Gains (Losses) Recognized in AOCI and Reclassified from AOCI on Derivatives (Effective Portion) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion), Net of Tax	$ (30.1)	$ (5.1)	$ 17.0
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	6.7	(3.7)
Net Investment Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion), Net of Tax	(36.0)	(4.2)	18.1
Net Investment Hedging [Member] | Foreign Exchange Forwards [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion), Net of Tax	1.2	(12.0)	13.4
Net Investment Hedging [Member] | Long-Term Debt [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion), Net of Tax	(37.2)	7.8	4.7
Cash Flow Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion), Net of Tax	5.9	(0.9)	(1.1)
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	6.7	(3.7)
Cash Flow Hedging [Member] | Cross-Currency Swap [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion), Net of Tax	6.3	(0.9)
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	7.8	$ (3.7)
Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion), Net of Tax	(0.4)		$ (1.1)
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	$ (1.1)