Northern States Power 10-Q 25 Oct 19 2019 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2019	Oct. 25, 2019
Cover page.
Entity Registrant Name	NORTHERN STATES POWER CO /WI/
Entity Central Index Key	0000072909
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	001-03140
Entity Tax Identification Number	39-0508315
Entity Incorporation, State or Country Code	WI
Entity Address, Address Line One	1414 West Hamilton Avenue
Entity Address, City or Town	Eau Claire
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	54701
City Area Code	715
Local Phone Number	839-2625
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		933,000

CONSOLIDATED STATEMENTS OF COMM

CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDER'S EQUITY - USD ($) $ in Millions	Total	Common stock	Additional Paid In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance (in shares) at Dec. 31, 2017		933,000
Beginning Balance at Dec. 31, 2017	$ 876.6	$ 93.3	$ 449.4	$ 334	$ (0.1)
Increase (Decrease) in Stockholder's Equity
Net income	77.6
Other comprehensive income	0.1				0.1
Common dividends declared to parent	(50.7)			(50.7)
Contribution of capital by parent	3.9		3.9
Balance (in shares) at Sep. 30, 2018		933,000
Ending Balance at Sep. 30, 2018	907.5	$ 93.3	453.3	360.9	0
Balance (in shares) at Jun. 30, 2018		933,000
Beginning Balance at Jun. 30, 2018	894.3	$ 93.3	452.9	348.1	0
Increase (Decrease) in Stockholder's Equity
Net income	31
Other comprehensive income	0
Common dividends declared to parent	(18.2)			(18.2)
Contribution of capital by parent	0.4		0.4
Balance (in shares) at Sep. 30, 2018		933,000
Ending Balance at Sep. 30, 2018	$ 907.5	$ 93.3	453.3	360.9	0
Balance (in shares) at Dec. 31, 2018	933,000	933,000
Beginning Balance at Dec. 31, 2018	$ 942.4	$ 93.3	510.1	339	0
Increase (Decrease) in Stockholder's Equity
Net income	61.9
Other comprehensive income	0
Common dividends declared to parent	(67.1)			(67.1)
Contribution of capital by parent	$ 3.5		3.5
Balance (in shares) at Sep. 30, 2019	933,000	933,000
Ending Balance at Sep. 30, 2019	$ 940.7	$ 93.3	513.6	333.8	0
Balance (in shares) at Jun. 30, 2019		933,000
Beginning Balance at Jun. 30, 2019	938.2	$ 93.3	513.6	331.3	0
Increase (Decrease) in Stockholder's Equity
Net income	29.4
Other comprehensive income	0
Common dividends declared to parent	$ (26.9)			(26.9)
Balance (in shares) at Sep. 30, 2019	933,000	933,000
Ending Balance at Sep. 30, 2019	$ 940.7	$ 93.3	$ 513.6	$ 333.8	$ 0

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Electric, Non-affiliate	$ 184.3	$ 200.4	$ 519.6	$ 550.2
Electric, affiliates	44.7	39.9	132.3	116
Natural gas	14.6	15.4	96.6	93.8
Other	0.1	0.3	0.3	0.9
Total operating revenues	243.7	256	748.8	760.9
Operating expenses
Electric Fuel and Purchased Power, Non-Affiliate	3.2	3.2	8.2	9.7
Related Party Transaction, Utilities Operating Expense, Purchased Power	94.9	106.8	298.3	309.7
Cost of Goods Sold	5.4	6.2	45.9	43.3
Operating and maintenance expenses	47.5	50	150.8	149.3
Conservation expenses	3.3	3	9.3	9.2
Depreciation and amortization	34.4	31.7	102.9	93.7
Taxes (other than income taxes)	7.3	7.1	22	21.5
Total operating expenses	196	208	637.4	636.4
Operating income	47.7	48	111.4	124.5
Other expense, net	(0.3)	(0.8)	(0.9)	(1.6)
Allowance for funds used during construction — equity	0.7	2.6	2.2	6.7
Interest charges and financing costs
Interest charges — includes other financing costs of $0.3, $0.5, $1.0 and $1.5, respectively	9.7	10.1	29.5	29.5
Allowance for funds used during construction — debt	(0.3)	(1.2)	(0.9)	(3)
Total interest charges and financing costs	9.4	8.9	28.6	26.5
Income before income taxes	38.7	40.9	84.1	103.1
Income taxes	9.3	9.9	22.2	25.5
Net income	$ 29.4	$ 31	$ 61.9	$ 77.6

CONSOLIDATED STATEMENTS OF IN_2

CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Interest charges and financing costs
Other financing costs	$ 0.3	$ 0.5	$ 1	$ 1.5

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Comprehensive income:
Net income	$ 29.4	$ 31	$ 61.9	$ 77.6
Derivative instruments:
Reclassification of losses to net income, net of tax of $0	0	0	0	0.1
Other comprehensive income	0	0	0	0.1
Comprehensive income	$ 29.4	$ 31	$ 61.9	$ 77.7

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative instruments:
Reclassification of losses to net income, tax	$ 0	$ 0	$ 0	$ 0

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net income	$ 61.9	$ 77.6
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	103.6	94.9
Deferred income taxes	4	15.8
Amortization of investment tax credits	(0.4)	(0.4)
Allowance for equity funds used during construction	(2.2)	(6.7)
Changes in operating assets and liabilities:
Accounts receivable	7.8	8.8
Accrued unbilled revenues	10.4	15.3
Inventories	(5.2)	(0.6)
Other current assets	10.2	5.1
Accounts payable	(9.1)	(7.5)
Net regulatory assets and liabilities	(0.8)	(13.6)
Other current liabilities	3.1	(4.9)
Pension and other employee benefit obligations	(7.1)	(8.6)
Other, net	2.2	2
Net cash provided by operating activities	178.4	177.2
Investing activities
Utility capital/construction expenditures	(145)	(174.5)
Other, net	(0.1)	0.2
Net cash used in investing activities	(145.1)	(174.3)
Financing activities
Proceeds from (repayments of) short-term borrowings, net	17	(11)
Proceeds from Issuance of Long-term Debt	0	197.1
Repayments of issuances of long-term debt	(0.1)	0
Capital contributions from parent	21.9	6.9
Dividends paid to parent	(72.6)	(48)
Other, net	0	(0.1)
Net cash used in financing activities	(33.8)	144.9
Net change in cash and cash equivalents	(0.5)	147.8
Cash and cash equivalents at beginning of period	2.2	1.4
Cash and cash equivalents at end of period	1.7	149.2
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(28.7)	(22)
Cash paid for income taxes, net	(8.4)	(15.8)
Supplemental disclosure of non-cash investing transactions:
Accrued property, plant and equipment additions	20.1	22.7
Inventory transfers to property, plant and equipment	4.3	6.4
Allowance for equity funds used during construction	$ 2.2	$ 6.7

CONSOLIDATED BALANCE SHEETS (UN

CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 1.7	$ 2.2
Accounts receivable, net	48.9	75.1
Accrued unbilled revenues	45.9	56.2
Other Receivables	7	6.8
Inventories	18	17.1
Regulatory assets	59.5	22.6
Prepaid taxes	18.9	30.2
Prepayments and other	4.6	3.3
Total current assets	204.5	213.5
Property, Plant and Equipment, Net [Abstract]
Property, plant and equipment, net	2,304.3	2,241.6
Other assets
Regulatory assets	238.5	285.5
Other investments	2.8	2.7
Other	0.2	0.2
Total other assets	241.5	288.4
Total assets	2,750.3	2,743.5
Current liabilities
Short-term debt	68	51
Notes payable to affiliates	0	0.6
Accounts payable	45.7	56.8
Accounts payable to affiliates	16.2	20
Dividends payable to parent	11.8	17.4
Regulatory liabilities	61.7	20.9
Taxes Accrued	6.2	3
Environmental liabilities	6.3	10.9
Accrued interest	7.7	8.8
Other	15	14.8
Total current liabilities	238.6	204.2
Deferred credits and other liabilities
Deferred income taxes	283.9	280.7
Deferred investment tax credits	6.6	7
Regulatory liabilities	375.8	400.1
Environmental liabilities	16.4	18
Customer advances	19.3	16.8
Pension and employee benefit obligations	37.8	44.5
Other	23.3	22.3
Total deferred credits and other liabilities	763.1	789.4
Capitalization
Long-term debt	807.9	807.5
Common stock — 1,000,000 shares authorized of $100 par value; 933,000 shares outstanding at Sept. 30, 2019 and Dec. 31, 2018, respectively	93.3	93.3
Additional paid in capital	513.6	510.1
Retained earnings	333.8	339
Total common stockholder’s equity	940.7	942.4
Total liabilities and equity	$ 2,750.3	$ 2,743.5

CONSOLIDATED BALANCE SHEETS (_2

CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
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

Management's Opinion

Management's Opinion	9 Months Ended
	Sep. 30, 2019
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 U.S. GAAP, the financial position of NSP-Wisconsin and its subsidiaries as of Sept. 30, 2019 and Dec. 31, 2018 ; the results of its operations, including the components of net income, change in stockholders' equity and comprehensive income for the three and nine months ended Sept. 30, 2019 and 2018; and its cash flows for the nine months ended Sept. 30, 2019 and 2018. All adjustments are of a normal, recurring nature, except as otherwise disclosed. Management has also evaluated the impact of events occurring after Sept. 30, 2019 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, 2018 balance sheet information has been derived from the audited 2018 consolidated financial statements included in the NSP-Wisconsin Annual Report on Form 10-K for the year ended Dec. 31, 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, 2018 , filed with the SEC on Feb. 22, 2019. 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.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
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, 2018 , appropriately represent, in all material respects, the current status of accounting policies and are incorporated herein by reference.

Accounting Pronouncements

Accounting Pronouncements	9 Months Ended
	Sep. 30, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Accounting Pronouncements	Accounting Pronouncements Recently Issued Credit Losses — In 2016, the FASB issued Financial Instruments - Credit Losses, Topic 326 (ASC Topic 326), which changes how entities account for losses on receivables and certain other assets. The guidance requires use of a current expected credit loss model, which may result in earlier recognition of credit losses than under previous accounting standards. ASC Topic 326 is effective for interim and annual periods beginning on or after Dec. 15, 2019, and will be applied on a modified-retrospective approach through a cumulative-effect adjustment to retained earnings as of Jan. 1, 2020. NSP-Wisconsin expects the impact of adoption of the new standard to include first-time recognition of expected credit losses (i.e., bad debt expense) on unbilled revenues, with the initial allowance established at Jan. 1, 2020 charged to retained earnings. Recently Adopted Leases — In 2016, the FASB issued Leases , Topic 842 (ASC Topic 842) , which provides new accounting and disclosure guidance for leasing activities, most significantly requiring that operating leases be recognized on the balance sheet. NSP-Wisconsin adopted the guidance on Jan. 1, 2019 utilizing the package of transition practical expedients provided by the new standard, including carrying forward prior conclusions on whether agreements existing before the adoption date contain leases and whether existing leases are operating or finance leases; ASC Topic 842 refers to capital leases as finance leases. Specifically for land easement contracts, NSP-Wisconsin has elected the practical expedient provided by ASU No. 2018-01 Leases: Land Easement Practical Expedient for Transition to Topic 842 , and as a result, only those easement contracts entered on or after Jan. 1, 2019 will be evaluated to determine if lease treatment is appropriate. NSP-Wisconsin also utilized the transition practical expedient offered by ASU No. 2018-11 Leases: Targeted Improvements to implement the standard on a prospective basis. As a result, reporting periods in the consolidated financial statements beginning Jan. 1, 2019 reflect the implementation of ASC Topic 842, while prior periods continue to be reported in accordance with Leases, Topic 840 (ASC Topic 840) . The impact of implementing ASC Topic 842 on NSP-Wisconsin's financial statements was insignificant; no amounts were recorded to the consolidated balance sheet as a result of its adoption.

Selected Balance Sheet Data

Selected Balance Sheet Data	9 Months Ended
	Sep. 30, 2019
Balance Sheet Related Disclosures [Abstract]
Selected Balance Sheet Data	(Millions of Dollars) Sept. 30, 2019 Dec. 31, 2018 Accounts receivable, net Accounts receivable $ 54.0 $ 80.7 Less allowance for bad debts (5.1 ) (5.6 ) Accounts receivable, net $ 48.9 $ 75.1 (Millions of Dollars) Sept. 30, 2019 Dec. 31, 2018 Inventories Materials and supplies $ 7.0 $ 6.7 Fuel 4.1 3.8 Natural gas 6.9 6.6 Total inventories $ 18.0 $ 17.1 (Millions of Dollars) Sept. 30, 2019 Dec. 31, 2018 Property, plant and equipment, net Electric plant $ 2,963.7 $ 2,895.5 Natural gas plant 358.9 345.7 Common and other property 199.2 189.7 Construction work in progress 80.1 55.0 Total property, plant and equipment 3,601.9 3,485.9 Less accumulated depreciation (1,297.6 ) (1,244.3 ) Property, plant and equipment, net $ 2,304.3 $ 2,241.6

Borrowings and Other Financing

Borrowings and Other Financing Instruments	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Borrowings and Other Financing Instruments	Borrowings and Other Financing Instruments NSP-Wisconsin meets its short-term liquidity requirements primarily through the issuance of commercial paper and borrowings under its credit facility. Commercial Paper — Commercial paper outstanding for NSP-Wisconsin was as follows: (Amounts in Millions, Except Interest Rates) Three Months Ended Sept. 30, 2019 Year Ended Dec. 31, 2018 Borrowing limit $ 150 $ 150 Amount outstanding at period end 68 51 Average amount outstanding 43 28 Maximum amount outstanding 68 103 Weighted average interest rate, computed on a daily basis 2.45 % 2.31 % Weighted average interest rate at period end 2.27 2.89 Letters of Credit — NSP-Wisconsin uses letters of credit, generally with terms of one year , to provide financial guarantees for certain operating obligations. At Sept. 30, 2019 and Dec. 31, 2018 , 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. Amended Credit Agreement — In June 2019, NSP-Wisconsin entered into an amended five-year credit agreement with a syndicate of banks. The amended credit agreements have substantially the same terms and conditions as the prior credit agreements with the exception of the maturity, which was extended from June 2021 to June 2024. NSP-Wisconsin has the right to request an extension of the revolving credit facility termination date for an additional one year period. All extension requests are subject to majority bank group approval. As of Sept. 30, 2019 , NSP-Wisconsin had the following committed credit facility available (in millions of dollars): Credit Facility (a) Outstanding (b) Available $ 150 $ 68 $ 82 (a) This credit facility expires in June 2024 . (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 Sept. 30, 2019 and Dec. 31, 2018 . 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) Sept. 30, 2019 Dec. 31, 2018 Notes payable to affiliates $ — $ 0.6 Weighted average interest rate at period end N/A 2.89 %

Revenues

Revenues	9 Months Ended
	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Revenues	Revenues Revenue is classified by the type of goods/services rendered and market/customer type. NSP-Wisconsin’s operating revenues consists of the following: Three Months Ended Sept. 30, 2019 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 63.6 $ 6.9 $ — $ 70.5 C&I 116.6 6.1 — 122.7 Other 0.9 — 0.1 1.0 Total retail 181.1 13.0 0.1 194.2 Interchange 44.7 — — 44.7 Other 0.3 1.0 — 1.3 Total revenue from contracts with customers 226.1 14.0 0.1 240.2 Alternative revenue and other 2.9 0.6 — 3.5 Total revenues $ 229.0 $ 14.6 $ 0.1 $ 243.7 Three Months Ended Sept. 30, 2018 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 67.9 $ 7.0 $ — $ 74.9 C&I 127.9 6.9 — 134.8 Other 1.3 — 0.3 1.6 Total retail 197.1 13.9 0.3 211.3 Interchange 40.0 — — 40.0 Other 0.4 0.9 — 1.3 Total revenue from contracts with customers 237.5 14.8 0.3 252.6 Alternative revenue and other 2.8 0.6 — 3.4 Total revenues $ 240.3 $ 15.4 $ 0.3 $ 256.0 Nine Months Ended Sept. 30, 2019 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 185.1 $ 51.3 $ — $ 236.4 C&I 320.2 40.5 — 360.7 Other 4.5 — 0.3 4.8 Total retail 509.8 91.8 0.3 601.9 Interchange 132.3 — — 132.3 Other 0.9 3.0 — 3.9 Total revenue from contracts with customers 643.0 94.8 0.3 738.1 Alternative revenue and other 8.9 1.8 — 10.7 Total revenues $ 651.9 $ 96.6 $ 0.3 $ 748.8 Nine Months Ended Sept. 30, 2018 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 194.5 $ 48.2 $ — $ 242.7 C&I 339.1 40.8 0.1 380.0 Other 4.7 — 0.8 5.5 Total retail 538.3 89.0 0.9 628.2 Interchange 116.0 — — 116.0 Other 3.2 3.0 — 6.2 Total revenue from contracts with customers 657.5 92.0 0.9 750.4 Alternative revenue and other 8.7 1.8 — 10.5 Total revenues $ 666.2 $ 93.8 $ 0.9 $ 760.9

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Note 7 to the consolidated financial statements included in NSP-Wisconsin’s Annual Report on Form 10-K for the year ended Dec. 31, 2018 represents, in all material respects, the current status of other income tax matters except to the extent noted below, and are incorporated herein by reference. The following table reconciles the difference between the statutory rate and the ETR: Nine Months Ended Sept. 30 2019 2018 Federal statutory rate 21.0 % 21.0 % State tax (net of federal tax effect) 6.2 6.2 Increases (decreases) in tax from: Tax credits and tax credit and NOL allowances (net) (1.5 ) (0.7 ) Prior period adjustments 0.4 (0.6 ) Plant regulatory differences (a) (0.4 ) (1.6 ) Other (net) 0.7 0.4 Effective income tax rate 26.4 % 24.7 % (a) Regulatory differences for income tax primarily relates to the credit of excess deferred taxes to customers through the average rate assumption method and the impact of AFUDC - equity. Year-to-date variations primarily relate to the impact of AFUDC - equity. Federal Audits — NSP-Wisconsin is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. Statute of limitations applicable to Xcel Energy’s consolidated federal income tax returns expire as follows: Tax Year(s) Expiration 2009 - 2013 June 2020 2014 - 2016 September 2020 In 2015, the IRS commenced an examination of tax years 2012 and 2013. In 2017, the IRS concluded the audit of tax years 2012 and 2013 and proposed an adjustment that would impact Xcel Energy’s NOL and ETR. Xcel Energy filed a protest with the IRS. As of Sept. 30, 2019 , the case has been forwarded to the Office of 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. In 2018, the IRS began an audit of tax years 2014-2016. As of Sept. 30, 2019 no adjustments have been proposed. State Audits — NSP-Wisconsin is a member of the Xcel Energy affiliated group that files consolidated state income tax returns. As of Sept. 30, 2019 , NSP-Wisconsin’s earliest open tax year subject to examination by state taxing authorities under applicable statutes of limitations is 2014. In 2018, Wisconsin began an audit of tax years 2014-2016. As of Sept. 30, 2019 no material adjustments have been proposed. Unrecognized Benefits — 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 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 to the taxing authority to an earlier period. Unrecognized tax benefits — permanent vs. temporary: (Millions of Dollars) Sept. 30, 2019 Dec. 31, 2018 Unrecognized tax benefit — Permanent tax positions $ 2.5 $ 2.0 Unrecognized tax benefit — Temporary tax positions 0.8 0.8 Total unrecognized tax benefit $ 3.3 $ 2.8 Unrecognized tax benefits were reduced by tax benefits associated with NOL and tax credit carryforwards: (Millions of Dollars) Sept. 30, 2019 Dec. 31, 2018 NOL and tax credit carryforwards $ (2.5 ) $ (2.1 ) Net deferred tax liability associated with the unrecognized tax benefit amounts and related NOLs and tax credits carryforwards were $1.6 million and $1.1 million for Sept. 30, 2019 and Dec. 31, 2018 , respectively. As the IRS Appeals and federal and state audits progresses, it is reasonably possible that the amount of unrecognized tax benefit could decrease up to approximately $2.2 million in the next 12 months. Payables for interest related to unrecognized tax benefits were not material and no amounts were accrued for penalties related to unrecognized tax benefits as of Sept. 30, 2019 or Dec. 31, 2018 .

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	9 Months Ended
	Sep. 30, 2019
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, hierarchical framework for measuring assets and liabilities and requires disclosure about assets and liabilities measured at fair value. 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: Cash equivalents — The fair values of cash equivalents are generally based on cost plus accrued interest; money market funds are measured using quoted NAVs. 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 generally utilize observable forward prices and volatilities, as well as observable pricing adjustments for specific delivery locations, and are generally assigned a Level 2 classification. When contractual settlements relate to delivery locations for which pricing is relatively unobservable, or extend to periods beyond those readily observable on active exchanges or quoted by brokers, the significance of the use of less observable inputs 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 may enter into various instruments that effectively fix the yield or price on a specified benchmark interest rate for an anticipated debt issuance for a specific period. These derivative instruments are generally designated as cash flow hedges for accounting purposes. At Sept. 30, 2019 , accumulated other comprehensive loss related to interest rate derivatives included no net gains or losses expected to be reclassified into earnings during the next 12 months. 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. Gross notional amounts of commodity options: (Amounts in Millions) (a)(b) Sept. 30, 2019 Dec. 31, 2018 Million British thermal Units (MMBtu) of natural gas 0.6 1.2 (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. Consideration of Credit Risk and Concentrations — NSP-Wisconsin continuously monitors the creditworthiness of 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. Impact of credit risk was immaterial to the fair value of unsettled commodity derivatives presented in the consolidated balance sheets. Impact of Derivative Activities on Income and Accumulated Other Comprehensive Loss — There were no pre-tax gains or losses related to interest rate derivatives reclassified from accumulated other comprehensive loss into earnings for the three and nine months ended Sept. 30, 2019 . There were immaterial pre-tax losses and $0.1 million of net losses reclassified from accumulated other comprehensive loss into earnings during the three and nine months ended Sept. 30, 2018 , respectively. Changes in the fair value of natural gas commodity derivatives resulted in $0.2 million of net losses and immaterial net losses for the three months ended Sept. 30, 2019 and 2018 , respectively, which were recognized as regulatory assets and liabilities. There were $0.2 million of net losses and immaterial net losses for the nine months ended Sept. 30, 2019 , and 2018 , respectively, which were recognized as regulatory assets and liabilities. The classification as a regulatory asset or liability is based on approved regulatory recovery mechanisms. During both the three months ended Sept. 30, 2019 and 2018 , there were no settlement gains or losses on natural gas commodity derivatives. For the nine months ended Sept. 30, 2019 and 2018 , there were $0.1 million of losses and no gains or losses, respectively, recognized 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. NSP-Wisconsin had no derivative instruments designated as fair value hedges during the three and nine months ended Sept. 30, 2019 and 2018 . Recurring Fair Value Measurements — The following tables presents for each of the fair value hierarchy levels, NSP-Wisconsin's derivative assets and liabilities measured at fair value on a recurring basis: Sept. 30, 2019 Fair Value Fair Value Total Netting (a) Total (b) (Millions of Dollars) Level 1 Level 2 Level 3 Current derivative assets Natural gas commodity $ — $ 0.8 $ — $ 0.8 $ — $ 0.8 Current derivative liabilities Natural gas commodity $ — $ 0.4 $ — $ 0.4 $ — $ 0.4 Dec. 31, 2018 Fair Value Fair Value Total Netting (a) Total (c) (Millions of Dollars) Level 1 Level 2 Level 3 Current derivative assets Natural gas commodity $ — $ 0.2 $ — $ 0.2 $ — $ 0.2 (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 Sept. 30, 2019 and Dec. 31, 2018 . 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 $4.6 million and other current liabilities balance of $15.0 million at Sept. 30, 2019 , in the consolidated balance sheets. (c) Included in prepayments and other current assets balance of $3.3 million at Dec. 31, 2018, in the consolidated balance sheets. Fair Value of Long-Term Debt Other financial instruments for which the carrying amount did not equal fair value: Sept. 30, 2019 Dec. 31, 2018 (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Long-term debt, including current portion $ 807.9 $ 954.0 $ 807.5 $ 850.4 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. Fair value estimates are based on information available to management as of Sept. 30, 2019 and Dec. 31, 2018 , and given the observability of the inputs, fair values presented for long-term debt were assigned as Level 2.

Benefit Plans and Other Postret

Benefit Plans and Other Postretirement Benefits	9 Months Ended
	Sep. 30, 2019
Retirement Benefits [Abstract]
Benefit Plans and Other Postretirement Benefits	Benefit Plans and Other Postretirement Benefits Components of Net Periodic Benefit Cost Three Months Ended Sept. 30 2019 2018 2019 2018 (Millions of Dollars) Pension Benefits Postretirement Health Care Benefits Service cost $ 1.1 $ 1.2 $ — $ — Interest cost (a) 1.4 1.4 0.1 0.2 Expected return on plan assets (a) (2.0 ) (2.3 ) — — Amortization of prior service credit (a) — — (0.1 ) (0.1 ) Amortization of net loss (a) 1.1 1.4 0.1 0.1 Settlement charge (b) — 5.2 — — Net periodic benefit cost 1.6 6.9 0.1 0.2 Costs not recognized due to the effects of regulation — (3.1 ) — — Net benefit cost recognized for financial reporting $ 1.6 $ 3.8 $ 0.1 $ 0.2 Nine Months Ended Sept. 30 2019 2018 2019 2018 (Millions of Dollars) Pension Benefits Postretirement Health Care Benefits Service cost $ 3.3 $ 3.6 $ — $ — Interest cost (a) 4.3 4.1 0.4 0.4 Expected return on plan assets (a) (6.2 ) (6.8 ) — — Amortization of prior service credit (a) — — (0.2 ) (0.2 ) Amortization of net loss (a) 3.3 4.2 0.2 0.4 Settlement charge (b) — 5.2 — — Net periodic benefit cost 4.7 10.3 0.4 0.6 Credits (costs) not recognized due to the effects of regulation 0.2 (2.8 ) — — Net benefit cost recognized for financial reporting $ 4.9 $ 7.5 $ 0.4 $ 0.6 (a) The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the consolidated statement of income or capitalized on the consolidated balance sheet as a regulatory asset. (b) A settlement charge is required when the amount of all lump-sum distributions during the year is greater than the sum of the service and interest cost components of the annual net periodic pension cost. In the third quarter of 2018 as a result of lump-sum distributions during the 2018 plan year, NSP-Wisconsin recorded a total pension settlement charge of $5.2 million , the majority of which was not recognized due to the effects of regulation. A total of $1.2 million of that amount was recorded in other expense in the third quarter of 2018. In January 2019, contributions of $150.0 million were made across four of Xcel Energy’s pension plans, of which $7.2 million was attributable to NSP-Wisconsin. Xcel Energy does not expect additional pension contributions during 2019.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies The following includes commitments, contingencies and unresolved contingencies that are material to NSP-Wisconsin’s financial position. Legal Contingencies NSP-Wisconsin is involved in various litigation matters 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 losses 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, would have a material effect on NSP-Wisconsin’s financial statements. Unless otherwise required by GAAP, legal fees are expensed as incurred. Gas Trading Litigation — 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. Multiple lawsuits seeking monetary damages were commenced against e prime and its affiliates, including Xcel Energy, between 2003 and 2009 alleging fraud and anticompetitive activities in conspiring to restrain the trade of natural gas and manipulate natural gas prices. Cases were all consolidated in the U.S. District Court in Nevada. Two cases remain active which include an MDL matter consisting of a Colorado purported class (Breckenridge) and a Wisconsin purported class (Arandell Corp.). Breckenridge/Colorado — In February 2019, the MDL panel remanded Breckenridge back to the U.S. District Court in Colorado. Arandell Corp. — In February 2019, the case was remanded back to the U.S. District Court in Wisconsin. Xcel Energy has concluded that a loss is remote for both remaining lawsuits. Rate Matters MISO ROE Complaints — In November 2013 and February 2015, customers filed complaints against MISO TOs including NSP-Minnesota and NSP-Wisconsin. The first complaint argued for a reduction in the base ROE in MISO transmission formula rates from 12.38% to 9.15% , and removal of ROE adders (including those for RTO membership). The second complaint sought to reduce base ROE from 12.38% to 8.67% . In September 2016, the FERC issued an order granting a 10.32% base ROE ( 10.82% with the RTO adder) effective for the first complaint period of Nov. 12, 2013 to Feb. 11, 2015 and subsequent to the date of the order. The D.C. Circuit subsequently vacated and remanded FERC Opinion No. 531, which had established the ROE methodology on which the September 2016 FERC order was based. In October 2018, the FERC issued an ROE order that addressed the D.C. Circuit’s actions. Under a new proposed two step ROE approach, the FERC indicated an intention to dismiss an ROE complaint if the existing ROE falls within the range of just and reasonable ROEs based on equal weighting of the Discounted Cash Flows (DCF), Capital Asset Pricing Model (CAPM), and Expected Earnings models. The FERC proposed that if necessary, it would then set a new ROE by averaging the results of these models plus a Risk Premium model. The FERC subsequently made preliminary determinations in a November 2018 order that the MISO TO's base ROE in effect for the first complaint period ( 12.38% ) was outside the range of reasonableness, and should be reduced. The FERC indicated its preliminary analysis using the new ROE approach resulted in a base ROE of 10.28% for the first complaint period, compared to the previously ordered base ROE of 10.32% . NSP-Minnesota has recognized a current refund liability consistent with its best estimate of the final ROE, pending further FERC action as early as the fourth quarter of 2019. On March 21, 2019, FERC announced a NOI seeking public comments on whether, and if so how, to revise ROE policies in light of the D.C. Circuit Court decision. FERC also initiated a NOI on whether to revise its policies on incentives for electric transmission investments, including the RTO membership incentive. Initial comments on both NOIs were due in June 2019, with reply comments submitted in the third quarter of 2019, pending further FERC action as early as the fourth quarter of 2019. Environmental MGP Sites Ashland MGP Site — NSP-Wisconsin was named a responsible party for contamination at the Ashland/Northern States Power Lakefront Superfund Site (the Site) in Ashland, Wisconsin. Remediation and restoration activities are anticipated to be completed in 2019 and groundwater treatment activities will continue for many years. The current cost estimate for remediation and restoration of the entire Site is approximately $194.0 million . At Sept. 30, 2019 and Dec. 31, 2018, NSP-Wisconsin had a total liability of $21.6 million and $26.9 million , respectively, for the entire site. NSP-Wisconsin has deferred the unrecovered portion of the estimated Site remediation and restoration costs as a regulatory asset. The PSCW has authorized NSP-Wisconsin rate recovery for all remediation and restoration costs incurred at the Site. In 2012, the PSCW agreed to allow NSP-Wisconsin to pre-collect certain costs, to amortize costs over 10 years and to apply a 3% carrying cost to the unamortized regulatory asset. MGP, Landfill or Disposal Sites — NSP-Wisconsin is currently investigating or remediating two other MGP, landfill or other disposal sites across its service territories. NSP-Wisconsin has recognized its best estimate of costs/liabilities that will result from final resolution of these issues, however, the outcome and timing is unknown. In addition, there may be insurance recovery and/or recovery from other potentially responsible parties, offsetting a portion of costs incurred.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2019
Segment Reporting [Abstract]
Segment Information	Segment Information Operating results from 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 - The regulated electric utility segment generates electricity, which is transmitted and distributed in Wisconsin and Michigan. • Regulated Natural Gas - The regulated natural gas utility segment purchases, transports, stores and distributes natural gas in portions of Wisconsin and Michigan. • All Other - 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. As an integrated electric and natural gas utility, NSP-Wisconsin operates significant assets that are not dedicated to a specific business segment. Reporting assets and capital expenditures by business segment would require arbitrary and potentially misleading allocations, which may not necessarily reflect the assets required for the operation of the business segments on a stand-alone basis. Certain costs, such as common depreciation, common O&M expenses and interest expense are allocated based on cost causation allocators across each segment. In addition, a general allocator is used for certain general and administrative expenses, including office supplies, rent, property insurance and general advertising. NSP-Wisconsin's segment information for the three and nine months ended Sept. 30 : Three Months Ended Sept. 30 (Millions of Dollars) 2019 2018 Regulated Electric Operating revenues (a) $ 229.0 $ 240.3 Intersegment revenues — 0.1 Total operating revenue 229.0 240.4 Net income 33.3 34.3 Regulated Natural Gas Operating revenues $ 14.6 $ 15.4 Intersegment revenues 0.1 — Total operating revenue 14.7 15.4 Net loss (4.1 ) (3.5 ) All Other Operating revenues $ 0.1 $ 0.3 Net income 0.2 0.2 Consolidated Total Operating revenues (a) $ 243.8 $ 256.1 Reconciling Eliminations (0.1 ) (0.1 ) Total operating revenue $ 243.7 $ 256.0 Net income 29.4 31.0 (a) Operating revenues include $44.7 million and $39.9 million of affiliate electric revenue for the three months ended Sept. 30, 2019 and 2018 , respectively. Nine Months Ended Sept. 30 (Millions of Dollars) 2019 2018 Regulated Electric Operating revenues (a) $ 651.9 $ 666.2 Intersegment revenues 0.2 0.3 Total operating revenue 652.1 666.5 Net income 57.4 70.2 Regulated Natural Gas Operating revenues $ 96.6 $ 93.8 Intersegment revenues 0.3 0.2 Total operating revenue 96.9 94.0 Net income 5.1 6.8 All Other Operating revenues $ 0.3 $ 0.9 Net (loss) income (0.6 ) 0.6 Consolidated Total Operating revenues (a) $ 749.3 $ 761.4 Reconciling Eliminations (0.5 ) (0.5 ) Total operating revenue $ 748.8 $ 760.9 Net income 61.9 77.6 (a) Operating revenues include $132.3 million and $116.0 million of affiliate electric revenue for the nine months ended Sept. 30 2019 and 2018 , respectively.

Selected Balance Sheet Data (Ta

Selected Balance Sheet Data (Tables)	9 Months Ended
	Sep. 30, 2019
Balance Sheet Related Disclosures [Abstract]
Accounts Receivable, Net	(Millions of Dollars) Sept. 30, 2019 Dec. 31, 2018 Accounts receivable, net Accounts receivable $ 54.0 $ 80.7 Less allowance for bad debts (5.1 ) (5.6 ) Accounts receivable, net $ 48.9 $ 75.1
Inventories	(Millions of Dollars) Sept. 30, 2019 Dec. 31, 2018 Inventories Materials and supplies $ 7.0 $ 6.7 Fuel 4.1 3.8 Natural gas 6.9 6.6 Total inventories $ 18.0 $ 17.1
Property, Plant and Equipment, Net	(Millions of Dollars) Sept. 30, 2019 Dec. 31, 2018 Property, plant and equipment, net Electric plant $ 2,963.7 $ 2,895.5 Natural gas plant 358.9 345.7 Common and other property 199.2 189.7 Construction work in progress 80.1 55.0 Total property, plant and equipment 3,601.9 3,485.9 Less accumulated depreciation (1,297.6 ) (1,244.3 ) Property, plant and equipment, net $ 2,304.3 $ 2,241.6

Borrowings and Other Financin_2

Borrowings and Other Financing Instruments (Tables)	9 Months Ended
	Sep. 30, 2019
Borrowings and Other Financing Instruments [Abstract]
Credit Facilities	As of Sept. 30, 2019 , NSP-Wisconsin had the following committed credit facility available (in millions of dollars): Credit Facility (a) Outstanding (b) Available $ 150 $ 68 $ 82 (a) This credit facility expires in June 2024 . (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 Sept. 30, 2019 Year Ended Dec. 31, 2018 Borrowing limit $ 150 $ 150 Amount outstanding at period end 68 51 Average amount outstanding 43 28 Maximum amount outstanding 68 103 Weighted average interest rate, computed on a daily basis 2.45 % 2.31 % Weighted average interest rate at period end 2.27 2.89
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) Sept. 30, 2019 Dec. 31, 2018 Notes payable to affiliates $ — $ 0.6 Weighted average interest rate at period end N/A 2.89 %

Revenues (Tables)

Revenues (Tables)	9 Months Ended
	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	NSP-Wisconsin’s operating revenues consists of the following: Three Months Ended Sept. 30, 2019 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 63.6 $ 6.9 $ — $ 70.5 C&I 116.6 6.1 — 122.7 Other 0.9 — 0.1 1.0 Total retail 181.1 13.0 0.1 194.2 Interchange 44.7 — — 44.7 Other 0.3 1.0 — 1.3 Total revenue from contracts with customers 226.1 14.0 0.1 240.2 Alternative revenue and other 2.9 0.6 — 3.5 Total revenues $ 229.0 $ 14.6 $ 0.1 $ 243.7 Three Months Ended Sept. 30, 2018 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 67.9 $ 7.0 $ — $ 74.9 C&I 127.9 6.9 — 134.8 Other 1.3 — 0.3 1.6 Total retail 197.1 13.9 0.3 211.3 Interchange 40.0 — — 40.0 Other 0.4 0.9 — 1.3 Total revenue from contracts with customers 237.5 14.8 0.3 252.6 Alternative revenue and other 2.8 0.6 — 3.4 Total revenues $ 240.3 $ 15.4 $ 0.3 $ 256.0 Nine Months Ended Sept. 30, 2019 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 185.1 $ 51.3 $ — $ 236.4 C&I 320.2 40.5 — 360.7 Other 4.5 — 0.3 4.8 Total retail 509.8 91.8 0.3 601.9 Interchange 132.3 — — 132.3 Other 0.9 3.0 — 3.9 Total revenue from contracts with customers 643.0 94.8 0.3 738.1 Alternative revenue and other 8.9 1.8 — 10.7 Total revenues $ 651.9 $ 96.6 $ 0.3 $ 748.8 Nine Months Ended Sept. 30, 2018 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 194.5 $ 48.2 $ — $ 242.7 C&I 339.1 40.8 0.1 380.0 Other 4.7 — 0.8 5.5 Total retail 538.3 89.0 0.9 628.2 Interchange 116.0 — — 116.0 Other 3.2 3.0 — 6.2 Total revenue from contracts with customers 657.5 92.0 0.9 750.4 Alternative revenue and other 8.7 1.8 — 10.5 Total revenues $ 666.2 $ 93.8 $ 0.9 $ 760.9

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The following table reconciles the difference between the statutory rate and the ETR: Nine Months Ended Sept. 30 2019 2018 Federal statutory rate 21.0 % 21.0 % State tax (net of federal tax effect) 6.2 6.2 Increases (decreases) in tax from: Tax credits and tax credit and NOL allowances (net) (1.5 ) (0.7 ) Prior period adjustments 0.4 (0.6 ) Plant regulatory differences (a) (0.4 ) (1.6 ) Other (net) 0.7 0.4 Effective income tax rate 26.4 % 24.7 % (a) Regulatory differences for income tax primarily relates to the credit of excess deferred taxes to customers through the average rate assumption method and the impact of AFUDC - equity. Year-to-date variations primarily relate to the impact of AFUDC - equity.
Summary of Statute of Limitations Applicable to Open Tax Years [Table Text Block]	Federal Audits — NSP-Wisconsin is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. Statute of limitations applicable to Xcel Energy’s consolidated federal income tax returns expire as follows: Tax Year(s) Expiration 2009 - 2013 June 2020 2014 - 2016 September 2020
Reconciliation of Unrecognized Tax Benefits	Unrecognized tax benefits — permanent vs. temporary: (Millions of Dollars) Sept. 30, 2019 Dec. 31, 2018 Unrecognized tax benefit — Permanent tax positions $ 2.5 $ 2.0 Unrecognized tax benefit — Temporary tax positions 0.8 0.8 Total unrecognized tax benefit $ 3.3 $ 2.8
Tax Benefits Associated with NOL and Tax Credit Carryforwards	Unrecognized tax benefits were reduced by tax benefits associated with NOL and tax credit carryforwards: (Millions of Dollars) Sept. 30, 2019 Dec. 31, 2018 NOL and tax credit carryforwards $ (2.5 ) $ (2.1 )

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Gross Notional Amounts of Commodity Forwards and Options	Gross notional amounts of commodity options: (Amounts in Millions) (a)(b) Sept. 30, 2019 Dec. 31, 2018 Million British thermal Units (MMBtu) of natural gas 0.6 1.2 (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 tables presents for each of the fair value hierarchy levels, NSP-Wisconsin's derivative assets and liabilities measured at fair value on a recurring basis: Sept. 30, 2019 Fair Value Fair Value Total Netting (a) Total (b) (Millions of Dollars) Level 1 Level 2 Level 3 Current derivative assets Natural gas commodity $ — $ 0.8 $ — $ 0.8 $ — $ 0.8 Current derivative liabilities Natural gas commodity $ — $ 0.4 $ — $ 0.4 $ — $ 0.4 Dec. 31, 2018 Fair Value Fair Value Total Netting (a) Total (c) (Millions of Dollars) Level 1 Level 2 Level 3 Current derivative assets Natural gas commodity $ — $ 0.2 $ — $ 0.2 $ — $ 0.2 (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 Sept. 30, 2019 and Dec. 31, 2018 . 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 $4.6 million and other current liabilities balance of $15.0 million at Sept. 30, 2019 , in the consolidated balance sheets. (c) Included in prepayments and other current assets balance of $3.3 million at Dec. 31, 2018, in the consolidated balance sheets.
Carrying Amount and Fair Value of Long-term Debt	Other financial instruments for which the carrying amount did not equal fair value: Sept. 30, 2019 Dec. 31, 2018 (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Long-term debt, including current portion $ 807.9 $ 954.0 $ 807.5 $ 850.4

Benefit Plans and Other Postr_2

Benefit Plans and Other Postretirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2019
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Cost	Components of Net Periodic Benefit Cost Three Months Ended Sept. 30 2019 2018 2019 2018 (Millions of Dollars) Pension Benefits Postretirement Health Care Benefits Service cost $ 1.1 $ 1.2 $ — $ — Interest cost (a) 1.4 1.4 0.1 0.2 Expected return on plan assets (a) (2.0 ) (2.3 ) — — Amortization of prior service credit (a) — — (0.1 ) (0.1 ) Amortization of net loss (a) 1.1 1.4 0.1 0.1 Settlement charge (b) — 5.2 — — Net periodic benefit cost 1.6 6.9 0.1 0.2 Costs not recognized due to the effects of regulation — (3.1 ) — — Net benefit cost recognized for financial reporting $ 1.6 $ 3.8 $ 0.1 $ 0.2 Nine Months Ended Sept. 30 2019 2018 2019 2018 (Millions of Dollars) Pension Benefits Postretirement Health Care Benefits Service cost $ 3.3 $ 3.6 $ — $ — Interest cost (a) 4.3 4.1 0.4 0.4 Expected return on plan assets (a) (6.2 ) (6.8 ) — — Amortization of prior service credit (a) — — (0.2 ) (0.2 ) Amortization of net loss (a) 3.3 4.2 0.2 0.4 Settlement charge (b) — 5.2 — — Net periodic benefit cost 4.7 10.3 0.4 0.6 Credits (costs) not recognized due to the effects of regulation 0.2 (2.8 ) — — Net benefit cost recognized for financial reporting $ 4.9 $ 7.5 $ 0.4 $ 0.6 (a) The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the consolidated statement of income or capitalized on the consolidated balance sheet as a regulatory asset. (b) A settlement charge is required when the amount of all lump-sum distributions during the year is greater than the sum of the service and interest cost components of the annual net periodic pension cost. In the third quarter of 2018 as a result of lump-sum distributions during the 2018 plan year, NSP-Wisconsin recorded a total pension settlement charge of $5.2 million , the majority of which was not recognized due to the effects of regulation. A total of $1.2 million of that amount was recorded in other expense in the third quarter of 2018.

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2019
Segment Reporting [Abstract]
Results from Operations by Reportable Segment	Nine Months Ended Sept. 30 (Millions of Dollars) 2019 2018 Regulated Electric Operating revenues (a) $ 651.9 $ 666.2 Intersegment revenues 0.2 0.3 Total operating revenue 652.1 666.5 Net income 57.4 70.2 Regulated Natural Gas Operating revenues $ 96.6 $ 93.8 Intersegment revenues 0.3 0.2 Total operating revenue 96.9 94.0 Net income 5.1 6.8 All Other Operating revenues $ 0.3 $ 0.9 Net (loss) income (0.6 ) 0.6 Consolidated Total Operating revenues (a) $ 749.3 $ 761.4 Reconciling Eliminations (0.5 ) (0.5 ) Total operating revenue $ 748.8 $ 760.9 Net income 61.9 77.6 (a) Operating revenues include $132.3 million and $116.0 million of affiliate electric revenue for the nine months ended Sept. 30 2019 and 2018 , respectively. NSP-Wisconsin's segment information for the three and nine months ended Sept. 30 : Three Months Ended Sept. 30 (Millions of Dollars) 2019 2018 Regulated Electric Operating revenues (a) $ 229.0 $ 240.3 Intersegment revenues — 0.1 Total operating revenue 229.0 240.4 Net income 33.3 34.3 Regulated Natural Gas Operating revenues $ 14.6 $ 15.4 Intersegment revenues 0.1 — Total operating revenue 14.7 15.4 Net loss (4.1 ) (3.5 ) All Other Operating revenues $ 0.1 $ 0.3 Net income 0.2 0.2 Consolidated Total Operating revenues (a) $ 243.8 $ 256.1 Reconciling Eliminations (0.1 ) (0.1 ) Total operating revenue $ 243.7 $ 256.0 Net income 29.4 31.0 (a) Operating revenues include $44.7 million and $39.9 million of affiliate electric revenue for the three months ended Sept. 30, 2019 and 2018 , respectively.

Selected Balance Sheet Data, Ac

Selected Balance Sheet Data, Accounts Receivable (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Accounts Receivable, Net
Accounts receivable	$ 54	$ 80.7
Less allowance for bad debts	(5.1)	(5.6)
Accounts receivable, net	$ 48.9	$ 75.1

Selected Balance Sheet Data, In

Selected Balance Sheet Data, Inventory (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Public Utilities, Inventory [Line Items]
Total Inventories	$ 18	$ 17.1
Materials and supplies
Public Utilities, Inventory [Line Items]
Inventories	7	6.7
Fuel
Public Utilities, Inventory [Line Items]
Inventories	4.1	3.8
Natural gas
Public Utilities, Inventory [Line Items]
Inventories	$ 6.9	$ 6.6

Selected Balance Sheet Data, Pr

Selected Balance Sheet Data, Property, Plant and Equipment (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 3,601.9	$ 3,485.9
Less accumulated depreciation	(1,297.6)	(1,244.3)
Property, plant and equipment, net	2,304.3	2,241.6
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2,963.7	2,895.5
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	358.9	345.7
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	199.2	189.7
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 80.1	$ 55

Borrowings and Other Financin_3

Borrowings and Other Financing Instruments, Commercial Paper (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Amount outstanding at period end	$ 68,000,000	$ 51,000,000
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	150,000,000	150,000,000
Amount outstanding at period end	68,000,000	51,000,000
Average amount outstanding	43,000,000	28,000,000
Maximum amount outstanding	$ 68,000,000	$ 103,000,000
Weighted average interest rate, computed on a daily basis	2.45%	2.31%
Weighted average interest rate at period end	2.27%	2.89%

Borrowings and Other Financin_4

Borrowings and Other Financing Instruments, Letters of Credit (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 68	$ 51
Letter of Credit
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 0	$ 0
Credit Facility
Line of Credit Facility [Line Items]
Term of letters of credit (in years)	1 year

Borrowings and Other Financin_5

Borrowings and Other Financing Instruments, Credit Facility (Details) - Credit Facility - USD ($)		Sep. 30, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Credit Facility	[1]	$ 150,000,000
Outstanding	[2]	68,000,000
Available		82,000,000
Direct advances on the credit facility outstanding		$ 0	$ 0
[1]	This credit facility expires in June 2024 .
[2]	Includes outstanding commercial paper.

Borrowings and Other Financin_6

Borrowings and Other Financing Instruments, Intercompany Borrowing Arrangement and Other Short-Term Borrowings (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Notes payable to affiliates	$ 0	$ 0.6
Notes Payable To Affiliates
Short-term Debt [Line Items]
Notes payable to affiliates	$ 0	$ 0.6
Weighted average interest rate at period end		2.89%

Revenues (Details)

Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ 243.7	$ 256	$ 748.8	$ 760.9
Regulated Electric | Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	229	240.3	651.9	666.2
Regulated Natural Gas | Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	14.6	15.4	96.6	93.8
All Other | Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	0.1	0.3	0.3	0.9
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	240.2	252.6	738.1	750.4
Total revenue from contracts with customers | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	226.1	237.5	643	657.5
Total revenue from contracts with customers | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14	14.8	94.8	92
Total revenue from contracts with customers | All Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0.1	0.3	0.3	0.9
Retail
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	194.2	211.3	601.9	628.2
Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	70.5	74.9	236.4	242.7
Retail | Commercial and industrial (C&I)
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	122.7	134.8	360.7	380
Retail | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1.6	4.8	5.5
Retail | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	181.1	197.1	509.8	538.3
Retail | Regulated Electric | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	63.6	67.9	185.1	194.5
Retail | Regulated Electric | Commercial and industrial (C&I)
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	116.6	127.9	320.2	339.1
Retail | Regulated Electric | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0.9	1.3	4.5	4.7
Retail | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	13.9	91.8	89
Retail | Regulated Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6.9	7	51.3	48.2
Retail | Regulated Natural Gas | Commercial and industrial (C&I)
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6.1	6.9	40.5	40.8
Retail | Regulated Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Retail | All Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0.1	0.3	0.3	0.9
Retail | All Other | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Retail | All Other | Commercial and industrial (C&I)
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0.1
Retail | All Other | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0.1	0.3	0.3	0.8
Interchange [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	44.7	40	132.3	116
Interchange [Member] | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	44.7	40	132.3	116
Interchange [Member] | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Interchange [Member] | All Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1.3	1.3	3.9	6.2
Other | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0.3	0.4	0.9	3.2
Other | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0.9	3	3
Other | All Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Alternative revenue and other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	3.5	3.4	10.7	10.5
Alternative revenue and other | Regulated Electric
Disaggregation of Revenue [Line Items]
Alternative revenue and other	2.9	2.8	8.9	8.7
Alternative revenue and other | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Alternative revenue and other	0.6	0.6	1.8	1.8
Alternative revenue and other | All Other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	$ 0	$ 0	$ 0	$ 0

Income Taxes (Details)

Income Taxes (Details) - USD ($)		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Tax Examination [Line Items]
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards		$ (1,600,000)		$ (1,100,000)
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent		6.20%	6.20%
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent		0.40%	(0.60%)
Regulatory difference - tax credits and tax credit and NOL allowances (net)		(1.50%)	(0.70%)
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent	[1]	(0.40%)	(1.60%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent		0.70%	0.40%
Effective Income Tax Rate Reconciliation, Percent		26.40%	24.70%
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions		$ 2,500,000		2,000,000
Unrecognized tax benefit — Temporary tax positions		800,000		800,000
Total unrecognized tax benefit		3,300,000		2,800,000
NOL and tax credit carryforwards		(2,500,000)		(2,100,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible		2,200,000
Amounts accrued for penalties related to unrecognized tax benefits		0		$ 0
Internal Revenue Service (IRS)
Tax Audits [Abstract]
Potential Tax Adjustments		0
State Jurisdiction (Wisconsin)
Tax Audits [Abstract]
Potential Tax Adjustments		$ 0
[1]	Regulatory differences for income tax primarily relates to the credit of excess deferred taxes to customers through the average rate assumption method and the impact of AFUDC - equity. Year-to-date variations primarily relate to the impact of AFUDC - equity.

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details) MMBTU in Millions, $ in Millions		Sep. 30, 2019USD ($)MMBTU	Dec. 31, 2018MMBTU
Interest Rate Swap
Derivative [Line Items]
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net | $		$ 0
Natural Gas Commodity (in million British thermal units)
Gross Notional Amounts of Commodity Options [Abstract]
Derivative, Nonmonetary Notional amount | MMBTU	[1],[2]	0.6	1.2
[1]	Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.
[2]	Amounts are not reflective of net positions in the underlying commodities.

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract]
Derivative instruments designated as fair value hedges	$ 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	200,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	0	0	(100,000)	$ 0
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	$ 0	$ 100,000	$ 0

Fair Value of Financial Asset_5

Fair Value of Financial Assets and Liabilities, Derivative Assets and Liabilities at Fair Value (Details) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Prepayments and other		$ 4.6	$ 3.3
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]	0.8	0.2
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[2]	0	0
Fair Value Measured on a Recurring Basis | Other Current Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		0
Derivative Liability		0.4
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0	0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		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		0.8	0.2
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0.4
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0	0
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis
Derivatives, Fair Value [Line Items]
Prepayments and other		4.6	3.3
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		0.8	$ 0.2
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		$ 0.4
[1]	Included in prepayments and other current assets balance of $4.6 million and other current liabilities balance of $15.0 million at Sept. 30, 2019 , 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 Sept. 30, 2019 and Dec. 31, 2018 . The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

Fair Value of Financial Asset_6

Fair Value of Financial Assets and Liabilities, Fair Value of Long-Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	$ 807.9	$ 807.5
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 954	$ 850.4

Benefit Plans and Other Postr_3

Benefit Plans and Other Postretirement Benefits (Details) $ in Millions		1 Months Ended	3 Months Ended		9 Months Ended
		Jan. 31, 2019USD ($)Plan	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)
Components of Net Periodic Benefit Cost [Abstract]
Operating and maintenance expenses			$ 47.5	$ 50	$ 150.8	$ 149.3
Pension Plan [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost			1.1	1.2	3.3	3.6
Interest cost (a)	[1]		1.4	1.4	4.3	4.1
Expected return on plan assets (a)	[1]		(2)	(2.3)	(6.2)	(6.8)
Amortization of prior service cost (credit) (a)	[1]		0	0	0	0
Amortization of net loss (a)	[1]		1.1	1.4	3.3	4.2
Settlement charge (b)	[2]		0	5.2	0	5.2
Net periodic benefit cost			1.6	6.9	4.7	10.3
Credits (costs) not recognized due to the effects of regulation			0	(3.1)	0.2	(2.8)
Net benefit cost recognized for financial reporting			1.6	3.8	4.9	7.5
Operating and maintenance expenses						1.2
Contributions to pension plans		$ 7.2
Pension Plan [Member] | Xcel Energy Inc.
Components of Net Periodic Benefit Cost [Abstract]
Contributions to pension plans		$ 150
Number of Xcel Energy's pension plans to which contributions were made | Plan		4
Other Postretirement Benefits Plan [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost			0	0	0	0
Interest cost (a)	[1]		0.1	0.2	0.4	0.4
Expected return on plan assets (a)	[1]		0	0	0	0
Amortization of prior service cost (credit) (a)	[1]		(0.1)	(0.1)	(0.2)	(0.2)
Amortization of net loss (a)	[1]		0.1	0.1	0.2	0.4
Settlement charge (b)	[2]		0	0	0	0
Net periodic benefit cost			0.1	0.2	0.4	0.6
Credits (costs) not recognized due to the effects of regulation			0	0	0	0
Net benefit cost recognized for financial reporting			$ 0.1	$ 0.2	$ 0.4	$ 0.6
[1]	The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the consolidated statement of income or capitalized on the consolidated balance sheet as a regulatory asset.
[2]	A settlement charge is required when the amount of all lump-sum distributions during the year is greater than the sum of the service and interest cost components of the annual net periodic pension cost. In the third quarter of 2018 as a result of lump-sum distributions during the 2018 plan year, NSP-Wisconsin recorded a total pension settlement charge of $5.2 million , the majority of which was not recognized due to the effects of regulation. A total of $1.2 million of that amount was recorded in other expense in the third quarter of 2018.

Commitments and Contingencies G

Commitments and Contingencies Gas Trading Litigation (Details)	Dec. 31, 2018
Gas Trading Litigation
Loss Contingencies [Line Items]
Loss Contingency, Pending Claims, Number	2

MISO ROE Complaints (Details)

MISO ROE Complaints (Details) - NSP-Minnesota - FERC Proceeding, MISO ROE Complaint	1 Months Ended		12 Months Ended
	Feb. 28, 2015	Nov. 30, 2013	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Rate Matters [Abstract]
Public Utilities, Base Return On Equity Charged To Customers Through Transmission Formula Rates	12.38%	12.38%
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Recommended By Third Parties	8.67%	9.15%
Public Utilities, Number of steps required			2
Public Utilities, ROE developed with new approach			10.28%
Federal Energy Regulatory Commission (FERC)
Rate Matters [Abstract]
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, Approved					10.32%
Public Utilities, ROE Applicable To Transmission Formula Rates In The MISO Region, with RTO Adder, Approved				10.82%

Commitments and Contingencies,

Commitments and Contingencies, Environmental Contingencies - Site Contingencies (Details) - Ashland MGP Site - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Ashland Manufactured Gas Plant (MGP) Site [Abstract]
Current Cost Estimate for Site Remediation	$ 194
Accrual for Environmental Loss Contingencies, Gross	$ 21.6	$ 26.9
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%

Commitments and Contingencies E

Commitments and Contingencies Environmental, MGP, Landfill or Disposal Sites (Details)	Sep. 30, 2019
Other MGP, Landfill, or Disposal Sites [Domain]
Site Contingency [Line Items]
Number of identified MGP, landfill, or disposal sites under current investigation and/or remediation in addition to those separately disclosed	2

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019		Sep. 30, 2018
Segment Reporting Information [Line Items]
Net income	$ 29.4		$ 31		$ 61.9		$ 77.6
Natural gas	14.6		15.4		96.6		93.8
Unregulated Operating Revenue	0.1		0.3		0.3		0.9
Regulated and Unregulated Operating Revenue	243.7		256		748.8		760.9
Affiliate Revenue	44.7		39.9		132.3		116
Regulated Electric
Segment Reporting Information [Line Items]
Revenues Including Intersegment Revenues	229		240.4		652.1		666.5
Net income	33.3		34.3		57.4		70.2
Regulated Natural Gas
Segment Reporting Information [Line Items]
Revenues Including Intersegment Revenues	14.7		15.4		96.9		94
Net income	(4.1)		(3.5)		5.1		6.8
All Other
Segment Reporting Information [Line Items]
Net income	0.2		0.2		(0.6)		0.6
Total revenues
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric	229	[1]	240.3	[1]	651.9	[2]	666.2	[2]
Natural gas	14.6		15.4		96.6		93.8
Unregulated Operating Revenue	0.1		0.3		0.3		0.9
Regulated and Unregulated Operating Revenue	243.8	[1]	256.1	[1]	749.3	[2]	761.4	[2]
Intersegment Eliminations
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric	0		0.1		0.2		0.3
Natural gas	0.1		0		0.3		0.2
Regulated and Unregulated Operating Revenue	$ (0.1)		$ (0.1)		$ (0.5)		$ (0.5)
[1]	Operating revenues include $44.7 million and $39.9 million of affiliate electric revenue for the three months ended Sept. 30, 2019 and 2018 , respectively.
[2]	Operating revenues include $132.3 million and $116.0 million of affiliate electric revenue for the nine months ended Sept. 30 2019 and 2018 , respectively.