Other Comprehensive Income (Loss) - Schedule of Components of Other Comprehensive Income (Loss) and Income Tax Expense (Benefit) Allocated to Each Component (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive income (loss), Before Tax Amount	$ 22.5	$ (25.3)
Other comprehensive income (loss), Income Tax	1.0	(2.7)
Other comprehensive income (loss)	21.5	(22.6)
Translation adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive income (loss), Before Tax Amount	18.9	9.0
Other comprehensive income (loss)	18.9	9.0
Adjustment for net periodic pension and other postretirement benefits plan cost
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive income (loss), Before Tax Amount	3.6	1.0
Other comprehensive income (loss), Income Tax	1.0	0.3
Other comprehensive income (loss)	$ 2.6	0.7
Adjustments for available-for-sale securities
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive income (loss), Before Tax Amount		(35.3)
Other comprehensive income (loss), Income Tax		(3.0)
Other comprehensive income (loss)		$ (32.3)