Property and Equipment, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Cost of property and equipment	$ 1,050	$ 1,002
Less accumulated depreciation	(841)	(749)
Property and equipment, net	209	253
Depreciation expense	117	124	$ 138
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	246	252
Computer equipment
Property, Plant and Equipment [Line Items]
Cost of property and equipment	704	654
Office furniture and other equipment
Property, Plant and Equipment [Line Items]
Cost of property and equipment	$ 95	$ 91