Components of Net Pension (Income) Expense (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 23.5	$ 37.7	$ 70.4	$ 113.5
Interest on projected benefit obligation	32.0	21.0	95.7	63.9
Expected return on assets	(57.8)	(53.2)	(172.9)	(162.0)
Amortization of prior service costs	0.3	0.2	1.0	0.5
Recognized actuarial loss	1.3	7.1	3.7	21.7
Net pension (income) expense	$ (0.7)	$ 12.8	$ (2.1)	$ 37.6