Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Regulatory Matters [Line Items]
Regulatory assets	$ 2,018	$ 2,010
IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	1,507	1,483
WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	511	$ 527
Deferred Fuel Costs | IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	15
Deferred Fuel Costs | WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets	$ 12