25 ) (15 ) Total, net of tax 35 19 Total amounts reclassified, net of tax $ 238 $ 242 (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.

Selected Balance Sheet Data (Ta

Selected Balance Sheet Data (Tables)	3 Months Ended
	Mar. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Accounts receivable, net	(Thousands of Dollars) March 31, 2017 Dec. 31, 2016 Accounts receivable, net Accounts receivable $ 348,348 $ 349,449 Less allowance for bad debts (19,980 ) (19,968 ) $ 328,368 $ 329,481
Inventories	(Thousands of Dollars) March 31, 2017 Dec. 31, 2016 Inventories Materials and supplies $ 217,287 $ 214,234 Fuel 85,069 97,527 Natural gas 10,198 33,431 $ 312,554 $ 345,192
Property, plant and equipment, net	(Thousands of Dollars) March 31, 2017 Dec. 31, 2016 Property, plant and equipment, net Electric plant $ 17,085,453 $ 17,059,993 Natural gas plant 1,316,661 1,311,235 Common and other property 702,387 710,958 Construction work in progress 565,146 509,891 Total property, plant and equipment 19,669,647 19,592,077 Less accumulated depreciation (6,771,090 ) (6,682,418 ) Nuclear fuel 2,652,026 2,571,770 Less accumulated amortization (2,211,488 ) (2,180,636 ) $ 13,339,095 $ 13,300,793

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 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) March 31, 2017 Dec. 31, 2016 Unrecognized tax benefit — Permanent tax positions $ 21.8 $ 21.5 Unrecognized tax benefit — Temporary tax positions 39.8 39.3 Total unrecognized tax benefit $ 61.6 $ 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) March 31, 2017 Dec. 31, 2016 NOL and tax credit carryforwards $ (19.5 ) $ (19.3 )
Interest Payable related to Unrecognized Tax Benefits [Table Text Block]	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 amount of the payable for interest related to unrecognized tax benefits reported are as follows: (Millions of Dollars) March 31, 2017 Dec. 31, 2016 Payable for interest related to unrecognized tax benefits at beginning of period $ (2.0 ) $ (0.2 ) Interest expense related to unrecognized tax benefits recorded during the period (0.3 ) (1.8 ) Payable for interest related to unrecognized tax benefits at end of period $ (2.3 ) $ (2.0 )

Rate Matters (Tables)

Rate Matters (Tables)	3 Months Ended
	Mar. 31, 2017
Public Utilities, General Disclosures [Abstract]
NSP-Minnesota's 2016 Multi-Year Electric Rate Case - Rate Request [Table Text Block]	In December 2015, the MPUC approved interim rates for 2016. The request is detailed in the table below: Request (Millions of Dollars) 2016 2017 2018 Rate request $ 194.6 $ 52.1 $ 50.4 Increase percentage 6.4 % 1.7 % 1.7 % Interim request $ 163.7 $ 44.9 N/A Rate base $ 7,800 $ 7,700 $ 7,700
NSP-Minnesota 2016 Rate Case Settlement [Table Text Block]	(Millions of Dollars, incremental) 2016 2017 2018 2019 Total Settlement 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

Commitments and Contingencies S

Commitments and Contingencies Schedule of Guarantor Obligations (Tables)	3 Months Ended
	Mar. 31, 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) March 31, 2017 Dec. 31, 2016 Guarantee issued and outstanding $ 4.8 $ 4.8

Borrowings and Other Financin26

Borrowings and Other Financing Instruments (Tables)	3 Months Ended
	Mar. 31, 2017
Borrowings and Other Financing Instruments [Abstract]
Credit Facilities	At March 31, 2017 , NSP-Minnesota had the following committed credit facility available (in millions of dollars): Credit Facility (a) Drawn (b) Available $ 500 $ 47 $ 453 (a) This credit facility matures in June 2021 . (b) Includes outstanding commercial paper and 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 March 31, 2017 Year Ended Dec. 31, 2016 Borrowing limit $ 250 $ 250 Amount outstanding at period end — — Average amount outstanding — 16 Maximum amount outstanding 21 225 Weighted average interest rate, computed on a daily basis 0.93 % 0.69 % Weighted average interest rate at period end N/A 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 March 31, 2017 Year Ended Dec. 31, 2016 Borrowing limit $ 500 $ 500 Amount outstanding at period end 39 85 Average amount outstanding 95 73 Maximum amount outstanding 237 353 Weighted average interest rate, computed on a daily basis 0.91 % 0.65 % Weighted average interest rate at period end 1.10 0.94

Fair Value of Financial Asset27

Fair Value of Financial Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2017 and Dec. 31, 2016 : March 31, 2017 Fair Value (Thousands of Dollars) Cost Level 1 Level 2 Level 3 Investments Measured at NAV (b) Total Nuclear decommissioning fund (a) Cash equivalents $ 24,161 $ 24,161 $ — $ — $ — $ 24,161 Commingled funds: Non U.S. equities 272,437 178,990 — — 98,876 277,866 Emerging market debt funds 94,772 — — — 101,269 101,269 Commodity funds 106,571 — — — 88,749 88,749 Private equity investments 137,176 — — — 194,912 194,912 Real estate 125,410 — — — 187,609 187,609 Other commingled funds 151,048 — — — 161,936 161,936 Debt securities: Government securities 27,369 — 27,199 — — 27,199 U.S. corporate bonds 127,841 — 128,799 — — 128,799 Non U.S. corporate bonds 25,345 — 25,556 — — 25,556 Municipal bonds 5 — 5 — — 5 Equity securities: U.S. equities 275,101 501,543 — — — 501,543 Non U.S. equities 188,763 232,851 — — — 232,851 Total $ 1,555,999 $ 937,545 $ 181,559 $ — $ 833,351 $ 1,952,455 (a) Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $48.9 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 March 31, 2017 : Final Contractual Maturity (Thousands of Dollars) Due in 1 Year or Less Due in 1 to 5 Years Due in 5 to 10 Years Due after 10 Years Total Government securities $ — $ 1,100 $ 3,017 $ 23,082 $ 27,199 U.S. corporate bonds 354 38,741 74,617 15,087 128,799 International corporate bonds — 8,085 13,443 4,028 25,556 Municipal bonds — — 5 — 5 Debt securities $ 354 $ 47,926 $ 91,082 $ 42,197 $ 181,559
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 March 31, 2017 and Dec. 31, 2016 : March 31, 2017 Fair Value (Thousands of Dollars) Cost Level 1 Level 2 Level 3 Total Rabbi Trust (a) Cash equivalents $ 392 $ 392 $ — $ — $ 392 Mutual funds 8,745 9,089 — — 9,089 Total $ 9,137 $ 9,481 $ — $ — $ 9,481 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 March 31, 2017 and Dec. 31, 2016 : (Amounts in Thousands) (a)(b) March 31, 2017 Dec. 31, 2016 Megawatt hours of electricity 21,044 37,805 Million British thermal units of natural gas 77,728 79,520 (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 months ended March 31, 2017 and 2016 on accumulated other comprehensive loss, regulatory assets and liabilities and income: Three Months Ended March 31, 2017 Pre-Tax Fair Value Pre-Tax (Gains) Losses Pre-Tax Gains (Losses) Recognized (Thousands of Dollars) Accumulated Regulatory Accumulated Regulatory Derivatives designated as cash flow hedges Interest rate $ — $ — $ 342 (a) $ — $ — Total $ — $ — $ 342 $ — $ — Other derivative instruments Commodity trading $ — $ — $ — $ — $ 622 (c) Electric commodity — (1,247 ) — (2,788 ) (d) — Natural gas commodity — (665 ) — 698 (e) (945 ) (e) Total $ — $ (1,912 ) $ — $ (2,090 ) $ (323 ) Three Months Ended March 31, 2016 Pre-Tax Fair Value Pre-Tax Losses Pre-Tax Gains (Losses) (Thousands of Dollars) Accumulated Regulatory Accumulated Regulatory Derivatives designated as cash flow hedges Interest rate $ — $ — $ 346 (a) $ — $ — Vehicle fuel and other commodity (2 ) — 31 (b) — — Total $ (2 ) $ — $ 377 $ — $ — Other derivative instruments Commodity trading $ — $ — $ — $ — $ 992 (c) Electric commodity — (1,558 ) — 10,712 (d) — Natural gas commodity — (631 ) — 3,460 (e) (1,595 ) (e) Total $ — $ (2,189 ) $ — $ 14,172 $ (603 ) (a) Amounts are recorded to interest charges. (b) Amounts are recorded to 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 March 31, 2017 : March 31, 2017 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 $ 4,015 $ 7,307 $ — $ 11,322 $ (6,258 ) $ 5,064 Electric commodity — — 5,659 5,659 (223 ) 5,436 Total current derivative assets $ 4,015 $ 7,307 $ 5,659 $ 16,981 $ (6,481 ) 10,500 PPAs (a) 617 Current derivative instruments $ 11,117 Noncurrent derivative assets Other derivative instruments: Commodity trading $ 198 $ 32,272 $ — $ 32,470 $ (7,295 ) $ 25,175 Total noncurrent derivative assets $ 198 $ 32,272 $ — $ 32,470 $ (7,295 ) 25,175 PPAs (a) 866 Noncurrent derivative instruments $ 26,041 March 31, 2017 Fair Value Fair Value Total Counterparty Netting (b) (Thousands of Dollars) Level 1 Level 2 Level 3 Total Current derivative liabilities Other derivative instruments: Commodity trading $ 4,777 $ 5,026 $ — $ 9,803 $ (6,777 ) $ 3,026 Electric commodity — — 223 223 (223 ) — Total current derivative liabilities $ 4,777 $ 5,026 $ 223 $ 10,026 $ (7,000 ) 3,026 PPAs (a) 14,110 Current derivative instruments $ 17,136 Noncurrent derivative liabilities Other derivative instruments: Commodity trading $ 204 $ 23,434 $ 793 $ 24,431 $ (10,463 ) $ 13,968 Total noncurrent derivative liabilities $ 204 $ 23,434 $ 793 $ 24,431 $ (10,463 ) 13,968 PPAs (a) 100,556 Noncurrent derivative instruments $ 114,524 (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 March 31, 2017 . At March 31, 2017 , 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 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 months ended March 31, 2017 and 2016 : Three Months Ended March 31 (Thousands of Dollars) 2017 2016 Balance at Jan. 1 $ 15,320 $ 12,970 Purchases 280 — Settlements (3,426 ) (5,038 ) Net transactions recorded during the period: Losses recognized in earnings (a) (792 ) (24 ) Net losses recognized as regulatory assets and liabilities (6,739 ) (2,784 ) Balance at March 31 $ 4,643 $ 5,124 (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 March 31, 2017 and Dec. 31, 2016 , other financial instruments for which the carrying amount did not equal fair value were as follows: March 31, 2017 Dec. 31, 2016 (Thousands of Dollars) Carrying Amount Fair Value Carrying Fair Value Long-term debt, including current portion $ 4,844,227 $ 5,304,592 $ 4,843,165 $ 5,310,925

Other (Expense) Income, Net (Ta

Other (Expense) Income, Net (Tables)	3 Months Ended
	Mar. 31, 2017
Other Income and Expenses [Abstract]
Other (Expense) Income, Net	Other income, net consisted of the following: Three Months Ended March 31 (Thousands of Dollars) 2017 2016 Interest income $ 2,709 $ 3,336 Other nonoperating income 10 164 Insurance policy expense (855 ) (640 ) Other income, net $ 1,864 $ 2,860

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2017 Operating revenues (a)(b) $ 1,079,030 $ 221,183 $ 6,927 $ — $ 1,307,140 Intersegment revenues 109 94 — (203 ) — Total revenues $ 1,079,139 $ 221,277 $ 6,927 $ (203 ) $ 1,307,140 Net income (loss) $ 78,082 $ 17,505 $ (1,421 ) $ — $ 94,166 (Thousands of Dollars) Regulated Electric Regulated Natural Gas All Other Reconciling Eliminations Consolidated Total Three Months Ended March 31, 2016 Operating revenues (a)(b) $ 1,033,643 $ 194,130 $ 6,860 $ — $ 1,234,633 Intersegment revenues 145 162 — (307 ) — Total revenues $ 1,033,788 $ 194,292 $ 6,860 $ (307 ) $ 1,234,633 Net income $ 71,321 $ 23,142 $ 166 $ — $ 94,629 (a) Operating revenues include $124 million and $125 million of affiliate electric revenue for the three months ended March 31, 2017 and 2016 . (b) Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended March 31, 2017 and 2016 .

Benefit Plans and Other Postr30

Benefit Plans and Other Postretirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2017
Compensation and Retirement Disclosure [Abstract]
Components of Net Periodic Benefit Cost (Credit)	Components of Net Periodic Benefit Cost Three Months Ended March 31 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 (15,017 ) (15,236 ) (54 ) (43 ) Amortization of prior service cost (credit) 265 234 (759 ) (759 ) Amortization of net loss 9,902 9,194 507 401 Net periodic benefit cost 12,285 12,627 584 611 Costs not recognized due to the effects of regulation (4,899 ) (5,296 ) — — Net benefit cost recognized for financial reporting $ 7,386 $ 7,331 $ 584 $ 611

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 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 months ended March 31, 2017 and 2016 were as follows: Three Months Ended March 31, 2017 (Thousands of Dollars) Gains and Unrealized Defined Benefit Total Accumulated other comprehensive (loss) income at Jan. 1 $ (18,208 ) $ 105 $ (2,680 ) $ (20,783 ) Losses reclassified from net accumulated other comprehensive loss 203 — 35 238 Net current period other comprehensive income 203 — 35 238 Accumulated other comprehensive (loss) income at March 31 $ (18,005 ) $ 105 $ (2,645 ) $ (20,545 ) Three Months Ended March 31, 2016 (Thousands of Dollars) Gains and Unrealized Defined Benefit Total Accumulated other comprehensive (loss) income at Jan. 1 $ (19,090 ) $ 105 $ (2,096 ) $ (21,081 ) Other comprehensive loss before reclassifications (1 ) — — (1 ) Losses reclassified from net accumulated other comprehensive loss 223 — 19 242 Net current period other comprehensive income 222 — 19 241 Accumulated other comprehensive (loss) income at March 31 $ (18,868 ) $ 105 $ (2,077 ) $ (20,840 )
Reclassifications out of Accumulated Other Comprehensive Loss	Reclassifications from accumulated other comprehensive loss for the three months ended March 31, 2017 and 2016 were as follows: Amounts Reclassified from (Thousands of Dollars) Three Months Ended March 31, 2017 Three Months Ended March 31, 2016 Losses on cash flow hedges: Interest rate derivatives $ 342 (a) $ 346 (a) Vehicle fuel derivatives — (b) 31 (b) Total, pre-tax 342 377 Tax benefit (139 ) (154 ) Total, net of tax 203 223 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 (25 ) (15 ) Total, net of tax 35 19 Total amounts reclassified, net of tax $ 238 $ 242 (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.

Selected Balance Sheet Data, Ac

Selected Balance Sheet Data, Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accounts receivable, net
Accounts receivable	$ 348,348	$ 349,449
Less allowance for bad debts	(19,980)	(19,968)
Accounts receivable, net	$ 328,368	$ 329,481

Selected Balance Sheet Data, In

Selected Balance Sheet Data, Inventories (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Public Utilities, Inventory [Line Items]
Inventories	$ 312,554	$ 345,192
Materials and supplies
Public Utilities, Inventory [Line Items]
Inventories	217,287	214,234
Fuel
Public Utilities, Inventory [Line Items]
Inventories	85,069	97,527
Natural gas
Public Utilities, Inventory [Line Items]
Inventories	$ 10,198	$ 33,431

Selected Balance Sheet Data, Pr

Selected Balance Sheet Data, Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 19,669,647	$ 19,592,077
Less accumulated depreciation	(6,771,090)	(6,682,418)
Property, plant and equipment, net	13,339,095	13,300,793
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	17,085,453	17,059,993
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,316,661	1,311,235
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	702,387	710,958
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	565,146	509,891
Nuclear fuel
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,652,026	2,571,770
Less accumulated depreciation	$ (2,211,488)	$ (2,180,636)

Income Taxes (Details)

Income Taxes (Details) - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2016	Mar. 31, 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		$ (2,300,000)		$ (2,000,000)	$ (200,000)
Interest Expense (Income) related to unrecognized tax benefits		(300,000)		(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		21,800,000		21,500,000
Unrecognized tax benefit — Temporary tax positions		39,800,000		39,300,000
Total unrecognized tax benefit		61,600,000		60,800,000
NOL and tax credit carryforwards		(19,500,000)		(19,300,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible		32,000,000
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								2,009
Potential Tax Adjustments		$ 14,000,000
Earliest year subject to examination		2,009
State Jurisdiction (Minnesota)
Tax Audits [Abstract]
Year(s) under examination	2010 through 2014
Earliest year subject to examination		2,009

Rate Matters (Details)

Rate Matters (Details) - NSP-Minnesota - USD ($) $ in Thousands	1 Months Ended							3 Months Ended
	Sep. 30, 2016	Aug. 31, 2016	Jun. 30, 2016	Dec. 31, 2015	Nov. 30, 2015	Feb. 28, 2015	Nov. 30, 2013	Mar. 31, 2017
MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case
Rate Matters [Abstract]
Public Utilities, Number Of Years Rate Case Is Applicable For					3 years
Public Utilities, Requested Return on Equity, Percentage					10.00%
Public Utilities, Requested Equity Capital Structure, Percentage					52.50%
MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2016
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 194,600
Public Utilities, Requested Rate Increase (Decrease), Percentage					6.40%
Public Utilities, Requested Rate Base, Amount					$ 7,800,000
MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2017
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 52,100
Public Utilities, Requested Rate Increase (Decrease), Percentage					1.70%
Public Utilities, Requested Interim Rate Increase (Decrease), Amount					$ 44,900
Public Utilities, Requested Rate Base, Amount					7,700,000
MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2018
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 50,400
Public Utilities, Requested Rate Increase (Decrease), Percentage					1.70%
Public Utilities, Requested Rate Base, Amount					$ 7,700,000
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 Regional Transmission Operator's Region, Recommended By Third Parties						8.67%	9.15%
Public Utilities, Maximum Equity Capital Structure Percentage Allowed Per The Complaint							50.00%
Minnesota Public Utilities Commission | MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2016
Rate Matters [Abstract]
Public Utilities, Approved Interim Rate Increase (Decrease), Amount				$ 163,700
Settlement Group | MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case
Rate Matters [Abstract]
Public Utilities, Number Of Years Rate Case Is Applicable For		4 years
Public Utilities, Requested Return on Equity, Percentage		9.20%
Public Utilities, Requested Equity Capital Structure, Percentage		52.50%
Public Utilities, Length of Stay-out Provision, In Years		4 years
Public Utilities, Rate Increase Under the Settlement		$ 184,970
Public Utilities, Increase (Decrease) Related to Sales True-up		59,750
Public Utilities, Rate Impact		244,720
Settlement Group | MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2016
Rate Matters [Abstract]
Public Utilities, Rate Increase Under the Settlement		74,990
Public Utilities, Increase (Decrease) Related to Sales True-up		59,950
Public Utilities, Rate Impact		134,940
Settlement Group | MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2017
Rate Matters [Abstract]
Public Utilities, Rate Increase Under the Settlement		59,860
Public Utilities, Increase (Decrease) Related to Sales True-up		0
Public Utilities, Rate Impact		59,860
Settlement Group | MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2018
Rate Matters [Abstract]
Public Utilities, Rate Increase Under the Settlement		0
Public Utilities, Increase (Decrease) Related to Sales True-up		0
Public Utilities, Rate Impact		0
Settlement Group | MPUC Proceeding - Minnesota 2016 Multi-Year Electric Rate Case, Rates 2019
Rate Matters [Abstract]
Public Utilities, Rate Increase Under the Settlement		50,120
Public Utilities, Increase (Decrease) Related to Sales True-up		(200)
Public Utilities, Rate Impact		$ 49,920
Administrative Law Judge | FERC Proceeding, MISO ROE Complaint
Rate Matters [Abstract]
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Recommended By Third Parties			9.70%
MPUC, NDPSC, SDPUC, and DOC | FERC Proceeding, MISO ROE Complaint
Rate Matters [Abstract]
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Recommended By Third Parties								8.81%
MISO TOs | FERC Proceeding, MISO ROE Complaint
Rate Matters [Abstract]
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Recommended By Third Parties								10.92%
FERC Staff | FERC Proceeding, MISO ROE Complaint
Rate Matters [Abstract]
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Recommended By Third Parties								8.78%
Federal Energy Regulatory Commission (FERC) | FERC Proceeding, MISO ROE Complaint
Rate Matters [Abstract]
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Approved	10.32%
Public Utilities, Length of Refund Period, In Months	15 months
Public Utilities, ROE Basis Point Adder, Approved								50
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, with RTO Adder, Approved								10.82%

Commitments and Contingencies,

Commitments and Contingencies, Purchased Power Agreements (Details) - MW	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
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)		2,028
Payment or Performance Guarantee
Purchased Power Agreements [Abstract]
Lease Guarantee Expiration (year)	2,019		2,019

Commitments and Contingencies C

Commitments and Contingencies Commitments and Contingencies, Guarantees and Indemnifications (Details) - Payment or Performance Guarantee - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Lease Guarantee Expiration (year)	2,019	2,019
Guarantees issued and outstanding	$ 4.8	$ 4.8

Commitments and Contingencies39

Commitments and Contingencies, Environmental Contingencies (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Fargo MGP Site
Environmental Requirements [Abstract]
Accrual for Environmental Loss Contingencies, Gross	$ 11.1	$ 11.3
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	6
Capital Addition Purchase Commitments [Member] | NSP-Minnesota | Federal Clean Water Act Effluent Limitations Guidelines [Member]
Environmental Requirements [Abstract]
Liability for estimated cost to comply with regulation	$ 10

Borrowings and Other Financin40

Borrowings and Other Financing Instruments, Short-Term Borrowings (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Amount outstanding at period end	$ 39,000,000	$ 85,000,000
Money Pool
Short-term Debt [Line Items]
Borrowing limit	250,000,000	250,000,000
Amount outstanding at period end	0	0
Average amount outstanding	0	16,000,000
Maximum amount outstanding	$ 21,000,000	$ 225,000,000
Weighted average interest rate, computed on a daily basis (percentage)	0.93%	0.69%
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	$ 500,000,000	$ 500,000,000
Amount outstanding at period end	39,000,000	85,000,000
Average amount outstanding	95,000,000	73,000,000
Maximum amount outstanding	$ 237,000,000	$ 353,000,000
Weighted average interest rate, computed on a daily basis (percentage)	0.91%	0.65%
Weighted average interest rate at period end (percentage)	1.10%	0.94%

Borrowings and Other Financin41

Borrowings and Other Financing Instruments, Letters of Credit (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 39,000	$ 85,000
Letter of Credit
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 8,000	$ 11,000
Letter of Credit | Letter of Credit
Line of Credit Facility [Line Items]
Term of letters of credit (in years)	1 year

Borrowings and Other Financin42

Borrowings and Other Financing Instruments, Credit Facility (Details) - Credit Facility - USD ($)		3 Months Ended
		Mar. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Credit Facility	[1]	$ 500,000,000
Drawn	[2]	47,000,000
Available		$ 453,000,000
Maturity Date		Jun. 30, 2021
Direct advances on the credit facility outstanding		$ 0	$ 0
[1]	This credit facility matures in June 2021.
[2]	Includes outstanding commercial paper and letters of credit.

Fair Value of Financial Asset43

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities (Details)	3 Months Ended
	Mar. 31, 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

Fair Value of Financial Asset44

Fair Value of Financial Assets and Liabilities, Cost and Fair Value of Nuclear Decommissioning Fund (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2017		Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Gross Unrealized Gain		$ 428,200		$ 378,600
Available-for-sale Securities, Gross Unrealized Loss		31,700		46,900
Investments [Abstract]
Miscellaneous investments		48,900		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		24,161	[1]	20,379	[2]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		1,555,999	[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		272,437	[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		94,772	[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		106,571	[1]	106,571	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Private equity investments
Available-for-sale Securities [Abstract]
Available-for-sale Securities		137,176	[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		125,410	[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		151,048	[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		27,369	[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		127,841	[1]	104,913	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | International corporate bonds
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		25,345	[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		5	[1]	13,609	[2]
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		275,101	[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		188,763	[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		24,161	[1]	20,379	[2]
Alternative Investments, Fair Value Disclosure		833,351	[1],[3]	839,465	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		1,952,455	[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 Investments, 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 Investments, Fair Value Disclosure		98,876	[1],[3]	112,233	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		277,866	[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 Investments, Fair Value Disclosure		101,269	[1],[3]	97,543	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		101,269	[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 Investments, Fair Value Disclosure		88,749	[1],[3]	92,091	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		88,749	[1]	92,091	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investments, Fair Value Disclosure		194,912	[1],[3]	190,462	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		194,912	[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 Investments, Fair Value Disclosure		187,609	[1],[3]	187,647	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		187,609	[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 Investments, Fair Value Disclosure		161,936	[1],[3]	159,489	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		161,936	[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 Investments, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		27,199	[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 Investments, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		128,799	[1]	105,772	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | International corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investments, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		25,556	[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 Investments, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		5	[1]	13,786	[2]
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 Investments, 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 Investments, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Equity Securities		501,543	[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 Investments, Fair Value Disclosure		0	[1],[3]	0	[2],[4]
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Equity Securities		232,851	[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		24,161	[1]	20,379	[2]
Available-for-sale Securities [Abstract]
Available-for-sale Securities		937,545	[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		178,990	[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		0	[1]	0	[2]
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		0	[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 | International 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		0	[1]	0	[2]
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		501,543	[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		232,851	[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		181,559	[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		0	[1]	0	[2]
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		27,199	[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		128,799	[1]	105,772	[2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | International corporate bonds
Available-for-sale Securities [Abstract]
Available-for-sale Securities, Debt Securities		25,556	[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		5	[1]	13,786	[2]
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		0	[1]	0	[2]
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 | International 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		0	[1]	0	[2]
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 $48.9 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.

Fair Value of Financial Asset45

Fair Value of Financial Assets and Liabilities, Final Contractual Maturity Dates of Debt Securities in Nuclear Decommissioning Fund (Details) $ in Thousands	Mar. 31, 2017USD ($)
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	$ 354
Due in 1 to 5 Years	47,926
Due in 5 to 10 Years	91,082
Due after 10 Years	42,197
Total	181,559
Government securities
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0
Due in 1 to 5 Years	1,100
Due in 5 to 10 Years	3,017
Due after 10 Years	23,082
Total	27,199
U.S. corporate bonds
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	354
Due in 1 to 5 Years	38,741
Due in 5 to 10 Years	74,617
Due after 10 Years	15,087
Total	128,799
International corporate bonds
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0
Due in 1 to 5 Years	8,085
Due in 5 to 10 Years	13,443
Due after 10 Years	4,028
Total	25,556
Municipal bonds
Final Contractual Maturity [Abstract]
Due in 1 Year or Less	0
Due in 1 to 5 Years	0
Due in 5 to 10 Years	5
Due after 10 Years	0
Total	$ 5

Fair Value of Financial Asset46

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		Mar. 31, 2017	Dec. 31, 2016
Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	$ 9,137	$ 9,122
Cost | Rabbi Trust [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	[1]	392	7,459
Cost | Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	8,745	1,663
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	9,481	9,360
Fair Value | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[1]	9,481	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]	392	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]	392	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]	9,089	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]	9,089	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.

Fair Value of Financial Asset47

Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details) MWh in Thousands, MMBTU in Thousands, $ in Millions		Mar. 31, 2017USD ($)MMBTUMWhCounterparty	Dec. 31, 2016MMBTUMWh
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		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		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		5
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $		$ 30.1
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		38.00%
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		4
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $		$ 17.1
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		22.00%
Credit Concentration Risk | Credit Quality Less Than 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		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 | $		$ (0.9)
Electric Commodity (in megawatt hours)
Gross Notional Amounts of Commodity Forwards, Options and FTRs [Abstract]
Derivative, Nonmonetary Notional amount | MWh	[1],[2]	21,044	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]	77,728	79,520
[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.

Fair Value of Financial Asset48

Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) - USD ($)		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract]
Derivative instruments designated as fair value hedges		$ 0	$ 0
Recognized gains (losses) from fair value hedges or related hedged transactions		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		0	(2,000)
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		0	0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		342,000	377,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0
Pre-tax gains (losses) recognized during the period in income		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
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		0	0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	[1]	342,000	346,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0
Pre-tax gains (losses) recognized during the period in income		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			(2,000)
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities			0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	[2]		31,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)			0
Pre-tax gains (losses) recognized during the period in income			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
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		(1,912,000)	(2,189,000)
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		0	0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		(2,090,000)	14,172,000
Pre-tax gains (losses) recognized during the period in income		(323,000)	(603,000)
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
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		0	0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		0	0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0
Pre-tax gains (losses) recognized during the period in income	[3]	622,000	992,000
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
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		(1,247,000)	(1,558,000)
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		0	0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	[4]	(2,788,000)	10,712,000
Pre-tax gains (losses) recognized during the period in income		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
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		(665,000)	(631,000)
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		0	0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	[5]	698,000	3,460,000
Pre-tax gains (losses) recognized during the period in income	[5]	$ (945,000)	$ (1,595,000)
[1]	Amounts are recorded to interest charges.
[2]	Amounts are recorded to 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.

Fair Value of Financial Asset49

Fair Value of Financial Assets and Liabilities, Credit Related Contingent Features (Details) - USD ($)	Mar. 31, 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

Fair Value of Financial Asset50

Fair Value of Financial Assets and Liabilities, Derivative Assets and Liabilities at Fair Value (Details) - USD ($) $ in Thousands		Mar. 31, 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		3,700		3,700
Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		11,117		22,028
Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		26,041		24,678
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		17,136		16,606
Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		114,524		116,804
Fair Value Measured on a Recurring Basis | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		10,500		21,436
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(6,481)	[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		5,064		5,204
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(6,258)	[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		5,436		15,320
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(223)	[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				912
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[2]			0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		25,175		23,806
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(7,295)	[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		25,175		23,806
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(7,295)	[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		3,026		2,524
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		(7,000)	[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		3,026		2,524
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		(6,777)	[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		(223)	[1]	(677)	[2]
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		13,968		12,786
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		(10,463)	[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		13,968		12,786
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		(10,463)	[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		4,015		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		4,015		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
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		198		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		198		100
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		4,777		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		4,777		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		204		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		204		89
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		7,307		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		7,307		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				912
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		32,272		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		32,272		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		5,026		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		5,026		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		23,434		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		23,434		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		5,659		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		0		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		5,659		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
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Assets
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 | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0		0
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		223		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		223		677
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		793		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		793		0
Fair Value, Measurements, Nonrecurring | Other Current Assets | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		617	[3]	592	[4]
Fair Value, Measurements, Nonrecurring | Other Noncurrent Assets | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		866	[3]	872	[4]
Fair Value, Measurements, Nonrecurring | Other Current Liabilities | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		14,110	[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		100,556	[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		16,981		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		11,322		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		5,659		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				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		32,470		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		32,470		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		10,026		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		9,803		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		223		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		24,431		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		$ 24,431		$ 23,513
[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 March 31, 2017. At March 31, 2017, 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.
[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.

Fair Value of Financial Asset51

Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) - Commodity Contract - USD ($)		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period		$ 15,320,000	$ 12,970,000
Purchases		280,000	0
Settlements		(3,426,000)	(5,038,000)
(Losses) recognized in earnings	[1]	(792,000)	(24,000)
Net losses recognized as regulatory assets and liabilities		(6,739,000)	(2,784,000)
Balance at end of period		4,643,000	5,124,000
Transfers into Level 3		0	0
Transfers out of Level 3		$ 0	$ 0
[1]	These amounts relate to commodity derivatives held at the end of the period.

Fair Value of Financial Asset52

Fair Value of Financial Assets and Liabilities, Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Carrying Amount
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	$ 4,844,227	$ 4,843,165
Fair Value
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	$ 5,304,592	$ 5,310,925

Other (Expense) Income, Net (De

Other (Expense) Income, Net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Other Income and Expenses [Abstract]
Interest income (expense)	$ 2,709	$ 3,336
Other nonoperating Income	10	164
Insurance policy expense	(855)	(640)
Other (expense) income, net	$ 1,864	$ 2,860

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Operating revenues		$ 1,307,140	$ 1,234,633
Net income (loss)		94,166	94,629
Affiliate electric revenue		123,689	124,896
Regulated Electric
Segment Reporting Information [Line Items]
Operating revenues		1,079,139	1,033,788
Net income (loss)		78,082	71,321
Regulated Natural Gas
Segment Reporting Information [Line Items]
Operating revenues		221,277	194,292
Net income (loss)		17,505	23,142
All Other
Segment Reporting Information [Line Items]
Operating revenues		6,927	6,860
Net income (loss)		(1,421)	166
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	[1],[2]	1,307,140	1,234,633
Operating Segments | Regulated Electric
Segment Reporting Information [Line Items]
Operating revenues	[1]	1,079,030	1,033,643
Operating Segments | Regulated Natural Gas
Segment Reporting Information [Line Items]
Operating revenues	[2]	221,183	194,130
Operating Segments | All Other
Segment Reporting Information [Line Items]
Operating revenues		6,927	6,860
Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating revenues		(203)	(307)
Net income (loss)		0	0
Intersegment Eliminations | Regulated Electric
Segment Reporting Information [Line Items]
Operating revenues		109	145
Intersegment Eliminations | Regulated Natural Gas
Segment Reporting Information [Line Items]
Operating revenues		94	162
Intersegment Eliminations | All Other
Segment Reporting Information [Line Items]
Operating revenues		$ 0	$ 0
[1]	Operating revenues include $124 million and $125 million of affiliate electric revenue for the three months ended March 31, 2017 and 2016.
[2]	Operating revenues include an immaterial amount of affiliate gas revenue for the three months ended March 31, 2017 and 2016.

Benefit Plans and Other Postr55

Benefit Plans and Other Postretirement Benefits (Details) $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2017USD ($)Plan	Mar. 31, 2017USD ($)	Mar. 31, 2016USD ($)
Pension Benefits
Components of Net Periodic Benefit Cost [Abstract]
Service cost		$ 6,958	$ 7,077
Interest cost		10,177	11,358
Expected return on plan assets		(15,017)	(15,236)
Amortization of prior service cost (credit)		265	234
Amortization of net loss		9,902	9,194
Net periodic benefit cost		12,285	12,627
Costs not recognized due to the effects of regulation		(4,899)	(5,296)
Net benefit cost recognized for financial reporting		7,386	7,331
Total contributions to the pension plans during the period	$ 59,400
Postretirement Health Care Benefits
Components of Net Periodic Benefit Cost [Abstract]
Service cost		36	31
Interest cost		854	981
Expected return on plan assets		(54)	(43)
Amortization of prior service cost (credit)		(759)	(759)
Amortization of net loss		507	401
Net periodic benefit cost		584	611
Costs not recognized due to the effects of regulation		0	0
Net benefit cost recognized for financial reporting		$ 584	$ 611
Xcel Energy Inc. | Pension Benefits
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 Comprehensive Income (Det

Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 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	238	$ 242
Accumulated other comprehensive (loss) income at end of period	5,424,286
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	(18,208)	(19,090)
Other comprehensive income (loss) before reclassifications		(1)
(Gains) losses reclassified from net accumulated other comprehensive loss	203	223
Net current period other comprehensive income (loss)	203	222
Accumulated other comprehensive (loss) income at end of period	(18,005)	(18,868)
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
Other comprehensive income (loss) before reclassifications		0
(Gains) losses reclassified from net accumulated other comprehensive loss	0	0
Net current period other comprehensive income (loss)	0	0
Accumulated other comprehensive (loss) income at end of period	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	(2,680)	(2,096)
Other comprehensive income (loss) before reclassifications		0
(Gains) losses reclassified from net accumulated other comprehensive loss	35	19
Net current period other comprehensive income (loss)	35	19
Accumulated other comprehensive (loss) income at end of period	(2,645)	(2,077)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income at beginning of period	(20,783)	(21,081)
Other comprehensive income (loss) before reclassifications		(1)
(Gains) losses reclassified from net accumulated other comprehensive loss	238	242
Net current period other comprehensive income (loss)	238	241
Accumulated other comprehensive (loss) income at end of period	$ (20,545)	$ (20,840)

Other Comprehensive Income (Rec

Other Comprehensive Income (Reclassification from AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating and maintenance expenses	$ 312,024	$ 320,496
Total, pre-tax	(133,181)	(141,097)
Tax benefit	39,015	46,468
Total amounts reclassified, net of tax	238	242
Gains and Losses on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amounts reclassified, net of tax	203	223
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	342	377
Tax benefit	(139)	(154)
Total, net of tax	203	223
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	342	346
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	0	31
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
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)
Defined Benefit Pension and Postretirement Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amounts reclassified, net of tax	35	19
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
Tax (benefit) expense	(25)	(15)
Total amounts reclassified, net of tax	$ 35	$ 19