Contingencies (Detail) (USD $)	3 Months Ended		9 Months Ended					9 Months Ended
	Sep. 30, 2013 Tronox Litigation [Member]	Sep. 30, 2012 Tronox Litigation [Member]	Sep. 30, 2013 Tronox Litigation [Member]	Sep. 30, 2012 Tronox Litigation [Member]	Sep. 30, 2013 Tronox Litigation [Member] Principal Portion of Maximum Loss Range [Member]	Sep. 30, 2011 Macondo Exploration Well [Member]	Sep. 30, 2013 Deepwater Horizon [Member] BP indemnification liability [Member]	Sep. 30, 2013 Third Party Bankruptcy Assignment [Member]
Loss Contingencies [Line Items]
Anadarko's nonoperated interest						25.00%
Loss contingency accrual at carrying value	$ 0		$ 0				$ 0
Damages sought, including interest, in excess of			18,900,000,000
Range of potential loss, minimum	0		0
Range of potential loss, maximum	1,400,000,000		1,400,000,000		985,000,000
Pretax loss	0	0	0	(250,000,000)				131,000,000
Decommissioning obligations included in accrued expenses								44,000,000
Decommissioning obligations included in other long-term liabilities								$ 85,000,000