Supplemental Oil and Gas Disclosures (Unaudited) (Details 3)	12 Months Ended
	Dec. 31, 2011 MBoe	Dec. 31, 2010 MBoe	Dec. 31, 2009 MBoe	Dec. 31, 2008 MBoe
Proved reserve data
Proved developed reserves	1,992,327,000	1,984,991,000	1,635,565,000	1,723,547,000
Proved undeveloped reserves	997,527,000	968,274,000	731,021,000	677,102,000
Total proved reserves:
Beginning Balance	2,953,265,000	2,366,586,000	2,400,648,000
Extensions, discoveries and other additions	342,078,000	245,108,000	194,903,000
Purchases of minerals in-place	80,420,000	593,051,000	20,993,000
Revisions of previous estimates	(59,086,000)	(11,370,000)	(37,043,000)
Production	(273,074,000)	(240,037,000)	(212,915,000)
Sales of properties	(53,749,000)	(73,000)
Ending Balance	2,989,854,000	2,953,265,000	2,366,586,000
Oil Reserves [Member]
Proved reserve data
Proved developed reserves	950,091,000	924,422,000	762,688,000	777,092,000
Proved undeveloped reserves	419,384,000	384,313,000	304,560,000	304,052,000
Total proved reserves:
Beginning Balance	1,308,735,000	1,067,248,000	1,081,144,000
Extensions, discoveries and other additions	178,412,000	129,210,000	75,080,000
Purchases of minerals in-place	50,238,000	248,832,000	13,023,000
Revisions of previous estimates	(29,487,000)	(11,339,000)	3,921,000
Production	(135,446,000)	(125,143,000)	(105,920,000)
Sales of properties	(2,977,000)	(73,000)
Ending Balance	1,369,475,000	1,308,735,000	1,067,248,000
Natural Gas Reserves [Member]
Proved reserve data
Proved developed reserves	6,253,418,000,000	6,363,417,000,000	5,237,265,000,000	5,678,727,000,000
Proved undeveloped reserves	3,468,855,000,000	3,503,765,000,000	2,558,766,000,000	2,238,298,000,000
Total proved reserves:
Beginning Balance	9,867,182,000,000	7,796,031,000,000	7,917,025,000,000
Extensions, discoveries and other additions	981,993,000,000	695,383,000,000	718,937,000,000
Purchases of minerals in-place	181,091,000,000	2,065,316,000,000	47,817,000,000
Revisions of previous estimates	(177,591,000,000)	(186,000,000)	(245,781,000,000)
Production	(825,770,000,000)	(689,361,000,000)	(641,967,000,000)
Sales of properties	(304,632,000,000)	(1,000,000)
Ending Balance	9,722,273,000,000	9,867,182,000,000	7,796,031,000,000
United States [Member]
Total proved reserves:
Extensions, discoveries and other additions	64,000,000
United States [Member] | Oil Reserves [Member]
Proved reserve data
Proved developed reserves	535,741,000	514,537,000	373,010,000	363,516,000
Proved undeveloped reserves	258,306,000	244,478,000	150,627,000	151,248,000
Total proved reserves:
Beginning Balance	759,015,000	523,637,000	514,764,000
Extensions, discoveries and other additions	89,591,000	72,928,000	17,642,000
Purchases of minerals in-place	5,683,000	195,131,000	13,023,000
Revisions of previous estimates	(7,191,000)	7,597,000	12,981,000
Production	(51,658,000)	(40,278,000)	(34,773,000)
Sales of properties	1,393,000
Ending Balance	794,047,000	759,015,000	523,637,000
United States [Member] | Natural Gas Reserves [Member]
Proved reserve data
Proved developed reserves	2,215,973,000,000	2,284,116,000,000	1,785,155,000,000	1,866,988,000,000
Proved undeveloped reserves	760,238,000,000	988,869,000,000	652,766,000,000	670,194,000,000
Total proved reserves:
Beginning Balance	3,272,985,000,000	2,437,921,000,000	2,537,182,000,000
Extensions, discoveries and other additions	169,506,000,000	102,180,000,000	150,668,000,000
Purchases of minerals in-place	67,595,000,000	951,654,000,000	47,782,000,000
Revisions of previous estimates	(7,716,000,000)	47,989,000,000	(54,591,000,000)
Production	(315,631,000,000)	(266,759,000,000)	(243,120,000,000)
Sales of properties	(210,528,000)
Ending Balance	2,976,211,000,000	3,272,985,000,000	2,437,921,000,000
Canada [Member]
Total proved reserves:
Extensions, discoveries and other additions	107,000,000
Canada [Member] | Oil Reserves [Member]
Proved reserve data
Proved developed reserves	105,102,000	113,993,000	89,222,000	85,038,000
Proved undeveloped reserves	67,939,000	60,997,000	57,552,000	70,707,000
Total proved reserves:
Beginning Balance	174,990,000	146,774,000	155,745,000
Extensions, discoveries and other additions	22,602,000	6,816,000	1,839,000
Purchases of minerals in-place	752,000	42,440,000
Revisions of previous estimates	(16,343,000)	(14,592,000)	(4,504,000)
Production	(7,376,000)	(6,375,000)	(6,306,000)
Sales of properties	(1,584,000)	(73,000)
Ending Balance	173,041,000	174,990,000	146,774,000
Canada [Member] | Natural Gas Reserves [Member]
Proved reserve data
Proved developed reserves	2,108,801,000,000	2,181,615,000,000	1,436,151,000,000	1,594,782,000,000
Proved undeveloped reserves	1,438,710,000,000	1,310,352,000,000	869,197,000,000	608,580,000,000
Total proved reserves:
Beginning Balance	3,491,967,000,000	2,305,348,000,000	2,203,361,000,000
Extensions, discoveries and other additions	505,049,000,000	274,755,000,000	340,278,000,000
Purchases of minerals in-place	8,838,000,000	1,064,618,000,000	35,000,000
Revisions of previous estimates	(133,359,000,000)	(8,211,000,000)	(107,205,000,000)
Production	(230,880,000,000)	(144,542,000,000)	(131,121,000,000)
Sales of properties	(94,104,000,000)	(1,000,000)
Ending Balance	3,547,511,000,000	3,491,967,000,000	2,305,348,000,000
Egypt [Member]
Total proved reserves:
Extensions, discoveries and other additions	58,000,000
Egypt [Member] | Oil Reserves [Member]
Proved reserve data
Proved developed reserves	105,840,000	109,657,000	97,787,000	93,103,000
Proved undeveloped reserves	22,195,000	17,470,000	17,806,000	21,303,000
Total proved reserves:
Beginning Balance	127,127,000	115,593,000	114,406,000
Extensions, discoveries and other additions	45,039,000	41,205,000	41,104,000
Purchases of minerals in-place		11,261,000
Revisions of previous estimates	(6,185,000)	(4,723,000)	(6,286,000)
Production	(37,946,000)	(36,209,000)	(33,631,000)
Ending Balance	128,035,000	127,127,000	115,593,000
Egypt [Member] | Natural Gas Reserves [Member]
Proved reserve data
Proved developed reserves	700,866,000,000	748,573,000,000	838,000,000,000	1,010,102,000,000
Proved undeveloped reserves	282,100,000,000	328,344,000,000	321,141,000,000	360,876,000,000
Total proved reserves:
Beginning Balance	1,076,917,000,000	1,159,141,000,000	1,370,978,000,000
Extensions, discoveries and other additions	77,049,000,000	46,692,000,000	2,142,000,000
Purchases of minerals in-place		49,044,000,000
Revisions of previous estimates	(37,623,000,000)	(41,137,000,000)	(81,623,000,000)
Production	(133,377,000,000)	(136,823,000,000)	(132,356,000,000)
Ending Balance	982,966,000,000	1,076,917,000,000	1,159,141,000,000
Australia [Member]
Total proved reserves:
Extensions, discoveries and other additions	41,000,000
Australia [Member] | Oil Reserves [Member]
Proved reserve data
Proved developed reserves	35,725,000	48,072,000	34,662,000	39,758,000
Proved undeveloped reserves	32,220,000	18,064,000	43,779,000	36,777,000
Total proved reserves:
Beginning Balance	66,136,000	78,441,000	76,535,000
Extensions, discoveries and other additions	15,762,000	4,452,000	3,574,000
Revisions of previous estimates			1,901,000
Production	(13,953,000)	(16,757,000)	(3,569,000)
Ending Balance	67,945,000	66,136,000	78,441,000
Australia [Member] | Natural Gas Reserves [Member]
Proved reserve data
Proved developed reserves	675,618,000,000	682,763,000,000	699,963,000,000	713,290,000,000
Proved undeveloped reserves	893,966,000,000	805,735,000,000	661,478,000,000	540,255,000,000
Total proved reserves:
Beginning Balance	1,488,498,000,000	1,361,441,000,000	1,253,545,000,000
Extensions, discoveries and other additions	148,640,000,000	199,958,000,000	174,883,000,000
Revisions of previous estimates			33,000,000
Production	(67,554,000,000)	(72,901,000,000)	(67,020,000,000)
Ending Balance	1,569,584,000,000	1,488,498,000,000	1,361,441,000,000
North Sea [Member] | Oil Reserves [Member]
Proved reserve data
Proved developed reserves	145,743,000	115,705,000	142,022,000	168,925,000
Proved undeveloped reserves	32,924,000	38,663,000	29,692,000	18,990,000
Total proved reserves:
Beginning Balance	154,368,000	171,714,000	187,915,000
Extensions, discoveries and other additions	404,000	3,383,000	6,056,000
Purchases of minerals in-place	43,803,000
Revisions of previous estimates			2,000
Production	(19,908,000)	(20,729,000)	(22,259,000)
Ending Balance	178,667,000	154,368,000	171,714,000
North Sea [Member] | Natural Gas Reserves [Member]
Proved reserve data
Proved developed reserves	105,028,000,000	4,144,000,000	4,851,000,000	5,585,000,000
Proved undeveloped reserves	3,414,000,000
Total proved reserves:
Beginning Balance	4,144,000,000	4,851,000,000	5,585,000,000
Extensions, discoveries and other additions	475,000,000	166,000,000	252,000,000
Purchases of minerals in-place	104,658,000
Production	(835,000,000)	(873,000,000)	(986,000,000)
Ending Balance	108,442,000,000	4,144,000,000	4,851,000,000
Argentina [Member] | Oil Reserves [Member]
Proved reserve data
Proved developed reserves	21,940,000	22,458,000	25,985,000	26,752,000
Proved undeveloped reserves	5,800,000	4,641,000	5,104,000	5,027,000
Total proved reserves:
Beginning Balance	27,099,000	31,089,000	31,779,000
Extensions, discoveries and other additions	5,014,000	426,000	4,865,000
Revisions of previous estimates	232,000	379,000	(173,000)
Production	(4,605,000)	(4,795,000)	(5,382,000)
Ending Balance	27,740,000	27,099,000	31,089,000
Argentina [Member] | Natural Gas Reserves [Member]
Proved reserve data
Proved developed reserves	447,132,000,000	462,206,000,000	473,145,000,000	487,980,000,000
Proved undeveloped reserves	90,427,000,000	70,465,000,000	54,184,000,000	58,393,000,000
Total proved reserves:
Beginning Balance	532,671,000,000	527,329,000,000	546,374,000,000
Extensions, discoveries and other additions	81,274,000,000	71,632,000,000	50,714,000,000
Revisions of previous estimates	1,107,000,000	1,173,000,000	(2,395,000,000)
Production	(77,493,000,000)	(67,463,000,000)	(67,364,000,000)
Ending Balance	537,559,000,000	532,671,000,000	527,329,000,000