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Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Amounts recognized on the balance sheets consist of: |  |
Pension and other benefit obligations | $ (509.1) | $ (504.0)
Pension Plans, Defined Benefit [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 0.0 | 0.0
Current liabilities | (2.3) | (2.2)
Pension and other benefit obligations | (364.1) | (350.2)
Net amounts recognized at December 31 | (366.4) | (352.4)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 505.2 | 509.1
Prior service credit | (5.8) | (6.5)
Net amount recognized at December 31 | 499.4 | 502.6
Other Postretirement Benefits Plans [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 7.5 | 8.8
Current liabilities | (9.6) | (9.1)
Pension and other benefit obligations | (104.9) | (110.9)
Net amounts recognized at December 31 | (107.0) | (111.2)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 44.5 | 47.4
Prior service credit | (1.1) | (1.3)
Net amount recognized at December 31 | 43.4 | 46.1
IPL [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Pension and other benefit obligations | (178.4) | (173.8)
IPL [Member] | Pension Plans, Defined Benefit [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 0.0 | 0.0
Current liabilities | (0.6) | (0.5)
Pension and other benefit obligations | (155.5) | (148.7)
Net amounts recognized at December 31 | (156.1) | (149.2)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 218.8 | 218.9
Prior service credit | (1.8) | (2.1)
Net amount recognized at December 31 | 217.0 | 216.8
IPL [Member] | Other Postretirement Benefits Plans [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 4.7 | 5.9
Current liabilities | (1.9) | (2.0)
Pension and other benefit obligations | (18.6) | (20.4)
Net amounts recognized at December 31 | (15.8) | (16.5)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 18.8 | 18.7
Prior service credit | 0.0 | 0.0
Net amount recognized at December 31 | 18.8 | 18.7
WPL [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Pension and other benefit obligations | (217.7) | (213.7)
WPL [Member] | Pension Plans, Defined Benefit [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 0.0 | 0.0
Current liabilities | (0.1) | (0.1)
Pension and other benefit obligations | (154.3) | (144.7)
Net amounts recognized at December 31 | (154.4) | (144.8)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 223.0 | 224.7
Prior service credit | (1.3) | (1.5)
Net amount recognized at December 31 | 221.7 | 223.2
WPL [Member] | Other Postretirement Benefits Plans [Member] |  |
Amounts recognized on the balance sheets consist of: |  |
Non-current assets | 2.8 | 2.9
Current liabilities | (7.4) | (6.8)
Pension and other benefit obligations | (61.9) | (67.8)
Net amounts recognized at December 31 | (66.5) | (71.7)
Amounts recognized in Regulatory Assets consist of: |  |
Net actuarial loss | 19.9 | 23.6
Prior service credit | (1.1) | (1.3)
Net amount recognized at December 31 | $ 18.8 | $ 22.3

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