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, 2019	Dec. 31, 2018
Change in plan assets
Plan assets – January 1	$ 281.3	$ 326.7
Actual return on plan assets	58.1	(16.9)
Employer contributions	22.9	11.2
Benefits and expenses paid	(40.5)	(33.4)
Settlement	0.0	(6.3)
Plan assets – December 31	321.8	281.3
Funded status at end of year	(203.6)	(218.5)
Other Postretirement Benefits Plan [Member]
Change in plan assets
Plan assets – January 1	2.9	5.2
Actual return on plan assets	0.4	(0.1)
Employer contributions	10.0	6.9
Benefits and expenses paid	(12.0)	(9.1)
Settlement	0.0	0.0
Plan assets – December 31	1.3	2.9
Funded status at end of year	(115.3)	(115.7)
Pension Plan [Member]
Change in plan assets
Plan assets – January 1	278.4
Plan assets – December 31	320.5	278.4
Funded status at end of year	(88.3)	(102.8)
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	3.0	3.4
Benefits and expenses paid	(3.0)	(3.0)
Settlement	0.0	(0.4)
Plan assets – December 31	0.6	0.6
Funded status at end of year	(97.8)	(88.8)
Pension Plan [Member] | United States
Change in plan assets
Plan assets – January 1	277.8	320.9
Actual return on plan assets	57.7	(16.8)
Employer contributions	9.9	0.9
Benefits and expenses paid	(25.5)	(21.3)
Settlement	0.0	(5.9)
Plan assets – December 31	319.9	277.8
Funded status at end of year	$ 9.5	$ (14.0)