Other Financial Data - Components of Fixed Assets, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fixed Assets, net [Line Items]
Fixed assets, gross	$ 1,847	$ 1,867
Less: Accumulated depreciation	1,318	1,268
Fixed assets, net	529	599
Depreciation of fixed assets	179	167	$ 172
Software
Fixed Assets, net [Line Items]
Fixed assets, gross	797	808
Leasehold improvements
Fixed Assets, net [Line Items]
Fixed assets, gross	425	375
Computer equipment
Fixed Assets, net [Line Items]
Fixed assets, gross	268	249
Furniture, fixtures and equipment
Fixed Assets, net [Line Items]
Fixed assets, gross	279	246
Construction in progress
Fixed Assets, net [Line Items]
Fixed assets, gross	45	155
Other
Fixed Assets, net [Line Items]
Fixed assets, gross	$ 33	$ 34