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Fair Value Measurements (Fair Value Measurements) (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Carrying Amount [Member]    
Assets:    
Money market fund investments $ 477 $ 52
Time deposits 250 0
Deferred proceeds 231 163
Liabilities:    
Long-term debt (incl. current maturities) 11,729 9,848
Carrying Amount [Member] | IPL [Member]    
Assets:    
Money market fund investments 194 9
Deferred proceeds 231 163
Liabilities:    
Long-term debt (incl. current maturities) 4,679 4,090
Carrying Amount [Member] | WPL [Member]    
Assets:    
Money market fund investments 0 43
Liabilities:    
Long-term debt (incl. current maturities) 3,372 3,370
Carrying Amount [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 82 75
Liabilities:    
Derivatives 48 58
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]    
Assets:    
Derivatives 52 48
Liabilities:    
Derivatives 10 13
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]    
Assets:    
Derivatives 30 27
Liabilities:    
Derivatives 38 45
Money market fund investments 477 52
Time deposits 250 0
Deferred proceeds 231 163
Long-term debt (incl. current maturities) 11,504 9,577
IPL [Member]    
Assets:    
Money market fund investments 194 9
Deferred proceeds 231 163
Liabilities:    
Long-term debt (incl. current maturities) 4,465 3,736
WPL [Member]    
Assets:    
Money market fund investments 0 43
Liabilities:    
Long-term debt (incl. current maturities) 3,287 3,170
Commodity Contracts [Member]    
Assets:    
Derivatives 82 75
Liabilities:    
Derivatives 48 58
Commodity Contracts [Member] | IPL [Member]    
Assets:    
Derivatives 52 48
Liabilities:    
Derivatives 10 13
Commodity Contracts [Member] | WPL [Member]    
Assets:    
Derivatives 30 27
Liabilities:    
Derivatives 38 45
Level 1 [Member]    
Assets:    
Money market fund investments 477 52
Time deposits 0 0
Deferred proceeds 0 0
Liabilities:    
Long-term debt (incl. current maturities) 0 0
Level 1 [Member] | IPL [Member]    
Assets:    
Money market fund investments 194 9
Deferred proceeds 0 0
Liabilities:    
Long-term debt (incl. current maturities) 0 0
Level 1 [Member] | WPL [Member]    
Assets:    
Money market fund investments 0 43
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
Time deposits 250 0
Deferred proceeds 0 0
Liabilities:    
Long-term debt (incl. current maturities) 11,504 9,577
Level 2 [Member] | IPL [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 0 0
Liabilities:    
Long-term debt (incl. current maturities) 4,465 3,736
Level 2 [Member] | WPL [Member]    
Assets:    
Money market fund investments 0 0
Liabilities:    
Long-term debt (incl. current maturities) 3,287 3,170
Level 2 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 42 48
Liabilities:    
Derivatives 47 56
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]    
Assets:    
Derivatives 21 26
Liabilities:    
Derivatives 9 11
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]    
Assets:    
Derivatives 21 22
Liabilities:    
Derivatives 38 45
Level 3 [Member]    
Assets:    
Money market fund investments 0 0
Time deposits 0 0
Deferred proceeds 231 163
Liabilities:    
Long-term debt (incl. current maturities) 0 0
Level 3 [Member] | IPL [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 231 163
Liabilities:    
Long-term debt (incl. current maturities) 0 0
Level 3 [Member] | WPL [Member]    
Assets:    
Money market fund investments 0 0
Liabilities:    
Long-term debt (incl. current maturities) 0 0
Level 3 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 40 27
Liabilities:    
Derivatives 1 2
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]    
Assets:    
Derivatives 31 22
Liabilities:    
Derivatives 1 2
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]    
Assets:    
Derivatives 9 5
Liabilities:    
Derivatives $ 0 $ 0