Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Regulatory assets	$ 2,018	$ 2,010
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	931	890
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	549	580
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	124	119
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	98	113
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	96	110
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	53	55
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	32	4
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	4	26
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	131	113
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,507	1,483
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	881	843
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	276	291
IPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	85	81
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	69	77
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	96	110
IPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	17	1
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	4	13
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	79	67
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	511	527
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	50	47
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	273	289
WPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	39	38
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	29	36
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	53	55
WPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	15	3
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	0	13
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 52	$ 46