Regulatory Matters (Assets Retired Early) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Regulatory assets	$ 2,010	$ 1,845
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	113	134
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,483	1,400
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	77	88
IPL [Member] | Assets retired early [Member] | Sutherland Units 1 and 3 [Member]
Regulatory Assets [Line Items]
Regulatory assets	23
IPL [Member] | Assets retired early [Member] | M.L. Kapp Unit 2 [Member]
Regulatory Assets [Line Items]
Regulatory assets	21
IPL [Member] | Assets retired early [Member] | Analog Electric Meters [Member]
Regulatory Assets [Line Items]
Regulatory assets	33
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	527	445
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	36	$ 46
WPL [Member] | Assets retired early [Member] | Nelson Dewey Units 1 and 2 and Edgewater Unit 3 [Member]
Regulatory Assets [Line Items]
Regulatory assets	13
WPL [Member] | Assets retired early [Member] | Edgewater Unit 4 [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 23