Pension and Postretirement Benefits - Components of Net Periodic Benefit Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.7	$ 0.8	$ 1.4	$ 1.6
Interest cost	66.5	64.0	133.2	128.0
Expected return on plan assets	(80.9)	(87.0)	(162.1)	(174.2)
Amortization of prior service benefit	(1.3)	(1.7)	(2.5)	(3.2)
Recognized net actuarial loss	37.6	42.0	75.2	84.1
Net periodic pension expense (benefit)/postretirement benefit expense	22.6	18.1	45.2	36.3
Pension Plans | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0	0.0
Interest cost	49.3	46.6	98.5	93.2
Expected return on plan assets	(54.5)	(57.6)	(109.0)	(115.2)
Amortization of prior service benefit	(0.7)	(0.7)	(1.3)	(1.3)
Recognized net actuarial loss	29.0	31.2	57.9	62.4
Net periodic pension expense (benefit)/postretirement benefit expense	23.1	19.5	46.1	39.1
Pension Plans | International Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.7	0.8	1.4	1.6
Interest cost	17.2	17.4	34.7	34.8
Expected return on plan assets	(26.4)	(29.4)	(53.1)	(59.0)
Amortization of prior service benefit	(0.6)	(1.0)	(1.2)	(1.9)
Recognized net actuarial loss	8.6	10.8	17.3	21.7
Net periodic pension expense (benefit)/postretirement benefit expense	(0.5)	(1.4)	(0.9)	(2.8)
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.2	0.3
Interest cost	1.2	1.2	2.4	2.4
Expected return on plan assets	(0.1)	(0.1)	(0.2)	(0.2)
Amortization of prior service benefit	(0.4)	(0.3)	(0.8)	(0.8)
Recognized net actuarial loss	0.2	0.2	0.3	0.5
Net periodic pension expense (benefit)/postretirement benefit expense	$ 1.0	$ 1.1	$ 1.9	$ 2.2