Components of Pension Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Net Periodic Benefit Cost [Abstract]
Service cost	$ 102.0	$ 108.3	$ 92.9
Interest on projected benefit obligation	95.6	85.8	81.1
Expected return on assets	(176.6)	(177.2)	(159.7)
Amortization of prior service costs	1.4	1.4	1.2
Recognized actuarial loss	20.5	35.3	25.4
Net pension expense	$ 42.9	$ 53.6	$ 40.9