Components of Net Periodic Benefit Cost (Detail) - Pension Plans, Defined Benefit - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 6.1	$ 3.7	$ 18.3	$ 14.4
Interest cost	5.4	5.3	16.1	16.0
Expected return on plan assets	(5.3)	(5.0)	(16.0)	(15.3)
Amortization prior service credit	0.1	(0.2)	0.4	(0.5)
Amortization of actuarial loss	2.0	1.4	5.9	4.4
Net Periodic Benefit Cost	$ 8.3	$ 5.2	$ 24.7	$ 19.0