Income Taxes - Deferred Tax Assets (Liabilities) Table (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Components of Deferred Tax Assets and Liabilities [Abstract]
Net current deferred tax assets	$ 328	$ 138
Deferred Tax Assets (Liabilities), Net [Line Items]
Other	(152)	(1)
Gross long-term deferred tax liabilities	(10,538)	(9,859)
Oil and gas exploration and development costs	762	127
Net operating loss carryforward	477	1,071
Foreign tax credit carryforward and alternative minimum tax credit carryforward	450	119
Other	1,012	618
Gross long-term deferred tax assets	2,701	1,935
Less valuation allowances on deferred tax assets not expected to be realized	(922)	(555)
Net long-term deferred tax assets	1,779	1,380
Net long-term deferred tax liabilities	(8,759)	(8,479)
Total deferred taxes	(8,431)	(8,341)
Oil and Gas Exploration and Development Operations [Member]
Deferred Tax Assets (Liabilities), Net [Line Items]
Deferred tax liabilities - property, plant, and equipment	(8,683)	(8,187)
Mineral Operations [Member]
Deferred Tax Assets (Liabilities), Net [Line Items]
Deferred tax liabilities - property, plant, and equipment	(408)	(407)
Midstream and Other Depreciable Properties [Member]
Deferred Tax Assets (Liabilities), Net [Line Items]
Deferred tax liabilities - property, plant, and equipment	$ (1,295)	$ (1,264)