Pension and Postretirement Benefits - Components of Net Periodic Benefit Expense (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.8	$ 0.7	$ 2.2	$ 2.1
Interest cost	54.1	66.1	161.7	199.3
Expected return on plan assets	(75.0)	(80.1)	(224.0)	(242.2)
Amortization of prior service (benefit) cost	(1.3)	(1.2)	(3.8)	(3.7)
Recognized net actuarial loss	44.8	37.9	133.8	113.1
Net periodic pension expense (benefit)/postretirement benefit expense	23.4	23.4	69.9	68.6
Pension Plans | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0	0.0
Interest cost	40.6	49.6	121.8	148.1
Expected return on plan assets	(52.1)	(54.7)	(156.4)	(163.7)
Amortization of prior service (benefit) cost	(0.6)	(0.6)	(1.9)	(1.9)
Recognized net actuarial loss	33.8	29.6	101.6	87.5
Net periodic pension expense (benefit)/postretirement benefit expense	21.7	23.9	65.1	70.0
Pension Plans | International Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.8	0.7	2.2	2.1
Interest cost	13.5	16.5	39.9	51.2
Expected return on plan assets	(22.9)	(25.4)	(67.6)	(78.5)
Amortization of prior service (benefit) cost	(0.7)	(0.6)	(1.9)	(1.8)
Recognized net actuarial loss	11.0	8.3	32.2	25.6
Net periodic pension expense (benefit)/postretirement benefit expense	1.7	(0.5)	4.8	(1.4)
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.3	0.3
Interest cost	1.1	1.2	3.3	3.6
Expected return on plan assets	(0.1)	(0.1)	(0.3)	(0.3)
Amortization of prior service (benefit) cost	(0.4)	(0.4)	(1.2)	(1.2)
Recognized net actuarial loss	0.3	0.2	0.8	0.5
Net periodic pension expense (benefit)/postretirement benefit expense	$ 1.0	$ 1.0	$ 2.9	$ 2.9