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Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2023 | Mar. 31, 2022 | Dec. 31, 2022
Derivative Instruments [Line Items] |  |  |
Non-current interest rate swap liabilities | $ 540 |  | $ 518
Accumulated other comprehensive loss, interest rate swap | (1) |  | $ 0
Interest expense, interest rate swap | 94 | $ 74 |
Alliant Energy Finance LLC [Member] | Interest Rate Swap [Member] | Term Loan Credit Agreement [Member] |  |  |
Derivative Instruments [Line Items] |  |  |
Interest rate swap | $ 300 |  |
Interest rate swap, fixed interest rate percentage | 3.93% |  |
Non-current interest rate swap liabilities | $ 1 |  |
Accumulated other comprehensive loss, interest rate swap | 1 |  |
Interest expense, interest rate swap | $ 1 |  |

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