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Postretirement Health Care and Life Insurance Benefits - Estimated Future Benefit Payments (Details) - Postretirement Health Care and Life Insurance Benefits
$ in Millions
Dec. 31, 2020
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
2021 $ 40.3
2022 37.6
2023 35.8
2024 34.1
2025 32.3
Years 2026-2030 $ 135.8