Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,255	$ 1,306
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	685	732
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	371	367
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	67	68
WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	38	38
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	26	28
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	68	73
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	661	676
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	327	331
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	242	238
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	39
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	18	25
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	34	43
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	594	630
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	358	401
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	129	129
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	27	29
WPL [Member] | WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	38	38
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	8	3
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 34	$ 30