Components of Pension Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Postemployment Benefits [Abstract]
Service cost	$ 22.2	$ 22.6	$ 46.0	$ 44.5
Interest on projected benefit obligation	20.0	24.1	40.4	47.7
Expected return on assets	(39.6)	(36.1)	(79.4)	(71.7)
Amortization of prior service costs	0.3	0.3	0.6	0.6
Recognized actuarial loss	5.9	7.4	12.6	13.9
Net pension expense	$ 8.8	$ 18.3	$ 20.2	$ 35.0