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, 2020	Dec. 31, 2019	Dec. 31, 2018
Net periodic postretirement cost
Service cost	$ 2.3	$ 2.1
Interest cost	10.7	16.6
Settlement charges	137.0	0.0	$ 1.7
Pension Plan [Member]
Net periodic postretirement cost
Service cost	1.5	1.4	1.7
Interest cost	7.9	12.6	11.5
Expected return on plan assets	(7.2)	(14.8)	(15.8)
Amortization of net actuarial loss	6.3	5.1	5.8
Amortization of prior service cost	0.0	0.7	0.9
Net periodic postretirement cost	8.5	5.0	4.1
Settlement charges	137.0	0.0	1.7
Total net periodic postretirement cost	145.5	5.0	5.8
Other changes in plan assets and benefit obligations recognized in other comprehensive loss
Net actuarial loss (gain)	37.9	0.1	16.2
Prior service cost	0.0	0.0	(0.1)
Amortization of net actuarial loss	(143.3)	(5.1)	(7.5)
Amortization of prior service cost	0.0	(0.7)	(0.9)
Foreign currency translation	2.9	(0.3)	(1.0)
Total change recognized in other comprehensive income	(102.5)	(6.0)	6.7
Total impact from net periodic postretirement cost and changes in other comprehensive income	43.0	(1.0)	12.5
Other Postretirement Benefits Plan [Member]
Net periodic postretirement cost
Service cost	0.8	0.7	0.9
Interest cost	2.8	4.0	4.5
Expected return on plan assets	0.0	(0.2)	(0.1)
Amortization of net actuarial loss	2.6	2.3	4.0
Amortization of prior service cost	(5.1)	(5.1)	(5.3)
Total net periodic postretirement cost	1.1	1.7	4.0
Other changes in plan assets and benefit obligations recognized in other comprehensive loss
Net actuarial loss (gain)	3.9	3.4	(15.6)
Prior service cost	0.0	1.7	0.0
Amortization of net actuarial loss	(2.6)	(2.3)	(4.0)
Amortization of prior service cost	5.1	5.1	5.3
Total change recognized in other comprehensive income	6.4	7.9	(14.3)
Total impact from net periodic postretirement cost and changes in other comprehensive income	7.5	9.6	(10.3)
United States | Pension Plan [Member]
Net periodic postretirement cost
Service cost	0.0	0.2	0.4
Interest cost	6.9	11.1	10.1
Expected return on plan assets	(7.2)	(14.8)	(15.8)
Amortization of net actuarial loss	4.8	4.3	4.9
Amortization of prior service cost	0.0	0.7	0.9
Net periodic postretirement cost	4.5	1.5	0.5
Settlement charges	136.9	0.0
Total net periodic postretirement cost	141.4	1.5	2.2
Other changes in plan assets and benefit obligations recognized in other comprehensive loss
Net actuarial loss (gain)	34.7	(10.2)	15.4
Prior service cost	0.0	0.0	0.0
Amortization of net actuarial loss	(141.7)	(4.3)	(6.6)
Amortization of prior service cost	0.0	(0.7)	(0.9)
Foreign currency translation	0.0	0.0	0.0
Total change recognized in other comprehensive income	(107.0)	(15.2)	7.9
Total impact from net periodic postretirement cost and changes in other comprehensive income	34.4	(13.7)	10.1
International Plan [Member] | Pension Plan [Member]
Net periodic postretirement cost
Service cost	1.5	1.2	1.3
Interest cost	1.0	1.5	1.4
Expected return on plan assets	0.0	0.0	0.0
Amortization of net actuarial loss	1.5	0.8	0.9
Amortization of prior service cost	0.0	0.0	0.0
Net periodic postretirement cost	4.0	3.5	3.6
Settlement charges	0.1	0.0	0.0
Total net periodic postretirement cost	4.1	3.5	3.6
Other changes in plan assets and benefit obligations recognized in other comprehensive loss
Net actuarial loss (gain)	3.2	10.3	0.8
Prior service cost	0.0	0.0	(0.1)
Amortization of net actuarial loss	(1.6)	(0.8)	(0.9)
Amortization of prior service cost	0.0	0.0	0.0
Foreign currency translation	2.9	(0.3)	(1.0)
Total change recognized in other comprehensive income	4.5	9.2	(1.2)
Total impact from net periodic postretirement cost and changes in other comprehensive income	$ 8.6	$ 12.7	$ 2.4