Property and Equipment, Net - Summary of Property and Equipment (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Cost	$ 1,019	$ 947
Accumulated depreciation	(614)	(531)
Net	405	416
Capitalized software [Member]
Property, Plant and Equipment [Line Items]
Cost	651	629
Accumulated depreciation	(447)	(386)
Net	204	243
Computer equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	282	274
Accumulated depreciation	(159)	(138)
Net	123	136
Building and leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Cost	16	12
Accumulated depreciation	(8)	(7)
Net	8	5
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Cost	70	32
Accumulated depreciation
Net	$ 70	$ 32