Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Regulatory assets	$ 1,836	$ 1,845
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	877	818
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	492	524
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	118	134
Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	115	112
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	110	108
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	20	39
Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	19	21
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	85	89
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,418	1,400
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	829	777
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	247	263
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	79	88
IPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	79	76
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	110	108
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	8	18
IPL [Member] | Emission allowances [Member]
Regulatory Assets [Line Items]
Regulatory assets	19	21
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	47	49
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	418	445
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	48	41
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	245	261
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	39	46
WPL [Member] | Asset retirement obligations [Member]
Regulatory Assets [Line Items]
Regulatory assets	36	36
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	12	21
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 38	$ 40