Derivative Instruments and Hedging Activities - Effect of Derivative Instruments Designated as Fair Value and Cash Flow Hedges and Not Designated as Hedges on Consolidated Statement of Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivatives not designated as hedges | Foreign exchange contracts | Cost of services/sales
Derivative Instruments Gain Loss [Line Items]
Gain (Loss) Recognized in Income (Loss)	$ (17)	$ (10)	$ 15	$ (3)
Fair Value Hedging | Derivatives designated as hedges | Cross currency swap | Interest expense
Derivative Instruments Gain Loss [Line Items]
Gain (Loss) Recognized in Income (Loss)	6	$ 19	(6)	$ 66
Cash Flow Hedging | Derivatives designated as hedges
Derivative Instruments Gain Loss [Line Items]
Gain (Loss) Recognized in Income (Loss)	(32)		28
Cash Flow Hedging | Derivatives designated as hedges | Cross currency swap | Interest expense
Derivative Instruments Gain Loss [Line Items]
Gain (Loss) Recognized in Income (Loss)	(30)		25
Cash Flow Hedging | Derivatives designated as hedges | Foreign exchange contracts | Cost of services/sales
Derivative Instruments Gain Loss [Line Items]
Gain (Loss) Recognized in Income (Loss)	$ (2)		$ 3