Property and Equipment, Net (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property and Equipment, Net
Land	$ 1	$ 1
Buildings	5	5
Leasehold improvements	80	72
Computer equipment	362	406
Office furniture and other equipment	65	49
Total cost of property and equipment	513	533
Less accumulated depreciation	(372)	(370)
Property and equipment, net	141	163
Depreciation expense	90	75	68
Operating Leases, Rent Expense	$ 37	$ 38	$ 37