Components of Net Pension Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Defined Benefit Plan Net Periodic Benefit Cost [Abstract]
Service cost	$ 43.3	$ 39.4	$ 75.8	$ 75.4
Interest on projected benefit obligation	23.8	16.7	42.9	33.3
Expected return on assets	(60.1)	(51.2)	(108.8)	(102.3)
Amortization of prior service costs	0.2	0.2	0.3	0.4
Recognized actuarial loss	9.0	15.3	14.6	29.5
Net pension expense	$ 16.2	$ 20.4	$ 24.8	$ 36.3