Pension and Postretirement Benefits - Components of Net Periodic Benefit Expense (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.8	$ 1.6
Interest cost	64.0	69.9
Expected return on plan assets	(87.2)	(89.4)
Amortization of prior service benefit	(1.5)	(1.3)
Recognized net actuarial loss	42.1	43.7
Net periodic pension expense (benefit)/postretirement benefit expense	18.2	24.5
Pension Plans | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0
Interest cost	46.6	52.5
Expected return on plan assets	(57.6)	(58.8)
Amortization of prior service benefit	(0.6)	(0.6)
Recognized net actuarial loss	31.2	30.9
Net periodic pension expense (benefit)/postretirement benefit expense	19.6	24.0
Pension Plans | International Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.8	1.6
Interest cost	17.4	17.4
Expected return on plan assets	(29.6)	(30.6)
Amortization of prior service benefit	(0.9)	(0.7)
Recognized net actuarial loss	10.9	12.8
Net periodic pension expense (benefit)/postretirement benefit expense	(1.4)	0.5
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.2	0.1
Interest cost	1.2	1.5
Expected return on plan assets	(0.1)	(0.1)
Amortization of prior service benefit	(0.5)	(0.1)
Recognized net actuarial loss	0.3	0.3
Net periodic pension expense (benefit)/postretirement benefit expense	$ 1.1	$ 1.7