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Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2024 | Mar. 31, 2023
Debt [Line Items] |  |
Maximum amount outstanding (based on daily outstanding balances) | $ 632 | $ 793
Average amount outstanding (based on daily outstanding balances) | $ 487 | $ 574
Weighted average interest rates | 5.50% | 4.80%
IPL [Member] |  |
Debt [Line Items] |  |
Maximum amount outstanding (based on daily outstanding balances) | $ 14 | $ 0
Average amount outstanding (based on daily outstanding balances) | $ 1 | $ 0
Weighted average interest rates | 5.50% | 0.00%
WPL [Member] |  |
Debt [Line Items] |  |
Maximum amount outstanding (based on daily outstanding balances) | $ 390 | $ 349
Average amount outstanding (based on daily outstanding balances) | $ 255 | $ 304
Weighted average interest rates | 5.50% | 4.80%

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