Schedule of Property and Equipment Net (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Land	$ 49	$ 47
Buildings and leasehold improvements	626	597
Capitalized software	583	524
Furniture, fixtures and equipment	387	354
Buses and support vehicles	93	91
Projects in process	118	99
Property and Equipment, gross	1,856	1,712
Less: Accumulated depreciation and amortization	(1,152)	(1,027)
Property, Plant and Equipment, Net, Total	$ 704	$ 685