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Income Taxes (Tables)
 12 Months Ended
Dec. 31, 2021
Income Tax Disclosure [Abstract]  
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. Statute of limitations applicable to Xcel Energy’s consolidated federal income tax returns expire as follows:
Tax Year(s)Expiration
2014 - 2016December 2022
2018September 2022
Reconciliation of Unrecognized Tax Benefits
Unrecognized tax benefits — permanent vs. temporary:
(Millions of Dollars)Dec. 31, 2021Dec. 31, 2020
Unrecognized tax benefit — Permanent tax positions$2 $1 
Unrecognized tax benefit — Temporary tax positions1 1 
Total unrecognized tax benefit$3 $2 
Changes in unrecognized tax benefits:
(Millions of Dollars)202120202019
Balance at Jan. 1$2 $3 $3 
Additions for tax positions of prior years1 1 — 
Reductions for tax positions of prior years— (2)— 
Balance at Dec. 31$3 $2 $3 
Tax Benefits Associated with NOL and Tax Credit Carryforwards
Unrecognized tax benefits were reduced by tax benefits associated with NOL and tax credit carryforwards:
(Millions of Dollars)Dec. 31, 2021Dec. 31, 2020
NOL and tax credit carryforwards$(2)$(2)
NOL and Tax Credit Carryforwards NOL amounts represent the tax loss that is carried forward and tax credits represent the deferred tax asset. NOL and tax credit carryforwards as of Dec. 31 were as follows:
(Millions of Dollars)20212020
Federal tax credit carryforwards$8 $7 
State NOL carryforward2 2 
Schedule of Effective Income Tax Rate Reconciliation
Effective income tax rate for years ended Dec. 31:
20212020
2019 (a)
Federal statutory rate21.0 %21.0 %21.0 %
State income tax on pretax income, net of federal tax effect6.2 6.2 6.2 
Increases (decreases) in tax from:
Plant regulatory differences (b)
(4.1)(19.3)(5.2)
Other tax credits, net NOL & tax credit allowances(1.0)(1.5)(1.8)
Change in unrecognized tax benefits0.3 (0.8)0.7 
Amortization of excess nonplant deferred taxes— (12.6)— 
Reversal of prior regulatory differences— — (3.6)
Other, net(0.7)— (0.5)
Effective income tax rate21.7 %(7.0)%16.8 %
(a)Prior periods have been reclassified to conform to current year presentation.
(b)Regulatory differences for income tax primarily relate to the credit of excess deferred taxes to customers through the average rate assumption method. Income tax benefits associated with the credit of excess deferred credits are offset by corresponding revenue reductions.
Schedule of Components of Income Tax Expense (Benefit)
Components of income tax expense for years ended Dec. 31:
(Millions of Dollars)202120202019
Current federal tax expense$17 $25 $6 
Current state tax expense4 6 5 
Current change in unrecognized tax (benefit) expense— (1)1 
Deferred federal tax expense (benefit)3 (37)3 
Deferred state tax expense6 1 2 
Deferred ITCs— (1)(1)
Total income tax expense (benefit)$30 $(7)$16 
Components of deferred income tax expense as of Dec. 31:
(Millions of Dollars)202120202019
Deferred tax expense excluding items below$18 $9 $17 
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities(10)(45)(12)
Other1 — — 
Deferred tax expense (benefit)$9 $(36)$5 
Schedule of Deferred Tax Assets and Liabilities
Components of net deferred tax liability as of Dec. 31:
(Millions of Dollars)2021
2020 (a)
Deferred tax liabilities:
Difference between book and tax bases of property$331 $324 
Regulatory assets29 32 
Pension expense11 12 
Deferred fuel costs8 — 
Other7 9 
Total deferred tax liabilities$386 $377 
Deferred tax assets:
Regulatory liabilities$38 $41 
Tax credit carryforward8 8 
Environmental remediation5 6 
Other employee benefits4 4 
Rate refund— 4 
Deferred ITCs2 3 
Other4 4 
Total deferred tax assets$61 $70 
Net deferred tax liability$325 $307 
(a) Prior periods have been reclassified to conform to current year presentation.