Debt (Credit Facilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Commercial paper and borrowings under the single credit facility:
Amount outstanding	$ 389	$ 337
Weighted average interest rates	0.20%	1.90%
Available credit facility capacity	$ 611	$ 663
IPL [Member]
Commercial paper and borrowings under the single credit facility:
Amount outstanding	0	0
Available credit facility capacity	250	250
WPL [Member]
Commercial paper and borrowings under the single credit facility:
Amount outstanding	$ 257	$ 168
Weighted average interest rates	0.10%	1.80%
Available credit facility capacity	$ 43	$ 132