Oil and Gas Exploration and Production Industries Disclosures (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Bcf	Dec. 31, 2010 Bcf	Dec. 31, 2009 Bcf	Dec. 31, 2008 Bcf
Capitalized Costs, Oil and Gas Producing Activities, Gross [Abstract]
Proved properties	32,353,380	27,693,700
Unproved properties	1,311,055	1,570,109
Total	33,664,435	29,263,809
Accumulated depreciation, depletion and amortization	(13,981,143)	(11,859,870)
Net capitalized costs	19,683,292	17,403,939
United States [Member] | Crude Oil (MBbl) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	355,457.0	188,452.0	133,362.0
Revisions of previous estimates	(21,188.0)	(8,313.0)	4,402.0
Purchases in place	9	13	15,666.0
Extensions, discoveries and other additions	202,552.0	199,479.0	58,258.0
Sales in place	(4,301.0)	(1,082.0)	(5,742.0)
Production	(37,233.0)	(23,092.0)	(17,494.0)
Net proved reserves - end of period	495,296.0	355,457.0	188,452.0
United States [Member] | Natural Gas Liquids (MBbl) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	150,434.0	91,489.0	72,484.0
Revisions of previous estimates	35,999.0	27,490.0	6,109.0
Purchases in place	17	0	5,801.0
Extensions, discoveries and other additions	65,288.0	42,221.0	18,546.0
Sales in place	(10,008.0)	(2)	(3,231.0)
Production	(15,144.0)	(10,764.0)	(8,220.0)
Net proved reserves - end of period	226,586.0	150,434.0	91,489.0
United States [Member] | Natural Gas (Bcf) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	6,491.5	6,350.1	4,889.0
Revisions of previous estimates	(344.0)	(222.7)	(378.0)
Purchases in place	3.0	0.0	450.8
Extensions, discoveries and other additions	634.6	821.3	1,925.0
Sales in place	(323.6)	(34.6)	(114.4)
Production	(415.7)	(422.6)	(422.3)
Net proved reserves - end of period	6,045.8	6,491.5	6,350.1	4,889.0
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	3,234.9	3,519.7	3,330.1	3,544.7
Net proved undeveloped reserves	2,810.8	2,971.7	3,020.0	1,344.3
United States [Member] | Oil Equivalents (MBoe) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	1,587,806.0	1,338,292.0	1,020,671.0
Revisions of previous estimates	(42,526.0)	(17,945.0)	(52,487.0)
Purchases in place	521.0	14	96,605.0
Extensions, discoveries and other additions	373,602.0	378,582.0	397,642.0
Sales in place	(68,247.0)	(6,860.0)	(28,032.0)
Production	(121,648.0)	(104,277.0)	(96,107.0)
Net proved reserves - end of period	1,729,508.0	1,587,806.0	1,338,292.0	1,020,671.0
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	877,301.0	839,928.0	744,339.0	750,389.0
Net proved undeveloped reserves	852,207.0	747,878.0	593,953.0	270,282.0
United States [Member] | Liquids (MBbl) [Member]
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	338,144.0	253,308.0	189,322.0	159,607.0
Net proved undeveloped reserves	383,739.0	252,583.0	90,619.0	46,239.0
Canada [Member] | Crude Oil (MBbl) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	25,636.0	25,586.0	7,498.0
Revisions of previous estimates	(4,611.0)	(104.0)	(183.0)
Purchases in place	0	0	0
Extensions, discoveries and other additions	449.0	3,198.0	19,783.0
Sales in place	0	(589.0)	(20)
Production	(2,882.0)	(2,455.0)	(1,492.0)
Net proved reserves - end of period	18,592.0	25,636.0	25,586.0
Canada [Member] | Natural Gas Liquids (MBbl) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	1,475.0	1,972.0	3,297.0
Revisions of previous estimates	43	(196.0)	(926.0)
Purchases in place	0	0	0
Extensions, discoveries and other additions	0	21	24
Sales in place	0	(6)	(30)
Production	(316.0)	(316.0)	(393.0)
Net proved reserves - end of period	1,202.0	1,475.0	1,972.0
Canada [Member] | Natural Gas (Bcf) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	1,133.8	1,549.5	1,237.2
Revisions of previous estimates	(49.8)	(29.9)	(447.2)
Purchases in place	0.0	0.0	0.0
Extensions, discoveries and other additions	0.0	3.4	846.5
Sales in place	0.0	(316.2)	(5.1)
Production	(48.1)	(73.0)	(81.9)
Net proved reserves - end of period	1,035.9	1,133.8	1,549.5	1,237.2
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	295.8	401.6	681.0	1,103.7
Net proved undeveloped reserves	740.1	732.2	868.5	133.6
Canada [Member] | Oil Equivalents (MBoe) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	216,084.0	285,808.0	217,002.0
Revisions of previous estimates	(12,865.0)	(5,288.0)	(75,638.0)
Purchases in place	0	0	0
Extensions, discoveries and other additions	448.0	3,789.0	160,882.0
Sales in place	0	(53,288.0)	(898.0)
Production	(11,219.0)	(14,937.0)	(15,540.0)
Net proved reserves - end of period	192,448.0	216,084.0	285,808.0	217,002.0
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	58,524.0	79,701.0	124,323.0	194,360.0
Net proved undeveloped reserves	133,924.0	136,383.0	161,486.0	22,642.0
Canada [Member] | Liquids (MBbl) [Member]
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	9,220.0	12,758.0	10,831.0	10,416.0
Net proved undeveloped reserves	10,574.0	14,352.0	16,727.0	379.0
Trinidad [Member] | Crude Oil (MBbl) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	4,731.0	5,443.0	8,326.0
Revisions of previous estimates	18	(754.0)	(1,760.0)
Purchases in place	0	0	0
Extensions, discoveries and other additions	0	1,751.0	0
Sales in place	0	0	0
Production	(1,242.0)	(1,709.0)	(1,123.0)
Net proved reserves - end of period	3,507.0	4,731.0	5,443.0
Trinidad [Member] | Natural Gas Liquids (MBbl) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	0	0	0
Revisions of previous estimates	0	0	0
Purchases in place	0	0	0
Extensions, discoveries and other additions	0	0	0
Sales in place	0	0	0
Production	0	0	0
Net proved reserves - end of period	0	0	0
Trinidad [Member] | Natural Gas (Bcf) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	827.6	985.8	1,198.1
Revisions of previous estimates	(24.2)	(88.6)	(104.9)
Purchases in place	0.0	0.0	0.0
Extensions, discoveries and other additions	74.7	63.0	0.0
Sales in place	0.0	0.0	0.0
Production	(127.4)	(132.6)	(107.4)
Net proved reserves - end of period	750.7	827.6	985.8	1,198.1
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	606.3	519.2	609.4	889.0
Net proved undeveloped reserves	144.4	308.5	376.4	309.0
Trinidad [Member] | Oil Equivalents (MBoe) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	142,669.0	169,747.0	208,013.0
Revisions of previous estimates	(4,011.0)	(15,513.0)	(19,250.0)
Purchases in place	0	0	0
Extensions, discoveries and other additions	12,455.0	12,250.0	0
Sales in place	0	0	0
Production	(22,484.0)	(23,815.0)	(19,016.0)
Net proved reserves - end of period	128,629.0	142,669.0	169,747.0	208,013.0
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	103,710.0	90,382.0	105,540.0	154,939.0
Net proved undeveloped reserves	24,919.0	52,287.0	64,207.0	53,074.0
Trinidad [Member] | Liquids (MBbl) [Member]
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	2,657.0	3,853.0	3,966.0	6,756.0
Net proved undeveloped reserves	850.0	879.0	1,477.0	1,570.0
Other International [Member] | Crude Oil (MBbl) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	98	58	65
Revisions of previous estimates	25	20	17
Purchases in place	0	0	0
Extensions, discoveries and other additions	0	48	0
Sales in place	0	0	0
Production	(25)	(28)	(24)
Net proved reserves - end of period	98	98	58
Other International [Member] | Natural Gas Liquids (MBbl) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	0	0	0
Revisions of previous estimates	0	0	0
Purchases in place	0	0	0
Extensions, discoveries and other additions	0	0	0
Sales in place	0	0	0
Production	0	0	0
Net proved reserves - end of period	0	0	0
Other International [Member] | Natural Gas (Bcf) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	17.3	12.7	14.9
Revisions of previous estimates	1.3	1.9	3.0
Purchases in place	0.0	0.0	0.0
Extensions, discoveries and other additions	4.5	7.9	0.0
Sales in place	0.0	0.0	0.0
Production	(4.6)	(5.2)	(5.2)
Net proved reserves - end of period	18.5	17.3	12.7	14.9
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	18.6	17.3	12.7	14.9
Net proved undeveloped reserves	0.0	0.0	0.0	0.0
Other International [Member] | Oil Equivalents (MBoe) [Member]
Proved Developed and Undeveloped Reserves [Rollforward]
Net proved reserves - beginning of period	2,976.0	2,172.0	2,548.0
Revisions of previous estimates	239.0	342.0	515.0
Purchases in place	0	0	0
Extensions, discoveries and other additions	750.0	1,363.0	0
Sales in place	0	0	0
Production	(787.0)	(901.0)	(891.0)
Net proved reserves - end of period	3,178.0	2,976.0	2,172.0	2,548.0
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	3,178.0	2,976.0	2,172.0	2,548.0
Net proved undeveloped reserves	0	0	0	0
Other International [Member] | Liquids (MBbl) [Member]
Net Proved Developed and Undeveloped Reserves [Abstract]
Net proved developed reserves	97	98	58	65
Net proved undeveloped reserves	0	0	0	0