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Postretirement Health Care and Life Insurance Benefits - Estimated Future Benefit Payments (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items] |  |
Average remaining service period (in years) | 2 years 10 months 24 days | 3 years 10 months 24 days
Postretirement Health Care and Life Insurance Benefits |  |
Defined Benefit Plan Disclosure [Line Items] |  |
2022 | $ 28.9 |
2023 | 25.8 |
2024 | 24.3 |
2025 | 22.7 |
2026 | 20.8 |
Years 2027-2031 | $ 81.5 |
Average remaining service period (in years) | 14 years 2 months 12 days |
Postretirement Health Care and Life Insurance Benefits | Retirement Plan Amendment One |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Average remaining service period (in years) | 3 years 10 months 24 days | 4 years 10 months 24 days
Postretirement Health Care and Life Insurance Benefits | Retirement Plan Amendment Two |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Average remaining service period (in years) | 9 years 6 months | 10 years 6 months

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- Definition Amount of benefit for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 + Details
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