Components of Net Pension Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Net Periodic Benefit Cost [Abstract]
Service cost	$ 27.1	$ 26.0	$ 51.8	$ 54.7
Interest on projected benefit obligation	24.3	21.7	48.0	43.0
Expected return on assets	(43.9)	(44.5)	(88.5)	(89.3)
Amortization of prior service costs	0.3	0.3	0.7	0.7
Recognized actuarial loss	5.9	10.1	10.3	17.8
Net pension expense	$ 13.7	$ 13.6	$ 22.3	$ 26.9