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Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
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Amounts recognized on the balance sheets consist of: |  |
Pension and other benefit obligations | $ (489.9) | $ (451.8)
Pension Plans, Defined Benefit [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 0.0 | 0.0
Other current liabilities | (6.5) | (2.6)
Pension and other benefit obligations | (342.1) | (308.7)
Net amounts recognized at December 31 | (348.6) | (311.3)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |
Net actuarial loss | 535.1 | 533.1
Prior service credit | (6.9) | (7.2)
Net amount recognized at December 31 | 528.2 | 525.9
Other Postretirement Benefits Plans [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 3.2 | 3.0
Other current liabilities | (8.6) | (6.2)
Pension and other benefit obligations | (108.9) | (111.3)
Net amounts recognized at December 31 | (114.3) | (114.5)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |
Net actuarial loss | 52.6 | 59.8
Prior service credit | (1.5) | (5.6)
Net amount recognized at December 31 | 51.1 | 54.2
IPL [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Pension and other benefit obligations | (173.2) | (160.2)
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 | (0.7) | (0.8)
Pension and other benefit obligations | (147.7) | (132.6)
Net amounts recognized at December 31 | (148.4) | (133.4)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |
Net actuarial loss | 233.6 | 235.5
Prior service credit | (2.3) | (2.5)
Net amount recognized at December 31 | 231.3 | 233.0
IPL [Member] | Other Postretirement Benefits Plans [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 0.4 | 0.0
Other current liabilities | (1.9) | 0.0
Pension and other benefit obligations | (20.4) | (22.1)
Net amounts recognized at December 31 | (21.9) | (22.1)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |
Net actuarial loss | 25.4 | 29.8
Prior service credit | 0.0 | (2.7)
Net amount recognized at December 31 | 25.4 | 27.1
WPL [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Pension and other benefit obligations | (207.8) | (188.7)
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 | (139.4) | (119.0)
Net amounts recognized at December 31 | (139.5) | (119.1)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |
Net actuarial loss | 236.1 | 232.1
Prior service credit | (1.4) | (1.2)
Net amount recognized at December 31 | 234.7 | 230.9
WPL [Member] | Other Postretirement Benefits Plans [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 2.7 | 3.0
Other current liabilities | (6.4) | (6.0)
Pension and other benefit obligations | (66.6) | (68.0)
Net amounts recognized at December 31 | (70.3) | (71.0)
Amounts recognized in Regulatory Assets and AOCL consist of: |  |
Net actuarial loss | 21.5 | 23.3
Prior service credit | (1.5) | (2.4)
Net amount recognized at December 31 | $ 20.0 | $ 20.9

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