Acquisitions and Divestitures - Additional Information (Detail) (USD $)	1 Months Ended		9 Months Ended			1 Months Ended	9 Months Ended	3 Months Ended
	Aug. 29, 2013	Apr. 30, 2012 acre	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Jan. 31, 2012 Yara International [Member]	Sep. 30, 2013 Gulf of Mexico Shelf [Member] Fieldwood Energy Llc [Member]	Feb. 28, 2013 Kitimat LNG [Member]	Feb. 28, 2013 Kitimat LNG [Member] Horn River and Liard Basins [Member] acre	Feb. 28, 2013 Kitimat LNG [Member] Chevron Canada and Apache Canada [Member]	Feb. 28, 2013 Kitimat LNG [Member] Apache Canada [Member]
Business Acquisition [Line Items]
Proceeds against participation in business	$ 3,100,000,000						$ 3,600,000,000
Percentage of participation in company's business	33.00%
Effective date of partnership	Jan. 01, 2013
Liabilities assumed							1,500,000,000
Preferential purchase right settlement							200,000,000
Percentage of ownership interest in assets							50.00%
Effective date of the transaction							Jul. 01, 2013
Proved properties			81,111,000,000		78,383,000,000
Unproved properties			8,328,000,000		8,754,000,000
Percentage of ownership						49.00%				50.00%
Business properties held									644,000
Percentage increase in ownership											40.00%
Proceeds from transaction			396,000,000					396,000,000
Proceeds from sale of other oil and gas properties			199,000,000	26,000,000
Acquisitions of oil and gas property			156,000,000	122,000,000
Cordillera's properties		312,000
Shares of common stock issued seller		6,272,667
Cash paid to seller		2,700,000,000
Ownership percentage by other party						51.00%
Amount paid for acquisition						$ 439,000,000