Comprehensive Income - Schedule of Components of Other Comprehensive (loss) Income and Income Tax Expense Allocated to Each Component (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Translation adjustments - Before Tax Amount	$ (55.7)	$ (45.2)	$ (22.8)
Adjustment for net periodic pension and other postretirement benefits plan cost - Before Tax Amount	60.2	(390.9)	919.0
Change in fair value of derivatives - Before Tax Amount	0.1	0.2	0.6
Other comprehensive (loss) income - Before Tax Amount	4.6	(435.9)	896.8
Translation adjustments - Income Tax Expense	0.0	0.0	0.0
Adjustment for net periodic pension and other postretirement benefits plan cost - Income Tax Expense	25.4	(150.0)	355.3
Change in fair value of derivatives - Income Tax Expense	0.0	0.1	0.2
Other comprehensive (loss) income - Income Tax Expense	25.4	(149.9)	355.5
Translation adjustments - Net of Tax Amount	(55.7)	(45.2)	(22.8)
Adjustment for net periodic pension and other postretirement benefits plan cost - Net of Tax Amount	34.8	(240.9)	563.7
Change in fair value of derivatives - Net of Tax Amount	0.1	0.1	0.4
Other comprehensive (loss) income	$ (20.8)	$ (286.0)	$ 541.3