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Property, Plant and Equipment (Property, Plant and Equipment) (Details) - USD ($) $ in Millions | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | ---
Property, Plant and Equipment [Line Items] |  |  |
Electric plant anticipated to be retired early | [1] | $ 0.0 | $ 157.6
Total electric plant |  | 10,444.9 | 10,365.1
Gas plant in service |  | 1,018.3 | 946.2
Other plant in service |  | 530.6 | 539.3
Accumulated depreciation | [1] | (3,939.6) | (3,923.1)
Net plant |  | 8,054.2 | 7,927.5
Construction work in progress |  | 897.5 | 479.1
Other, net |  | 18.5 | 22.3
Total utility |  | 8,970.2 | 8,428.9
Non-regulated Generation, net | [2] | 229.3 | 240.1
Corporate Services and other, net | [3] | 319.6 | 269.4
Total non-regulated and other |  | 548.9 | 509.5
Total property, plant and equipment |  | 9,519.1 | 8,938.4
Non-regulated Generation, accumulated depreciation |  | 59.0 | 49.5
Corporate Services and other, accumulated depreciation |  | 252.9 | 229.1
Generation [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Electric plant in service |  | 5,643.7 | 5,463.0
Distribution [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Electric plant in service |  | 4,489.9 | 4,435.4
Other [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Electric plant in service |  | 311.3 | 309.1
IPL [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Total electric plant |  | 5,671.7 | 5,559.6
Gas plant in service |  | 513.6 | 474.0
Other plant in service |  | 296.0 | 298.8
Accumulated depreciation | [1] | (2,152.8) | (2,124.5)
Net plant |  | 4,328.5 | 4,207.9
Construction work in progress |  | 578.2 | 325.0
Other, net |  | 18.4 | 21.8
Total utility |  | 4,925.1 | 4,554.7
Total property, plant and equipment |  | 4,925.1 | 4,554.7
IPL [Member] | Generation [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Electric plant in service |  | 3,011.6 | 2,872.4
IPL [Member] | Distribution [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Electric plant in service |  | 2,447.9 | 2,471.7
IPL [Member] | Other [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Electric plant in service |  | 212.2 | 215.5
WPL [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Electric plant anticipated to be retired early | [1] | 0.0 | 157.6
Total electric plant |  | 4,773.2 | 4,805.5
Gas plant in service |  | 504.7 | 472.2
Other plant in service |  | 234.6 | 240.5
Accumulated depreciation | [1] | (1,786.8) | (1,798.6)
Net plant |  | 3,725.7 | 3,719.6
Leased Sheboygan Falls Energy Facility, net | [4] | 58.6 | 64.7
Construction work in progress |  | 319.3 | 154.1
Other, net |  | 0.1 | 0.5
Total utility |  | 4,103.7 | 3,938.9
Total property, plant and equipment |  | 4,103.7 | 3,938.9
Leased Sheboygan Falls Energy Facility, accumulated depreciation |  | 65.2 | 59.1
WPL [Member] | Generation [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Electric plant in service |  | 2,632.1 | 2,590.6
WPL [Member] | Distribution [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Electric plant in service |  | 2,042.0 | 1,963.7
WPL [Member] | Other [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Electric plant in service |  | $ 99.1 | $ 93.6
[1] | In December 2015, WPL retired Nelson Dewey Units 1 and 2 and Edgewater Unit 3 and transferred the remaining net book value from property, plant and equipment to regulatory assets pursuant to orders from the PSCW and FERC. Refer to Note 2 for discussion of the recovery of the remaining net book value of these EGUs.
[2] | Less accumulated depreciation of $59.0 million and $49.5 million for Alliant Energy as of December 31, 2015 and 2014, respectively.
[3] | Less accumulated depreciation of $252.9 million and $229.1 million for Alliant Energy as of December 31, 2015 and 2014, respectively.
[4] | Less accumulated amortization of $65.2 million and $59.1 million for WPL as of December 31, 2015 and 2014, respectively.

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