Components of Net Pension (Income) Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 21.9	$ 43.3	$ 46.9	$ 75.8
Interest on projected benefit obligation	32.6	23.8	63.7	42.9
Expected return on assets	(57.6)	(60.1)	(115.1)	(108.8)
Amortization of prior service costs	0.4	0.2	0.7	0.3
Recognized actuarial loss	1.7	9.0	2.4	14.6
Net pension (income) expense	$ (1.0)	$ 16.2	$ (1.4)	$ 24.8