Debt (Credit Facilities) (Details) $ in Millions	Mar. 31, 2024 USD ($)
Debt [Line Items]
Amount outstanding	$ 334
Weighted average interest rates	5.50%
Available credit facility capacity	$ 666
IPL [Member]
Debt [Line Items]
Amount outstanding	$ 0
Weighted average interest rates	0.00%
Available credit facility capacity	$ 200
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 0
Weighted average interest rates	0.00%
Available credit facility capacity	$ 300