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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.

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