Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Assets:
Money market fund investments	$ 8	$ 44
Deferred proceeds	107	188
Liabilities:
Long-term debt (incl. current maturities)	7,614	8,109
IPL [Member]
Assets:
Money market fund investments	8	44
Deferred proceeds	107	188
Liabilities:
Long-term debt (incl. current maturities)	3,745	4,021
WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,495	2,690
Commodity Contracts [Member]
Assets:
Derivatives	28	34
Liabilities:
Derivatives	13	25
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	19	29
Liabilities:
Derivatives	6	12
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	9	5
Liabilities:
Derivatives	7	13
Level 1 [Member]
Assets:
Money market fund investments	8	44
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Money market fund investments	8	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)	7,613	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)	3,745	4,021
Level 2 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,495	2,690
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	12	5
Liabilities:
Derivatives	13	25
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	4	3
Liabilities:
Derivatives	6	12
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	8	2
Liabilities:
Derivatives	7	13
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	107	188
Liabilities:
Long-term debt (incl. current maturities)	1	2
Level 3 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	107	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	16	29
Liabilities:
Derivatives	0	0
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	15	26
Liabilities:
Derivatives	0	0
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	1	3
Liabilities:
Derivatives	0	0
Carrying Amount [Member]
Assets:
Money market fund investments	8	44
Deferred proceeds	107	188
Liabilities:
Long-term debt (incl. current maturities)	6,779	6,777
Carrying Amount [Member] | IPL [Member]
Assets:
Money market fund investments	8	44
Deferred proceeds	107	188
Liabilities:
Long-term debt (incl. current maturities)	3,346	3,345
Carrying Amount [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,131	2,130
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	28	34
Liabilities:
Derivatives	13	25
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	19	29
Liabilities:
Derivatives	6	12
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	9	5
Liabilities:
Derivatives	$ 7	$ 13