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Employee Benefits - Fair Value of Plan Assets (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
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Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | $ 79.5 | $ 77.1 |
Salaried VEBA |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | 59.2 | 60.5 | $ 57.6
Postretirement Health Coverage | Salaried VEBA | Equity Funds | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount |  | 34.7 |
Postretirement Health Coverage | Salaried VEBA | Fixed Income Funds | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount |  | 22.7 |
Pension Plan |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | 9.8 | 8.7 | $ 7.8
Pension Plan | Equity Funds | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | 0.1 |  |
Pension Plan | Fixed Income Funds | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | 0.1 |  |
Pension Plan | Diversified Investment Funds In Registered Investment Companies | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | 9.6 | 8.7 |
Level 1 | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | 69.7 | 1.4 |
Deferred Compensation Plan Assets | 10.5 |  |
Level 1 | Postretirement Health Coverage | Salaried VEBA | Equity Funds | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | 38.6 |  |
Level 1 | Postretirement Health Coverage | Salaried VEBA | Fixed Income Funds | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | 20.6 |  |
Level 1 | Postretirement Health Coverage | Salaried VEBA | Cash and Cash Equivalents | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount |  | 1.4 |
Level 2 | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount |  | 9.6 |
Deferred Compensation Plan Assets |  | 9.6 |
Fair Value, Inputs, Level 1, 2 and 3 | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | 69.7 | 11.0 |
Deferred Compensation Plan Assets | 10.5 | 9.6 |
Fair Value, Inputs, Level 1, 2 and 3 | Postretirement Health Coverage | Salaried VEBA | Equity Funds | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | 38.6 |  |
Fair Value, Inputs, Level 1, 2 and 3 | Postretirement Health Coverage | Salaried VEBA | Fixed Income Funds | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount | $ 20.6 |  |
Fair Value, Inputs, Level 1, 2 and 3 | Postretirement Health Coverage | Salaried VEBA | Cash and Cash Equivalents | Fair Value, Measurements, Recurring |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Defined Benefit Plan, Plan Assets, Amount |  | $ 1.4 |

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