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v3.20.4

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Debt Instrument [Line Items] |  |
Maximum amount outstanding (based on daily outstanding balances) | $ 495 | $ 601
Average amount outstanding (based on daily outstanding balances) | $ 292 | $ 453
Weighted average interest rates | 0.70% | 2.50%
IPL [Member] |  |
Debt Instrument [Line Items] |  |
Maximum amount outstanding (based on daily outstanding balances) | $ 8 | $ 50
Average amount outstanding (based on daily outstanding balances) | $ 0 | $ 0
Weighted average interest rates | 0.50% | 2.80%
WPL [Member] |  |
Debt Instrument [Line Items] |  |
Maximum amount outstanding (based on daily outstanding balances) | $ 266 | $ 195
Average amount outstanding (based on daily outstanding balances) | $ 117 | $ 93
Weighted average interest rates | 0.70% | 2.40%

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