Debt (Credit Facilities) (Details) $ in Millions	Sep. 30, 2023 USD ($)
Debt [Line Items]
Amount outstanding	$ 451
Weighted average interest rates	5.50%
Available credit facility capacity	$ 549
IPL [Member]
Debt [Line Items]
Amount outstanding	$ 0
Weighted average interest rates	0.00%
Available credit facility capacity	$ 250
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 120
Weighted average interest rates	5.40%
Available credit facility capacity	$ 180