Pension and Postretirement Benefits - Schedule of Components of Net Periodic Benefit Cost (Credit) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 9.3	$ 14.0	$ 16.4	$ 24.0
Interest cost	14.6	11.9	25.7	20.6
Expected return on assets	(20.3)	(22.5)	(35.7)	(38.7)
Prior service cost (credit)	1.7	1.4	2.9	2.5
Actuarial loss (gain)	0.2	1.2	0.3	2.0
Net periodic benefit cost (credit)	5.5	6.0	9.6	10.4
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0	0.0
Interest cost	0.2	0.1	0.2	0.2
Expected return on assets	0.0	0.0	0.0	0.0
Prior service cost (credit)	(0.1)	(0.2)	(0.1)	(0.4)
Actuarial loss (gain)	(0.2)	(0.1)	(0.3)	(0.1)
Net periodic benefit cost (credit)	$ (0.1)	$ (0.2)	$ (0.2)	$ (0.3)