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Income Taxes (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Dec. 31, 2024
Income Taxes [Line Items] |  |  |  |  |
Asset valuation charge for IPL's Lansing Generating Station | $ 0 | $ 0 | $ 60 | $ 0 |
Income tax expense (benefit) | (62) | 5 | (104) | 3 |
Steam Plant |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Asset retirement obligation charge for IPL's steam assets |  |  | 20 |  |
Tax-related [Member] |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Income tax expense (benefit) |  | 8 |  |  |
Forecast [Member] |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
State income tax rate, percent |  |  |  |  | 7.10%
IPL [Member] |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Asset valuation charge for IPL's Lansing Generating Station | 0 | 0 | 60 | 0 |
Asset retirement obligation charge for IPL's steam assets | 96 | 84 | 281 | 264 |
Income tax expense (benefit) | (68) | (31) | (112) | (55) |
IPL [Member] | Steam Plant |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Asset retirement obligation charge for IPL's steam assets |  |  | 20 |  |
WPL [Member] |  |  |  |  |
Income Taxes [Line Items] |  |  |  |  |
Asset retirement obligation charge for IPL's steam assets | 72 | 64 | 200 | 197 |
Income tax expense (benefit) | $ 4 | $ 21 | $ 13 | $ 47 |

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