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Debt (Other Short-Term Borrowings) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Debt [Line Items]        
Maximum amount outstanding (based on daily outstanding balances) $ 372 $ 330 $ 741 $ 632
Average amount outstanding (based on daily outstanding balances) $ 263 $ 197 $ 417 $ 320
Weighted average interest rates 4.50% 5.40% 4.60% 5.50%
IPL [Member]        
Debt [Line Items]        
Maximum amount outstanding (based on daily outstanding balances) $ 78 $ 0 $ 141 $ 19
Average amount outstanding (based on daily outstanding balances) $ 9 0 $ 32 $ 1
Weighted average interest rates 4.60%   4.60% 5.50%
WPL [Member]        
Debt [Line Items]        
Maximum amount outstanding (based on daily outstanding balances) $ 297 0 $ 297 $ 390
Average amount outstanding (based on daily outstanding balances) $ 177 $ 0 $ 187 $ 87
Weighted average interest rates 4.50%   4.50% 5.50%