Components of Net Pension Expense (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Defined Benefit Plan Net Periodic Benefit Cost [Abstract]
Service cost	$ 32.5	$ 36.0
Interest on projected benefit obligation	19.1	16.6
Expected return on assets	(48.7)	(51.1)
Amortization of prior service costs	0.1	0.2
Recognized actuarial loss	5.6	14.2
Net pension expense	$ 8.6	$ 15.9