NORTHERN STATES POWER CO /WI/, 10-Q filed on 7/27/2018
Quarterly Report
v3.10.0.1
Document and Entity Information - shares
 6 Months Ended
Jun. 30, 2018
Jul. 27, 2018
Document and Entity Information [Abstract]    
Entity Registrant Name NORTHERN STATES POWER CO /WI/  
Entity Central Index Key 0000072909  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Document Type 10-Q  
Document Period End Date Jun. 30, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q2  
Amendment Flag false  
Entity Common Stock, Shares Outstanding   933,000
Entity Well-known Seasoned Issuer No  
Entity Voluntary Filers No  
Entity Current Reporting Status Yes  
v3.10.0.1
CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Operating revenues        
Electric $ 209,502 $ 210,742 $ 425,868 $ 427,051
Natural gas 21,981 19,027 78,481 67,374
Other 271 257 549 532
Total operating revenues 231,754 230,026 504,898 494,957
Operating expenses        
Electric fuel and purchased power, non-affiliates 3,562 3,583 6,460 6,456
Purchased power, affiliates 101,629 101,793 202,940 208,251
Cost of natural gas sold and transported 8,507 8,563 37,230 34,550
Operating and maintenance expenses 48,934 48,532 99,278 97,716
Conservation expenses 3,144 3,177 6,122 6,231
Depreciation and amortization 31,449 27,628 62,036 54,677
Taxes (other than income taxes) 7,053 7,005 14,366 13,878
Total operating expenses 204,278 200,281 428,432 421,759
Operating income 27,476 29,745 76,466 73,198
Other expense, net (509) (595) (869) (1,027)
Allowance for funds used during construction — equity 2,246 1,751 4,101 3,038
Interest charges and financing costs        
Interest charges — includes other financing costs of $485 and $461, $963, and $917 respectively 9,763 8,656 19,358 17,338
Allowance for funds used during construction — debt (1,009) (749) (1,845) (1,299)
Total interest charges and financing costs 8,754 7,907 17,513 16,039
Income before income taxes 20,459 22,994 62,185 59,170
Income taxes 5,270 8,753 15,580 22,510
Net income $ 15,189 $ 14,241 $ 46,605 $ 36,660
v3.10.0.1
CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (Parenthetical) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Interest charges and financing costs        
Other financing costs $ 485 $ 461 $ 963 $ 917
v3.10.0.1
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Comprehensive income:        
Net income $ 15,189 $ 14,241 $ 46,605 $ 36,660
Derivative instruments:        
Reclassification of losses to net income, net of tax of $9, $12, $17 and $24, respectively 23 19 46 38
Other comprehensive income 23 19 46 38
Comprehensive income $ 15,212 $ 14,260 $ 46,651 $ 36,698
v3.10.0.1
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Derivative instruments:        
Reclassification of losses to net income, tax $ 9 $ 12 $ 17 $ 24
v3.10.0.1
CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)
$ in Thousands
 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Operating activities    
Net income $ 46,605 $ 36,660
Adjustments to reconcile net income to cash provided by operating activities:    
Depreciation and amortization 62,840 55,434
Deferred income taxes 2,426 22,588
Amortization of investment tax credits (261) (262)
Allowance for equity funds used during construction (4,101) (3,038)
Net derivative losses 166 115
Other, net 506 (1,505)
Changes in operating assets and liabilities:    
Accounts receivable 2,571 (295)
Accrued unbilled revenues 14,811 10,846
Inventories 3,959 2,669
Other current assets (129) (58)
Accounts payable (8,236) 28,882
Net regulatory assets and liabilities 14,584 (3,112)
Other current liabilities (331) (9,191)
Pension and other employee benefit obligations (8,969) (8,735)
Change in other noncurrent assets 179 (359)
Change in other noncurrent liabilities 365 (2,696)
Net cash provided by operating activities 126,985 127,943
Investing activities    
Utility capital/construction expenditures (121,198) (90,735)
Allowance for equity funds used during construction 4,101 3,038
Other, net (104) (33)
Net cash used in investing activities (117,201) (87,730)
Financing activities    
Proceeds from (repayments of) short-term borrowings, net 19,000 (14,000)
Repayments of long-term debt (10) (27)
Capital contributions from parent 3,326 12,282
Dividends paid to parent (31,522) (38,800)
Other, net (413) (70)
Net cash used in financing activities (9,619) (40,615)
Net change in cash and cash equivalents 165 (402)
Cash and cash equivalents at beginning of period 1,403 1,546
Cash and cash equivalents at end of period 1,568 1,144
Supplemental disclosure of cash flow information:    
Cash paid for interest (net of amounts capitalized) (16,494) (15,062)
Cash paid for income taxes, net (12,495) (9,699)
Supplemental disclosure of non-cash investing transactions:    
Property, plant and equipment additions in accounts payable $ 18,785 $ 21,867
v3.10.0.1
CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Current assets    
Cash and cash equivalents $ 1,568 $ 1,403
Accounts receivable, net 60,880 63,200
Accrued unbilled revenues 45,197 60,008
Other Receivables 15,339 15,144
Inventories 13,798 17,758
Regulatory assets 22,933 23,113
Prepaid taxes 24,670 23,606
Prepayments and other 2,865 3,450
Total current assets 187,250 207,682
Property, plant and equipment, net 2,150,296 2,088,728
Other assets    
Regulatory assets 279,753 282,217
Other investments 3,001 2,892
Other 81 201
Total other assets 282,835 285,310
Total assets 2,620,381 2,581,720
Current liabilities    
Current portion of long-term debt 151,067 151,080
Short-term debt 30,000 11,000
Notes payable to affiliates 500 500
Accounts payable 44,930 58,365
Accounts payable to affiliates 25,859 29,628
Dividends payable to parent 16,463 15,481
Regulatory liabilities 41,243 20,712
Environmental liabilities 10,960 10,469
Accrued interest 8,226 8,025
Other 32,955 34,474
Total current liabilities 362,203 339,734
Deferred credits and other liabilities    
Deferred income taxes 260,506 256,687
Deferred investment tax credits 7,252 7,514
Regulatory liabilities 391,151 386,807
Environmental liabilities 18,258 19,190
Customer advances 17,553 16,325
Pension and employee benefit obligations 40,899 50,027
Other 18,085 18,747
Total deferred credits and other liabilities 753,704 755,297
Commitments and contingencies
Capitalization    
Long-term debt 610,161 610,100
Common stock — 1,000,000 shares authorized of $100 par value; 933,000 shares outstanding at June 30, 2018 and Dec. 31, 2017, respectively 93,300 93,300
Additional paid in capital 452,929 449,350
Retained earnings 348,107 334,008
Accumulated other comprehensive loss (23) (69)
Total common stockholder’s equity 894,313 876,589
Total liabilities and equity $ 2,620,381 $ 2,581,720
v3.10.0.1
CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares
Jun. 30, 2018
Dec. 31, 2017
Capitalization    
Common stock, shares authorized (in shares) 1,000,000 1,000,000
Common stock, par value (in dollars per share) $ 100 $ 100
Common stock, shares outstanding (in shares) 933,000 933,000
v3.10.0.1
Management's Opinion
 6 Months Ended
Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]  
Management's Opinion
In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly, in accordance with accounting principles generally accepted in the United States of America (GAAP), the financial position of NSP-Wisconsin and its subsidiaries as of June 30, 2018 and Dec. 31, 2017; the results of its operations, including the components of net income and comprehensive income, for the three and six months ended June 30, 2018 and 2017; and its cash flows for the six months ended June 30, 2018 and 2017. All adjustments are of a normal, recurring nature, except as otherwise disclosed. Management has also evaluated the impact of events occurring after June 30, 2018 up to the date of issuance of these consolidated financial statements. These statements contain all necessary adjustments and disclosures resulting from that evaluation. The Dec. 31, 2017 balance sheet information has been derived from the audited 2017 consolidated financial statements included in the NSP-Wisconsin Annual Report on Form 10-K for the year ended Dec. 31, 2017, as amended by the NSP-Wisconsin Amendment No. 1 to its Annual Report on Form 10-K/A, filed with the SEC on July 27, 2018. 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-Wisconsin Annual Report on Form 10-K for the year ended Dec. 31, 2017, filed with the SEC on Feb. 26, 2018, as amended by the NSP-Wisconsin Amendment No. 1 to its Annual Report on Form 10-K/A, filed with the SEC on July 27, 2018. Due to the seasonality of NSP-Wisconsin’s electric and natural gas sales, interim results are not necessarily an appropriate base from which to project annual results.
v3.10.0.1
Summary of Significant Accounting Policies
 6 Months Ended
Jun. 30, 2018
Accounting Policies [Abstract]  
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies

The significant accounting policies set forth in Note 1 to the consolidated financial statements in the NSP-Wisconsin Annual Report on Form 10-K for the year ended Dec. 31, 2017, as amended by the NSP-Wisconsin Amendment No. 1 to its Annual Report on Form 10-K/A, filed with the SEC on July 27, 2018, appropriately represent, in all material respects, the current status of accounting policies and are incorporated herein by reference.
v3.10.0.1
Accounting Pronouncements
 6 Months Ended
Jun. 30, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]  
Accounting Pronouncements
Accounting Pronouncements

Recently Issued

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

Recently Adopted

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

Classification and Measurement of Financial Instruments — In January 2016, the FASB issued Recognition and Measurement of Financial Assets and Financial Liabilities, Subtopic 825-10 (ASU No. 2016-01), which eliminated the available-for-sale classification for marketable equity securities and also replaced the cost method of accounting for non-marketable equity securities with a model for recognizing impairments and observable price changes. Under the new standard, other than when the consolidation or equity method of accounting is utilized, changes in the fair value of equity securities are recognized in earnings. NSP-Wisconsin implemented the guidance on Jan. 1, 2018 and the implementation did not have a material impact on its consolidated financial statements.

Presentation of Net Periodic Benefit Cost — In March 2017, the FASB issued Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost, Topic 715 (ASU No. 2017-07), which establishes that only the service cost element of pension cost may be presented as a component of operating income in the income statement. Also under the guidance, only the service cost component of pension cost is eligible for capitalization. As a result of the application of accounting principles for rate regulated entities, a similar amount of pension cost, including non-service components, will be recognized consistent with the historical ratemaking treatment, and the impacts of adoption will be limited to changes in classification of non-service costs in the consolidated statement of income. NSP-Wisconsin implemented the new guidance on Jan. 1, 2018, and as a result, $1.4 million of pension costs were retrospectively reclassified from operating and maintenance expenses to other income, net on the consolidated income statement for the six months ended June 30, 2017. Under a practical expedient permitted by the standard, NSP-Wisconsin used benefit cost amounts disclosed for prior periods as the basis for retrospective application.
v3.10.0.1
Selected Balance Sheet Data
 6 Months Ended
Jun. 30, 2018
Balance Sheet Related Disclosures [Abstract]  
Selected Balance Sheet Data
Selected Balance Sheet Data
(Thousands of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
Accounts receivable, net (a)
 
 
 
 
Accounts receivable
 
$
65,606

 
$
68,073

Less allowance for bad debts
 
(4,726
)
 
(4,873
)
 
 
$
60,880

 
$
63,200



(a) 
Accounts receivable, net includes $3.8 million and $3.4 million due from affiliates as of June 30, 2018 and Dec. 31, 2017, respectively.

(Thousands of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
Inventories
 
 
 
 
Materials and supplies
 
$
6,879

 
$
6,916

Fuel
 
3,780

 
3,866

Natural gas
 
3,139

 
6,976

 
 
$
13,798

 
$
17,758


(Thousands of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
Property, plant and equipment, net
 
 
 
 
Electric plant
 
$
2,632,764

 
$
2,602,671

Natural gas plant
 
334,329

 
326,723

Common and other property
 
187,120

 
181,105

Construction work in progress
 
205,502

 
148,770

Total property, plant and equipment
 
3,359,715

 
3,259,269

Less accumulated depreciation
 
(1,209,419
)
 
(1,170,541
)
 
 
$
2,150,296

 
$
2,088,728
v3.10.0.1
Income Taxes
 6 Months Ended
Jun. 30, 2018
Income Tax Disclosure [Abstract]  
Income Taxes
Income Taxes

Except to the extent noted below, Note 6 to the consolidated financial statements included in the NSP-Wisconsin Annual Report on Form 10-K for the year ended Dec. 31, 2017, as amended by the NSP-Wisconsin Amendment No. 1 to its Annual Report on Form 10-K/A, filed with the SEC on July 27, 2018, appropriately represents, in all material respects, the current status of other income tax matters, and are incorporated herein by reference.

Total income tax expense from operations differs from the amount computed by applying the statutory federal income tax rate to income before income tax expense. The following reconciles such differences:
 
 
Six Months Ended June 30
 
 
2018
 
2017
Federal statutory rate
 
21.0
 %
 
35.0
 %
State tax, net of federal tax effect
 
6.2

 
5.1

Increases (decreases) in tax from:
 

 

Regulatory differences - ARAM (a)
 
(4.7
)
 
(0.1
)
Regulatory differences - ARAM deferral (b)
 
4.6

 
—

Regulatory differences - other utility plant items
 
(1.6
)
 
(1.2
)
Tax credits, net of federal income tax expense
 
(0.9
)
 
(0.7
)
Other, net
 
0.5

 
(0.1
)
Effective income tax rate
 
25.1
 %
 
38.0
 %

(a)  
The average rate assumption method (ARAM); a method to flow back excess deferred taxes to customers.
(b)
As we receive direction from our regulatory commissions regarding the return of excess deferred taxes (to our customers resulting from the Tax Cuts and Jobs Act
(TCJA)), the ARAM deferral may decrease during the year, which would result in a reduction to tax expense with a corresponding reduction to revenue.

Federal Audits — NSP-Wisconsin is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. The statute of limitations applicable to Xcel Energy’s federal income tax returns expire as follows:
Tax Year(s)
 
Expiration
2009 - 2011
 
December 2018
2012 - 2014
 
October 2019
2015
 
September 2019
2016
 
September 2020


In 2012, the Internal Revenue Service (IRS) commenced an examination of tax years 2010 and 2011, including the 2009 carryback claim. The IRS proposed an adjustment to the federal tax loss carryback claims and in 2015 the IRS forwarded the issue to the Office of Appeals (Appeals). In 2017 Xcel Energy and Appeals reached an agreement and the benefit related to the agreed upon portions was recognized. NSP-Wisconsin did not accrue any income tax benefit related to this adjustment. In the second quarter of 2018, the Joint Committee on Taxation completed its review and took no exception to the agreement. As a result, the remaining unrecognized tax benefit was released and recorded as a payable to the IRS.

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

State Audits — NSP-Wisconsin is a member of the Xcel Energy affiliated group that files consolidated state income tax returns. As of June 30, 2018, NSP-Wisconsin’s earliest open tax year that is subject to examination by state taxing authorities under applicable statutes of limitations is 2012. In 2016, the state of Wisconsin began an audit of years 2012 and 2013. As of June 30, 2018, NSP-Wisconsin is evaluating the state’s proposed audit adjustments. No material accruals are expected. There were no other state income tax audits in progress.

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


A reconciliation of the amount of unrecognized tax benefit is as follows:
(Millions of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
Unrecognized tax benefit — Permanent tax positions
 
$
1.8

 
$
1.4

Unrecognized tax benefit — Temporary tax positions
 
0.9

 
1.0

Total unrecognized tax benefit
 
$
2.7

 
$
2.4



The unrecognized tax benefit amounts were reduced by the tax benefits associated with NOL and tax credit carryforwards. The amounts of tax benefits associated with NOL and tax credit carryforwards are as follows:
(Millions of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
NOL and tax credit carryforwards
 
$
(2.1
)
 
$
(1.9
)


It is reasonably possible that NSP-Wisconsin’s amount of unrecognized tax benefits could significantly change in the next 12 months as the IRS Appeals progresses and audit resumes, the Wisconsin audit progresses, and other state audits resume. As the IRS Appeals and Wisconsin audit progress and the IRS audit resumes, it is reasonably possible that the amount of unrecognized tax benefit could decrease up to approximately $2 million.

The payable for interest related to unrecognized tax benefits is partially offset by the interest benefit associated with NOL and tax credit carryforwards. The payables for interest related to unrecognized tax benefits at June 30, 2018 and Dec. 31, 2017 were not material. No amounts were accrued for penalties related to unrecognized tax benefits as of June 30, 2018 or Dec. 31, 2017.
v3.10.0.1
Rate Matters Rate Matters
 6 Months Ended
Jun. 30, 2018
Public Utilities, General Disclosures [Abstract]  
Rate Matters
Rate Matters

Except to the extent noted below, the circumstances set forth in Note 10 to the consolidated financial statements included in the NSP-Wisconsin Annual Report on Form 10-K for the year ended Dec. 31, 2017, as amended by the NSP-Wisconsin Amendment No. 1 to its Annual Report on Form 10-K/A, filed with the SEC on July 27, 2018, and in Note 5 to the consolidated financial statements to NSP-Wisconsin's Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018, appropriately represent, in all material respects, the current status of other rate matters, and are incorporated herein by reference.

Tax Reform — Regulatory Proceedings

In May 2018, the Public Service Commission of Wisconsin (PSCW) issued its final order which requires customer refunds of $27 million and defers approximately $5 million until NSP-Wisconsin’s next rate case proceeding.

NSP-Wisconsin — Michigan — In May 2018, the Michigan Public Service Commission (MPSC) approved electric and natural gas tax reform settlement agreements. Most of the electric TCJA benefits were included in NSP-Wisconsin’s recently approved Michigan 2018 electric base rate case. Natural gas TCJA benefits are to be returned to customers commencing in July 2018.

Recently Concluded Regulatory Proceeding — MPSC

Michigan 2018 Electric Gas Rate Case — In November 2017, NSP-Wisconsin filed a request with the MPSC to increase rates for electric service by $1 million, or 7.1 percent. The filing was based on a 2018 forecast test year, a 10.1 percent return on equity (ROE), an equity ratio of 52.5 percent and a forecasted average rate base of approximately $43 million. The primary driver of the requested increase is continuing investment in transmission and distribution infrastructure. The filing also included a request for step increases in 2019 and 2020 related to electric distribution system investments in those years. In addition to the MPSC staff, intervenors in the case include the Michigan Attorney General and the Association of Businesses Advocating Tariff Equity, a voluntary association of large industrial businesses.

In March 2018, NSP-Wisconsin reached a settlement in principle with the parties authorizing a 2018 rate increase of approximately $300 thousand, or approximately 2.0 percent, which reflects a portion of the TCJA benefits. The settlement was based on a 9.8 percent ROE and a 52.5 percent equity ratio. In April 2018, the MPSC issued an order approving the settlement agreement, and new rates were implemented on May 1, 2018.

Pending Regulatory Proceeding — Federal Energy Regulatory Commission (FERC)

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

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

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

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

v3.10.0.1
Commitments and Contingencies
 6 Months Ended
Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]  
Commitments and Contingencies
Commitments and Contingencies

Except to the extent noted below and in Note 5 to the financial statements, the circumstances set forth in Notes 10 and 11 to the consolidated financial statements included in the NSP-Wisconsin Annual Report on Form 10-K for the year ended Dec. 31, 2017, as amended by the NSP-Wisconsin Amendment No. 1 to its Annual Report on Form 10-K/A, filed with the SEC on July 27, 2018, and in Notes 5 and 6 to NSP-Wisconsin's Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018, appropriately represent, in all material respects, the current status of commitments and contingent liabilities and are incorporated herein by reference. The following include commitments, contingencies and unresolved contingencies that are material to NSP-Wisconsin’s financial position.

Guarantees

NSP-Wisconsin provides a guarantee for payment of customer loans related to NSP-Wisconsin’s farm rewiring program. NSP-Wisconsin’s exposure under the guarantee is based upon the net liability under the agreement. The guarantee issued by NSP-Wisconsin has a stated maximum amount. The guarantee contains no recourse provisions and requires no collateral. These agreements have expiration dates through 2020.

The following table presents the guarantee issued and outstanding for NSP-Wisconsin:
(Millions of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
Guarantee issued and outstanding
 
$
1.0

 
$
1.0

Current exposure under this guarantee
 
—

 
—



Environmental Contingencies

Ashland Manufactured Gas Plant (MGP) Site — NSP-Wisconsin was named a potentially responsible party for contamination at a site in Ashland, Wis. The Ashland/Northern States Power Lakefront Superfund Site (the Site) includes NSP-Wisconsin property, previously operated as a MGP facility (the Upper Bluff), an adjacent city lakeshore park area (Kreher Park) (collectively the Phase I Area); and a sediment area of Lake Superior’s Chequamegon Bay (Phase II Area). NSP-Wisconsin initiated a wet dredge remedy of the Phase II area in 2017. NSP-Wisconsin anticipates completion of Phase II activities in 2018 with final site restoration activities in early 2019. Groundwater treatment activities at the Site will continue for many years.

The current cost estimate for the remediation of the entire site is approximately $175 million, of which approximately $146 million has been spent. As of June 30, 2018 and Dec. 31, 2017, NSP-Wisconsin recorded a total liability of $29 million and $30 million, respectively, for the entire site.

NSP-Wisconsin has deferred the unrecovered portion of the estimated Site remediation costs as a regulatory asset. The PSCW has authorized NSP-Wisconsin rate recovery for all remediation costs incurred at the Site. In 2012, the PSCW agreed to allow NSP-Wisconsin to pre-collect certain costs, to amortize costs over a ten-year period and to apply a three percent carrying cost to the unamortized regulatory asset. In December 2017, the PSCW approved an NSP-Wisconsin natural gas rate case, which included recovery of additional expenses associated with remediating the Site. The annual recovery of MGP clean-up costs increased from $12 million in 2017 to $18 million in 2018.

Other MGP, Landfill or Disposal Sites — In addition to the Ashland MGP Site, NSP-Wisconsin is currently involved in investigating and/or remediating an MGP, landfill or other disposal site. NSP-Wisconsin has identified one site where contamination is present and where investigation and/or remediation activities are currently underway. Other parties may have responsibility for some portion of the investigation and/or remediation activities. NSP-Wisconsin anticipates that these investigation or remediation activities will continue through at least 2018. NSP-Wisconsin accrued $0.1 million for this site as of June 30, 2018 and Dec. 31, 2017. NSP-Wisconsin anticipates that any amounts spent will be fully recovered from customers.
Legal Contingencies

NSP-Wisconsin 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-Wisconsin’s financial statements. Unless otherwise required by GAAP, legal fees are expensed as incurred.

Employment, Tort and Commercial Litigation

Gas Trading Litigation — e prime, inc. (e prime) is a wholly owned subsidiary of Xcel Energy. e prime was in the business of natural gas trading and marketing but has not engaged in natural gas trading or marketing activities since 2003.  Thirteen lawsuits were commenced against e prime and Xcel Energy (and NSP-Wisconsin, in two instances) between 2003 and 2009 alleging fraud and anticompetitive activities in conspiring to restrain the trade of natural gas and manipulate natural gas prices.

e prime, Xcel Energy Inc. and its other affiliates were sued along with several other gas marketing companies. These cases were all consolidated in the U.S. District Court in Nevada. Six of the cases remain active, which includes a multi-district litigation (MDL) matter consisting of a Colorado class (Breckenridge), a Wisconsin class (Arandell Corp.), a Missouri class, a Kansas class, and two other cases identified as “Sinclair Oil” and “Farmland.” In March 2017, summary judgment was granted by the MDL judge in favor of Xcel Energy and e prime in the Sinclair Oil and Farmland cases. In November 2017, the U.S. District Court in Nevada granted summary judgment against two plaintiffs in the Arandell Corp. case in favor of Xcel Energy and NSP-Wisconsin, leaving only three individual plaintiffs remaining in the litigation. In addition, the plaintiffs’ motions for class certification and remand back to originating courts in these cases were denied in March 2017. Plaintiffs appealed the summary judgment motions granted in the Farmland and Sinclair Oil cases and the denial of class certification and remand to the U.S. Court of Appeals for the Ninth Circuit (Ninth Circuit). In March 2018, the Ninth Circuit reversed and remanded the summary judgment in the Farmland case. The Farmland defendants subsequently filed a request for further review by the Ninth Circuit, which was denied. In light of the decision in the Farmland case, the Sinclair plaintiffs have requested the Ninth Circuit to reverse the grant of summary judgment without hearing. Oral arguments were presented to the Ninth Circuit in July 2018 regarding this issue and the denial of class certification and it is uncertain when a decision will be issued. In addition, Xcel Energy, NSP-Wisconsin and e prime have concluded that a loss is remote.
v3.10.0.1
Borrowings and Other Financing Instruments
 6 Months Ended
Jun. 30, 2018
Debt Disclosure [Abstract]  
Borrowings and Other Financing Instruments
Borrowings and Other Financing Instruments

Commercial Paper — NSP-Wisconsin meets its short-term liquidity requirements primarily through the issuance of commercial paper and borrowings under its credit facility. Commercial paper outstanding for NSP-Wisconsin was as follows:
(Amounts in Millions, Except Interest Rates)
 
Three Months Ended June 30, 2018
 
Year Ended Dec. 31, 2017
Borrowing limit
 
$
150

 
$
150

Amount outstanding at period end
 
30

 
11

Average amount outstanding
 
18

 
52

Maximum amount outstanding
 
41

 
129

Weighted average interest rate, computed on a daily basis
 
2.20
%
 
1.23
%
Weighted average interest rate at period end
 
2.29

 
1.73



Letters of Credit — NSP-Wisconsin uses letters of credit, generally with terms of one year, to provide financial guarantees for certain operating obligations. At June 30, 2018 and Dec. 31, 2017, there were no letters of credit outstanding.

Credit Facility — In order to use its commercial paper program to fulfill short-term funding needs, NSP-Wisconsin 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 aggregate amount exceeding available capacity under this credit facility.  The line of credit provides short-term financing in the form of notes payable to banks, letters of credit and back-up support for commercial paper borrowings.

At June 30, 2018, NSP-Wisconsin had the following committed credit facility available (in millions of dollars):
Credit Facility (a)
 
Drawn (b)
 
Available
$
150

 
$
30

 
$
120


(a) 
This credit facility expires in June 2021.
(b) 
Includes outstanding commercial paper.

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

Other Short-Term Borrowings — The following table presents the notes payable of Clearwater Investments, Inc., a NSP-Wisconsin subsidiary, to Xcel Energy Inc.:
(Amounts in Millions, Except Interest Rates)
 
June 30, 2018
 
Dec. 31, 2017
Notes payable to affiliates
 
$
0.5

 
$
0.5

Weighted average interest rate at period end
 
2.53
%
 
1.73
%
v3.10.0.1
Fair Value of Financial Assets and Liabilities
 6 Months Ended
Jun. 30, 2018
Fair Value Disclosures [Abstract]  
Fair Value of Financial Assets and Liabilities
Fair Value of Financial Assets and Liabilities

Fair Value Measurements

The accounting guidance for fair value measurements and 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 values.

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

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

Derivative Instruments Fair Value Measurements

NSP-Wisconsin 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 and utility commodity prices.

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

At June 30, 2018, accumulated other comprehensive loss related to interest rate derivatives included immaterial 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.

Commodity Derivatives — NSP-Wisconsin may enter 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 natural gas to generate electric energy and natural gas for resale.

The following table details the gross notional amounts of commodity options at June 30, 2018 and Dec. 31, 2017:
(Amounts in Thousands) (a)(b)
 
June 30, 2018
 
Dec. 31, 2017
Million British thermal units of natural gas
 
58

 
42


(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 Activities on Income and Accumulated Other Comprehensive Loss — There were immaterial pre-tax losses related to interest rate derivatives reclassified from accumulated other comprehensive loss into earnings during the three months ended June 30, 2018 and 2017. There were $0.1 million of net losses reclassified from accumulated other comprehensive loss into earnings during both the six months ended June 30, 2018 and 2017.

During the three and six months ended June 30, 2018, changes in the fair value of natural gas commodity derivatives resulted in immaterial net losses recognized as regulatory assets and liabilities. For the three and six months ended June 30, 2017, changes in the fair value of natural gas commodity derivatives resulted in immaterial and $0.1 million of net losses recognized as regulatory assets and liabilities, respectively. The classification as a regulatory asset or liability is based on commission approved regulatory recovery mechanisms.

There were no natural gas commodity derivative settlement gains or losses recognized and $0.2 million of losses recognized for the six months ended June 30, 2018 and 2017, respectively, and were subject to purchased natural gas cost recovery mechanisms, which result in reclassifications of derivative settlement gains and losses out of income to a regulatory asset or liability, as appropriate. There were no gains or losses recognized during the three months ended June 30, 2018 and 2017.

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

Consideration of Credit Risk and Concentrations — NSP-Wisconsin 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-Wisconsin’s own credit risk when determining the fair value of derivative liabilities, the impact of credit risk was immaterial to the fair value of unsettled commodity derivatives presented in the consolidated balance sheets.

NSP-Wisconsin 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.

Recurring Fair Value Measurements — The following table presents for each of the fair value hierarchy levels, NSP-Wisconsin’s derivative assets and liabilities measured at fair value on a recurring basis:
 
 
June 30, 2018
 
 
Fair Value
 
Fair Value
Total
 
Counterparty
Netting (a)
 
Total (b)
(Thousands of Dollars)
 
Level 1
 
Level 2
 
Level 3
 
 
 
Current derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Natural gas commodity
 
$
—

 
$
28

 
$
—

 
$
28

 
$
—

 
$
28

 
 
Dec. 31, 2017
 
 
Fair Value
 
Fair Value
Total
 
Counterparty
Netting (a)
 
Total (b)
(Thousands of Dollars)
 
Level 1
 
Level 2
 
Level 3
 
 
 
Current derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Natural gas commodity
 
$
—

 
$
14

 
$
—

 
$
14

 
$
—

 
$
14


(a) 
NSP-Wisconsin nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at June 30, 2018 and Dec. 31, 2017.  The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.
(b) 
Included in prepayments and other current assets balance of $2.9 million and $3.5 million at June 30, 2018 and Dec. 31, 2017, respectively, in the consolidated balance sheets.

Fair Value of Long-Term Debt

As of June 30, 2018 and Dec. 31, 2017, other financial instruments for which the carrying amount did not equal fair value were as follows:
 
 
June 30, 2018
 
Dec. 31, 2017
(Thousands of Dollars)
 
Carrying Amount
 
Fair Value
 
Carrying Amount
 
Fair Value
Long-term debt, including current portion
 
$
761,228

 
$
816,474

 
$
761,180

 
$
856,106



The fair value of NSP-Wisconsin’s long-term debt is estimated based on recent trades and observable spreads from benchmark interest rates for similar securities. The fair value estimates are based on information available to management as of June 30, 2018 and Dec. 31, 2017, and given the observability of the inputs to these estimates, the fair values presented for long-term debt have been assigned a Level 2.
v3.10.0.1
Other Income, Net
 6 Months Ended
Jun. 30, 2018
Other Income and Expenses [Abstract]  
Other Income, Net
Other Expense, Net

Other expense, net consisted of the following:
 
 
Three Months Ended June 30
 
Six Months Ended June 30
(Thousands of Dollars)
 
2018
 
2017
 
2018
 
2017
Interest (expense) income
 
$
(15
)
 
$
61

 
$
141

 
$
204

Other nonoperating income
 
42

 
75

 
48

 
230

Other nonoperating expense
 
(3
)
 
(4
)
 
(7
)
 
(7
)
Insurance policy expense
 
(47
)
 
(49
)
 
(94
)
 
(98
)
Benefits non-service cost
 
(486
)
 
(678
)
 
(957
)
 
(1,356
)
Other expense, net
 
$
(509
)
 
$
(595
)
 
$
(869
)
 
$
(1,027
)
v3.10.0.1
Segment Information
 6 Months Ended
Jun. 30, 2018
Segment Reporting [Abstract]  
Segment Information
Segment Information

Operating results from the regulated electric utility and regulated natural gas utility are each separately and regularly reviewed by NSP-Wisconsin’s chief operating decision maker.  NSP-Wisconsin 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-Wisconsin has the following reportable segments: regulated electric utility, regulated natural gas utility and all other.

•
NSP-Wisconsin’s regulated electric utility segment generates, transmits and distributes electricity primarily in portions of Wisconsin and Michigan. 
•
NSP-Wisconsin’s regulated natural gas utility segment purchases, transports, stores and distributes natural gas primarily in portions of Wisconsin and Michigan.
•
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 investments in rental housing projects that qualify for low-income housing tax credits.

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

To report income from operations for regulated electric and regulated natural gas utility segments, the majority of costs are directly assigned to each segment.  However, some costs, such as common depreciation, common operating and maintenance (O&M) expenses and interest expense are allocated based on cost causation allocators.  A general allocator is used for certain general and administrative expenses, including office supplies, rent, property insurance and general advertising.
(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Reconciling Eliminations
 
Consolidated Total
Three Months Ended June 30, 2018
 
 
 
 
 
 
 
 
 
 
Operating revenues (a)
 
$
209,502

 
$
21,981

 
$
271

 
$
—

 
$
231,754

Intersegment revenues
 
106

 
127

 
—

 
(233
)
 
—

Total revenues
 
$
209,608

 
$
22,108

 
$
271

 
$
(233
)
 
$
231,754

Net income (loss)
 
$
15,481

 
$
(148
)
 
$
(144
)
 
$
—

 
$
15,189

(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Reconciling Eliminations
 
Consolidated Total
Three Months Ended June 30, 2017
 
 
 
 
 
 
 
 
 
 
Operating revenues (a)
 
$
210,742

 
$
19,027

 
$
257

 
$
—

 
$
230,026

Intersegment revenues
 
123

 
68

 
—

 
(191
)
 
—

Total revenues
 
$
210,865

 
$
19,095

 
$
257

 
$
(191
)
 
$
230,026

Net income (loss)
 
$
14,516

 
$
(973
)
 
$
698

 
$
—

 
$
14,241


(a) 
Operating revenues include $38 million and $43 million of affiliate electric revenue for the three months ended June 30, 2018 and 2017, respectively.

(Thousands of Dollars)
 
Regulated
Electric
 
Regulated
Natural Gas
 
All
Other
 
Reconciling
Eliminations
 
Consolidated
Total
Six Months Ended June 30, 2018
 
 
 
 
 
 
 
 
 
 
Operating revenues (a)
 
$
425,868

 
$
78,481

 
$
549

 
$
—

 
$
504,898

Intersegment revenues
 
215

 
275

 
—

 
(490
)
 
—

Total revenues
 
$
426,083

 
$
78,756

 
$
549

 
$
(490
)
 
$
504,898

Net income
 
$
35,925

 
$
10,250

 
$
430

 
$
—

 
$
46,605

(Thousands of Dollars)
 
Regulated
Electric
 
Regulated
Natural Gas
 
All
Other
 
Reconciling
Eliminations
 
Consolidated
Total
Six Months Ended June 30, 2017
 
 
 
 

 
 
 
 
 
 
Operating revenues (a)
 
$
427,051

 
$
67,374

 
$
532

 
$
—

 
$
494,957

Intersegment revenues
 
219

 
182

 
—

 
(401
)
 
—

Total revenues
 
$
427,270

 
$
67,556

 
$
532

 
$
(401
)
 
$
494,957

Net income
 
$
29,986

 
$
5,572

 
$
1,102

 
$
—

 
$
36,660


(a) 
Operating revenues include $76 million and $85 million of affiliate electric revenue for the six months ended June 30, 2018 and 2017, respectively.
v3.10.0.1
Benefit Plans and Other Postretirement Benefits
 6 Months Ended
Jun. 30, 2018
Retirement Benefits [Abstract]  
Benefit Plans and Other Postretirement Benefits
Benefit Plans and Other Postretirement Benefits

Components of Net Periodic Benefit Cost
 
 
Three Months Ended June 30
 
 
2018
 
2017
 
2018
 
2017
(Thousands of Dollars)
 
Pension Benefits
 
Postretirement Health
Care Benefits
Service cost
 
$
1,194

 
$
1,155

 
$
9

 
$
7

Interest cost (a)
 
1,360

 
1,555

 
142

 
148

Expected return on plan assets (a)
 
(2,257
)
 
(2,295
)
 
(16
)
 
(8
)
Amortization of prior service (credit) cost (a)
 
(6
)
 
34

 
(88
)
 
(88
)
Amortization of net loss (a)
 
1,419

 
1,461

 
139

 
109

Net periodic benefit cost
 
1,710

 
1,910

 
186

 
168

Costs not recognized due to the effects of regulation
 
—

 
—

 
—

 
—

Net benefit cost recognized for financial reporting
 
$
1,710

 
$
1,910

 
$
186

 
$
168


 
 
Six Months Ended June 30
 
 
2018

2017

2018

2017
(Thousands of Dollars)
 
Pension Benefits
 
Postretirement Health
Care Benefits
Service cost
 
$
2,389

 
$
2,309

 
$
18

 
$
14

Interest cost (a)
 
2,720

 
3,109

 
284

 
296

Expected return on plan assets (a)
 
(4,513
)
 
(4,590
)
 
(32
)
 
(16
)
Amortization of prior service (credit) cost (a)
 
(14
)
 
69

 
(176
)
 
(176
)
Amortization of net loss (a)
 
2,837

 
2,923

 
278

 
218

Net periodic benefit cost
 
3,419

 
3,820

 
372

 
336

Credits not recognized due to the effects of regulation
 
221

 
—

 
—

 
—

Net benefit cost recognized for financial reporting
 
$
3,640

 
$
3,820

 
$
372

 
$
336


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

In January 2018, contributions of $150 million were made across four of Xcel Energy’s pension plans, of which $10.0 million was attributable to NSP-Wisconsin. Xcel Energy does not expect additional pension contributions during 2018.
v3.10.0.1
Other Comprehensive Income
 6 Months Ended
Jun. 30, 2018
Stockholders' Equity Note [Abstract]  
Other Comprehensive Income
Other Comprehensive Income (Loss)

Changes in accumulated other comprehensive loss, net of tax, for the three and six months ended June 30, 2018 and 2017 were as follows:
 
 
Gains and Losses on
Cash Flow Hedges
(Thousands of Dollars)
 
Three Months Ended June 30, 2018
 
Three Months Ended June 30, 2017
Accumulated other comprehensive loss at April 1
 
$
(46
)
 
$
(114
)
Losses reclassified from net accumulated other comprehensive loss
 
23

 
19

Net current period other comprehensive income
 
23

 
19

Accumulated other comprehensive loss at June 30
 
$
(23
)
 
$
(95
)
 
 
Gains and Losses on
Cash Flow Hedges
(Thousands of Dollars)
 
Six Months Ended June 30, 2018
 
Six Months Ended June 30, 2017
Accumulated other comprehensive loss at Jan. 1
 
$
(69
)
 
$
(133
)
Losses reclassified from net accumulated other comprehensive loss
 
46

 
38

Net current period other comprehensive income
 
46

 
38

Accumulated other comprehensive loss at June 30
 
$
(23
)
 
$
(95
)


Reclassifications from accumulated other comprehensive loss for the three and six months ended June 30, 2018 and 2017 were as follows:
 
 
Amounts Reclassified from
Accumulated Other
Comprehensive Loss
 
(Thousands of Dollars)
 
Three Months Ended June 30, 2018
 
Three Months Ended June 30, 2017
 
Losses on cash flow hedges:
 
 
 
 
 
Interest rate derivatives
 
$
32

(a) 
$
31

(a) 
Total, pre-tax
 
32

 
31

 
Tax benefit
 
(9
)
 
(12
)
 
Total amounts reclassified, net of tax
 
$
23

 
$
19

 
 
 
Amounts Reclassified from
Accumulated Other
Comprehensive Loss
 
(Thousands of Dollars)
 
Six Months Ended June 30, 2018
 
Six Months Ended June 30, 2017
 
Losses on cash flow hedges:
 
 
 
 
 
Interest rate derivatives
 
$
63

(a) 
$
62

(a) 
Total, pre-tax
 
63

 
62

 
Tax benefit
 
(17
)
 
(24
)
 
Total amounts reclassified, net of tax
 
$
46

 
$
38

 

(a) 
Included in interest charges.
v3.10.0.1
Revenues
 6 Months Ended
Jun. 30, 2018
Revenue from Contract with Customer [Abstract]  
Revenues
Revenues

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

NSP-Wisconsin has various rate-adjustment mechanisms in place that provide for the recovery of natural gas, electric fuel and purchased energy costs. These cost-adjustment tariffs may increase or decrease the level of revenue collected from customers and are revised periodically for differences between the total amount collected under the clauses and the costs incurred. When applicable,
under governing regulatory commission rate orders, fuel cost over-recoveries (the excess of fuel revenue billed to customers over fuel
costs incurred) are deferred as regulatory liabilities and under-recoveries (the excess of fuel costs incurred over fuel revenues billed to
customers) are deferred as regulatory assets. NSP-Wisconsin must submit a forward looking fuel cost plan annually for approval by the PSCW. The rules also allow for deferral of any under-recovery or over-recovery of fuel costs in excess of a two percent annual tolerance band, for future rate recovery or refund, subject to PSCW approval.

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

In the following tables, revenue is classified by the type of goods/services rendered and market/customer type. The tables also reconcile revenue to the reportable segments.
 
 
Three Months Ended June 30, 2018
(Thousands of Dollars)
 
Electric
 
Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
58,734

 
$
10,912

 
$
10

 
$
69,656

Commercial and industrial (C&I)
 
106,367

 
9,407

 
25

 
115,799

Other
 
1,782

 
—

 
236

 
2,018

Total retail
 
166,883

 
20,319

 
271

 
187,473

Interchange
 
38,370

 
—

 
—

 
38,370

Other
 
1,360

 
1,069

 
—

 
2,429

Total revenue from contracts with customers
 
206,613

 
21,388

 
271

 
228,272

Alternative revenue and other
 
2,889

 
593

 
—

 
3,482

Total revenues
 
$
209,502

 
$
21,981

 
$
271

 
$
231,754

 
 
Three Months Ended June 30, 2017
(Thousands of Dollars)
 
Electric
 
Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
54,754

 
$
9,015

 
$
—

 
$
63,769

C&I
 
107,899

 
8,577

 
27

 
116,503

Other
 
1,678

 
—

 
230

 
1,908

Total retail
 
164,331

 
17,592

 
257

 
182,180

Interchange
 
42,965

 
—

 
—

 
42,965

Other
 
523

 
910

 
—

 
1,433

Total revenue from contracts with customers
 
207,819

 
18,502

 
257

 
226,578

Alternative revenue and other
 
2,923

 
525

 
—

 
3,448

Total revenues
 
$
210,742

 
$
19,027

 
$
257

 
$
230,026

 
 
Six Months Ended June 30, 2018
(Thousands of Dollars)
 
Electric
 
Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
126,537

 
$
41,238

 
$
26

 
$
167,801

Commercial and industrial (C&I)
 
211,184

 
33,957

 
50

 
245,191

Other
 
3,388

 
—

 
473

 
3,861

Total retail
 
341,109

 
75,195

 
549

 
416,853

Interchange
 
76,044

 
—

 
—

 
76,044

Other
 
2,864

 
2,076

 
—

 
4,940

Total revenue from contracts with customers
 
420,017

 
77,271

 
549

 
497,837

Alternative revenue and other
 
5,851

 
1,210

 
—

 
7,061

Total revenues
 
$
425,868

 
$
78,481

 
$
549

 
$
504,898

 
 
Six Months Ended June 30, 2017
(Thousands of Dollars)
 
Electric
 
Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
120,797

 
$
35,643

 
$
20

 
$
156,460

C&I
 
210,279

 
28,835

 
51

 
239,165

Other
 
3,198

 
—

 
461

 
3,659

Total retail
 
334,274

 
64,478

 
532

 
399,284

Interchange
 
85,343

 
—

 
—

 
85,343

Other
 
1,492

 
1,818

 
—

 
3,310

Total revenue from contracts with customers
 
421,109

 
66,296

 
532

 
487,937

Alternative revenue and other
 
5,942

 
1,078

 
—

 
7,020

Total revenues
 
$
427,051

 
$
67,374

 
$
532

 
$
494,957
v3.10.0.1
Selected Balance Sheet Data (Tables)
 6 Months Ended
Jun. 30, 2018
Balance Sheet Related Disclosures [Abstract]  
Accounts Receivable, Net
(Thousands of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
Accounts receivable, net (a)
 
 
 
 
Accounts receivable
 
$
65,606

 
$
68,073

Less allowance for bad debts
 
(4,726
)
 
(4,873
)
 
 
$
60,880

 
$
63,200
Inventories
(Thousands of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
Inventories
 
 
 
 
Materials and supplies
 
$
6,879

 
$
6,916

Fuel
 
3,780

 
3,866

Natural gas
 
3,139

 
6,976

 
 
$
13,798

 
$
17,758
Property, Plant and Equipment, Net
(Thousands of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
Property, plant and equipment, net
 
 
 
 
Electric plant
 
$
2,632,764

 
$
2,602,671

Natural gas plant
 
334,329

 
326,723

Common and other property
 
187,120

 
181,105

Construction work in progress
 
205,502

 
148,770

Total property, plant and equipment
 
3,359,715

 
3,259,269

Less accumulated depreciation
 
(1,209,419
)
 
(1,170,541
)
 
 
$
2,150,296

 
$
2,088,728
v3.10.0.1
Income Taxes (Tables)
 6 Months Ended
Jun. 30, 2018
Income Tax Disclosure [Abstract]  
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
Total income tax expense from operations differs from the amount computed by applying the statutory federal income tax rate to income before income tax expense. The following reconciles such differences:
 
 
Six Months Ended June 30
 
 
2018
 
2017
Federal statutory rate
 
21.0
 %
 
35.0
 %
State tax, net of federal tax effect
 
6.2

 
5.1

Increases (decreases) in tax from:
 

 

Regulatory differences - ARAM (a)
 
(4.7
)
 
(0.1
)
Regulatory differences - ARAM deferral (b)
 
4.6

 
—

Regulatory differences - other utility plant items
 
(1.6
)
 
(1.2
)
Tax credits, net of federal income tax expense
 
(0.9
)
 
(0.7
)
Other, net
 
0.5

 
(0.1
)
Effective income tax rate
 
25.1
 %
 
38.0
 %

(a)  
The average rate assumption method (ARAM); a method to flow back excess deferred taxes to customers.
(b)
As we receive direction from our regulatory commissions regarding the return of excess deferred taxes (to our customers resulting from the Tax Cuts and Jobs Act
(TCJA)), the ARAM deferral may decrease during the year, which would result in a reduction to tax expense with a corresponding reduction to revenue.

Summary of Statute of Limitations Applicable to Open Tax Years [Table Text Block]
NSP-Wisconsin is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. The statute of limitations applicable to Xcel Energy’s federal income tax returns expire as follows:
Tax Year(s)
 
Expiration
2009 - 2011
 
December 2018
2012 - 2014
 
October 2019
2015
 
September 2019
2016
 
September 2020
Reconciliation of Unrecognized Tax Benefits
A reconciliation of the amount of unrecognized tax benefit is as follows:
(Millions of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
Unrecognized tax benefit — Permanent tax positions
 
$
1.8

 
$
1.4

Unrecognized tax benefit — Temporary tax positions
 
0.9

 
1.0

Total unrecognized tax benefit
 
$
2.7

 
$
2.4
Tax Benefits Associated with NOL and Tax Credit Carryforwards
The unrecognized tax benefit amounts were reduced by the tax benefits associated with NOL and tax credit carryforwards. The amounts of tax benefits associated with NOL and tax credit carryforwards are as follows:
(Millions of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
NOL and tax credit carryforwards
 
$
(2.1
)
 
$
(1.9
)
v3.10.0.1
Commitments and Contingencies (Tables)
 6 Months Ended
Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]  
Guarantees Issued and Outstanding
The following table presents the guarantee issued and outstanding for NSP-Wisconsin:
(Millions of Dollars)
 
June 30, 2018
 
Dec. 31, 2017
Guarantee issued and outstanding
 
$
1.0

 
$
1.0

Current exposure under this guarantee
 
—

 
—
v3.10.0.1
Borrowings and Other Financing Instruments (Tables)
 6 Months Ended
Jun. 30, 2018
Borrowings and Other Financing Instruments [Abstract]  
Credit Facilities
At June 30, 2018, NSP-Wisconsin had the following committed credit facility available (in millions of dollars):
Credit Facility (a)
 
Drawn (b)
 
Available
$
150

 
$
30

 
$
120


(a) 
This credit facility expires in June 2021.
(b) 
Includes outstanding commercial paper.
Commercial Paper  
Borrowings and Other Financing Instruments [Abstract]  
Short-Term Borrowings
Commercial paper outstanding for NSP-Wisconsin was as follows:
(Amounts in Millions, Except Interest Rates)
 
Three Months Ended June 30, 2018
 
Year Ended Dec. 31, 2017
Borrowing limit
 
$
150

 
$
150

Amount outstanding at period end
 
30

 
11

Average amount outstanding
 
18

 
52

Maximum amount outstanding
 
41

 
129

Weighted average interest rate, computed on a daily basis
 
2.20
%
 
1.23
%
Weighted average interest rate at period end
 
2.29

 
1.73
Notes Payable To Affiliates  
Borrowings and Other Financing Instruments [Abstract]  
Short-Term Borrowings
Other Short-Term Borrowings — The following table presents the notes payable of Clearwater Investments, Inc., a NSP-Wisconsin subsidiary, to Xcel Energy Inc.:
(Amounts in Millions, Except Interest Rates)
 
June 30, 2018
 
Dec. 31, 2017
Notes payable to affiliates
 
$
0.5

 
$
0.5

Weighted average interest rate at period end
 
2.53
%
 
1.73
%
v3.10.0.1
Fair Value of Financial Assets and Liabilities (Tables)
 6 Months Ended
Jun. 30, 2018
Fair Value Disclosures [Abstract]  
Gross Notional Amounts of Commodity Forwards and Options
The following table details the gross notional amounts of commodity options at June 30, 2018 and Dec. 31, 2017:
(Amounts in Thousands) (a)(b)
 
June 30, 2018
 
Dec. 31, 2017
Million British thermal units of natural gas
 
58

 
42


(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.
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-Wisconsin’s derivative assets and liabilities measured at fair value on a recurring basis:
 
 
June 30, 2018
 
 
Fair Value
 
Fair Value
Total
 
Counterparty
Netting (a)
 
Total (b)
(Thousands of Dollars)
 
Level 1
 
Level 2
 
Level 3
 
 
 
Current derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Natural gas commodity
 
$
—

 
$
28

 
$
—

 
$
28

 
$
—

 
$
28

 
 
Dec. 31, 2017
 
 
Fair Value
 
Fair Value
Total
 
Counterparty
Netting (a)
 
Total (b)
(Thousands of Dollars)
 
Level 1
 
Level 2
 
Level 3
 
 
 
Current derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Natural gas commodity
 
$
—

 
$
14

 
$
—

 
$
14

 
$
—

 
$
14


(a) 
NSP-Wisconsin nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at June 30, 2018 and Dec. 31, 2017.  The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.
(b) 
Included in prepayments and other current assets balance of $2.9 million and $3.5 million at June 30, 2018 and Dec. 31, 2017, respectively, in the consolidated balance sheets.
Carrying Amount and Fair Value of Long-term Debt
As of June 30, 2018 and Dec. 31, 2017, other financial instruments for which the carrying amount did not equal fair value were as follows:
 
 
June 30, 2018
 
Dec. 31, 2017
(Thousands of Dollars)
 
Carrying Amount
 
Fair Value
 
Carrying Amount
 
Fair Value
Long-term debt, including current portion
 
$
761,228

 
$
816,474

 
$
761,180

 
$
856,106
v3.10.0.1
Other Income, Net (Tables)
 6 Months Ended
Jun. 30, 2018
Other Income and Expenses [Abstract]  
Other Income, Net
Other expense, net consisted of the following:
 
 
Three Months Ended June 30
 
Six Months Ended June 30
(Thousands of Dollars)
 
2018
 
2017
 
2018
 
2017
Interest (expense) income
 
$
(15
)
 
$
61

 
$
141

 
$
204

Other nonoperating income
 
42

 
75

 
48

 
230

Other nonoperating expense
 
(3
)
 
(4
)
 
(7
)
 
(7
)
Insurance policy expense
 
(47
)
 
(49
)
 
(94
)
 
(98
)
Benefits non-service cost
 
(486
)
 
(678
)
 
(957
)
 
(1,356
)
Other expense, net
 
$
(509
)
 
$
(595
)
 
$
(869
)
 
$
(1,027
)
v3.10.0.1
Segment Information (Tables)
 6 Months Ended
Jun. 30, 2018
Segment Reporting [Abstract]  
Results from Operations by Reportable Segment
(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Reconciling Eliminations
 
Consolidated Total
Three Months Ended June 30, 2018
 
 
 
 
 
 
 
 
 
 
Operating revenues (a)
 
$
209,502

 
$
21,981

 
$
271

 
$
—

 
$
231,754

Intersegment revenues
 
106

 
127

 
—

 
(233
)
 
—

Total revenues
 
$
209,608

 
$
22,108

 
$
271

 
$
(233
)
 
$
231,754

Net income (loss)
 
$
15,481

 
$
(148
)
 
$
(144
)
 
$
—

 
$
15,189

(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Reconciling Eliminations
 
Consolidated Total
Three Months Ended June 30, 2017
 
 
 
 
 
 
 
 
 
 
Operating revenues (a)
 
$
210,742

 
$
19,027

 
$
257

 
$
—

 
$
230,026

Intersegment revenues
 
123

 
68

 
—

 
(191
)
 
—

Total revenues
 
$
210,865

 
$
19,095

 
$
257

 
$
(191
)
 
$
230,026

Net income (loss)
 
$
14,516

 
$
(973
)
 
$
698

 
$
—

 
$
14,241


(a) 
Operating revenues include $38 million and $43 million of affiliate electric revenue for the three months ended June 30, 2018 and 2017, respectively.

(Thousands of Dollars)
 
Regulated
Electric
 
Regulated
Natural Gas
 
All
Other
 
Reconciling
Eliminations
 
Consolidated
Total
Six Months Ended June 30, 2018
 
 
 
 
 
 
 
 
 
 
Operating revenues (a)
 
$
425,868

 
$
78,481

 
$
549

 
$
—

 
$
504,898

Intersegment revenues
 
215

 
275

 
—

 
(490
)
 
—

Total revenues
 
$
426,083

 
$
78,756

 
$
549

 
$
(490
)
 
$
504,898

Net income
 
$
35,925

 
$
10,250

 
$
430

 
$
—

 
$
46,605

(Thousands of Dollars)
 
Regulated
Electric
 
Regulated
Natural Gas
 
All
Other
 
Reconciling
Eliminations
 
Consolidated
Total
Six Months Ended June 30, 2017
 
 
 
 

 
 
 
 
 
 
Operating revenues (a)
 
$
427,051

 
$
67,374

 
$
532

 
$
—

 
$
494,957

Intersegment revenues
 
219

 
182

 
—

 
(401
)
 
—

Total revenues
 
$
427,270

 
$
67,556

 
$
532

 
$
(401
)
 
$
494,957

Net income
 
$
29,986

 
$
5,572

 
$
1,102

 
$
—

 
$
36,660


(a) 
Operating revenues include $76 million and $85 million of affiliate electric revenue for the six months ended June 30, 2018 and 2017, respectively.
v3.10.0.1
Benefit Plans and Other Postretirement Benefits (Tables)
 6 Months Ended
Jun. 30, 2018
Retirement Benefits [Abstract]  
Components of Net Periodic Benefit Cost
Components of Net Periodic Benefit Cost
 
 
Three Months Ended June 30
 
 
2018
 
2017
 
2018
 
2017
(Thousands of Dollars)
 
Pension Benefits
 
Postretirement Health
Care Benefits
Service cost
 
$
1,194

 
$
1,155

 
$
9

 
$
7

Interest cost (a)
 
1,360

 
1,555

 
142

 
148

Expected return on plan assets (a)
 
(2,257
)
 
(2,295
)
 
(16
)
 
(8
)
Amortization of prior service (credit) cost (a)
 
(6
)
 
34

 
(88
)
 
(88
)
Amortization of net loss (a)
 
1,419

 
1,461

 
139

 
109

Net periodic benefit cost
 
1,710

 
1,910

 
186

 
168

Costs not recognized due to the effects of regulation
 
—

 
—

 
—

 
—

Net benefit cost recognized for financial reporting
 
$
1,710

 
$
1,910

 
$
186

 
$
168


 
 
Six Months Ended June 30
 
 
2018

2017

2018

2017
(Thousands of Dollars)
 
Pension Benefits
 
Postretirement Health
Care Benefits
Service cost
 
$
2,389

 
$
2,309

 
$
18

 
$
14

Interest cost (a)
 
2,720

 
3,109

 
284

 
296

Expected return on plan assets (a)
 
(4,513
)
 
(4,590
)
 
(32
)
 
(16
)
Amortization of prior service (credit) cost (a)
 
(14
)
 
69

 
(176
)
 
(176
)
Amortization of net loss (a)
 
2,837

 
2,923

 
278

 
218

Net periodic benefit cost
 
3,419

 
3,820

 
372

 
336

Credits not recognized due to the effects of regulation
 
221

 
—

 
—

 
—

Net benefit cost recognized for financial reporting
 
$
3,640

 
$
3,820

 
$
372

 
$
336


(a) The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the income statement or capitalized on the balance sheet as a regulatory asset.
v3.10.0.1
Other Comprehensive Income (Tables)
 6 Months Ended
Jun. 30, 2018
Stockholders' Equity Note [Abstract]  
Changes in Accumulated Other Comprehensive Loss, Net of Tax
Changes in accumulated other comprehensive loss, net of tax, for the three and six months ended June 30, 2018 and 2017 were as follows:
 
 
Gains and Losses on
Cash Flow Hedges
(Thousands of Dollars)
 
Three Months Ended June 30, 2018
 
Three Months Ended June 30, 2017
Accumulated other comprehensive loss at April 1
 
$
(46
)
 
$
(114
)
Losses reclassified from net accumulated other comprehensive loss
 
23

 
19

Net current period other comprehensive income
 
23

 
19

Accumulated other comprehensive loss at June 30
 
$
(23
)
 
$
(95
)
 
 
Gains and Losses on
Cash Flow Hedges
(Thousands of Dollars)
 
Six Months Ended June 30, 2018
 
Six Months Ended June 30, 2017
Accumulated other comprehensive loss at Jan. 1
 
$
(69
)
 
$
(133
)
Losses reclassified from net accumulated other comprehensive loss
 
46

 
38

Net current period other comprehensive income
 
46

 
38

Accumulated other comprehensive loss at June 30
 
$
(23
)
 
$
(95
)
Reclassifications out of Accumulated Other Comprehensive Loss
Reclassifications from accumulated other comprehensive loss for the three and six months ended June 30, 2018 and 2017 were as follows:
 
 
Amounts Reclassified from
Accumulated Other
Comprehensive Loss
 
(Thousands of Dollars)
 
Three Months Ended June 30, 2018
 
Three Months Ended June 30, 2017
 
Losses on cash flow hedges:
 
 
 
 
 
Interest rate derivatives
 
$
32

(a) 
$
31

(a) 
Total, pre-tax
 
32

 
31

 
Tax benefit
 
(9
)
 
(12
)
 
Total amounts reclassified, net of tax
 
$
23

 
$
19

 
 
 
Amounts Reclassified from
Accumulated Other
Comprehensive Loss
 
(Thousands of Dollars)
 
Six Months Ended June 30, 2018
 
Six Months Ended June 30, 2017
 
Losses on cash flow hedges:
 
 
 
 
 
Interest rate derivatives
 
$
63

(a) 
$
62

(a) 
Total, pre-tax
 
63

 
62

 
Tax benefit
 
(17
)
 
(24
)
 
Total amounts reclassified, net of tax
 
$
46

 
$
38

 

(a) 
Included in interest charges.
v3.10.0.1
Revenues (Tables)
 6 Months Ended
Jun. 30, 2018
Disaggregation of Revenue [Line Items]  
Disaggregation of Revenue [Table Text Block]
In the following tables, revenue is classified by the type of goods/services rendered and market/customer type. The tables also reconcile revenue to the reportable segments.
 
 
Three Months Ended June 30, 2018
(Thousands of Dollars)
 
Electric
 
Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
58,734

 
$
10,912

 
$
10

 
$
69,656

Commercial and industrial (C&I)
 
106,367

 
9,407

 
25

 
115,799

Other
 
1,782

 
—

 
236

 
2,018

Total retail
 
166,883

 
20,319

 
271

 
187,473

Interchange
 
38,370

 
—

 
—

 
38,370

Other
 
1,360

 
1,069

 
—

 
2,429

Total revenue from contracts with customers
 
206,613

 
21,388

 
271

 
228,272

Alternative revenue and other
 
2,889

 
593

 
—

 
3,482

Total revenues
 
$
209,502

 
$
21,981

 
$
271

 
$
231,754

 
 
Three Months Ended June 30, 2017
(Thousands of Dollars)
 
Electric
 
Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
54,754

 
$
9,015

 
$
—

 
$
63,769

C&I
 
107,899

 
8,577

 
27

 
116,503

Other
 
1,678

 
—

 
230

 
1,908

Total retail
 
164,331

 
17,592

 
257

 
182,180

Interchange
 
42,965

 
—

 
—

 
42,965

Other
 
523

 
910

 
—

 
1,433

Total revenue from contracts with customers
 
207,819

 
18,502

 
257

 
226,578

Alternative revenue and other
 
2,923

 
525

 
—

 
3,448

Total revenues
 
$
210,742

 
$
19,027

 
$
257

 
$
230,026

 
 
Six Months Ended June 30, 2018
(Thousands of Dollars)
 
Electric
 
Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
126,537

 
$
41,238

 
$
26

 
$
167,801

Commercial and industrial (C&I)
 
211,184

 
33,957

 
50

 
245,191

Other
 
3,388

 
—

 
473

 
3,861

Total retail
 
341,109

 
75,195

 
549

 
416,853

Interchange
 
76,044

 
—

 
—

 
76,044

Other
 
2,864

 
2,076

 
—

 
4,940

Total revenue from contracts with customers
 
420,017

 
77,271

 
549

 
497,837

Alternative revenue and other
 
5,851

 
1,210

 
—

 
7,061

Total revenues
 
$
425,868

 
$
78,481

 
$
549

 
$
504,898

 
 
Six Months Ended June 30, 2017
(Thousands of Dollars)
 
Electric
 
Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
120,797

 
$
35,643

 
$
20

 
$
156,460

C&I
 
210,279

 
28,835

 
51

 
239,165

Other
 
3,198

 
—

 
461

 
3,659

Total retail
 
334,274

 
64,478

 
532

 
399,284

Interchange
 
85,343

 
—

 
—

 
85,343

Other
 
1,492

 
1,818

 
—

 
3,310

Total revenue from contracts with customers
 
421,109

 
66,296

 
532

 
487,937

Alternative revenue and other
 
5,942

 
1,078

 
—

 
7,020

Total revenues
 
$
427,051

 
$
67,374

 
$
532

 
$
494,957
v3.10.0.1
Accounting Pronouncements Accounting Pronouncements (Details) - Accounting Standards Update 2017-07
$ in Millions
 6 Months Ended
Jun. 30, 2017
USD ($)
Operating and Maintenance Expense  
New Accounting Pronouncements or Change in Accounting Principle [Line Items]  
Net periodic benefit cost (credit) $ (1.4)
Other Income  
New Accounting Pronouncements or Change in Accounting Principle [Line Items]  
Net periodic benefit cost (credit) $ 1.4
v3.10.0.1
Selected Balance Sheet Data, Accounts Receivable (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]    
Due from Affiliate, Current $ 3,800 $ 3,400
Accounts Receivable, Net    
Accounts receivable 65,606 68,073
Less allowance for bad debts (4,726) (4,873)
Accounts receivable, net $ 60,880 $ 63,200
v3.10.0.1
Selected Balance Sheet Data, Inventory (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Public Utilities, Inventory [Line Items]    
Inventories $ 13,798 $ 17,758
Materials and supplies    
Public Utilities, Inventory [Line Items]    
Inventories 6,879 6,916
Fuel    
Public Utilities, Inventory [Line Items]    
Inventories 3,780 3,866
Natural gas    
Public Utilities, Inventory [Line Items]    
Inventories $ 3,139 $ 6,976
v3.10.0.1
Selected Balance Sheet Data, Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Public Utility, Property, Plant and Equipment [Line Items]    
Property, Plant and Equipment, Gross $ 3,359,715 $ 3,259,269
Less accumulated depreciation (1,209,419) (1,170,541)
Property, plant and equipment, net 2,150,296 2,088,728
Electric plant    
Public Utility, Property, Plant and Equipment [Line Items]    
Property, Plant and Equipment, Gross 2,632,764 2,602,671
Natural gas plant    
Public Utility, Property, Plant and Equipment [Line Items]    
Property, Plant and Equipment, Gross 334,329 326,723
Common and other property    
Public Utility, Property, Plant and Equipment [Line Items]    
Property, Plant and Equipment, Gross 187,120 181,105
Construction work in progress    
Public Utility, Property, Plant and Equipment [Line Items]    
Property, Plant and Equipment, Gross $ 205,502 $ 148,770
v3.10.0.1
Income Taxes (Details) - USD ($)
 6 Months Ended 9 Months Ended 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Sep. 30, 2015
Dec. 31, 2016
Dec. 31, 2012
Dec. 31, 2017
Income Tax Examination [Line Items]            
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent 21.00% 35.00%        
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent 6.20% 5.10%        
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent (4.70%) (0.10%)        
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Percent 4.60% 0.00%        
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent (1.60%) (1.20%)        
Effective Income Tax Rate Reconciliation Regulatory Differences Utility Plant Items (0.90%) (0.70%)        
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent 0.50% (0.10%)        
Effective Income Tax Rate Reconciliation, Percent 25.10% 38.00%        
Unrecognized Tax Benefits [Abstract]            
Unrecognized tax benefit — Permanent tax positions $ 1,800,000         $ 1,400,000
Unrecognized tax benefit — Temporary tax positions 900,000         1,000,000
Total unrecognized tax benefit 2,700,000         2,400,000
NOL and tax credit carryforwards (2,100,000)         (1,900,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible 2,000,000          
Amounts accrued for penalties related to unrecognized tax benefits $ 0         $ 0
Internal Revenue Service (IRS)            
Tax Audits [Abstract]            
Year(s) under examination     2012 and 2013   2010 and 2011  
Year of carryback claim under examination         2009  
State Jurisdiction (Wisconsin)            
Tax Audits [Abstract]            
Year(s) under examination       2012 and 2013    
Earliest year subject to examination 2012          
v3.10.0.1
Rate Matters Rate Matters (Details) - USD ($)
$ in Thousands
 1 Months Ended 6 Months Ended
May 31, 2018
Mar. 31, 2018
Nov. 30, 2017
Sep. 30, 2016
Jun. 30, 2016
Feb. 28, 2015
Nov. 30, 2013
Jun. 30, 2018
Public Service Commission of Wisconsin (PSCW) [Member] | PSCW Proceeding - Tax Cuts and Jobs Act of 2017 [Member]                
Public Utilities, General Disclosures [Line Items]                
Tax Cuts and Jobs Act of 2017, Approved Refund of 2018 TCJA Benefits $ 27,000              
Tax Cuts and Jobs Act of 2017, Approved Deferral of 2018 TCJA Benefits $ 5,000              
NSP-Wisconsin | MPSC Proceeding - Michigan 2018 Electric Rate Case [Member]                
Public Utilities, General Disclosures [Line Items]                
Public Utilities, Requested Rate Increase (Decrease), Amount     $ 1,000          
Public Utilities, Requested Rate Increase (Decrease), Percentage     7.10%          
Public Utilities, Requested Return on Equity, Percentage     10.10%          
Public Utilities, Requested Rate Base, Amount     $ 43,000          
Public Utilities, Requested Equity Capital Structure, Percentage     52.50%          
NSP-Wisconsin | MPSC Staff [Member] | MPSC Proceeding - Michigan 2018 Electric Rate Case [Member]                
Public Utilities, General Disclosures [Line Items]                
Public Utilities, Requested Return on Equity, Percentage   9.80%            
Public Utilities, Rate Increase Under the Settlement   $ 300            
Public Utilities, Rate Increase Under the Settlement, Percentage   2.00%            
Public Utilities, Requested Equity Capital Structure, Percentage   52.50%            
NSP-Minnesota | FERC Proceeding, MISO ROE Complaint                
Public Utilities, General Disclosures [Line Items]                
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%  
NSP-Minnesota | Federal Energy Regulatory Commission (FERC) | FERC Proceeding, MISO ROE Complaint                
Public Utilities, General Disclosures [Line Items]                
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Approved       10.32%        
Public Utilities, Length of Refund Period, In Months       15 months        
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, with RTO Adder, Approved               10.82%
Public Utilities, ROE Basis Point Adder, Approved               50
NSP-Minnesota | Administrative Law Judge | FERC Proceeding, MISO ROE Complaint                
Public Utilities, General Disclosures [Line Items]                
Public Utilities, ROE Applicable To Transmission Formula Rates In The Regional Transmission Operator's Region, Recommended By Third Parties         9.70%      
v3.10.0.1
Commitments and Contingencies, Guarantees and Indemnifications (Details) - USD ($)
 6 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Guarantor Obligations [Line Items]    
Assets Held As Collateral $ 0 $ 0
Payment or Performance Guarantee | Customer Loans for Farm Rewiring Program    
Guarantor Obligations [Line Items]    
Payment Guarantee Expiration (year) 2020  
Guarantee issued and outstanding $ 1,000,000 1,000,000
Current exposure under this guarantee $ 0 $ 0
v3.10.0.1
Commitments and Contingencies, Environmental Contingencies - Site Contingencies (Details)
$ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2018
USD ($)
Dec. 31, 2017
USD ($)
Ashland MGP Site    
Ashland Manufactured Gas Plant (MGP) Site [Abstract]    
Current Cost Estimate for Site Remediation $ 175.0  
Estimated amount spent on cleanup 146.0  
Accrual for Environmental Loss Contingencies, Gross $ 29.0 $ 30.0
Approved amortization period for recovery of remediation costs in natural gas rates (in years) 10 years  
Carrying cost percentage to be applied to unamortized regulatory asset 3.00%  
Other MGP Sites [Member]    
Ashland Manufactured Gas Plant (MGP) Site [Abstract]    
Accrual for Environmental Loss Contingencies, Gross $ 0.1 0.1
Number of identified MGP sites under current investigation and/or remediation in addition to those separately disclosed 1  
PSCW Proceeding - Gas Rate Case 2017 - Gas Rates 2017 [Member] | Ashland MGP Site    
Ashland Manufactured Gas Plant (MGP) Site [Abstract]    
Public Utilities, Approved annual recovery collected through base rates   $ 12.0
PSCW Proceeding - Gas Rate Case 2017 - Gas Rates 2018 [Member] | Ashland MGP Site    
Ashland Manufactured Gas Plant (MGP) Site [Abstract]    
Public Utilities, Requested annual recovery collected through base rates $ 18.0  
v3.10.0.1
Commitments and Contingencies Commitments and Contingencies - Legal Contingencies (Details) - Gas Trading Litigation
Jun. 30, 2018
Dec. 31, 2009
Loss Contingencies [Line Items]    
Loss Contingency, Pending Claims, Number 6 13
Loss Contingency, Subset of Cases within Multi-District Litigation, Number 2  
NSP-Wisconsin    
Loss Contingencies [Line Items]    
Loss Contingency, Pending Claims, Number   2
v3.10.0.1
Borrowings and Other Financing Instruments, Commercial Paper (Details) - USD ($)
 3 Months Ended 12 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Short-term Debt [Line Items]    
Amount outstanding at period end $ 30,000,000 $ 11,000,000
Commercial Paper    
Short-term Debt [Line Items]    
Borrowing limit 150,000,000 150,000,000
Amount outstanding at period end 30,000,000 11,000,000
Average amount outstanding 18,000,000 52,000,000
Maximum amount outstanding $ 41,000,000 $ 129,000,000
Weighted average interest rate, computed on a daily basis (percentage) 2.20% 1.23%
Weighted average interest rate at period end (percentage) 2.29% 1.73%
v3.10.0.1
Borrowings and Other Financing Instruments, Letters of Credit (Details) - USD ($)
$ in Thousands
 6 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Line of Credit Facility [Line Items]    
Amount outstanding at period end $ 30,000 $ 11,000
Letter of Credit    
Line of Credit Facility [Line Items]    
Amount outstanding at period end $ 0 $ 0
Letter of Credit | Letter of Credit    
Line of Credit Facility [Line Items]    
Term of letters of credit (in years) 1 year  
v3.10.0.1
Borrowings and Other Financing Instruments, Credit Facility (Details) - Credit Facility - USD ($)
 6 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Line of Credit Facility [Line Items]    
Credit Facility [1] $ 150,000,000  
Drawn [2] 30,000,000  
Available $ 120,000,000  
Maturity Date Jun. 30, 2021  
Direct advances on the credit facility outstanding $ 0 $ 0
[1] This credit facility expires in June 2021.
[2] Includes outstanding commercial paper.
v3.10.0.1
Borrowings and Other Financing Instruments, Intercompany Borrowing Arrangement and Other Short-Term Borrowings (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Short-term Debt [Line Items]    
Notes payable to affiliates $ 500 $ 500
Notes Payable To Affiliates    
Short-term Debt [Line Items]    
Notes payable to affiliates $ 500 $ 500
Weighted average interest rate at period end (percentage) 2.53% 1.73%
v3.10.0.1
Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details) - MMBTU
MMBTU in Thousands
Jun. 30, 2018
Dec. 31, 2017
Natural Gas Commodity (in million British thermal units)    
Gross Notional Amounts of Commodity Options [Abstract]    
Derivative, Nonmonetary Notional amount [1],[2] 58 42
[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.
v3.10.0.1
Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) - USD ($)
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract]        
Derivative instruments designated as fair value hedges $ 0 $ 0 $ 0 $ 0
Recognized gains (losses) from fair value hedges or related hedged transactions 0 0 0 0
Other Derivative Instruments | Natural Gas Commodity        
Derivative Instruments, Gain (Loss) [Line Items]        
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities       (100,000)
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities) $ 0 $ 0 0 200,000
Cash Flow Hedges | Designated as Hedging Instrument | Interest Rate Contract [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net     $ (100,000) $ (100,000)
v3.10.0.1
Fair Value of Financial Assets and Liabilities, Derivative Assets and Liabilities at Fair Value (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Derivatives, Fair Value [Line Items]    
Prepayments and other $ 2,865 $ 3,450
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 [1] 28 14
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset [2] 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 28 14
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis    
Derivatives, Fair Value [Line Items]    
Prepayments and other 2,900 3,500
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 $ 28 $ 14
[1] Included in prepayments and other current assets balance of $2.9 million and $3.5 million at June 30, 2018 and Dec. 31, 2017, respectively, in the consolidated balance sheets.
[2] NSP-Wisconsin nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at June 30, 2018 and Dec. 31, 2017. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.
v3.10.0.1
Fair Value of Financial Assets and Liabilities, Fair Value of Long-Term Debt (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Carrying Amount    
Financial Liabilities, Balance Sheet Groupings [Abstract]    
Long-term debt, including current portion $ 761,228 $ 761,180
Fair Value    
Financial Liabilities, Balance Sheet Groupings [Abstract]    
Long-term debt, including current portion $ 816,474 $ 856,106
v3.10.0.1
Other Income, Net (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Other Income and Expenses [Abstract]        
Interest (expense) income $ (15) $ 61 $ 141 $ 204
Other nonoperating income 42 75 48 230
Other nonoperating expense (3) (4) (7) (7)
Insurance policy expense (47) (49) (94) (98)
Defined Benefit Plan, Non-service Costs (486) (678) (957) (1,356)
Other expense, net $ (509) $ (595) $ (869) $ (1,027)
v3.10.0.1
Segment Information (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Segment Reporting Information [Line Items]        
Operating revenues $ 231,754 $ 230,026 $ 504,898 $ 494,957
Net income (loss) 15,189 14,241 46,605 36,660
Affiliate electric revenue 38,000 43,000 76,000 85,000
Regulated Electric        
Segment Reporting Information [Line Items]        
Operating revenues 209,608 210,865 426,083 427,270
Net income (loss) 15,481 14,516 35,925 29,986
Regulated Natural Gas        
Segment Reporting Information [Line Items]        
Operating revenues 22,108 19,095 78,756 67,556
Net income (loss) (148) (973) 10,250 5,572
All Other        
Segment Reporting Information [Line Items]        
Operating revenues 271 257 549 532
Net income (loss) (144) 698 430 1,102
Operating Segments        
Segment Reporting Information [Line Items]        
Operating revenues [1] 231,754 230,026 504,898 494,957
Operating Segments | Regulated Electric        
Segment Reporting Information [Line Items]        
Operating revenues [1] 209,502 210,742 425,868 427,051
Operating Segments | Regulated Natural Gas        
Segment Reporting Information [Line Items]        
Operating revenues 21,981 19,027 78,481 67,374
Operating Segments | All Other        
Segment Reporting Information [Line Items]        
Operating revenues 271 257 549 532
Intersegment Eliminations        
Segment Reporting Information [Line Items]        
Operating revenues (233) (191) (490) (401)
Net income (loss) 0 0 0 0
Intersegment Eliminations | Regulated Electric        
Segment Reporting Information [Line Items]        
Operating revenues 106 123 215 219
Intersegment Eliminations | Regulated Natural Gas        
Segment Reporting Information [Line Items]        
Operating revenues 127 68 275 182
Intersegment Eliminations | All Other        
Segment Reporting Information [Line Items]        
Operating revenues $ 0 $ 0 $ 0 $ 0
[1] (a) Operating revenues include $76 million and $85 million of affiliate electric revenue for the six months ended June 30, 2018 and 2017, respectively.
v3.10.0.1
Benefit Plans and Other Postretirement Benefits (Details)
$ in Thousands
 1 Months Ended 3 Months Ended 6 Months Ended
Jan. 31, 2018
USD ($)
Plan
Jun. 30, 2018
USD ($)
Jun. 30, 2017
USD ($)
Jun. 30, 2018
USD ($)
Jun. 30, 2017
USD ($)
Pension Plan [Member]          
Components of Net Periodic Benefit Cost [Abstract]          
Service cost   $ 1,194 $ 1,155 $ 2,389 $ 2,309
Interest cost   1,360 1,555 2,720 3,109
Expected return on plan assets   (2,257) (2,295) (4,513) (4,590)
Amortization of prior service cost (credit)   (6) 34 (14) 69
Amortization of net loss   1,419 1,461 2,837 2,923
Defined Benefit Plan Net Benefit Cost (Credit) Recognized Before Regulatory Adjustments   1,710 1,910 3,419 3,820
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation   0 0 221 0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)   1,710 1,910 3,640 3,820
Total contributions to the pension plans during the period $ 10,000        
Other Postretirement Benefits Plan [Member]          
Components of Net Periodic Benefit Cost [Abstract]          
Service cost   9 7 18 14
Interest cost   142 148 284 296
Expected return on plan assets   (16) (8) (32) (16)
Amortization of prior service cost (credit)   (88) (88) (176) (176)
Amortization of net loss   139 109 278 218
Defined Benefit Plan Net Benefit Cost (Credit) Recognized Before Regulatory Adjustments   186 168 372 336
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation   0 0 0 0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)   $ 186 $ 168 $ 372 $ 336
Xcel Energy Inc. | Pension Plan [Member]          
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        
v3.10.0.1
Other Comprehensive Income (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Accumulated other comprehensive loss at beginning of period     $ 876,589  
Accumulated other comprehensive loss at end of period $ 894,313   894,313  
Gains and Losses on Cash Flow Hedges        
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Accumulated other comprehensive loss at beginning of period (46) $ (114) (69) $ (133)
Losses reclassified from net accumulated other comprehensive loss 23 19 46 38
Net current period other comprehensive income 23 19 46 38
Accumulated other comprehensive loss at end of period $ (23) $ (95) $ (23) $ (95)
v3.10.0.1
Other Comprehensive Income (Reclassification from AOCI) (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]        
Total, pre-tax $ (20,459) $ (22,994) $ (62,185) $ (59,170)
Tax benefit 5,270 8,753 15,580 22,510
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 32 31 63 62
Tax benefit (9) (12) (17) (24)
Total, net of tax 23 19 46 38
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 $ 32 $ 31 $ 63 $ 62
v3.10.0.1
Revenues (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers $ 228,272 $ 226,578 $ 497,837 $ 487,937
Alternative revenue and other 3,482 3,448 7,061 7,020
Total operating revenues 231,754 230,026 $ 504,898 494,957
Maximum number of months following end of annual period in which revenues are earned to be included in incentive programs     24 months  
Tolerance band     2  
Operating Segments        
Disaggregation of Revenue [Line Items]        
Total operating revenues [1] 231,754 230,026 $ 504,898 494,957
Retail        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 187,473 182,180 416,853 399,284
Retail | Residential        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 69,656 63,769 167,801 156,460
Retail | Commercial and industrial (C&I)        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 115,799 116,503 245,191 239,165
Retail | Other        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 2,018 1,908 3,861 3,659
Interchange        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 38,370 42,965 76,044 85,343
Other        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 2,429 1,433 4,940 3,310
Regulated Electric        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 206,613 207,819 420,017 421,109
Alternative revenue and other 2,889 2,923 5,851 5,942
Total operating revenues 209,608 210,865 426,083 427,270
Regulated Electric | Operating Segments        
Disaggregation of Revenue [Line Items]        
Total operating revenues [1] 209,502 210,742 425,868 427,051
Regulated Electric | Retail        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 166,883 164,331 341,109 334,274
Regulated Electric | Retail | Residential        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 58,734 54,754 126,537 120,797
Regulated Electric | Retail | Commercial and industrial (C&I)        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 106,367 107,899 211,184 210,279
Regulated Electric | Retail | Other        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 1,782 1,678 3,388 3,198
Regulated Electric | Interchange        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 38,370 42,965 76,044 85,343
Regulated Electric | Other        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 1,360 523 2,864 1,492
Regulated Natural Gas        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 21,388 18,502 77,271 66,296
Alternative revenue and other 593 525 1,210 1,078
Total operating revenues 22,108 19,095 78,756 67,556
Regulated Natural Gas | Operating Segments        
Disaggregation of Revenue [Line Items]        
Total operating revenues 21,981 19,027 78,481 67,374
Regulated Natural Gas | Retail        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 20,319 17,592 75,195 64,478
Regulated Natural Gas | Retail | Residential        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 10,912 9,015 41,238 35,643
Regulated Natural Gas | Retail | Commercial and industrial (C&I)        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 9,407 8,577 33,957 28,835
Regulated Natural Gas | Retail | Other        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 0 0 0 0
Regulated Natural Gas | Interchange        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 0 0 0 0
Regulated Natural Gas | Other        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 1,069 910 2,076 1,818
All Other        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 271 257 549 532
Alternative revenue and other 0 0 0 0
Total operating revenues 271 257 549 532
All Other | Operating Segments        
Disaggregation of Revenue [Line Items]        
Total operating revenues 271 257 549 532
All Other | Retail        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 271 257 549 532
All Other | Retail | Residential        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 10 0 26 20
All Other | Retail | Commercial and industrial (C&I)        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 25 27 50 51
All Other | Retail | Other        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 236 230 473 461
All Other | Interchange        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers 0 0 0 0
All Other | Other        
Disaggregation of Revenue [Line Items]        
Total revenue from contracts with customers $ 0 $ 0 $ 0 $ 0
[1] (a) Operating revenues include $76 million and $85 million of affiliate electric revenue for the six months ended June 30, 2018 and 2017, respectively.