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Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions | Sep. 30, 2025 | Jun. 30, 2025 | Dec. 31, 2024 | Sep. 30, 2024 | Jun. 30, 2024 | Dec. 31, 2023
--- | --- | --- | --- | --- | --- | ---
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |  |
Fair value, net derivative assets | $ 39 | $ 56 | $ 25 | $ 37 | $ 51 | $ 24
Excluding Financial Transmission Rights [Member] |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |  |
Fair value, net derivative assets | 3 |  | 0 |  |  |
Financial Transmission Rights [Member] |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |  |
Fair value, net derivative assets | 36 |  | 25 |  |  |
IPL [Member] |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |  |
Fair value, net derivative assets | 30 | 44 | 20 | 29 | 40 | 19
IPL [Member] | Excluding Financial Transmission Rights [Member] |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |  |
Fair value, net derivative assets | 3 |  | 0 |  |  |
IPL [Member] | Financial Transmission Rights [Member] |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |  |
Fair value, net derivative assets | 27 |  | 20 |  |  |
WPL [Member] |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |  |
Fair value, net derivative assets | 9 | $ 12 | 5 | $ 8 | $ 11 | $ 5
WPL [Member] | Excluding Financial Transmission Rights [Member] |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |  |
Fair value, net derivative assets | 0 |  | 0 |  |  |
WPL [Member] | Financial Transmission Rights [Member] |  |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |  |
Fair value, net derivative assets | $ 9 |  | $ 5 |  |  |

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