Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,351	$ 1,424
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	746	836
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	371	388
Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	62	88
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	20
WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	36	0
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	22	24
WPL's earnings sharing mechanism [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	22	22
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	52	46
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	691	715
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	334	351
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	241	257
IPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	30	51
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	27	17
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	19	9
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	40	30
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	660	709
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	412	485
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	130	131
WPL [Member] | Electric transmission cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	32	37
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	13	3
WPL [Member] | WPL's West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	36
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3	15
WPL [Member] | WPL's earnings sharing mechanism [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	22	22
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 12	$ 16