Other Financial Data - Components of Fixed Assets, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fixed Assets, net [Line Items]
Fixed assets, gross	$ 2,136	$ 1,949
Less: Accumulated depreciation	1,498	1,391
Fixed assets, net	638	558
Depreciation of fixed assets	167	151	$ 179
Software
Fixed Assets, net [Line Items]
Fixed assets, gross	983	861
Leasehold improvements
Fixed Assets, net [Line Items]
Fixed assets, gross	430	409
Computer equipment
Fixed Assets, net [Line Items]
Fixed assets, gross	294	269
Furniture, fixtures and equipment
Fixed Assets, net [Line Items]
Fixed assets, gross	269	267
Construction in progress
Fixed Assets, net [Line Items]
Fixed assets, gross	130	109
Other
Fixed Assets, net [Line Items]
Fixed assets, gross	$ 30	$ 34