Postretirement Benefit Plans - Other Changes in Plan Assets and Net Periodic Postretirement Cost Recognized in Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net periodic postretirement cost
Service cost	$ 6.8	$ 6.3
Interest cost	16.5	18.3
Other Postretirement Benefits Plan [Member]
Net periodic postretirement cost
Service cost	0.8	0.9	$ 0.9
Interest cost	4.4	4.9	5.0
Expected return on plan assets	(0.3)	(0.5)	(0.9)
Amortization of net actuarial loss	4.4	4.6	4.6
Amortization of prior service cost	(5.8)	(6.5)	(11.0)
Net periodic postretirement cost	3.5	3.4	(1.4)
Curtailment or settlement charges	0.0	0.0	(4.2)
Total net periodic postretirement cost	3.5	3.4	(5.6)
Other changes in plan assets and benefit obligations recognized in other comprehensive loss
Net actuarial (gain) loss	1.0	(1.9)	7.7
Prior service cost	0.5	0.0	0.0
Amortization of net actuarial (loss) gain	(4.4)	(4.6)	(4.6)
Amortization of prior service cost	5.8	6.5	11.0
Acceleration of prior service costs	0.0	0.0	6.2
Total change recognized in other comprehensive loss	2.9	0.0	20.3
Total impact from net periodic postretirement cost and changes in other comprehensive loss	6.4	3.4	14.7
Pension Plan [Member]
Net periodic postretirement cost
Service cost	6.0	5.4	5.0
Interest cost	12.1	13.4	14.5
Expected return on plan assets	(18.3)	(20.1)	(20.8)
Amortization of net actuarial loss	7.6	7.8	8.5
Amortization of prior service cost	1.0	0.9	1.0
Net periodic postretirement cost	8.4	7.4	8.2
Curtailment or settlement charges	3.7	12.7	0.1
Total net periodic postretirement cost	12.1	20.1	8.3
Other changes in plan assets and benefit obligations recognized in other comprehensive loss
Net actuarial (gain) loss	(8.2)	6.1	11.0
Prior service cost	1.6	0.4	0.0
Amortization of net actuarial (loss) gain	(7.6)	(20.5)	(8.6)
Amortization of prior service cost	(4.7)	(0.9)	(1.0)
Foreign currency translation	2.9	(0.5)	(2.5)
Total change recognized in other comprehensive loss	(16.0)	(15.4)	(1.1)
Total impact from net periodic postretirement cost and changes in other comprehensive loss	(3.9)	4.7	7.2
International Plan [Member] | Pension Plan [Member]
Net periodic postretirement cost
Service cost	1.4	1.3	1.5
Interest cost	1.6	1.5	1.5
Expected return on plan assets	0.0	0.0	0.0
Amortization of net actuarial loss	1.0	0.7	1.0
Amortization of prior service cost	0.0	0.0	0.0
Net periodic postretirement cost	4.0	3.5	4.0
Curtailment or settlement charges	0.0	0.0	0.1
Total net periodic postretirement cost	4.0	3.5	4.1
Other changes in plan assets and benefit obligations recognized in other comprehensive loss
Net actuarial (gain) loss	(0.3)	4.0	(2.9)
Prior service cost	0.0	0.4	0.0
Amortization of net actuarial (loss) gain	(1.0)	(0.7)	(1.1)
Amortization of prior service cost	0.0	0.0	0.0
Foreign currency translation	2.9	(0.5)	(2.5)
Total change recognized in other comprehensive loss	1.6	3.2	(6.5)
Total impact from net periodic postretirement cost and changes in other comprehensive loss	5.6	6.7	(2.4)
U.S. Plan [Member] | Pension Plan [Member]
Net periodic postretirement cost
Service cost	4.6	4.1	3.5
Interest cost	10.5	11.9	13.0
Expected return on plan assets	(18.3)	(20.1)	(20.8)
Amortization of net actuarial loss	6.6	7.1	7.5
Amortization of prior service cost	1.0	0.9	1.0
Net periodic postretirement cost	4.4	3.9	4.2
Curtailment or settlement charges	3.7	12.7	0.0
Total net periodic postretirement cost	8.1	16.6	4.2
Other changes in plan assets and benefit obligations recognized in other comprehensive loss
Net actuarial (gain) loss	(7.9)	2.1	13.9
Prior service cost	1.6	0.0	0.0
Amortization of net actuarial (loss) gain	(6.6)	(19.8)	(7.5)
Amortization of prior service cost	(4.7)	(0.9)	(1.0)
Foreign currency translation	0.0	0.0	0.0
Total change recognized in other comprehensive loss	(17.6)	(18.6)	5.4
Total impact from net periodic postretirement cost and changes in other comprehensive loss	$ (9.5)	$ (2.0)	$ 9.6