Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Regulatory assets	$ 1,995	$ 2,010
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	914	890
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	559	580
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	123	119
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	103	113
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	102	110
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	54	55
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	3	26
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	137	117
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,488	1,483
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	865	843
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	281	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	72	77
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	102	110
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	2	13
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	81	68
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	507	527
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	49	47
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	278	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	31	36
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	54	55
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	1	13
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 56	$ 49