Components of Pension Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Net Periodic Benefit Cost [Abstract]
Service cost	$ 108.3	$ 92.9	$ 88.6
Interest on projected benefit obligation	85.8	81.1	94.3
Expected return on assets	(177.2)	(159.7)	(141.7)
Amortization of prior service costs	1.4	1.2	1.2
Recognized actuarial loss	35.3	25.4	27.7
Net pension expense	$ 53.6	$ 40.9	$ 70.1