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Benefit Plans (Expected Benefit Payments) (Details)
$ in Millions
Dec. 31, 2020
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2021 $ 94
Expected benefit payments, 2022 96
Expected benefit payments, 2023 96
Expected benefit payments, 2024 96
Expected benefit payments, 2025 97
Expected benefit payments, 2026 - 2030 472
Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2021 76
Expected benefit payments, 2022 78
Expected benefit payments, 2023 79
Expected benefit payments, 2024 79
Expected benefit payments, 2025 80
Expected benefit payments, 2026 - 2030 398
Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2021 18
Expected benefit payments, 2022 18
Expected benefit payments, 2023 17
Expected benefit payments, 2024 17
Expected benefit payments, 2025 17
Expected benefit payments, 2026 - 2030 74
IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2021 45
Expected benefit payments, 2022 45
Expected benefit payments, 2023 46
Expected benefit payments, 2024 45
Expected benefit payments, 2025 45
Expected benefit payments, 2026 - 2030 210
IPL [Member] | Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2021 38
Expected benefit payments, 2022 38
Expected benefit payments, 2023 39
Expected benefit payments, 2024 38
Expected benefit payments, 2025 38
Expected benefit payments, 2026 - 2030 181
IPL [Member] | Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2021 7
Expected benefit payments, 2022 7
Expected benefit payments, 2023 7
Expected benefit payments, 2024 7
Expected benefit payments, 2025 7
Expected benefit payments, 2026 - 2030 29
WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2021 39
Expected benefit payments, 2022 39
Expected benefit payments, 2023 39
Expected benefit payments, 2024 40
Expected benefit payments, 2025 39
Expected benefit payments, 2026 - 2030 191
WPL [Member] | Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2021 32
Expected benefit payments, 2022 32
Expected benefit payments, 2023 32
Expected benefit payments, 2024 33
Expected benefit payments, 2025 33
Expected benefit payments, 2026 - 2030 162
WPL [Member] | Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2021 7
Expected benefit payments, 2022 7
Expected benefit payments, 2023 7
Expected benefit payments, 2024 7
Expected benefit payments, 2025 6
Expected benefit payments, 2026 - 2030 $ 29