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Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023 | Dec. 31, 2023
Derivative Instruments [Line Items] |  |  |  |  |
Non-current interest rate derivative assets | $ 160 |  | $ 160 |  | $ 177
Accumulated other comprehensive income, interest rate swap | 3 |  | 3 |  | $ 1
Interest expense, interest rate swap | 108 | $ 96 | 215 | $ 190 |
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 |  | 3 |  |
Accumulated other comprehensive income, interest rate swap | 3 |  | 3 |  |
Interest expense, interest rate swap | $ 1 | $ 1 | $ 2 | $ 1 |

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