Components of Net Periodic Benefit Cost from Continuing Operations (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Service cost	$ 4.9	$ 4.9	$ 14.8	$ 14.3
Interest cost	4.6	5.0	13.9	14.9
Expected return on plan assets	(5.6)	(4.8)	(16.8)	(14.6)
Amortization prior service cost	0.1	0.2	0.2	0.3
Amortization of actuarial loss	0.8	2.0	2.5	5.8
Net Periodic Benefit Cost	$ 4.8	$ 7.3	$ 14.6	$ 20.7