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Fair Value Measurements (Fair Value Measurements) (Details) - USD ($)
$ in Millions
Sep. 30, 2021
Dec. 31, 2020
Assets:    
Money market fund investments $ 9 $ 44
Deferred proceeds 164 188
Liabilities:    
Long-term debt (incl. current maturities) 8,084 8,109
IPL [Member]    
Assets:    
Money market fund investments 9 44
Deferred proceeds 164 188
Liabilities:    
Long-term debt (incl. current maturities) 3,849 4,021
WPL [Member]    
Liabilities:    
Long-term debt (incl. current maturities) 2,869 2,690
Commodity Contracts [Member]    
Assets:    
Derivatives 236 34
Liabilities:    
Derivatives 4 25
Commodity Contracts [Member] | IPL [Member]    
Assets:    
Derivatives 115 29
Liabilities:    
Derivatives 4 12
Commodity Contracts [Member] | WPL [Member]    
Assets:    
Derivatives 121 5
Liabilities:    
Derivatives 0 13
Level 1 [Member]    
Assets:    
Money market fund investments 9 44
Deferred proceeds 0 0
Liabilities:    
Long-term debt (incl. current maturities) 0 0
Level 1 [Member] | IPL [Member]    
Assets:    
Money market fund investments 9 44
Deferred proceeds 0 0
Liabilities:    
Long-term debt (incl. current maturities) 0 0
Level 1 [Member] | WPL [Member]    
Liabilities:    
Long-term debt (incl. current maturities) 0 0
Level 1 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 0 0
Liabilities:    
Derivatives 0 0
Level 1 [Member] | Commodity Contracts [Member] | IPL [Member]    
Assets:    
Derivatives 0 0
Liabilities:    
Derivatives 0 0
Level 1 [Member] | Commodity Contracts [Member] | WPL [Member]    
Assets:    
Derivatives 0 0
Liabilities:    
Derivatives 0 0
Level 2 [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 0 0
Liabilities:    
Long-term debt (incl. current maturities) 8,083 8,107
Level 2 [Member] | IPL [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 0 0
Liabilities:    
Long-term debt (incl. current maturities) 3,849 4,021
Level 2 [Member] | WPL [Member]    
Liabilities:    
Long-term debt (incl. current maturities) 2,869 2,690
Level 2 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 207 5
Liabilities:    
Derivatives 4 25
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]    
Assets:    
Derivatives 96 3
Liabilities:    
Derivatives 4 12
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]    
Assets:    
Derivatives 111 2
Liabilities:    
Derivatives 0 13
Level 3 [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 164 188
Liabilities:    
Long-term debt (incl. current maturities) 1 2
Level 3 [Member] | IPL [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 164 188
Liabilities:    
Long-term debt (incl. current maturities) 0 0
Level 3 [Member] | WPL [Member]    
Liabilities:    
Long-term debt (incl. current maturities) 0 0
Level 3 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 29 29
Liabilities:    
Derivatives 0 0
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]    
Assets:    
Derivatives 19 26
Liabilities:    
Derivatives 0 0
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]    
Assets:    
Derivatives 10 3
Liabilities:    
Derivatives 0 0
Carrying Amount [Member]    
Assets:    
Money market fund investments 9 44
Deferred proceeds 164 188
Liabilities:    
Long-term debt (incl. current maturities) 7,075 6,777
Carrying Amount [Member] | IPL [Member]    
Assets:    
Money market fund investments 9 44
Deferred proceeds 164 188
Liabilities:    
Long-term debt (incl. current maturities) 3,347 3,345
Carrying Amount [Member] | WPL [Member]    
Liabilities:    
Long-term debt (incl. current maturities) 2,429 2,130
Carrying Amount [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 236 34
Liabilities:    
Derivatives 4 25
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]    
Assets:    
Derivatives 115 29
Liabilities:    
Derivatives 4 12
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]    
Assets:    
Derivatives 121 5
Liabilities:    
Derivatives $ 0 $ 13