Regulatory Matters (Assets Retired Early (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory assets	$ 1,844.7	$ 1,737.3
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	134.0	111.6
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,399.3	1,279.0
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	87.9	55.4
IPL [Member] | Assets retired early [Member] | Sutherland Units 1 and 3 [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 28.5
Recovery period, authorized	10 years
IPL [Member] | Assets retired early [Member] | M.L. Kapp Unit 2 [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 23.6
Recovery period, authorized	10 years
IPL [Member] | Assets retired early [Member] | Analog Electric Meters [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 35.8
Recovery period, authorized	10 years
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 445.4	458.3
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	46.1	$ 56.2
WPL [Member] | Assets retired early [Member] | Nelson Dewey Units 1 and 2 and Edgewater Unit 3 [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 20.2
Recovery period, authorized	10 years
WPL [Member] | Assets retired early [Member] | Edgewater Unit 4 [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 25.9
Recovery period, authorized	10 years