Retirement Plans - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5.1	$ 5.6
Interest cost	2.3	1.5
Expected return on assets	(3.9)	(3.1)
Net loss	0.5	1.2
Prior service cost (credit)	0.2	0.2
Total benefit cost (credit)	4.2	5.4
Retiree Health Care Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost
Interest cost	0.1	0.1
Expected return on assets
Net loss
Prior service cost (credit)	(0.2)	(0.2)
Total benefit cost (credit)	$ (0.1)	$ (0.1)