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Benefit Plans (Estimated Amoritization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss) (Details) - Scenario, Forecast [Member] $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($)
Defined Benefit Pension Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Actuarial loss | $ 37.5
Prior service cost (credit) | (0.4)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL | 37.1
Defined Benefit Pension Plans [Member] | IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Actuarial loss | 16.1
Prior service cost (credit) | (0.2)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL | 15.9
Defined Benefit Pension Plans [Member] | WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Actuarial loss | 18.5
Prior service cost (credit) | 0.1
Estimated amortization from regulatory assets, regulatory liabilities and AOCL | 18.6
Other Postretirement Benefits Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Actuarial loss | 3.8
Prior service cost (credit) | (0.2)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL | 3.6
Other Postretirement Benefits Plans [Member] | IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Actuarial loss | 2.0
Prior service cost (credit) | 0.0
Estimated amortization from regulatory assets, regulatory liabilities and AOCL | 2.0
Other Postretirement Benefits Plans [Member] | WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Actuarial loss | 1.6
Prior service cost (credit) | (0.2)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL | $ 1.4

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- Definition Amount included in accumulated other comprehensive income (AOCI) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position, including gain (loss), prior service cost (credit), and transition asset (obligation). + References No definition available. + Details
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