Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Assets:
Money market fund investments	$ 183	$ 5
Deferred proceeds	201	188
Liabilities:
Long-term debt (incl. current maturities)	7,851	6,920
IPL [Member]
Assets:
Money market fund investments	183	5
Deferred proceeds	201	188
Liabilities:
Long-term debt (incl. current maturities)	3,987	3,489
WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,667	2,268
Commodity Contracts [Member]
Assets:
Derivatives	48	27
Liabilities:
Derivatives	19	38
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	34	22
Liabilities:
Derivatives	8	18
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	14	5
Liabilities:
Derivatives	11	20
Level 1 [Member]
Assets:
Money market fund investments	183	5
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Money market fund investments	183	5
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)	7,849	6,918
Level 2 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	3,987	3,489
Level 2 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,667	2,268
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	17	5
Liabilities:
Derivatives	18	37
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	7	3
Liabilities:
Derivatives	7	17
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	10	2
Liabilities:
Derivatives	11	20
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	201	188
Liabilities:
Long-term debt (incl. current maturities)	2	2
Level 3 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	201	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	31	22
Liabilities:
Derivatives	1	1
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	27	19
Liabilities:
Derivatives	1	1
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	4	3
Liabilities:
Derivatives	0	0
Carrying Amount [Member]
Assets:
Money market fund investments	183	5
Deferred proceeds	201	188
Liabilities:
Long-term debt (incl. current maturities)	6,581	6,190
Carrying Amount [Member] | IPL [Member]
Assets:
Money market fund investments	183	5
Deferred proceeds	201	188
Liabilities:
Long-term debt (incl. current maturities)	3,344	3,147
Carrying Amount [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,130	1,933
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	48	27
Liabilities:
Derivatives	19	38
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	34	22
Liabilities:
Derivatives	8	18
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	14	5
Liabilities:
Derivatives	$ 11	$ 20