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Derivative Instruments (Balance Sheet Offsetting) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Derivative Instruments [Line Items] |  |
Derivative assets, Gross (as reported) | $ 82 | $ 75
Derivative assets, Net | 72 | 64
Derivative liabilities, Gross (as reported) | 48 | 58
Derivative liabilities, Net | 38 | 47
IPL [Member] |  |
Derivative Instruments [Line Items] |  |
Derivative assets, Gross (as reported) | 52 | 48
Derivative assets, Net | 47 | 43
Derivative liabilities, Gross (as reported) | 10 | 13
Derivative liabilities, Net | 5 | 8
WPL [Member] |  |
Derivative Instruments [Line Items] |  |
Derivative assets, Gross (as reported) | 30 | 27
Derivative assets, Net | 25 | 21
Derivative liabilities, Gross (as reported) | 38 | 45
Derivative liabilities, Net | $ 33 | $ 39

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