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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, 2021 | Dec. 31, 2020
Regulatory Matters [Line Items] |  |  |  |  |  |
Regulatory assets |  |  | $ 2,261 | $ 2,046 |  |
Collected from retail electric customers |  |  | 3,345 | 3,421 | $ 3,081 |
Regulatory liabilities |  |  | 1,130 | 1,324 |  |
IPL [Member] |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |
Regulatory assets not earning a return |  |  | 74 |  |  |
Regulatory assets |  |  | 1,577 | 1,386 |  |
Collected from retail electric customers |  |  | 1,761 | 1,859 | 1,752 |
Regulatory liabilities |  |  | 644 | 754 |  |
WPL [Member] |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |
Regulatory assets not earning a return |  |  | 32 |  |  |
Regulatory assets |  |  | 684 | 660 |  |
Collected from retail electric customers |  |  | 1,584 | 1,562 | $ 1,329 |
Regulatory liabilities |  |  | 486 | 570 |  |
2021 Test Period Fuel-related Costs [Member] | WPL [Member] |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |
Regulatory assets |  |  |  | 37 |  |
2022 Test Period Fuel-related Costs [Member] | WPL [Member] |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |
Regulatory assets |  |  |  | 117 |  |
Collected from retail electric customers |  |  | 12 |  |  |
2023 Test Period Fuel-related Costs | WPL [Member] |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |
Regulatory liabilities |  |  | 34 |  |  |
2022 Test Period Retail Electric [Member] | WPL [Member] |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |
Authorized increase (decrease) in final rates, amount |  |  |  | 114 |  |
2022 Test Period Retail Gas [Member] | WPL [Member] |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |
Authorized increase (decrease) in final rates, amount |  |  |  | $ 15 |  |
2023 Test Period Retail Gas [Member] | WPL [Member] |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |
Authorized increase (decrease) in final rates, amount |  |  | $ 9 |  |  |
DAEC PPA [Member] |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |
Buyout payment |  |  |  |  |  | $ 110
PPA term amendment |  |  | 5 years |  |  |
Forecast [Member] | 2024 Test Period Retail Electric [Member] | WPL [Member] |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |
Authorized increase (decrease) in final rates, amount |  | $ 49 |  |  |  |
Forecast [Member] | 2024 Test Period Retail Gas [Member] | WPL [Member] |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |
Authorized increase (decrease) in final rates, amount |  | $ 13 |  |  |  |
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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