Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,361	$ 1,306
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	611	732
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	383	367
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	221	28
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	53	68
WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	38
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	53	73
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	720	676
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	313	331
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	252	238
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	104	25
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	29	39
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	22	43
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	641	630
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	298	401
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	131	129
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	117	3
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	24	29
WPL [Member] | WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	38
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 31	$ 30