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Employee Benefits - Summary of Total Expense Related to All Postretirement Benefit Plans (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Other Postretirement Benefits Plan |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Defined contribution plan, cost | $ 1.4 | $ 1.7 | $ 7.0 | $ 7.3
Deferred compensation arrangement with individual, compensation expense | 0.4 | 0.3 | 0.8 | 1.3
Multiemployer plan, contributions by employer | 1.3 | 1.3 | 3.8 | 3.7
Total other employee benefit plans | 4.3 | 4.9 | 15.2 | 17.2
Postretirement Health Coverage | Salaried VEBA |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Total net periodic postretirement benefit cost relating to Salaried VEBA | $ 1.2 | $ 1.6 | $ 3.6 | $ 4.9

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