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Employee Benefits - Benefit Obligations and Funded Status of Pension Plans, OPEB and Salaried VEBAs (Parenthetical) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020
Other Postretirement Benefits Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | $ (83.5) |
Other Postretirement Benefits Plan | Long term Liabilities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | 81.9 |
Other Postretirement Benefits Plan | Current Liabilities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | 1.6 |
Salaried VEBA |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Actuarial gain (loss) due to change in discount rate | 3.0 | $ (5.7)
Actuarial gain due to changes in census data | 3.9 | 1.0
Defined Benefit Plan, Funded (Unfunded) Status of Plan | $ (20.6) | $ (17.8)

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