Pension and Postretirement Benefits - Components of Net Periodic Benefit Expense (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.7	$ 0.7
Interest cost	53.8	66.7
Expected return on plan assets	(75.1)	(81.2)
Amortization of prior service benefit	(1.2)	(1.2)
Recognized net actuarial loss	44.3	37.6
Net periodic pension expense (benefit)/postretirement benefit expense	22.5	22.6
Pension Plans | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0
Interest cost	40.4	49.2
Expected return on plan assets	(52.3)	(54.5)
Amortization of prior service benefit	(0.6)	(0.6)
Recognized net actuarial loss	33.5	28.9
Net periodic pension expense (benefit)/postretirement benefit expense	21.0	23.0
Pension Plans | International Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.7	0.7
Interest cost	13.4	17.5
Expected return on plan assets	(22.8)	(26.7)
Amortization of prior service benefit	(0.6)	(0.6)
Recognized net actuarial loss	10.8	8.7
Net periodic pension expense (benefit)/postretirement benefit expense	1.5	(0.4)
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1
Interest cost	1.1	1.2
Expected return on plan assets	(0.1)	(0.1)
Amortization of prior service benefit	(0.4)	(0.4)
Recognized net actuarial loss	0.3	0.1
Net periodic pension expense (benefit)/postretirement benefit expense	$ 1.0	$ 0.9