Derivatives and Financial Instruments - Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of Intangible Assets (Excluding Goodwill)	$ 8.8
Foreign currency contract liabilities	(47.2)	$ (45.5)
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contract assets	0.6
Foreign currency contract liabilities	(47.2)	(45.5)
Deferred compensation plan	23.2	27.5
Total recurring fair value measurements	(23.4)	(18.0)
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contract assets	0.0
Foreign currency contract liabilities	0.0	0.0
Deferred compensation plan	18.7	24.3
Total recurring fair value measurements	18.7	24.3
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contract assets	0.6
Foreign currency contract liabilities	(47.2)	(45.5)
Deferred compensation plan	4.5	3.2
Total recurring fair value measurements	(42.1)	(42.3)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contract assets	0.0
Foreign currency contract liabilities	0.0	0.0
Deferred compensation plan	0.0	0.0
Total recurring fair value measurements	$ 0.0	$ 0.0