Gains (Losses) Recognized in AOCI and Reclassified from AOCI on Derivatives (Effective Portion) (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	$ 6.7	$ (3.7)
Cash Flow Hedging [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	6.7	(3.7)
Cash Flow Hedging [Member] | Currency Swap [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	7.8	(3.7)
Cash Flow Hedging [Member] | Currency Swap [Member] | Other Nonoperating Income (Expense) [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	12.6	6.0
Cash Flow Hedging [Member] | Currency Swap [Member] | Tax Effect [Member]
Derivative Instruments Gain Loss [Line Items]
Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion)	$ 4.8	$ 2.3