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Benefit Plans (Expected Benefit Payments) (Details)
$ in Millions
Dec. 31, 2017
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2018 $ 90.4
Expected benefit payments, 2019 92.3
Expected benefit payments, 2020 94.1
Expected benefit payments, 2021 94.6
Expected benefit payments, 2022 110.1
Expected benefit payments, 2023 - 2027 478.3
Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2018 72.2
Expected benefit payments, 2019 73.9
Expected benefit payments, 2020 76.4
Expected benefit payments, 2021 77.1
Expected benefit payments, 2022 92.9
Expected benefit payments, 2023 - 2027 398.2
Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2018 18.2
Expected benefit payments, 2019 18.4
Expected benefit payments, 2020 17.7
Expected benefit payments, 2021 17.5
Expected benefit payments, 2022 17.2
Expected benefit payments, 2023 - 2027 80.1
IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2018 41.0
Expected benefit payments, 2019 40.9
Expected benefit payments, 2020 43.7
Expected benefit payments, 2021 43.7
Expected benefit payments, 2022 44.6
Expected benefit payments, 2023 - 2027 221.0
IPL [Member] | Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2018 33.9
Expected benefit payments, 2019 33.8
Expected benefit payments, 2020 36.5
Expected benefit payments, 2021 36.6
Expected benefit payments, 2022 37.6
Expected benefit payments, 2023 - 2027 188.4
IPL [Member] | Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2018 7.1
Expected benefit payments, 2019 7.1
Expected benefit payments, 2020 7.2
Expected benefit payments, 2021 7.1
Expected benefit payments, 2022 7.0
Expected benefit payments, 2023 - 2027 32.6
WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2018 39.7
Expected benefit payments, 2019 40.3
Expected benefit payments, 2020 39.9
Expected benefit payments, 2021 39.7
Expected benefit payments, 2022 39.7
Expected benefit payments, 2023 - 2027 199.6
WPL [Member] | Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2018 31.4
Expected benefit payments, 2019 32.0
Expected benefit payments, 2020 32.4
Expected benefit payments, 2021 32.4
Expected benefit payments, 2022 32.7
Expected benefit payments, 2023 - 2027 167.8
WPL [Member] | Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2018 8.3
Expected benefit payments, 2019 8.3
Expected benefit payments, 2020 7.5
Expected benefit payments, 2021 7.3
Expected benefit payments, 2022 7.0
Expected benefit payments, 2023 - 2027 $ 31.8