Oil and Gas Exploration and Production Industries Disclosures, Discounted Future Net Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
United States [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	$ 84,518,638	$ 62,063,123	$ 34,506,336
Future production costs	(33,294,343)	(22,616,039)	(11,977,152)
Future development costs	(13,811,449)	(9,596,005)	(5,696,619)
Future income taxes	(10,539,182)	(8,503,301)	(5,307,041)
Future net cash flows	26,873,664	21,347,778	11,525,524
Discount to present value at 10% annual rate	(12,498,010)	(10,718,854)	(5,702,608)
Standardized measure of discounted future net cash flows relating to proved oil and gas reserves	14,375,654	10,628,924	5,822,916
Per unit price used to calculate future cash inflows - Crude Oil	97.75	76.38	53.64
Per unit price used to calculate future cash inflows - Natural Gas Liquids	51.77	43.85	28.75
Per unit price used to calculate future cash inflows - Natural Gas	4.03	4.36	3.43
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]
Balance at Beginning of Period	10,628,924	5,822,916	6,307,712
Sales and transfers of oil and gas produced net of production costs	(4,296,926)	(2,792,005)	(1,904,912)
Net changes in prices and production costs	716,682	2,468,907	(1,482,778)
Extensions, discoveries, additions and improved recovery, net of related costs	6,223,552	4,319,659	1,702,471
Development costs incurred	1,422,500	864,700	344,500
Revisions of estimated development costs	(210,919)	(257,360)	595,875
Revisions of previous quantity estimates	(482,496)	(164,748)	(422,294)
Accretion of discount	1,352,740	755,001	829,631
Net change in income taxes	(1,049,641)	(1,171,384)	261,513
Purchases of reserves in place	5,241	265	209,130
Sales of reserves in place	(658,468)	(54,057)	(264,482)
Changes in timing and other	724,465	837,030	(353,450)
Balance at End of Period	14,375,654	10,628,924	5,822,916
Canada [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	5,056,501	6,040,422	6,887,530
Future production costs	(2,315,110)	(2,711,415)	(2,537,001)
Future development costs	(1,566,917)	(1,716,734)	(2,255,088)
Future income taxes	(81,590)	(129,816)	(249,986)
Future net cash flows	1,092,884	1,482,457	1,845,455
Discount to present value at 10% annual rate	(456,537)	(736,222)	(808,211)
Standardized measure of discounted future net cash flows relating to proved oil and gas reserves	636,347	746,235	1,037,244
Per unit price used to calculate future cash inflows - Crude Oil	90.70	72.59	56.85
Per unit price used to calculate future cash inflows - Natural Gas Liquids	46.97	26.56	19.31
Per unit price used to calculate future cash inflows - Natural Gas	3.28	3.67	3.50
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]
Balance at Beginning of Period	746,235	1,037,244	1,751,152
Sales and transfers of oil and gas produced net of production costs	(278,910)	(292,857)	(259,301)
Net changes in prices and production costs	(57,545)	(559)	(902,629)
Extensions, discoveries, additions and improved recovery, net of related costs	22,591	75,162	259,305
Development costs incurred	48,200	175,100	14,200
Revisions of estimated development costs	64,001	260,290	68,883
Revisions of previous quantity estimates	(70,718)	(38,382)	(425,018)
Accretion of discount	62,725	102,022	199,330
Net change in income taxes	(118,988)	101,966	259,169
Purchases of reserves in place	0	0	0
Sales of reserves in place	0	(290,592)	(13,912)
Changes in timing and other	218,756	(383,159)	86,065
Balance at End of Period	636,347	746,235	1,037,244
Trinidad [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	2,851,545	2,760,819	2,133,778
Future production costs	(388,199)	(384,147)	(398,318)
Future development costs	(149,884)	(198,072)	(264,104)
Future income taxes	(794,856)	(850,699)	(525,873)
Future net cash flows	1,518,606	1,327,901	945,483
Discount to present value at 10% annual rate	(334,399)	(339,035)	(279,920)
Standardized measure of discounted future net cash flows relating to proved oil and gas reserves	1,184,207	988,866	665,563
Per unit price used to calculate future cash inflows - Crude Oil	92.50	69.56	51.35
Per unit price used to calculate future cash inflows - Natural Gas	3.37	2.94	1.88
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]
Balance at Beginning of Period	988,866	665,563	601,053
Sales and transfers of oil and gas produced net of production costs	(504,205)	(395,379)	(200,892)
Net changes in prices and production costs	331,196	721,796	338,053
Extensions, discoveries, additions and improved recovery, net of related costs	102,548	183,453	0
Development costs incurred	74,800	67,300	0
Revisions of estimated development costs	(14,074)	(767)	(3,380)
Revisions of previous quantity estimates	(56,884)	(175,002)	(124,222)
Accretion of discount	159,715	101,549	84,521
Net change in income taxes	9,511	(258,354)	(105,766)
Purchases of reserves in place	0	0	0
Sales of reserves in place	0	0	0
Changes in timing and other	92,734	78,707	76,196
Balance at End of Period	1,184,207	988,866	665,563
Other International [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	103,853	91,805	52,738
Future production costs	(62,938)	(48,953)	(27,791)
Future development costs	(331)	(334)	(346)
Future income taxes	(2,457)	(3,598)	(4,276)
Future net cash flows	38,127	38,920	20,325
Discount to present value at 10% annual rate	(9,054)	(11,121)	(5,030)
Standardized measure of discounted future net cash flows relating to proved oil and gas reserves	29,073	27,799	15,295
Per unit price used to calculate future cash inflows - Crude Oil	102.86	73.88	52.87
Per unit price used to calculate future cash inflows - Natural Gas	5.07	5.02	3.92
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]
Balance at Beginning of Period	27,799	15,295	19,984
Sales and transfers of oil and gas produced net of production costs	(15,614)	(17,720)	(12,443)
Net changes in prices and production costs	3,328	7,259	(13,868)
Extensions, discoveries, additions and improved recovery, net of related costs	0	0	0
Development costs incurred	0	0	0
Revisions of estimated development costs	2	9	4,555
Revisions of previous quantity estimates	801	4,006	1,016
Accretion of discount	2,782	1,778	3,232
Net change in income taxes	13	2,469	9,847
Purchases of reserves in place	0	0	0
Sales of reserves in place	0	0	0
Changes in timing and other	9,962	14,703	2,972
Balance at End of Period	$ 29,073	$ 27,799	$ 15,295