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Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Derivative [Line Items] |  |  |
Interest rate swap | $ 9,109 | $ 8,143 |
Non-current interest rate swap assets | 177 | 227 |
Accumulated other comprehensive income | 1 | 0 |
Interest expense, interest rate swap | 394 | 325 | $ 277
IPL [Member] |  |  |
Derivative [Line Items] |  |  |
Interest rate swap | 3,975 | 3,675 |
Non-current interest rate swap assets | 84 | 110 |
Interest expense, interest rate swap | 155 | 148 | 139
WPL [Member] |  |  |
Derivative [Line Items] |  |  |
Interest rate swap | 3,100 | 2,800 |
Non-current interest rate swap assets | 61 | 98 |
Interest expense, interest rate swap | 149 | $ 121 | $ 105
Alliant Energy Finance, LLC [Member] | Interest Rate Swap | Term Loan Credit Agreement [Member] |  |  |
Derivative [Line Items] |  |  |
Interest rate swap | $ 300 |  |
Interest rate swap, fixed interest rate percentage | 3.93% |  |
Non-current interest rate swap assets | $ 1 |  |
Accumulated other comprehensive income | 1 |  |
Interest expense, interest rate swap | $ 3 |  |

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