Property, Plant and Equipment (Property, Plant and Equipment) (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total electric plant		$ 13,864.6	$ 12,663.6
Gas plant in service		1,462.7	1,387.6
Other plant in service		519.7	513.2
Accumulated depreciation		(4,601.4)	(4,314.6)
Net plant		11,245.6	10,249.8
Construction work in progress		1,835.0	1,774.8
Other, net		6.1	6.1
Total utility		13,086.7	12,030.7
Non-utility Generation, net	[1]	82.9	86.9
Corporate Services and other, net	[2]	357.5	344.8
Total non-utility and other		440.4	431.7
Total property, plant and equipment		13,527.1	12,462.4
Non-utility Generation, accumulated depreciation		58.5	54.5
Corporate Services and other, accumulated depreciation		172.4	167.5
Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		7,625.3	6,800.6
Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		5,783.3	5,452.2
Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		456.0	410.8
IPL [Member]
Property, Plant and Equipment [Line Items]
Total electric plant		7,921.0	6,894.5
Gas plant in service		801.5	763.1
Other plant in service		344.7	322.4
Accumulated depreciation		(2,498.3)	(2,294.7)
Net plant		6,568.9	5,685.3
Construction work in progress		906.8	1,091.2
Other, net		5.0	5.0
Total utility		7,480.7	6,781.5
Total property, plant and equipment		7,480.7	6,781.5
IPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		4,432.4	3,610.4
IPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		3,190.0	3,023.7
IPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		298.6	260.4
WPL [Member]
Property, Plant and Equipment [Line Items]
Total electric plant		5,943.6	5,769.1
Gas plant in service		661.2	624.5
Other plant in service		175.0	190.8
Accumulated depreciation		(2,103.1)	(2,019.9)
Net plant		4,676.7	4,564.5
Leased Sheboygan Falls Energy Facility, net	[3]	32.3	38.1
Construction work in progress		928.2	683.6
Other, net		1.1	1.1
Total utility		5,638.3	5,287.3
Total property, plant and equipment		5,638.3	5,287.3
Leased Sheboygan Falls Energy Facility, accumulated depreciation		88.7	82.8
WPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		3,192.9	3,190.2
WPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,593.3	2,428.5
WPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		$ 157.4	$ 150.4

[1] Less accumulated depreciation of $58.5 million and $54.5 million for Alliant Energy as of December 31, 2019 and 2018, respectively.

[2] Less accumulated depreciation of $172.4 million and $167.5 million for Alliant Energy as of December 31, 2019 and 2018, respectively.

[3] Less accumulated amortization of $88.7 million and $82.8 million for WPL as of December 31, 2019 and 2018, 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.