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Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Dec. 31, 2023
Derivative Instruments [Line Items] |  |  |  |  |
Non-current interest rate derivative liabilities | $ 939 |  | $ 939 |  | $ 617
Accumulated other comprehensive loss, interest rate swap | 1 |  | 1 |  | $ (1)
Alliant Energy Finance LLC [Member] | Interest Rate Swap [Member] | Term Loan Credit Agreement [Member] |  |  |  |  |
Derivative Instruments [Line Items] |  |  |  |  |
Non-current interest rate derivative liabilities | 1 |  | 1 |  |
Accumulated other comprehensive loss, interest rate swap | 1 |  | 1 |  |
Interest expense, interest rate swap | $ 1 | $ 1 | $ 3 | $ 2 |

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