Pension and Post Employment Benefits - Plan Net Pension Credit (Detail) - Foreign Pension Plan [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
United Kingdom [Member]
Plan net pension credit/(charge):
Interest cost on projected benefit obligation	$ (3.9)	$ (3.7)
Expected return on plan assets	5.7	5.9
Amortization of prior service credit	0.3	0.3
Amortization of actuarial net losses	(0.5)	(1.2)
Net pension credit total	1.6	1.3
Germany [Member]
Plan net pension credit/(charge):
Interest cost on projected benefit obligation	(0.1)	(0.1)
Amortization of actuarial net losses	(0.1)	(0.1)
Net pension credit total	$ (0.2)	$ (0.2)