Property and Equipment, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Cost of property and equipment	$ 805	$ 597
Less accumulated depreciation	(547)	(408)
Property and equipment, net	258	189	$ 157
Depreciation expense	121	82	76
Rental expense	65	39	$ 38
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	162	109
Computer equipment
Property, Plant and Equipment [Line Items]
Cost of property and equipment	560	431
Office furniture and other equipment
Property, Plant and Equipment [Line Items]
Cost of property and equipment	$ 78	$ 52