Retirement Plans - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4.1	$ 3.8
Interest cost	4.8	5.2
Expected return on assets	(4.7)	(4.6)
Net gain	(0.4)	(0.9)
Prior service cost (credit)	0.2	0.2
Total benefit cost (credit)	4.0	3.7
Retiree Health Care Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0
Interest cost	0.1	0.1
Expected return on assets	0.0	0.0
Net gain	0.0	0.0
Prior service cost (credit)	(0.2)	(0.2)
Total benefit cost (credit)	$ (0.1)	$ (0.1)