Fair Value Measurements (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets:
Money market fund investments	$ 44	$ 5
Deferred proceeds	188	188
Liabilities and equity:
Long-term debt (including current maturities)	8,109	6,920
Commodity Contracts [Member]
Assets:
Derivatives	34	27
Liabilities and equity:
Derivatives	25	38
Level 1 [Member]
Assets:
Money market fund investments	44	5
Deferred proceeds	0	0
Liabilities and equity:
Long-term debt (including current maturities)	0	0
Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities and equity:
Derivatives	0	0
Level 2 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities and equity:
Long-term debt (including current maturities)	8,107	6,918
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	5	5
Liabilities and equity:
Derivatives	25	37
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	188	188
Liabilities and equity:
Long-term debt (including current maturities)	2	2
Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	29	22
Liabilities and equity:
Derivatives	0	1
Carrying Amount [Member]
Assets:
Money market fund investments	44	5
Deferred proceeds	188	188
Liabilities and equity:
Long-term debt (including current maturities)	6,777	6,190
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	34	27
Liabilities and equity:
Derivatives	25	38
IPL [Member]
Assets:
Money market fund investments	44	5
Deferred proceeds	188	188
Liabilities and equity:
Long-term debt (including current maturities)	4,021	3,489
IPL [Member] | Commodity Contracts [Member]
Assets:
Derivatives	29	22
Liabilities and equity:
Derivatives	12	18
IPL [Member] | Level 1 [Member]
Assets:
Money market fund investments	44	5
Deferred proceeds	0	0
Liabilities and equity:
Long-term debt (including current maturities)	0	0
IPL [Member] | Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities and equity:
Derivatives	0	0
IPL [Member] | Level 2 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	0	0
Liabilities and equity:
Long-term debt (including current maturities)	4,021	3,489
IPL [Member] | Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	3	3
Liabilities and equity:
Derivatives	12	17
IPL [Member] | Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	188	188
Liabilities and equity:
Long-term debt (including current maturities)	0	0
IPL [Member] | Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	26	19
Liabilities and equity:
Derivatives	0	1
IPL [Member] | Carrying Amount [Member]
Assets:
Money market fund investments	44	5
Deferred proceeds	188	188
Liabilities and equity:
Long-term debt (including current maturities)	3,345	3,147
IPL [Member] | Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	29	22
Liabilities and equity:
Derivatives	12	18
WPL [Member]
Liabilities and equity:
Long-term debt (including current maturities)	2,690	2,268
WPL [Member] | Commodity Contracts [Member]
Assets:
Derivatives	5	5
Liabilities and equity:
Derivatives	13	20
WPL [Member] | Level 1 [Member]
Liabilities and equity:
Long-term debt (including current maturities)	0	0
WPL [Member] | Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities and equity:
Derivatives	0	0
WPL [Member] | Level 2 [Member]
Liabilities and equity:
Long-term debt (including current maturities)	2,690	2,268
WPL [Member] | Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	2	2
Liabilities and equity:
Derivatives	13	20
WPL [Member] | Level 3 [Member]
Liabilities and equity:
Long-term debt (including current maturities)	0	0
WPL [Member] | Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	3	3
Liabilities and equity:
Derivatives	0	0
WPL [Member] | Carrying Amount [Member]
Liabilities and equity:
Long-term debt (including current maturities)	2,130	1,933
WPL [Member] | Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	5	5
Liabilities and equity:
Derivatives	$ 13	$ 20