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, 2017	Dec. 31, 2016
Change in plan assets
Plan assets - January 1	$ 269.2	$ 286.9
Actual return on plan assets	46.4	24.5
Employer contributions	45.0	19.0
Benefits and expenses paid	(33.6)	(32.7)
Settlement	(0.4)	(28.5)
Foreign currency translation	0.1	0.0
Plan assets - December 31	326.7	269.2
Funded status at end of year	(230.4)	(261.8)
Other Postretirement Benefits Plan [Member]
Change in plan assets
Plan assets - January 1	6.1	7.9
Actual return on plan assets	1.2	0.5
Employer contributions	6.1	6.2
Benefits and expenses paid	(8.2)	(8.5)
Settlement	0.0	0.0
Foreign currency translation	0.0	0.0
Plan assets - December 31	5.2	6.1
Funded status at end of year	(132.9)	(132.7)
Pension Plan [Member]
Change in plan assets
Plan assets - January 1	263.1
Plan assets - December 31	321.5	263.1
Funded status at end of year	(97.5)	(129.1)
Pension Plan [Member] | International Plan [Member]
Change in plan assets
Plan assets - January 1	0.9	0.9
Actual return on plan assets	0.0	0.0
Employer contributions	3.0	3.2
Benefits and expenses paid	(3.0)	(2.7)
Settlement	(0.4)	(0.5)
Foreign currency translation	0.1	0.0
Plan assets - December 31	0.6	0.9
Funded status at end of year	(92.7)	(79.0)
Pension Plan [Member] | U.S. Plan [Member]
Change in plan assets
Plan assets - January 1	262.2	278.1
Actual return on plan assets	45.2	24.0
Employer contributions	35.9	9.6
Benefits and expenses paid	(22.4)	(21.5)
Settlement	0.0	(28.0)
Foreign currency translation	0.0	0.0
Plan assets - December 31	320.9	262.2
Funded status at end of year	$ (4.8)	$ (50.1)