Segment Reporting Information by Business Segments (Detail) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011
Segment Reporting Disclosure [Line Items]
Total Assets	$ 16,589,837,000				$ 16,589,837,000				$ 14,138,138,000
External Revenues	7,122,277,000		7,220,220,000	[1]	21,236,818,000		20,844,088,000	[1]
Inter-segment Revenues	0		42,700,000	[1]	0		137,400,000	[1]
Income (Loss)	226,681,000		406,114,000	[1]	812,189,000		986,630,000	[1]
Total Operating Segments
Segment Reporting Disclosure [Line Items]
Total Assets	14,908,000,000				14,908,000,000
External Revenues	7,130,700,000		7,190,400,000	[1]	21,231,400,000		20,800,400,000	[1]
Inter-segment Revenues	0		42,700,000	[1]	0		137,400,000	[1]
Income (Loss)	263,900,000		342,300,000	[1]	879,100,000		888,100,000	[1]
Total Operating Segments | Exploration and production
Segment Reporting Disclosure [Line Items]
Total Assets	11,824,400,000	[2]			11,824,400,000	[2]
External Revenues	1,083,800,000	[2]	1,009,100,000	[1],[2]	3,311,500,000	[2]	2,945,300,000	[1],[2]
Inter-segment Revenues	0	[2]	42,700,000	[1],[2]	0	[2]	137,400,000	[1],[2]
Income (Loss)	221,100,000	[2]	273,400,000	[1],[2]	760,000,000	[2]	758,800,000	[1],[2]
Total Operating Segments | Exploration and production | United States
Segment Reporting Disclosure [Line Items]
Total Assets	2,862,700,000				2,862,700,000
External Revenues	248,800,000		173,200,000	[1]	671,600,000		539,700,000	[1]
Inter-segment Revenues	0		0	[1]	0		0	[1]
Income (Loss)	33,500,000		38,200,000	[1]	83,100,000		106,800,000	[1]
Total Operating Segments | Exploration and production | Canada
Segment Reporting Disclosure [Line Items]
Total Assets	4,065,700,000				4,065,700,000
External Revenues	232,800,000		307,400,000	[1]	804,700,000		827,700,000	[1]
Inter-segment Revenues	0		42,700,000	[1]	0		137,400,000	[1]
Income (Loss)	29,300,000		102,300,000	[1]	146,300,000		284,500,000	[1]
Total Operating Segments | Exploration and production | Malaysia
Segment Reporting Disclosure [Line Items]
Total Assets	4,586,000,000				4,586,000,000
External Revenues	602,200,000		484,800,000	[1]	1,777,500,000		1,442,100,000	[1]
Inter-segment Revenues	0		0	[1]	0		0	[1]
Income (Loss)	215,700,000		197,700,000	[1]	662,900,000		559,500,000	[1]
Total Operating Segments | Exploration and production | Republic of the Congo
Segment Reporting Disclosure [Line Items]
Total Assets	249,600,000				249,600,000
External Revenues	0		43,700,000	[1]	57,600,000		111,400,000	[1]
Inter-segment Revenues	0		0	[1]	0		0	[1]
Income (Loss)	(4,700,000)		(700,000)	[1]	(8,400,000)		(400,000)	[1]
Total Operating Segments | Exploration and production | Other Regions
Segment Reporting Disclosure [Line Items]
Total Assets	60,400,000				60,400,000
External Revenues	0		0	[1]	100,000		24,400,000	[1]
Inter-segment Revenues	0		0	[1]	0		0	[1]
Income (Loss)	(52,700,000)		(64,100,000)	[1]	(123,900,000)		(191,600,000)	[1]
Total Operating Segments | Refining and Marketing
Segment Reporting Disclosure [Line Items]
Total Assets	3,083,600,000				3,083,600,000
External Revenues	6,046,900,000		6,181,300,000	[1]	17,919,900,000		17,855,100,000	[1]
Inter-segment Revenues	0		0	[1]	0		0	[1]
Income (Loss)	42,800,000		68,900,000	[1]	119,100,000		129,300,000	[1]
Total Operating Segments | Refining and Marketing | United States
Segment Reporting Disclosure [Line Items]
Total Assets	1,955,300,000				1,955,300,000
External Revenues	4,475,500,000		4,629,200,000	[1]	13,251,800,000		13,356,100,000	[1]
Inter-segment Revenues	0		0	[1]	0		0	[1]
Income (Loss)	17,300,000		88,000,000	[1]	83,400,000		172,900,000	[1]
Total Operating Segments | Refining and Marketing | United Kingdom
Segment Reporting Disclosure [Line Items]
Total Assets	1,128,300,000				1,128,300,000
External Revenues	1,571,400,000		1,552,100,000	[1]	4,668,100,000		4,499,000,000	[1]
Inter-segment Revenues	0		0	[1]	0		0	[1]
Income (Loss)	25,500,000		(19,100,000)	[1]	35,700,000		(43,600,000)	[1]
Corporate
Segment Reporting Disclosure [Line Items]
Total Assets	1,473,300,000				1,473,300,000
External Revenues	(8,500,000)		29,800,000	[1]	5,400,000		43,700,000	[1]
Inter-segment Revenues	0		0	[1]	0		0	[1]
Income (Loss)	(35,000,000)		5,000,000	[1]	(77,400,000)		(40,700,000)	[1]
Continuing Operations
Segment Reporting Disclosure [Line Items]
Total Assets	16,381,300,000				16,381,300,000
External Revenues	7,122,200,000		7,220,200,000	[1]	21,236,800,000		20,844,100,000	[1]
Inter-segment Revenues	0		42,700,000	[1]	0		137,400,000	[1]
Income (Loss)	228,900,000		347,300,000	[1]	801,700,000		847,400,000	[1]
Discontinued Operations
Segment Reporting Disclosure [Line Items]
Total Assets	208,500,000				208,500,000
External Revenues	0		0	[1]	0		0	[1]
Inter-segment Revenues	0		0	[1]	0		0	[1]
Income (Loss)	$ (2,200,000)		$ 58,800,000	[1]	$ 10,500,000		$ 139,200,000	[1]

[1] Reclassified to conform to current presentation.

[2] Additional details about results of oil and gas operations are presented in the tables on pages 24 and 25.