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Employee Benefits - Summary of Total Expense (Benefit) Related to All Postretirement Benefit Plans (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2022 | Jun. 30, 2021 | Jun. 30, 2022 | Jun. 30, 2021
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total net periodic postretirement benefit cost | $ 1.5 | $ 1.2 | $ 2.9 | $ 1.8
Other Postretirement Benefits Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined contribution plan, cost | 4.0 | 3.6 | 9.7 | 7.0
Deferred compensation arrangement with individual, compensation expense | (0.5) | 0.4 | (0.8) | 0.4
Multiemployer plan, contributions by employer | 1.4 | 1.3 | 2.6 | 2.4
Total net periodic postretirement benefit cost | 1.0 | 1.0 | 1.9 | 1.0
Total other employee benefit plans | 8.2 | 8.3 | 18.0 | 13.4
Postretirement Health Coverage | Salaried VEBA |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total net periodic postretirement benefit cost | 1.0 | 0.5 | 1.9 | 1.1
Pension Plans |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Total net periodic postretirement benefit cost | $ 1.3 | $ 1.5 | $ 2.7 | $ 1.5

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