Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross		$ 2,507
Right-of-use lease assets	$ 287
Property and equipment, gross	3,042
Less accumulated depreciation and amortization	(1,506)
Less accumulated depreciation and amortization		(1,266)
Property and equipment, net	$ 1,536
Property and equipment, net		1,241
Minimum
Property, Plant and Equipment [Line Items]
Right-of-use lease assets, useful life	1 year
Maximum
Property, Plant and Equipment [Line Items]
Right-of-use lease assets, useful life	16 years
Software and internally developed software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,056	919
Software and internally developed software | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Software and internally developed software | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	7 years
Computer and network equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 742	682
Computer and network equipment | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Computer and network equipment | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 146	145
Buildings and building improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 309	294
Buildings and building improvements | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	15 years
Buildings and building improvements | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	40 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 269	242
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	4 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	12 years
Equipment, aircraft and office furniture
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 233	$ 225
Equipment, aircraft and office furniture | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	4 years
Equipment, aircraft and office furniture | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	15 years