Pension and Postretirement Benefits - Components of Net Periodic Benefit Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.7	$ 0.7	$ 1.4	$ 1.4
Interest cost	53.8	66.5	107.6	133.2
Expected return on plan assets	(73.9)	(80.9)	(149.0)	(162.1)
Amortization of prior service benefit	(1.3)	(1.3)	(2.5)	(2.5)
Recognized net actuarial loss	44.7	37.6	89.0	75.2
Net periodic pension expense (benefit)/postretirement benefit expense	24.0	22.6	46.5	45.2
Pension Plans | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0	0.0
Interest cost	40.8	49.3	81.2	98.5
Expected return on plan assets	(52.0)	(54.5)	(104.3)	(109.0)
Amortization of prior service benefit	(0.7)	(0.7)	(1.3)	(1.3)
Recognized net actuarial loss	34.3	29.0	67.8	57.9
Net periodic pension expense (benefit)/postretirement benefit expense	22.4	23.1	43.4	46.1
Pension Plans | International Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.7	0.7	1.4	1.4
Interest cost	13.0	17.2	26.4	34.7
Expected return on plan assets	(21.9)	(26.4)	(44.7)	(53.1)
Amortization of prior service benefit	(0.6)	(0.6)	(1.2)	(1.2)
Recognized net actuarial loss	10.4	8.6	21.2	17.3
Net periodic pension expense (benefit)/postretirement benefit expense	1.6	(0.5)	3.1	(0.9)
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.2	0.2
Interest cost	1.1	1.2	2.2	2.4
Expected return on plan assets	(0.1)	(0.1)	(0.2)	(0.2)
Amortization of prior service benefit	(0.4)	(0.4)	(0.8)	(0.8)
Recognized net actuarial loss	0.2	0.2	0.5	0.3
Net periodic pension expense (benefit)/postretirement benefit expense	$ 0.9	$ 1.0	$ 1.9	$ 1.9