Property, Plant and Equipment (Property, Plant and Equipment) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	[1],[2]		$ 93.0	$ 108.3
Total electric plant			12,296.9	11,043.5
Gas plant in service			1,244.0	1,107.6
Other plant in service			571.9	549.3
Accumulated depreciation			(4,283.1)	(4,135.7)
Net plant			9,829.7	8,564.7
Construction work in progress			962.2	1,226.8
Other, net			6.0	18.4
Total utility			10,797.9	9,809.9
Non-utility Generation, net	[3]		90.9	135.0
Corporate Services and other, net	[4]		345.7	334.3
Total non-utility and other			436.6	469.3
Total property, plant and equipment			11,234.5	10,279.2
Non-utility Generation, accumulated depreciation			50.5	46.5
Corporate Services and other, accumulated depreciation			285.6	272.0
Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service			6,655.3	5,866.9
Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service			5,123.5	4,739.2
Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service			425.1	329.1
IPL [Member]
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	[1]		0.0	108.3
Total electric plant			6,819.1	5,837.9
Gas plant in service			654.8	556.7
Other plant in service			333.4	313.0
Accumulated depreciation			(2,311.0)	(2,258.3)
Net plant			5,496.3	4,449.3
Construction work in progress			424.4	968.1
Other, net			5.5	18.2
Total utility			5,926.2	5,435.6
Total property, plant and equipment			5,926.2	5,435.6
IPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service			3,715.9	2,916.8
IPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service			2,820.9	2,589.3
IPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service			282.3	223.5
WPL [Member]
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	[2]		93.0	0.0
Total electric plant			5,477.8	5,205.6
Gas plant in service			589.2	550.9
Other plant in service			238.5	236.3
Accumulated depreciation			(1,972.1)	(1,877.4)
Net plant			4,333.4	4,115.4
Leased Sheboygan Falls Energy Facility, net	[5]		46.2	52.4
Construction work in progress			537.8	258.7
Other, net			0.5	0.2
Total utility			4,917.9	4,426.7
Total property, plant and equipment			4,917.9	4,426.7
Leased Sheboygan Falls Energy Facility, accumulated depreciation			77.6	71.4
WPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service			2,939.4	2,950.1
WPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service			2,302.6	2,149.9
WPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service			$ 142.8	$ 105.6
PSCW [Member] | Scenario, Forecast [Member] | WPL [Member] | Edgewater Unit 4 [Member]
Property, Plant and Equipment [Line Items]
Recovery period, authorized		10 years

[1] In 2017, IPL retired Sutherland Unit 3 and reclassified the remaining net book value of this EGU from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. Refer to Note 2 for further discussion, including recovery of the remaining net book value of Sutherland Unit 3.

[2] In 2017, WPL received approval from MISO to retire Edgewater Unit 4 and currently anticipates retiring this EGU by September 30, 2018. In 2016, the PSCW authorized WPL to recover the remaining net book value of Edgewater Unit 4 over a 10-year period beginning the later of the retirement date of the EGU or January 1, 2019.

[3] Less accumulated depreciation of $50.5 million and $46.5 million for Alliant Energy as of December 31, 2017 and 2016, respectively. Refer to “Franklin County Wind Farm” below for discussion of the April 2017 transfer of the Franklin County wind farm from AEF to IPL pursuant to a February 2017 FERC order.

[4] Less accumulated depreciation of $285.6 million and $272.0 million for Alliant Energy as of December 31, 2017 and 2016, respectively.

[5] Less accumulated amortization of $77.6 million and $71.4 million for WPL as of December 31, 2017 and 2016, respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.