Schedule of Property and Equipment Net (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property And Equipment, Net [Abstract]
Land	$ 58	$ 58
Buildings and leasehold improvements	521	492
Capitalized software	419	400
Furniture, fixtures and equipment	319	259
Buses and support vehicles	64	54
Projects in process	37	37
Property and Equipment, gross	1,418	1,300
Less: Accumulated depreciation and amortization	(889)	(807)
Property, Plant and Equipment, Net, Total	$ 529	$ 493	$ 425