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Benefit Plans (Expected Benefit Payments) (Details) $ in Millions | Dec. 31, 2019 USD ($)
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Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2020 | $ 104.1
Expected benefit payments, 2021 | 92.2
Expected benefit payments, 2022 | 94.1
Expected benefit payments, 2023 | 94.6
Expected benefit payments, 2024 | 95.0
Expected benefit payments, 2025 - 2029 | 466.8
Defined Benefit Pension Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2020 | 86.4
Expected benefit payments, 2021 | 74.5
Expected benefit payments, 2022 | 76.6
Expected benefit payments, 2023 | 77.5
Expected benefit payments, 2024 | 78.2
Expected benefit payments, 2025 - 2029 | 390.2
Other Postretirement Benefits Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2020 | 17.7
Expected benefit payments, 2021 | 17.7
Expected benefit payments, 2022 | 17.5
Expected benefit payments, 2023 | 17.1
Expected benefit payments, 2024 | 16.8
Expected benefit payments, 2025 - 2029 | 76.6
IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2020 | 42.3
Expected benefit payments, 2021 | 42.4
Expected benefit payments, 2022 | 43.7
Expected benefit payments, 2023 | 44.7
Expected benefit payments, 2024 | 43.5
Expected benefit payments, 2025 - 2029 | 213.1
IPL [Member] | Defined Benefit Pension Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2020 | 35.1
Expected benefit payments, 2021 | 35.3
Expected benefit payments, 2022 | 36.6
Expected benefit payments, 2023 | 37.7
Expected benefit payments, 2024 | 36.6
Expected benefit payments, 2025 - 2029 | 182.5
IPL [Member] | Other Postretirement Benefits Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2020 | 7.2
Expected benefit payments, 2021 | 7.1
Expected benefit payments, 2022 | 7.1
Expected benefit payments, 2023 | 7.0
Expected benefit payments, 2024 | 6.9
Expected benefit payments, 2025 - 2029 | 30.6
WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2020 | 39.3
Expected benefit payments, 2021 | 39.4
Expected benefit payments, 2022 | 39.2
Expected benefit payments, 2023 | 39.2
Expected benefit payments, 2024 | 39.8
Expected benefit payments, 2025 - 2029 | 195.4
WPL [Member] | Defined Benefit Pension Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2020 | 32.0
Expected benefit payments, 2021 | 32.0
Expected benefit payments, 2022 | 32.1
Expected benefit payments, 2023 | 32.4
Expected benefit payments, 2024 | 33.1
Expected benefit payments, 2025 - 2029 | 165.2
WPL [Member] | Other Postretirement Benefits Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Expected benefit payments, 2020 | 7.3
Expected benefit payments, 2021 | 7.4
Expected benefit payments, 2022 | 7.1
Expected benefit payments, 2023 | 6.8
Expected benefit payments, 2024 | 6.7
Expected benefit payments, 2025 - 2029 | $ 30.2

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