Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Regulatory assets	$ 2,007	$ 2,010
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	901	890
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	570	580
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	120	119
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	108	113
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	108	110
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	55	55
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	13	26
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	132	117
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,494	1,483
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	853	843
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	286	291
IPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	82	81
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	74	77
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	108	110
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	6	13
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	85	68
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	513	527
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	48	47
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	284	289
WPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	38	38
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	34	36
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	55	55
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	7	13
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 47	$ 49