Employee Benefits - Summary of Total Expense Related to All Postretirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 3.4	$ 3.9
Deferred compensation arrangement with individual, compensation expense		(0.4)
Multiemployer plan, contributions by employer	1.1	1.3
Total other employee benefit plans	5.1	6.0
Postretirement Health Coverage | Salaried VEBA
Defined Benefit Plan Disclosure [Line Items]
Total net periodic postretirement benefit cost relating to Salaried VEBA	$ 0.6	$ 1.2