Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Assets:
Money market fund investments	$ 6	$ 44
Deferred proceeds	154	188
Liabilities:
Long-term debt (incl. current maturities)	7,847	8,109
IPL [Member]
Assets:
Money market fund investments	6	44
Deferred proceeds	154	188
Liabilities:
Long-term debt (incl. current maturities)	3,880	4,021
WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,593	2,690
Commodity Contracts [Member]
Assets:
Derivatives	102	34
Liabilities:
Derivatives	4	25
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	56	29
Liabilities:
Derivatives	2	12
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	46	5
Liabilities:
Derivatives	2	13
Level 1 [Member]
Assets:
Money market fund investments	6	44
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Money market fund investments	6	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)	7,846	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)	3,880	4,021
Level 2 [Member] | WPL [Member]
Liabilities:
Long-term debt (incl. current maturities)	2,593	2,690
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	62	5
Liabilities:
Derivatives	3	25
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	25	3
Liabilities:
Derivatives	1	12
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	37	2
Liabilities:
Derivatives	2	13
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	154	188
Liabilities:
Long-term debt (incl. current maturities)	1	2
Level 3 [Member] | IPL [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	154	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	40	29
Liabilities:
Derivatives	1	0
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	31	26
Liabilities:
Derivatives	1	0
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	9	3
Liabilities:
Derivatives	0	0
Carrying Amount [Member]
Assets:
Money market fund investments	6	44
Deferred proceeds	154	188
Liabilities:
Long-term debt (incl. current maturities)	6,776	6,777
Carrying Amount [Member] | IPL [Member]
Assets:
Money market fund investments	6	44
Deferred proceeds	154	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	102	34
Liabilities:
Derivatives	4	25
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	56	29
Liabilities:
Derivatives	2	12
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	46	5
Liabilities:
Derivatives	$ 2	$ 13