Components of Net Pension Expense (Income) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 27.8	$ 25.0
Interest on projected benefit obligation	33.6	31.1
Expected return on assets	(60.6)	(57.5)
Amortization of prior service costs	0.3	0.3
Recognized actuarial loss	1.2	0.7
Net pension expense (income)	$ 2.3	$ (0.4)