Pension and Postretirement Benefits - Components of Net Periodic Benefit Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.8	$ 1.6	$ 1.6	$ 3.2
Interest cost	64.0	70.9	128.0	140.8
Expected return on plan assets	(87.0)	(90.1)	(174.2)	(179.5)
Amortization of prior service benefit	(1.7)	(1.2)	(3.2)	(2.5)
Recognized net actuarial loss	42.0	45.3	84.1	89.0
Curtailment gain	0.0	(5.2)	0.0	(5.2)
Net periodic pension expense (benefit)/postretirement benefit expense	18.1	21.3	36.3	45.8
Pension Plans | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0	0.0
Interest cost	46.6	53.2	93.2	105.7
Expected return on plan assets	(57.6)	(58.8)	(115.2)	(117.6)
Amortization of prior service benefit	(0.7)	(0.7)	(1.3)	(1.3)
Recognized net actuarial loss	31.2	32.3	62.4	63.2
Curtailment gain	0.0	0.0	0.0	0.0
Net periodic pension expense (benefit)/postretirement benefit expense	19.5	26.0	39.1	50.0
Pension Plans | International Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.8	1.6	1.6	3.2
Interest cost	17.4	17.7	34.8	35.1
Expected return on plan assets	(29.4)	(31.3)	(59.0)	(61.9)
Amortization of prior service benefit	(1.0)	(0.5)	(1.9)	(1.2)
Recognized net actuarial loss	10.8	13.0	21.7	25.8
Curtailment gain	0.0	(5.2)	0.0	(5.2)
Net periodic pension expense (benefit)/postretirement benefit expense	(1.4)	(4.7)	(2.8)	(4.2)
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.3	0.2
Interest cost	1.2	1.5	2.4	3.0
Expected return on plan assets	(0.1)	(0.1)	(0.2)	(0.2)
Amortization of prior service benefit	(0.3)	(0.1)	(0.8)	(0.2)
Recognized net actuarial loss	0.2	0.3	0.5	0.6
Net periodic pension expense (benefit)/postretirement benefit expense	$ 1.1	$ 1.7	$ 2.2	$ 3.4