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Income Taxes (Tables)
 12 Months Ended
Dec. 31, 2022
Income Tax Disclosure [Abstract]  
Summary of Statute of Limitations Applicable to Open Tax Years
Tax Year(s)Expiration
2014 - 2016March 2024
2019October 2023
Reconciliation of Unrecognized Tax Benefits
Unrecognized tax benefits - permanent vs temporary:
(Millions of Dollars)Dec. 31, 2022Dec. 31, 2021
Unrecognized tax benefit — Permanent tax positions$11 $9 
Unrecognized tax benefit — Temporary tax positions2 2 
Total unrecognized tax benefit$13 $11 
Changes in unrecognized tax benefits:
(Millions of Dollars)202220212020
Balance at Jan. 1$11 $9 $12 
Additions based on tax positions related to the current year2 2 2 
Additions for tax positions of prior years— — 6 
Reductions for tax positions of prior years— — (11)
Balance at Dec. 31$13 $11 $9 
Tax Benefits Associated with NOL and Tax Credit Carryforwards
Unrecognized tax benefits were reduced by tax benefits associated with NOL and tax credit carryforwards:
(Millions of Dollars)Dec. 31, 2022Dec. 31, 2021
NOL and tax credit carryforwards$(12)$(11)
Interest Payable related to Unrecognized Tax Benefits
Interest payable related to unrecognized tax benefits:
(Millions of Dollars)202220212020
Payable for interest related to unrecognized tax benefits at Jan. 1$— $— $(1)
Interest income related to unrecognized tax benefits— — 1 
Payable for interest related to unrecognized tax benefits at Dec. 31$— $— $— 
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)20222021
Federal NOL carryforward$5 $161 
Federal tax credit carryforwards368 259 
State NOL carryforwards223 342 
State tax credit carryforwards, net of federal detriment (a)
16 17 
Valuation allowances for state credit carryforwards, net of federal benefit (b)
(6)(8)
(a)State tax credit carryforwards are net of federal detriment of $4 million and $5 million as of Dec. 31, 2022 and 2021.
(b)Valuation allowances for state tax credit carryforwards were net of federal benefit of $2 million as of Dec. 31, 2022 and 2021.
Schedule of Effective Income Tax Rate Reconciliation
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.
Effective income tax rate for years ended Dec. 31:
2022
2021 (c)
2020 (c)
Federal statutory rate21.0 %21.0 %21.0 %
State income tax on pretax income, net of federal tax effect3.5 3.6 3.6 
Increases (decreases) in tax from:
Wind PTCs (a)
(14.3)(14.3)(10.3)
Plant regulatory differences (b)
(4.5)(4.6)(5.0)
Other tax credits, net NOL & tax credit allowances(1.1)(1.0)(1.1)
Other, net0.2 0.1 (1.1)
Effective income tax rate4.8 %4.8 %7.1 %
(a)Wind PTCs are credited to customers (reduction to revenue) and do not materially impact net income.
(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 taxes are offset by corresponding revenue reductions and additional prepaid pension asset amortization.
(c)Prior period amounts have been restated to conform with current year presentation.
Schedule of Components of Income Tax Expense (Benefit)
Components of income tax expense for the years ended Dec. 31:
(Millions of Dollars)202220212020
Current federal tax expense$39 $16 $44 
Current state tax expense11 — 4 
Current change in unrecognized tax benefit— (1)(3)
Deferred federal tax benefit(32)(13)(26)
Deferred state tax expense21 31 26 
Deferred change in unrecognized tax expense1 3 2 
Deferred ITCs(3)(3)(2)
Total income tax expense$37 $33 $45 
Components of deferred income tax expense as of Dec. 31:
(Millions of Dollars)202220212020
Deferred tax expense excluding items below$23 $63 $46 
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities(32)(42)(43)
Tax expense allocated to other comprehensive income, and other(1)— (1)
Deferred tax (benefit) expense$(10)$21 $2 
Schedule of Deferred Tax Assets and Liabilities
Components of the net deferred tax liability as of Dec. 31:
(Millions of Dollars)2022
2021 (a)
Deferred tax liabilities:
Differences between book and tax bases of property$2,315 $2,226 
Regulatory assets246 255 
Deferred fuel costs125 126 
Operating lease assets112 106 
Pension expense and other employee benefits27 23 
Other11 4 
Total deferred tax liabilities$2,836 $2,740 
Deferred tax assets:
Regulatory liabilities$295 $320 
Tax credit carryforward385 276 
Operating lease liabilities112 106 
Bad debts14 10 
NOL carryforward9 46 
Deferred ITCs7 8 
Tax credit valuation allowances(6)(8)
Rate refund21 8 
Other16 14 
Total deferred tax assets$853 $780 
Net deferred tax liability$1,983 $1,960 
(a) Prior periods have been reclassified to conform to current year presentation.