Commitments and Contingencies - Changes to Net Insurance Liabilities (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Contingencies And Commitments [Line Items]
Beginning Balance	$ 350	$ 353	$ 347
Self-insurance expense (benefit)	163	162	141
Cash (paid) received	(146)	(165)	(135)
Ending Balance	367	350	353
Current portion at December 31, 2012	90
Long-term portion at December 31, 2012	277
Gross Claims Liability [Member]
Contingencies And Commitments [Line Items]
Beginning Balance	511	523	541
Self-insurance expense (benefit)	222	176	179
Cash (paid) received	(164)	(188)	(197)
Ending Balance	569	511	523
Current portion at December 31, 2012	109
Long-term portion at December 31, 2012	460
Receivables Associated with Insured Claims [Member]
Contingencies And Commitments [Line Items]
Beginning Balance	(161)	(170)	(194)
Self-insurance expense (benefit)	(59)	(14)	(38)
Cash (paid) received	18	23	62
Ending Balance	(202)	(161)	(170)
Current portion at December 31, 2012	(19)
Long-term portion at December 31, 2012	$ (183)