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Income Taxes (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022 | Dec. 31, 2024 | Dec. 31, 2023
Income Taxes [Line Items] |  |  |  |  |  |
Regulatory assets |  |  | $ (40) | $ 102 |  |
Income tax expense (benefit) | $ 5 | $ 14 | 3 | 26 |  |
Tax-related [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Regulatory assets | 73 |  |  |  |  |
Income tax expense (benefit) | 8 | 8 |  |  |  |
Forecast [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
State income tax rate, percent |  |  |  |  | 7.10% | 8.40%
IPL [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Regulatory assets |  |  | (55) | (18) |  |
Income tax expense (benefit) | (31) | (16) | (55) | (39) |  |
IPL [Member] | Tax-related [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Regulatory assets | 73 |  |  |  |  |
WPL [Member] |  |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |  |
Regulatory assets |  |  | 16 | 120 |  |
Income tax expense (benefit) | $ 21 | $ 16 | $ 47 | $ 50 |  |

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