Property and Equipment, Net (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Total cost of property and equipment	$ 586	$ 513
Less accumulated depreciation	(448)	(372)
Property and equipment, net	138	141
Depreciation expense	84	90	75
Rental expense	35	37	38
Land
Property, Plant and Equipment [Line Items]
Total cost of property and equipment	1	1
Buildings
Property, Plant and Equipment [Line Items]
Total cost of property and equipment	5	5
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total cost of property and equipment	96	80
Computer equipment
Property, Plant and Equipment [Line Items]
Total cost of property and equipment	424	362
Office furniture and other equipment
Property, Plant and Equipment [Line Items]
Total cost of property and equipment	$ 60	$ 65