Property and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,004	$ 897
Less accumulated depreciation and amortization	(537)	(467)
Property and equipment, net	467	430
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	102	96
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	238	212
Non-rental vehicles
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	112	93
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	103	87
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	204	188
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 245	$ 221