Supplemental Oil and Gas Information (Summary of Proved Reserves Based on Average Prices) (Details)	12 Months Ended
	Dec. 31, 2014 MMBbls	Dec. 31, 2013 MMBbls	Dec. 31, 2012 MMBbls	Dec. 31, 2011 MMBbls
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	471,200,000	414,800,000	349,700,000
Revisions of previous estimates	(9,300,000)	27,400,000	2,300,000
Improved recovery	7,500,000	27,400,000	7,200,000
Extensions and discoveries	42,600,000	69,600,000	84,000,000
Sales of properties	(24,300,000)
Purchases of properties	6,100,000	(20,400,000)	12,500,000
Production	(52,000,000)	(47,600,000)	(40,900,000)
Proved developed and undeveloped reserves, Ending Balance	441,800,000	471,200,000	414,800,000
Proved developed reserves	324,100,000	289,900,000	267,700,000	238,500,000
Proved undeveloped reserves	117,700,000	181,300,000	147,100,000	111,200,000
Crude Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	354,200,000	295,700,000	220,200,000
Revisions of previous estimates	(2,300,000)	24,800,000	7,600,000
Improved recovery	7,500,000	27,400,000	7,200,000
Extensions and discoveries	42,600,000	69,600,000	84,000,000
Sales of properties	(24,300,000)
Purchases of properties	6,100,000	(20,400,000)	12,500,000
Production	(47,600,000)	(42,900,000)	(35,800,000)
Proved developed and undeveloped reserves, Ending Balance	336,200,000	354,200,000	295,700,000
Proved developed reserves	218,500,000	172,900,000	148,600,000	118,000,000
Proved undeveloped reserves	117,700,000	181,300,000	147,100,000	102,200,000
Natural Gas Liquids Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	24,400,000
Revisions of previous estimates	5,100,000	15,700,000	300,000
Extensions and discoveries	4,700,000	10,000,000
Sales of properties	(200,000)
Production	(3,400,000)	(1,300,000)	(300,000)
Proved developed and undeveloped reserves, Ending Balance	30,600,000	24,400,000
Proved developed reserves	17,500,000	14,200,000
Proved undeveloped reserves	13,100,000	10,200,000
Natural Gas Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	1,153,600,000,000	1,137,000,000,000	1,106,100,000,000
Revisions of previous estimates	167,200,000,000	33,700,000,000	20,200,000,000
Improved recovery	7,000,000,000	3,200,000,000	7,200,000,000
Extensions and discoveries	696,800,000,000	153,400,000,000	173,500,000,000
Sales of properties	(162,600,000,000)	(19,000,000,000)
Purchases of properties	5,500,000,000		9,400,000,000
Production	(162,800,000,000)	(154,700,000,000)	(179,400,000,000)
Proved developed and undeveloped reserves, Ending Balance	1,704,700,000,000	1,153,600,000,000	1,137,000,000,000
Proved developed reserves	812,100,000,000	786,200,000,000	706,000,000,000	711,600,000,000
Proved undeveloped reserves	892,600,000,000	367,400,000,000	431,000,000,000	394,500,000,000
United States [Member] | Crude Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	191,500,000	142,600,000	55,300,000
Revisions of previous estimates	(3,200,000)	13,100,000	13,000,000
Extensions and discoveries	32,700,000	52,400,000	77,300,000
Sales of properties	(300,000)
Purchases of properties	6,100,000		6,500,000
Production	(21,900,000)	(16,600,000)	(9,500,000)
Proved developed and undeveloped reserves, Ending Balance	204,900,000	191,500,000	142,600,000
Proved developed reserves	106,200,000	75,800,000	48,000,000	20,800,000
Proved undeveloped reserves	98,700,000	115,700,000	94,600,000	34,500,000
United States [Member] | Natural Gas Liquids Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	23,200,000
Revisions of previous estimates	5,000,000	15,600,000
Extensions and discoveries	4,000,000	8,700,000
Production	(3,100,000)	(1,100,000)
Proved developed and undeveloped reserves, Ending Balance	29,100,000	23,200,000
Proved developed reserves	16,500,000	13,100,000
Proved undeveloped reserves	12,600,000	10,100,000
United States [Member] | Natural Gas Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	185,000,000,000	209,700,000,000	98,400,000,000
Revisions of previous estimates	47,700,000,000	(38,600,000,000)	16,500,000,000
Extensions and discoveries	24,100,000,000	33,300,000,000	107,200,000,000
Sales of properties	(3,700,000,000)
Purchases of properties	5,500,000,000		7,000,000,000
Production	(32,300,000,000)	(19,400,000,000)	(19,400,000,000)
Proved developed and undeveloped reserves, Ending Balance	226,300,000,000	185,000,000,000	209,700,000,000
Proved developed reserves	145,600,000,000	112,600,000,000	78,800,000,000	58,200,000,000
Proved undeveloped reserves	80,700,000,000	72,400,000,000	130,900,000,000	40,200,000,000
Canada [Member] | Crude Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	38,700,000	36,800,000	36,600,000
Revisions of previous estimates	2,700,000	8,400,000	(3,400,000)
Extensions and discoveries	2,400,000	200,000	2,900,000
Sales of properties	(500,000)
Purchases of properties			6,000,000
Production	(5,900,000)	(6,700,000)	(5,300,000)
Proved developed and undeveloped reserves, Ending Balance	37,400,000	38,700,000	36,800,000
Proved developed reserves	32,400,000	31,600,000	29,500,000	32,600,000
Proved undeveloped reserves	5,000,000	7,100,000	7,300,000	4,000,000
Canada [Member] | Synthetic Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	117,000,000	119,100,000	129,500,000
Revisions of previous estimates	(7,000,000)	2,600,000	(5,300,000)
Production	(4,400,000)	(4,700,000)	(5,100,000)
Proved developed and undeveloped reserves, Ending Balance	105,600,000	117,000,000	119,100,000
Proved developed reserves	105,600,000	117,000,000	119,100,000	120,500,000
Proved undeveloped reserves				9,000,000
Canada [Member] | Natural Gas Liquids Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	100,000
Extensions and discoveries	600,000	100,000
Proved developed and undeveloped reserves, Ending Balance	700,000	100,000
Proved developed reserves	200,000
Proved undeveloped reserves	500,000	100,000
Canada [Member] | Natural Gas Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	562,800,000,000	550,400,000,000	638,900,000,000
Revisions of previous estimates	105,600,000,000	34,000,000,000	(37,200,000,000)
Extensions and discoveries	231,500,000,000	42,500,000,000	25,800,000,000
Purchases of properties			2,400,000,000
Production	(57,100,000,000)	(64,100,000,000)	(79,500,000,000)
Proved developed and undeveloped reserves, Ending Balance	842,800,000,000	562,800,000,000	550,400,000,000
Proved developed reserves	467,400,000,000	384,000,000,000	415,800,000,000	427,100,000,000
Proved undeveloped reserves	375,400,000,000	178,800,000,000	134,600,000,000	211,800,000,000
Malaysia [Member] | Crude Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	124,000,000	95,700,000	104,400,000
Revisions of previous estimates	(1,800,000)	3,300,000	(700,000)
Improved recovery	7,500,000	27,400,000	7,200,000
Extensions and discoveries	7,500,000	17,000,000	3,800,000
Sales of properties	(23,500,000)
Production	(19,800,000)	(19,400,000)	(19,000,000)
Proved developed and undeveloped reserves, Ending Balance	93,900,000	124,000,000	95,700,000
Proved developed reserves	79,900,000	65,500,000	67,000,000	57,200,000
Proved undeveloped reserves	14,000,000	58,500,000	28,700,000	47,200,000
Malaysia [Member] | Natural Gas Liquids Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	1,100,000
Revisions of previous estimates	100,000	100,000	300,000
Extensions and discoveries	100,000	1,200,000
Sales of properties	(200,000)
Production	(300,000)	(200,000)	(300,000)
Proved developed and undeveloped reserves, Ending Balance	800,000	1,100,000
Proved developed reserves	800,000	1,100,000
Malaysia [Member] | Natural Gas Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	405,800,000,000	357,600,000,000	347,800,000,000
Revisions of previous estimates	13,900,000,000	38,300,000,000	41,400,000,000
Improved recovery	7,000,000,000	3,200,000,000	7,200,000,000
Extensions and discoveries	441,200,000,000	77,600,000,000	40,500,000,000
Sales of properties	(158,900,000,000)
Production	(73,400,000,000)	(70,900,000,000)	(79,300,000,000)
Proved developed and undeveloped reserves, Ending Balance	635,600,000,000	405,800,000,000	357,600,000,000
Proved developed reserves	199,100,000,000	289,600,000,000	197,300,000,000	210,500,000,000
Proved undeveloped reserves	436,500,000,000	116,200,000,000	160,300,000,000	137,300,000,000
United Kingdom [Member] | Crude Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance		20,600,000	21,600,000
Revisions of previous estimates			300,000
Purchases of properties		(20,400,000)
Production		(200,000)	(1,300,000)
Proved developed and undeveloped reserves, Ending Balance		0	20,600,000
Proved developed reserves			4,100,000	5,100,000
Proved undeveloped reserves			16,500,000	16,500,000
United Kingdom [Member] | Natural Gas Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance		19,300,000,000	21,000,000,000
Revisions of previous estimates			(500,000,000)
Sales of properties		(19,000,000,000)
Production		(300,000,000)	(1,200,000,000)
Proved developed and undeveloped reserves, Ending Balance			19,300,000,000
Proved developed reserves			14,100,000,000	15,800,000,000
Proved undeveloped reserves			5,200,000,000	5,200,000,000
Other [Member] | Crude Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance			2,300,000
Revisions of previous estimates			(1,600,000)
Production			(700,000)
Proved developed reserves				2,300,000