Property and Equipment, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Cost of property and equipment	$ 597	$ 501
Less accumulated depreciation	(408)	(344)
Property and equipment, net	189	157	$ 138
Depreciation expense	82	76	84
Rental expense	39	38	$ 35
Land
Property, Plant and Equipment [Line Items]
Cost of property and equipment	1	1
Buildings
Property, Plant and Equipment [Line Items]
Cost of property and equipment	4	4
Leasehold improvements
Property, Plant and Equipment [Line Items]
Cost of property and equipment	109	104
Computer equipment
Property, Plant and Equipment [Line Items]
Cost of property and equipment	431	347
Office furniture and other equipment
Property, Plant and Equipment [Line Items]
Cost of property and equipment	$ 52	$ 45