Retirement Plans - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3.9	$ 4.7	$ 11.6	$ 14.7
Interest cost	5.3	2.1	15.8	6.6
Expected return on assets	(4.8)	(3.6)	(14.2)	(11.1)
Net (gain) loss	(0.8)	0.5	(2.5)	1.4
Prior service credit	0.2	0.2	0.5	0.5
Total benefit cost (credit)	3.8	3.9	11.2	12.1
Retiree Health Care Plan
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0.1	0.1	0.4	0.2
Net (gain) loss	0.0	0.0	0.0	0.1
Prior service credit	(0.2)	(0.2)	(0.6)	(0.6)
Total benefit cost (credit)	$ (0.1)	$ (0.1)	$ (0.2)	$ (0.3)