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Debt (Credit Facilities) (Details) $ in Millions | Sep. 30, 2020 USD ($)
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Debt [Line Items] |
Amount outstanding | $ 422
Weighted average interest rates | 0.20%
Available credit facility capacity | $ 578
IPL [Member] |
Debt [Line Items] |
Amount outstanding | 0
Available credit facility capacity | 250
WPL [Member] |
Debt [Line Items] |
Amount outstanding | $ 139
Weighted average interest rates | 0.10%
Available credit facility capacity | $ 161

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