Employee Benefits - Summary of Total Expense Related to All Postretirement Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Net periodic postretirement benefit cost	$ 5.2	$ 7.0	$ 6.6
Total other employee benefit plans	19.9	22.4	21.0
Canadian pension plan | Canadian pension plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic postretirement benefit cost	0.4	0.4	0.4
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	8.3	8.8	8.8
Deferred compensation arrangement with individual, compensation expense	1.5	1.6	1.0
Multiemployer plan, contributions by employer	4.9	5.0	4.7
Postretirement Health Coverage | Salaried VEBA
Defined Benefit Plan Disclosure [Line Items]
Net periodic postretirement benefit cost	$ 4.8	$ 6.6	$ 6.1