Debt (Credit Facilities) (Details) $ in Millions	Sep. 30, 2025 USD ($)
Debt [Line Items]
Amount outstanding	$ 192
Weighted average interest rates	4.30%
Available credit facility capacity	$ 1,108
IPL [Member]
Debt [Line Items]
Amount outstanding	0
Available credit facility capacity	350
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 192
Weighted average interest rates	4.30%
Available credit facility capacity	$ 208