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Benefit Plans (Expected Benefit Payments) (Details) $ in Millions | Dec. 31, 2018 USD ($)
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Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2019 | $ 91.0
Expected benefit payments, 2020 | 104.2
Expected benefit payments, 2021 | 92.5
Expected benefit payments, 2022 | 93.8
Expected benefit payments, 2023 | 94.8
Expected benefit payments, 2024 - 2028 | 466.0
Defined Benefit Pension Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2019 | 71.7
Expected benefit payments, 2020 | 86.1
Expected benefit payments, 2021 | 74.7
Expected benefit payments, 2022 | 76.3
Expected benefit payments, 2023 | 77.8
Expected benefit payments, 2024 - 2028 | 388.3
Other Postretirement Benefits Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2019 | 19.3
Expected benefit payments, 2020 | 18.1
Expected benefit payments, 2021 | 17.8
Expected benefit payments, 2022 | 17.5
Expected benefit payments, 2023 | 17.0
Expected benefit payments, 2024 - 2028 | 77.7
IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2019 | 40.3
Expected benefit payments, 2020 | 42.4
Expected benefit payments, 2021 | 42.3
Expected benefit payments, 2022 | 43.5
Expected benefit payments, 2023 | 44.4
Expected benefit payments, 2024 - 2028 | 214.2
IPL [Member] | Defined Benefit Pension Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2019 | 33.0
Expected benefit payments, 2020 | 35.1
Expected benefit payments, 2021 | 35.1
Expected benefit payments, 2022 | 36.4
Expected benefit payments, 2023 | 37.5
Expected benefit payments, 2024 - 2028 | 182.9
IPL [Member] | Other Postretirement Benefits Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2019 | 7.3
Expected benefit payments, 2020 | 7.3
Expected benefit payments, 2021 | 7.2
Expected benefit payments, 2022 | 7.1
Expected benefit payments, 2023 | 6.9
Expected benefit payments, 2024 - 2028 | 31.3
WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2019 | 40.2
Expected benefit payments, 2020 | 39.4
Expected benefit payments, 2021 | 39.3
Expected benefit payments, 2022 | 39.1
Expected benefit payments, 2023 | 39.3
Expected benefit payments, 2024 - 2028 | 196.0
WPL [Member] | Defined Benefit Pension Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2019 | 31.4
Expected benefit payments, 2020 | 31.8
Expected benefit payments, 2021 | 31.9
Expected benefit payments, 2022 | 32.0
Expected benefit payments, 2023 | 32.5
Expected benefit payments, 2024 - 2028 | 165.3
WPL [Member] | Other Postretirement Benefits Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2019 | 8.8
Expected benefit payments, 2020 | 7.6
Expected benefit payments, 2021 | 7.4
Expected benefit payments, 2022 | 7.1
Expected benefit payments, 2023 | 6.8
Expected benefit payments, 2024 - 2028 | $ 30.7

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