Components of Net Pension Expense (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Defined Benefit Plan Net Periodic Benefit Cost [Abstract]
Service cost	$ 37.7	$ 37.6	$ 113.5	$ 113.0
Interest on projected benefit obligation	21.0	16.7	63.9	50.0
Expected return on assets	(53.2)	(51.1)	(162.0)	(153.4)
Amortization of prior service costs	0.2	0.2	0.5	0.6
Recognized actuarial loss	7.1	14.7	21.7	44.2
Net pension expense	$ 12.8	$ 18.1	$ 37.6	$ 54.4