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Regulatory Matters (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, 2020
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory assets |  | $ 2,274 | $ 2,261 |  |
Collected from retail electric customers |  | 3,372 | 3,345 | $ 3,421 |
Regulatory liabilities |  | 1,028 | 1,130 |  |
IPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory assets not earning a return |  | 199 |  |  |
Regulatory assets |  | 1,586 | 1,577 |  |
Collected from retail electric customers |  | 1,747 | 1,761 | 1,859 |
Regulatory liabilities |  | 546 | 644 |  |
WPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory assets not earning a return |  | 23 |  |  |
Regulatory assets |  | 688 | 684 |  |
Collected from retail electric customers |  | 1,625 | 1,584 | 1,562 |
Regulatory liabilities |  | 482 | 486 |  |
2022 Test Period Fuel-related Costs [Member] | WPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory assets |  |  |  | $ 117 |
Collected from retail electric customers |  | 50 | 12 |  |
2023 Test Period Fuel-related Costs | WPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Regulatory liabilities |  |  | 34 |  |
2024 Test Period Retail Electric [Member] | WPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Authorized increase (decrease) in final rates, amount |  | 49 |  |  |
2024 Test Period Retail Gas [Member] | WPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Authorized increase (decrease) in final rates, amount |  | 13 |  |  |
2021 Test Period Fuel-related Costs [Member] | WPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Collected from retail electric customers |  |  | $ 37 |  |
October 2024 Through September 2025 Test Period Retail Electric [Member] | IPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Authorized increase (decrease) in final rates, amount |  | 185 |  |  |
October 2024 Through September 2025 Test Period Retail Gas [Member] | IPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Authorized increase (decrease) in final rates, amount |  | $ 10 |  |  |
DAEC PPA [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Buyout payment |  |  |  |  | $ 110
PPA term amendment |  |  |  |  | 5 years
Forecast [Member] | 2025 Test Period Retail Electric [Member] | WPL [Member] |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |
Authorized increase (decrease) in final rates, amount | $ 60 |  |  |  |

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