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Benefit Plans (Fair Value Of Plan Assets By Asset Category And Fair Value Hierarchy Level) (Details) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 895.7 $ 895.0 $ 1,018.1
Assets measured at net asset value 405.9 608.5  
Total plan assets 895.7 895.0  
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 30.4 23.1  
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 5.0 0.0  
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 25.4 23.1  
Pension Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Equity securites - domestic [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 183.6 116.4  
Pension Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 183.6 116.4  
Pension Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 97.4 93.9  
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 97.4 93.9  
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 53.0 52.9  
Pension Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 53.0 52.9  
Pension Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 125.4 0.0  
Pension Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 53.6 0.0  
Pension Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 71.8 0.0  
Pension Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Subtotal [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Total plan assets 489.8 286.3  
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 392.6 263.2  
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 97.2 23.1  
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Accrued Investment Income [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1.1 0.2  
Pension Plans, Defined Benefit [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 422.0 422.7 484.7
Assets measured at net asset value 191.2 287.4  
Total plan assets 422.0 422.7  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 14.4 10.9  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2.4 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 12.0 10.9  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 86.5 54.9  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 86.5 54.9  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 45.9 44.4  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 45.9 44.4  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 24.9 25.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 24.9 25.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 59.1 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 25.3 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 33.8 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Total plan assets 230.8 135.2  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 185.0 124.3  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 45.8 10.9  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Accrued Investment Income [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.5 0.1  
Pension Plans, Defined Benefit [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 389.7 386.8 440.3
Assets measured at net asset value 176.6 263.0  
Total plan assets 389.7 386.8  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 13.3 10.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2.2 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 11.1 10.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - domestic [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 79.9 50.3  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - domestic [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 79.9 50.3  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - domestic [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securites - domestic [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 42.4 40.6  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 42.4 40.6  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities - international [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 23.0 22.8  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 23.0 22.8  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 54.5 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 23.3 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 31.2 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Total plan assets 213.1 123.7  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 170.8 113.7  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 42.3 10.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Accrued Investment Income [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.5 0.1  
Other Postretirement Benefit Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 105.8 106.9 121.6
Assets measured at net asset value 3.0 5.5  
Total plan assets 102.8 101.4  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 100.7 97.8  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2.1 3.6  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 3.5 3.6  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1.5 3.6  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Equivalents [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - domestic [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 22.5 22.1  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 22.5 22.1  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securites - domestic [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 13.5 13.4  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 13.5 13.4  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities - international [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 16.5 16.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 16.5 16.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 46.8 46.3  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 46.2 46.3  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.6 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 68.2 69.2 78.7
Assets measured at net asset value 0.0 0.6  
Total plan assets 68.2 68.6  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 68.2 67.7  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.9  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.8 0.9  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.8 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.9  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and Equivalents [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 17.0 16.7  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 17.0 16.7  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securites - domestic [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 11.0 10.8  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 11.0 10.8  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities - international [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 7.0 6.9  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 7.0 6.9  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 32.4 33.3  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 32.4 33.3  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed Income Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 18.6 18.7 $ 21.8
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 17.3 16.4  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1.3 2.3  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2.0 2.3  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.7 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1.3 2.3  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and Equivalents [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 5.5 5.4  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 5.5 5.4  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Global Asset Allocation Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 11.1 11.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 11.1 11.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed Income Securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Defined Benefit Plan Due To Brokers Net [Member] | Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets (1.1) 0.0  
Defined Benefit Plan Due To Brokers Net [Member] | Pension Plans, Defined Benefit [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets (0.5) 0.0  
Defined Benefit Plan Due To Brokers Net [Member] | Pension Plans, Defined Benefit [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ (0.5) $ 0.0