Derivatives - Schedule of Pre-Tax Gains Related to Derivatives Not Designated as Hedges (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Not Designated as Hedging Instrument | Foreign Currency Contracts | Selling, General and Administrative Expenses
Derivative Instruments Gain Loss [Line Items]
Gain related to derivatives	$ (1.7)	$ (5.7)	$ (28.2)