Segment Information (Detail) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Segment Reporting Information [Line Items]
Net income (loss)	$ 158,700,000	$ 226,700,000	$ 295,400,000	$ 290,100,000	$ (113,900,000)	$ 406,100,000	$ 311,600,000	$ 268,900,000	$ 970,876,000	$ 872,702,000	[1]	$ 798,081,000	[1]
Revenues from external customers									28,626,000,000	27,638,100,000		20,036,100,000
Intersegment revenues									0	142,800,000		118,900,000
Interest income									6,500,000	10,100,000		6,900,000
Interest expense, net of capitalization									14,900,000	40,700,000		34,700,000
Income tax expense (benefit)									658,936,000	763,173,000	[1]	576,572,000	[1]
Significant noncash charges (credits)
Depreciation, depletion, amortization									1,375,577,000	1,079,750,000	[1]	1,092,107,000	[1]
Accretion of asset retirement obligations									39,341,000	34,724,000	[1]	29,580,000	[1]
Amortization of undeveloped leases									129,750,000	118,211,000	[1]	108,026,000	[1]
Impairment of long-lived assets									260,988,000	368,600,000	[1]	0	[1]
Deferred and noncurrent income taxes									316,600,000	157,000,000		146,600,000
Additions to property, plant, equipment									4,133,800,000	2,572,200,000		2,263,700,000
Total assets at year-end	17,522,643,000				14,138,138,000				17,522,643,000	14,138,138,000		14,233,200,000
Exploration and production
Segment Reporting Information [Line Items]
Net income (loss)									905,000,000	614,200,000		776,400,000
Revenues from external customers									4,608,100,000	4,102,500,000		3,437,600,000
Intersegment revenues									0	142,800,000		118,900,000
Interest income									0	0		0
Interest expense, net of capitalization									0	0		0
Income tax expense (benefit)									605,000,000	680,800,000		544,300,000
Significant noncash charges (credits)
Depreciation, depletion, amortization									1,244,400,000	956,000,000		982,600,000
Accretion of asset retirement obligations									38,400,000	33,800,000		28,800,000
Amortization of undeveloped leases									129,800,000	118,200,000		108,000,000
Impairment of long-lived assets									200,000,000	368,600,000
Deferred and noncurrent income taxes									375,100,000	177,400,000		130,500,000
Additions to property, plant, equipment									3,933,800,000	2,376,800,000		1,855,100,000
Total assets at year-end	13,102,900,000				10,132,900,000				13,102,900,000	10,132,900,000		8,994,800,000
Exploration and production | United States
Segment Reporting Information [Line Items]
Net income (loss)									168,000,000	152,700,000		72,700,000
Revenues from external customers									1,038,000,000	737,700,000		659,900,000
Intersegment revenues									0	0		0
Interest income									0	0		0
Interest expense, net of capitalization									0	0		0
Income tax expense (benefit)									99,800,000	86,500,000		30,000,000
Significant noncash charges (credits)
Depreciation, depletion, amortization									330,200,000	183,000,000		281,100,000
Accretion of asset retirement obligations									11,400,000	9,900,000		6,900,000
Amortization of undeveloped leases									71,600,000	62,200,000		68,500,000
Impairment of long-lived assets									0	0
Deferred and noncurrent income taxes									231,000,000	54,200,000		(48,600,000)
Additions to property, plant, equipment									1,615,900,000	696,600,000		369,400,000
Total assets at year-end	3,625,900,000				2,227,600,000				3,625,900,000	2,227,600,000		1,651,300,000
Exploration and production | Canada
Segment Reporting Information [Line Items]
Net income (loss)									208,100,000	328,000,000		213,800,000
Revenues from external customers									1,084,300,000	1,145,800,000		780,200,000
Intersegment revenues									0	142,800,000		118,900,000
Interest income									0	0		0
Interest expense, net of capitalization									0	0		0
Income tax expense (benefit)									65,100,000	135,500,000		79,100,000
Significant noncash charges (credits)
Depreciation, depletion, amortization									345,800,000	326,000,000		225,500,000
Accretion of asset retirement obligations									13,600,000	12,500,000		11,200,000
Amortization of undeveloped leases									29,300,000	28,800,000		33,700,000
Impairment of long-lived assets									0	0
Deferred and noncurrent income taxes									72,300,000	39,600,000		34,500,000
Additions to property, plant, equipment									887,200,000	885,200,000		804,400,000
Total assets at year-end	4,477,700,000				3,746,800,000				4,477,700,000	3,746,800,000		3,242,600,000
Exploration and production | Malaysia
Segment Reporting Information [Line Items]
Net income (loss)									894,200,000	812,700,000		659,400,000
Revenues from external customers									2,428,100,000	2,045,600,000		1,837,900,000
Intersegment revenues									0	0		0
Interest income									0	0		0
Interest expense, net of capitalization									0	0		0
Income tax expense (benefit)									544,700,000	434,900,000		414,100,000
Significant noncash charges (credits)
Depreciation, depletion, amortization									532,100,000	357,300,000		379,000,000
Accretion of asset retirement obligations									12,500,000	10,600,000		9,800,000
Amortization of undeveloped leases									0	0		0
Impairment of long-lived assets									0	0
Deferred and noncurrent income taxes									73,300,000	84,600,000		145,500,000
Additions to property, plant, equipment									1,426,700,000	694,800,000		467,900,000
Total assets at year-end	4,811,500,000				3,826,900,000				4,811,500,000	3,826,900,000		3,333,100,000
Exploration and production | Republic of the Congo
Segment Reporting Information [Line Items]
Net income (loss)									(241,100,000)	(385,300,000)		(77,200,000)
Revenues from external customers									57,600,000	148,800,000		155,700,000
Intersegment revenues									0	0		0
Interest income									0	0		0
Interest expense, net of capitalization									0	0		0
Income tax expense (benefit)									(64,500,000)	16,400,000		20,600,000
Significant noncash charges (credits)
Depreciation, depletion, amortization									33,900,000	87,800,000		95,500,000
Accretion of asset retirement obligations									900,000	500,000		400,000
Amortization of undeveloped leases									0	0		0
Impairment of long-lived assets									200,000,000	368,600,000
Deferred and noncurrent income taxes									(300,000)	(900,000)		(900,000)
Additions to property, plant, equipment									(20,700,000)	79,600,000		163,600,000
Total assets at year-end	112,200,000				257,500,000				112,200,000	257,500,000		678,900,000
Exploration and production | Other
Segment Reporting Information [Line Items]
Net income (loss)									(124,200,000)	(293,900,000)		(92,300,000)
Revenues from external customers									100,000	24,600,000		3,900,000
Intersegment revenues									0	0		0
Interest income									0	0		0
Interest expense, net of capitalization									0	0		0
Income tax expense (benefit)									(40,100,000)	7,500,000		500,000
Significant noncash charges (credits)
Depreciation, depletion, amortization									2,400,000	1,900,000		1,500,000
Accretion of asset retirement obligations									0	300,000		500,000
Amortization of undeveloped leases									28,900,000	27,200,000		5,800,000
Impairment of long-lived assets									0	0
Deferred and noncurrent income taxes									(1,200,000)	(100,000)		0
Additions to property, plant, equipment									24,700,000	20,600,000		49,800,000
Total assets at year-end	75,600,000				74,100,000				75,600,000	74,100,000		88,900,000
Refining and Marketing
Segment Reporting Information [Line Items]
Net income (loss)									157,600,000	190,300,000		130,600,000
Revenues from external customers									24,006,400,000	23,502,200,000		16,655,400,000
Intersegment revenues									0	0		0
Interest income									0	0		0
Interest expense, net of capitalization									0	0		0
Income tax expense (benefit)									97,400,000	134,500,000		79,500,000
Significant noncash charges (credits)
Depreciation, depletion, amortization									122,500,000	115,000,000		101,500,000
Accretion of asset retirement obligations									900,000	900,000		800,000
Amortization of undeveloped leases									0	0		0
Impairment of long-lived assets									61,000,000	0
Deferred and noncurrent income taxes									(26,200,000)	23,200,000		8,300,000
Additions to property, plant, equipment									133,700,000	122,300,000		290,100,000
Total assets at year-end	3,186,800,000				3,000,300,000				3,186,800,000	3,000,300,000		4,110,200,000
Refining and Marketing | United States
Segment Reporting Information [Line Items]
Net income (loss)									105,400,000	223,600,000		165,300,000
Revenues from external customers									17,723,400,000	17,471,900,000		13,750,400,000
Intersegment revenues									0	0		0
Interest income									0	0		0
Interest expense, net of capitalization									0	0		0
Income tax expense (benefit)									72,700,000	146,600,000		101,800,000
Significant noncash charges (credits)
Depreciation, depletion, amortization									75,200,000	68,300,000		60,100,000
Accretion of asset retirement obligations									900,000	900,000		800,000
Amortization of undeveloped leases									0	0		0
Impairment of long-lived assets									61,000,000	0
Deferred and noncurrent income taxes									(20,000,000)	28,500,000		5,100,000
Additions to property, plant, equipment									111,500,000	100,100,000		221,000,000
Total assets at year-end	2,026,500,000				1,806,500,000				2,026,500,000	1,806,500,000		2,996,600,000
Refining and Marketing | United Kingdom
Segment Reporting Information [Line Items]
Net income (loss)									52,200,000	(33,300,000)		(34,700,000)
Revenues from external customers									6,283,000,000	6,030,300,000		2,905,000,000
Intersegment revenues									0	0		0
Interest income									0	0		0
Interest expense, net of capitalization									0	0		0
Income tax expense (benefit)									24,700,000	(12,100,000)		(22,300,000)
Significant noncash charges (credits)
Depreciation, depletion, amortization									47,300,000	46,700,000		41,400,000
Accretion of asset retirement obligations									0	0		0
Amortization of undeveloped leases									0	0		0
Impairment of long-lived assets									0	0
Deferred and noncurrent income taxes									(6,200,000)	(5,300,000)		3,200,000
Additions to property, plant, equipment									22,200,000	22,200,000		69,100,000
Total assets at year-end	1,160,300,000				1,193,800,000				1,160,300,000	1,193,800,000		1,113,600,000
Corporate and Other
Segment Reporting Information [Line Items]
Net income (loss)									(98,500,000)	(75,000,000)		(157,900,000)
Revenues from external customers									11,500,000	33,400,000		(56,900,000)
Intersegment revenues									0	0		0
Interest income									6,500,000	10,100,000		6,900,000
Interest expense, net of capitalization									14,900,000	40,700,000		34,700,000
Income tax expense (benefit)									(43,500,000)	(52,100,000)		(47,200,000)
Significant noncash charges (credits)
Depreciation, depletion, amortization									8,700,000	8,700,000		8,000,000
Accretion of asset retirement obligations									0	0		0
Amortization of undeveloped leases									0	0		0
Impairment of long-lived assets									0	0
Deferred and noncurrent income taxes									(32,300,000)	(43,600,000)		7,800,000
Additions to property, plant, equipment									8,200,000	5,300,000		5,900,000
Total assets at year-end	1,009,600,000				790,800,000				1,009,600,000	790,800,000		940,300,000
Discontinued Operations
Segment Reporting Information [Line Items]
Net income (loss)									6,800,000	143,200,000		49,000,000
Revenues from external customers									0	0		0
Intersegment revenues									0	0		0
Interest income									0	0		0
Interest expense, net of capitalization									0	0		0
Income tax expense (benefit)									0	0		0
Significant noncash charges (credits)
Depreciation, depletion, amortization									0	0		0
Accretion of asset retirement obligations									0	0		0
Amortization of undeveloped leases									0	0		0
Impairment of long-lived assets									0	0
Deferred and noncurrent income taxes									0	0		0
Additions to property, plant, equipment									58,100,000	67,800,000		112,600,000
Total assets at year-end	$ 223,300,000				$ 214,100,000				$ 223,300,000	$ 214,100,000		$ 187,900,000

[1] Reclassified to conform to current presentation.