Debt (Narrative) (Details) $ in Millions	Sep. 30, 2021 USD ($)
Debt [Line Items]
Line of credit facility, current borrowing capacity	$ 1,000
Parent Company [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	500
IPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	100
WPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	400
Debentures | 1.95% debenture, due 2031 | WPL [Member]
Debt [Line Items]
Long-term debt	$ 300
Interest rate, percent	1.95%