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Income Taxes (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Income Tax [Line Items] |  |  |  |  |  |
Overall income tax rate |  |  | 1.00% | 3.00% | (12.00%) |
State income tax rate, percent |  |  | 2.00% | 3.00% | 2.00% |
Reduction of tax-related regulatory assets |  |  | $ 24 | $ (108) | $ 51 |
Income tax expense (benefit) |  |  | 4 | 22 | $ (74) |
Tax-related [Member] |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |
Reduction of tax-related regulatory assets |  |  | 74 | 77 |  |
Income tax expense (benefit) |  |  | $ 10 | $ 8 |  |
IPL [Member] |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |
Overall income tax rate |  |  | (19.00%) | (16.00%) | (11.00%) |
State income tax rate, percent |  |  | (2.00%) | (2.00%) | (1.00%) |
Reduction of tax-related regulatory assets |  |  | $ 58 | $ 56 | $ 30 |
Income tax expense (benefit) |  |  | (58) | (50) | $ (36) |
IPL [Member] | Tax-related [Member] |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |
Reduction of tax-related regulatory assets |  |  | $ 74 | $ 77 |  |
WPL [Member] |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |
Overall income tax rate |  |  | 15.00% | 17.00% | (24.00%) |
State income tax rate, percent |  |  | 5.00% | 6.00% | 6.00% |
Reduction of tax-related regulatory assets |  |  | $ (34) | $ (163) | $ 21 |
Income tax expense (benefit) |  |  | $ 60 | $ 66 | $ (51) |
State [Member] |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |
Overall income tax rate |  |  |  |  | 9.80% | 12.00%
State income tax rate, percent |  |  | 8.40% |  |  |
State [Member] | Forecast [Member] |  |  |  |  |  |
Income Tax [Line Items] |  |  |  |  |  |
State income tax rate, percent | 5.50% | 7.10% |  |  |  |

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