Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - Domestic Plan [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.0	$ 2.9	$ 2.1	$ 5.8
Interest cost	3.0	4.1	6.0	8.2
Expected return on plan assets	(2.2)	(2.9)	(4.5)	(5.8)
Net periodic benefit cost	$ 1.8	$ 4.1	$ 3.6	$ 8.2