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Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023
Derivative Instruments [Line Items] |  |  |
Non-current interest rate derivative assets | $ 173 |  | $ 177
Accumulated other comprehensive income, interest rate swap | 2 |  | $ 1
Interest expense, interest rate swap | 107 | $ 94 |
Alliant Energy Finance LLC [Member] | Interest Rate Swap [Member] | Term Loan Credit Agreement [Member] |  |  |
Derivative Instruments [Line Items] |  |  |
Non-current interest rate derivative assets | 3 |  |
Accumulated other comprehensive income, interest rate swap | 2 |  |
Interest expense, interest rate swap | $ 1 | $ 1 |

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