Components of Net Pension Expense (Income) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 25.3	$ 23.5	$ 80.7	$ 70.4
Interest on projected benefit obligation	34.4	32.0	101.4	95.7
Expected return on assets	(60.8)	(57.8)	(181.9)	(172.9)
Amortization of prior service costs	0.3	0.3	1.0	1.0
Recognized actuarial loss	2.5	1.3	5.3	3.7
Net pension expense (income)	$ 1.7	$ (0.7)	$ 6.5	$ (2.1)