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Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions | Dec. 31, 2015 | Dec. 31, 2014
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Amounts recognized on the balance sheets consist of: |  |  |
Pension and other benefit obligations |  | $ (451.8) | $ (421.7)
Pension Plans, Defined Benefit [Member] |  |  |
Amounts recognized on the balance sheets consist of: |  |  |
Non-current assets |  | 0.0 | 0.0
Other current liabilities |  | (2.6) | (2.5)
Pension and other benefit obligations |  | (308.7) | (280.9)
Net amounts recognized at December 31 |  | (311.3) | (283.4)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |  |
Net actuarial loss | [1] | 533.1 | 533.4
Prior service credit | [1] | (7.2) | (7.4)
Net amount recognized at December 31 | [1] | 525.9 | 526.0
Other Postretirement Benefits Plans [Member] |  |  |
Amounts recognized on the balance sheets consist of: |  |  |
Non-current assets |  | 3.0 | 6.1
Other current liabilities |  | (6.2) | (5.6)
Pension and other benefit obligations |  | (111.3) | (110.0)
Net amounts recognized at December 31 |  | (114.5) | (109.5)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |  |
Net actuarial loss | [1] | 59.8 | 60.7
Prior service credit | [1] | (5.6) | (16.7)
Net amount recognized at December 31 | [1] | 54.2 | 44.0
IPL [Member] |  |  |
Amounts recognized on the balance sheets consist of: |  |  |
Pension and other benefit obligations |  | (160.2) | (142.4)
IPL [Member] | Pension Plans, Defined Benefit [Member] |  |  |
Amounts recognized on the balance sheets consist of: |  |  |
Non-current assets |  | 0.0 | 0.0
Other current liabilities |  | (0.8) | (0.8)
Pension and other benefit obligations |  | (132.6) | (117.6)
Net amounts recognized at December 31 |  | (133.4) | (118.4)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |  |
Net actuarial loss | [2] | 235.5 | 233.1
Prior service credit | [2] | (2.5) | (2.6)
Net amount recognized at December 31 | [2] | 233.0 | 230.5
IPL [Member] | Other Postretirement Benefits Plans [Member] |  |  |
Amounts recognized on the balance sheets consist of: |  |  |
Non-current assets |  | 0.0 | 1.2
Other current liabilities |  | 0.0 | 0.0
Pension and other benefit obligations |  | (22.1) | (18.9)
Net amounts recognized at December 31 |  | (22.1) | (17.7)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |  |
Net actuarial loss | [2] | 29.8 | 27.9
Prior service credit | [2] | (2.7) | (8.7)
Net amount recognized at December 31 | [2] | 27.1 | 19.2
WPL [Member] |  |  |
Amounts recognized on the balance sheets consist of: |  |  |
Pension and other benefit obligations |  | (188.7) | (180.4)
WPL [Member] | Pension Plans, Defined Benefit [Member] |  |  |
Amounts recognized on the balance sheets consist of: |  |  |
Non-current assets |  | 0.0 | 0.0
Other current liabilities |  | (0.1) | (0.1)
Pension and other benefit obligations |  | (119.0) | (107.2)
Net amounts recognized at December 31 |  | (119.1) | (107.3)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |  |
Net actuarial loss | [3] | 232.1 | 233.5
Prior service credit | [3] | (1.2) | (1.0)
Net amount recognized at December 31 | [3] | 230.9 | 232.5
WPL [Member] | Other Postretirement Benefits Plans [Member] |  |  |
Amounts recognized on the balance sheets consist of: |  |  |
Non-current assets |  | 3.0 | 4.9
Other current liabilities |  | (6.0) | (5.5)
Pension and other benefit obligations |  | (68.0) | (71.6)
Net amounts recognized at December 31 |  | (71.0) | (72.2)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |  |
Net actuarial loss | [3] | 23.3 | 26.3
Prior service credit | [3] | (2.4) | (5.6)
Net amount recognized at December 31 | [3] | $ 20.9 | $ 20.7
[1] | Refer to Note 2 and Alliant Energy’s common equity statements for amounts recognized in “Regulatory assets” and “AOCL,” respectively, on Alliant Energy’s balance sheets.
[2] | Refer to Note 2 for amounts recognized in “Regulatory assets” on IPL’s balance sheets.
[3] | Refer to Note 2 for amounts recognized in “Regulatory assets” on WPL’s balance sheets.

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