Financial Instruments - Valuation Techniques and Fair Value Hierarchy Level (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Marketable Securities, Equity Securities	$ 45.6	$ 43.8
Foreign currency contract
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Foreign currency derivative contracts, net	31.1	(22.8)
Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Marketable Securities, Equity Securities	45.6	43.8
Recurring | Foreign currency contract
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Foreign currency derivative contracts, net	31.1	(22.8)
Level 1 | Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Marketable Securities, Equity Securities	45.6	43.8
Level 1 | Recurring | Foreign currency contract
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Foreign currency derivative contracts, net	0.0	0.0
Level 2 | Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Marketable Securities, Equity Securities	0.0	0.0
Level 2 | Recurring | Foreign currency contract
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Foreign currency derivative contracts, net	31.1	(22.8)
Level 3 | Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Marketable Securities, Equity Securities	0.0	0.0
Level 3 | Recurring | Foreign currency contract
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Foreign currency derivative contracts, net	$ 0.0	$ 0.0