Employee benefit plans (Detail) - Defined Benefit Pension Plans - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
USA
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Interest cost	5.8	6.8	11.6	13.6
Expected return on plan assets	(7.2)	(6.3)	(14.3)	(12.6)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0.0	0.0	0.0	0.0
Net periodic (benefit) cost	(1.4)	0.5	(2.7)	1.0
Foreign Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.4	0.6	0.9	1.2
Interest cost	3.0	3.9	6.1	7.8
Expected return on plan assets	(3.8)	(5.1)	(7.8)	(10.1)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0.1	0.1	0.1	0.1
Net periodic (benefit) cost	$ (0.3)	$ (0.5)	$ (0.7)	$ (1.0)