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, 2012	Dec. 31, 2011	Dec. 31, 2010
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	$ 94,612,613	$ 92,530,537	$ 70,956,169
Future production costs	(37,184,832)	(36,060,590)	(25,760,554)
Future development costs	(17,031,731)	(15,528,581)	(11,511,145)
Future income taxes	(11,150,742)	(11,418,085)	(9,487,414)
Future net cash flows	29,245,308	29,523,281	24,197,056
Discount to present value at 10% annual rate	(12,329,836)	(13,298,000)	(11,805,232)
Standardized measure of discounted future net cash flows relating to proved oil and gas reserves	16,915,472	16,225,281	12,391,824
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	16,225,281	12,391,824	7,541,018
Sales and transfers of oil and gas produced net of production costs	(5,888,317)	(5,095,655)	(3,497,961)
Net changes in prices and production costs	(301,232)	993,661	3,197,403
Extensions, discoveries, additions and improved recovery, net of related costs	6,082,122	6,348,691	4,578,274
Development costs incurred	2,094,600	1,545,500	1,107,100
Revisions of estimated development costs	2,341,476	(160,990)	2,172
Revisions of previous quantity estimates	(3,742,827)	(609,297)	(374,126)
Accretion of discount	2,077,217	1,577,962	960,350
Net change in income taxes	125,065	(1,159,105)	(1,325,303)
Purchases of reserves in place	69,940	5,241	265
Sales of reserves in place	(913,761)	(658,468)	(344,649)
Changes in timing and other	(1,254,092)	1,045,917	547,281
Balance at End of Period	16,915,472	16,225,281	12,391,824
United States [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	89,324,274	84,518,638	62,063,123
Future production costs	(35,892,997)	(33,294,343)	(22,616,039)
Future development costs	(15,825,040)	(13,811,449)	(9,596,005)
Future income taxes	(10,247,007)	(10,539,182)	(8,503,301)
Future net cash flows	27,359,230	26,873,664	21,347,778
Discount to present value at 10% annual rate	(12,177,896)	(12,498,010)	(10,718,854)
Standardized measure of discounted future net cash flows relating to proved oil and gas reserves	15,181,334	14,375,654	10,628,924
Per unit price used to calculate future cash inflows - Crude Oil	99.78	97.75	76.38
Per unit price used to calculate future cash inflows - Natural Gas Liquids	36.95	51.77	43.85
Per unit price used to calculate future cash inflows - Natural Gas	2.63	4.03	4.36
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	14,375,654	10,628,924	5,822,916
Sales and transfers of oil and gas produced net of production costs	(5,192,392)	(4,296,926)	(2,792,005)
Net changes in prices and production costs	(393,585)	716,682	2,468,907
Extensions, discoveries, additions and improved recovery, net of related costs	5,517,945	6,223,552	4,319,659
Development costs incurred	2,042,300	1,422,500	864,700
Revisions of estimated development costs	1,987,330	(210,919)	(257,360)
Revisions of previous quantity estimates	(3,286,943)	(482,496)	(164,748)
Accretion of discount	1,832,377	1,352,740	755,001
Net change in income taxes	174,418	(1,049,641)	(1,171,384)
Purchases of reserves in place	64,317	5,241	265
Sales of reserves in place	(869,534)	(658,468)	(54,057)
Changes in timing and other	(1,070,553)	724,465	837,030
Balance at End of Period	15,181,334	14,375,654	10,628,924
Canada [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	1,816,369	5,056,501	6,040,422
Future production costs	(751,113)	(2,315,110)	(2,711,415)
Future development costs	(813,061)	(1,566,917)	(1,716,734)
Future income taxes	0	(81,590)	(129,816)
Future net cash flows	252,195	1,092,884	1,482,457
Discount to present value at 10% annual rate	146,954	(456,537)	(736,222)
Standardized measure of discounted future net cash flows relating to proved oil and gas reserves	399,149	636,347	746,235
Per unit price used to calculate future cash inflows - Crude Oil	84.77	90.70	72.59
Per unit price used to calculate future cash inflows - Natural Gas Liquids	47.80	46.97	26.56
Per unit price used to calculate future cash inflows - Natural Gas	2.22	3.28	3.67
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	636,347	746,235	1,037,244
Sales and transfers of oil and gas produced net of production costs	(159,577)	(278,910)	(292,857)
Net changes in prices and production costs	(67,964)	(57,545)	(559)
Extensions, discoveries, additions and improved recovery, net of related costs	79,529	22,591	75,162
Development costs incurred	23,600	48,200	175,100
Revisions of estimated development costs	383,215	64,001	260,290
Revisions of previous quantity estimates	(396,408)	(70,718)	(38,382)
Accretion of discount	63,635	62,725	102,022
Net change in income taxes	0	(118,988)	101,966
Purchases of reserves in place	0	0	0
Sales of reserves in place	(44,227)	0	(290,592)
Changes in timing and other	(119,001)	218,756	(383,159)
Balance at End of Period	399,149	636,347	746,235
Trinidad [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	2,408,116	2,851,545	2,760,819
Future production costs	(342,113)	(388,199)	(384,147)
Future development costs	(171,737)	(149,884)	(198,072)
Future income taxes	(691,109)	(794,856)	(850,699)
Future net cash flows	1,203,157	1,518,606	1,327,901
Discount to present value at 10% annual rate	(242,087)	(334,399)	(339,035)
Standardized measure of discounted future net cash flows relating to proved oil and gas reserves	961,070	1,184,207	988,866
Per unit price used to calculate future cash inflows - Crude Oil	94.46	92.50	69.56
Per unit price used to calculate future cash inflows - Natural Gas	3.61	3.37	2.94
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	1,184,207	988,866	665,563
Sales and transfers of oil and gas produced net of production costs	(526,134)	(504,205)	(395,379)
Net changes in prices and production costs	162,600	331,196	721,796
Extensions, discoveries, additions and improved recovery, net of related costs	0	102,548	183,453
Development costs incurred	23,500	74,800	67,300
Revisions of estimated development costs	(28,835)	(14,074)	(767)
Revisions of previous quantity estimates	(62,285)	(56,884)	(175,002)
Accretion of discount	178,298	159,715	101,549
Net change in income taxes	88,853	9,511	(258,354)
Purchases of reserves in place	0	0	0
Sales of reserves in place	0	0	0
Changes in timing and other	(59,134)	92,734	78,707
Balance at End of Period	961,070	1,184,207	988,866
Other International [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash inflows	1,063,854	103,853	91,805
Future production costs	(198,609)	(62,938)	(48,953)
Future development costs	(221,893)	(331)	(334)
Future income taxes	(212,626)	(2,457)	(3,598)
Future net cash flows	430,726	38,127	38,920
Discount to present value at 10% annual rate	(56,807)	(9,054)	(11,121)
Standardized measure of discounted future net cash flows relating to proved oil and gas reserves	373,919	29,073	27,799
Per unit price used to calculate future cash inflows - Crude Oil	109.94	102.86	73.88
Per unit price used to calculate future cash inflows - Natural Gas	5.04	5.07	5.02
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	29,073	27,799	15,295
Sales and transfers of oil and gas produced net of production costs	(10,214)	(15,614)	(17,720)
Net changes in prices and production costs	(2,283)	3,328	7,259
Extensions, discoveries, additions and improved recovery, net of related costs	484,648	0	0
Development costs incurred	5,200	0	0
Revisions of estimated development costs	(234)	2	9
Revisions of previous quantity estimates	2,809	801	4,006
Accretion of discount	2,907	2,782	1,778
Net change in income taxes	(138,206)	13	2,469
Purchases of reserves in place	5,623	0	0
Sales of reserves in place	0	0	0
Changes in timing and other	(5,404)	9,962	14,703
Balance at End of Period	$ 373,919	$ 29,073	$ 27,799