Employee Benefits - Summary of Components of Net Periodic Postretirement Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Net periodic postretirement benefit cost	$ 4.1	$ 4.7	$ 6.5
Salaried VEBA
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1
Interest cost	1.5	2.5
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	4.1	0.3	0.3
Interest cost	0.5	0.3	0.3
Expected return on plan assets	(0.4)	(0.3)	(0.3)
Amortization of net actuarial loss	0.1	0.1	0.1
Net periodic postretirement benefit cost	4.3	0.4	0.4
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.1
Interest cost	1.7
Net periodic postretirement benefit cost	2.8
Postretirement Health Coverage | Salaried VEBA
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.1
Interest cost	1.5	2.5	3.2
Expected return on plan assets	(3.1)	(2.8)	(2.7)
Amortization of prior service cost	3.5	4.7	5.6
Amortization of net actuarial loss	0.3	0.3	0.4
Net periodic postretirement benefit cost	$ 2.3	$ 4.8	$ 6.6