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Income Taxes (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2026 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Income Tax [Line Items] |  |  |  |
Asset valuation charge for IPL's Lansing Generating Station |  | $ 60 | $ 0 | $ 0
State income tax rate, percent |  | (1.00%) | 2.00% | 3.00%
Reduction of tax-related regulatory assets |  | $ 70 | $ 24 | $ (108)
Income tax expense (benefit) |  | (114) | 4 | 22
Tax-related [Member] |  |  |  |
Income Tax [Line Items] |  |  |  |
Reduction of tax-related regulatory assets |  | 26 | 74 | 77
Income tax expense (benefit) |  | 11 | 10 | 8
IPL [Member] |  |  |  |
Income Tax [Line Items] |  |  |  |
Asset valuation charge for IPL's Lansing Generating Station |  | $ 60 | $ 0 | $ 0
State income tax rate, percent |  | (12.00%) | (2.00%) | (2.00%)
Reduction of tax-related regulatory assets |  | $ (2) | $ 58 | $ 56
Income tax expense (benefit) |  | (129) | (58) | (50)
IPL [Member] | Tax-related [Member] |  |  |  |
Income Tax [Line Items] |  |  |  |
Reduction of tax-related regulatory assets |  | $ 26 | $ 74 | $ 77
WPL [Member] |  |  |  |
Income Tax [Line Items] |  |  |  |
State income tax rate, percent |  | 6.00% | 5.00% | 6.00%
Reduction of tax-related regulatory assets |  | $ 72 | $ (34) | $ (163)
Income tax expense (benefit) |  | $ 11 | $ 60 | $ 66
State [Member] |  |  |  |
Income Tax [Line Items] |  |  |  |
State income tax rate, percent |  | 7.10% | 8.40% | 9.80%
State [Member] | Forecast [Member] |  |  |  |
Income Tax [Line Items] |  |  |  |
State income tax rate, percent | 5.50% |  |  |

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