Benefit Plans (Accumulated Benefit Obligations) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	$ 1,305	$ 1,234
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,305	1,234
Fair value of plan assets	984	931
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,351	1,280
Fair value of plan assets	984	931
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	227	214
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	227	214
Fair value of plan assets	108	105
IPL [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	589	558
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	589	558
Fair value of plan assets	453	436
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	615	581
Fair value of plan assets	453	436
IPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	91	86
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	91	86
Fair value of plan assets	74	72
WPL [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	573	536
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	573	536
Fair value of plan assets	436	406
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	588	550
Fair value of plan assets	436	406
WPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	89	85
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	89	85
Fair value of plan assets	$ 18	$ 17