Debt (Credit Facilities) (Details) $ in Millions	Mar. 31, 2025 USD ($)
Debt [Line Items]
Amount outstanding	$ 678
Weighted average interest rates	4.60%
Available credit facility capacity	$ 522
IPL [Member]
Debt [Line Items]
Amount outstanding	$ 109
Weighted average interest rates	4.60%
Available credit facility capacity	$ 141
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 212
Weighted average interest rates	4.60%
Available credit facility capacity	$ 188