Property, Plant and Equipment (Property, Plant and Equipment) (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	[1]	$ 108.3	$ 0.0
Total electric plant		11,043.5	10,444.9
Gas plant in service		1,107.6	1,018.3
Other plant in service		549.3	530.6
Accumulated depreciation		(4,135.7)	(3,939.6)
Net plant		8,564.7	8,054.2
Construction work in progress		1,226.8	897.5
Other, net		18.4	18.5
Total utility		9,809.9	8,970.2
Non-regulated Generation, net	[2]	135.0	229.3
Corporate Services and other, net	[3]	334.3	319.6
Total non-regulated and other		469.3	548.9
Total property, plant and equipment		10,279.2	9,519.1
Non-regulated Generation, accumulated depreciation		46.5	59.0
Corporate Services and other, accumulated depreciation		272.0	252.9
Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		5,866.9	5,643.7
Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		4,739.2	4,489.9
Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		329.1	311.3
IPL [Member]
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	[1]	108.3	0.0
Total electric plant		5,837.9	5,671.7
Gas plant in service		556.7	513.6
Other plant in service		313.0	296.0
Accumulated depreciation		(2,258.3)	(2,152.8)
Net plant		4,449.3	4,328.5
Construction work in progress		968.1	578.2
Other, net		18.2	18.4
Total utility		5,435.6	4,925.1
Total property, plant and equipment		5,435.6	4,925.1
IPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,916.8	3,011.6
IPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,589.3	2,447.9
IPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		223.5	212.2
WPL [Member]
Property, Plant and Equipment [Line Items]
Total electric plant		5,205.6	4,773.2
Gas plant in service		550.9	504.7
Other plant in service		236.3	234.6
Accumulated depreciation		(1,877.4)	(1,786.8)
Net plant		4,115.4	3,725.7
Leased Sheboygan Falls Energy Facility, net	[4]	52.4	58.6
Construction work in progress		258.7	319.3
Other, net		0.2	0.1
Total utility		4,426.7	4,103.7
Total property, plant and equipment		4,426.7	4,103.7
Leased Sheboygan Falls Energy Facility, accumulated depreciation		71.4	65.2
WPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,950.1	2,632.1
WPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		2,149.9	2,042.0
WPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service		$ 105.6	$ 99.1

[1] In 2016, IPL received approval from MISO to retire Sutherland Unit 3 and currently anticipates retiring this EGU by June 30, 2017. The recovery of the remaining net book value of this EGU is expected to be addressed in IPL’s next retail electric base rate case, which is currently expected to be filed in the second quarter of 2017.

[2] Less accumulated depreciation of $46.5 million and $59.0 million for Alliant Energy as of December 31, 2016 and 2015, respectively.

[3] Less accumulated depreciation of $272.0 million and $252.9 million for Alliant Energy as of December 31, 2016 and 2015, respectively.

[4] Less accumulated amortization of $71.4 million and $65.2 million for WPL as of December 31, 2016 and 2015, respectively. The Sheboygan Falls Energy Facility is eliminated from WPL upon consolidation and is included in the “Non-regulated Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.