Components of Net Pension Expense (Income) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 27.6	$ 21.9	$ 55.4	$ 46.9
Interest on projected benefit obligation	33.4	32.6	67.0	63.7
Expected return on assets	(60.5)	(57.6)	(121.1)	(115.1)
Amortization of prior service costs	0.4	0.4	0.7	0.7
Recognized actuarial loss	1.6	1.7	2.8	2.4
Net pension expense (income)	$ 2.5	$ (1.0)	$ 4.8	$ (1.4)