Other Post-Employment Benefits and Other Employee Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components of net periodic benefit cost:
Service cost	$ 7.0	$ 10.6	$ 11.4
Interest cost	22.9	26.1	30.4
Amortization of net loss	6.5	7.5	7.8
Amortization of prior service credit	(0.1)	0.0	0.0
Income of settlement/curtailment	5.1	0.7	1.0
Total benefit cost	1.0	11.9	10.9
Other Post-Employment Benefits and Other Employee Benefit Plans
Components of net periodic benefit cost:
Service cost	0.1	0.2	0.8
Interest cost	1.6	1.9	2.9
Amortization of net loss	(0.2)	0.0	0.4
Amortization of prior service credit	(1.2)	(1.6)	(0.8)
Net periodic benefit cost	0.3	0.5	3.3
Income of settlement/curtailment	(13.5)	0.0	(1.2)
Total benefit cost	$ (13.2)	$ 0.5	$ 2.1