Derivative Instruments and Hedging Activities - Net Investment Hedge Gains Recognized on Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain / (Loss) Recognized in AOCI	$ 120.4	$ (146.0)	$ 18.8
Euro Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain / (Loss) Recognized in AOCI	57.6	$ (146.0)	9.4
Cross-currency Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain / (Loss) Recognized in AOCI	$ 62.8
Foreign Exchange Forward Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain / (Loss) Recognized in AOCI			$ 9.4