Postretirement Benefit Plans - Changes in Fair Value of Plan Assets of Pension and Other Employee-Related Defined Benefit Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Change in plan assets
Plan assets – January 1	$ 321.8	$ 281.3
Actual return on plan assets	20.0	58.1
Employer contributions	18.0	22.9
Benefits and expenses paid	(30.8)	(40.5)
Settlement	(328.5)	0.0
Plan assets – December 31	0.5	321.8
Funded status at end of year	(242.3)	(203.6)
Pension Plan [Member]
Change in plan assets
Plan assets – January 1	320.5
Plan assets – December 31	0.5	320.5
Funded status at end of year	(124.0)	(88.3)
Pension Plan [Member] | United States
Change in plan assets
Plan assets – January 1	319.9	277.8
Actual return on plan assets	20.0	57.7
Employer contributions	9.3	9.9
Benefits and expenses paid	(21.3)	(25.5)
Settlement	(327.9)	0.0
Plan assets – December 31	0.0	319.9
Funded status at end of year	(15.5)	9.5
Pension Plan [Member] | International Plan [Member]
Change in plan assets
Plan assets – January 1	0.6	0.6
Actual return on plan assets	0.0	0.0
Employer contributions	4.1	3.0
Benefits and expenses paid	(3.6)	(3.0)
Settlement	(0.6)	0.0
Plan assets – December 31	0.5	0.6
Funded status at end of year	(108.5)	(97.8)
Other Postretirement Benefits Plan [Member]
Change in plan assets
Plan assets – January 1	1.3	2.9
Actual return on plan assets	0.0	0.4
Employer contributions	4.6	10.0
Benefits and expenses paid	(5.9)	(12.0)
Settlement	0.0	0.0
Plan assets – December 31	0.0	1.3
Funded status at end of year	$ (118.3)	$ (115.3)