Segment Reporting Information by Business Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Segment Reporting Disclosure [Line Items]
Total Assets	$ 18,824,975				$ 18,824,975				$ 17,522,643
External Revenues	7,217,842		7,157,605	[1]	13,857,796		14,114,541	[1]
Income (Loss)	402,644		295,437	[1]	763,243		585,508	[1]
Discontinued Operations
Segment Reporting Disclosure [Line Items]
Total Assets	4,100				4,100
External Revenues	0		0		0		0
Income (Loss)	70,500		4,100		223,100		12,800
Operating Segments
Segment Reporting Disclosure [Line Items]
Total Assets	1,742,700				1,742,700
External Revenues	7,201,200		7,146,800		13,849,200		14,100,700
Income (Loss)	362,400		306,500		619,600		615,200
Operating Segments | Exploration and production
Segment Reporting Disclosure [Line Items]
Total Assets	14,461,500	[2]			14,461,500	[2]
External Revenues	1,315,300	[2]	107,800	[2]	2,614,300	[2]	2,227,700	[2]
Income (Loss)	290,200	[2]	226,000	[2]	522,100	[2]	538,900	[2]
Operating Segments | Exploration and production | United States
Segment Reporting Disclosure [Line Items]
Total Assets	4,331,400	[2]			4,331,400	[2]
External Revenues	444,200	[2]	201,700	[2]	853,100	[2]	422,800	[2]
Income (Loss)	122,900	[2]	(1,200)	[2]	216,700	[2]	49,600	[2]
Operating Segments | Exploration and production | Canada
Segment Reporting Disclosure [Line Items]
Total Assets	4,258,300	[2]			4,258,300	[2]
External Revenues	316,800	[2]	264,900	[2]	577,600	[2]	571,900	[2]
Income (Loss)	51,700	[2]	43,700	[2]	6,500	[2]	11,700	[2]
Operating Segments | Exploration and production | Malaysia
Segment Reporting Disclosure [Line Items]
Total Assets	5,709,700	[2]			5,709,700	[2]
External Revenues	554,700	[2]	611,300	[2]	1,114,700	[2]	1,175,300	[2]
Income (Loss)	213,500	[2]	223,200	[2]	418,700	[2]	447,200	[2]
Operating Segments | Exploration and production | Republic of the Congo
Segment Reporting Disclosure [Line Items]
Total Assets	6,800	[2]			6,800	[2]
External Revenues	0	[2]	0	[2]	69,500	[2]	57,600	[2]
Income (Loss)	(11,700)	[2]	(5,300)	[2]	(26,500)	[2]	(3,700)	[2]
Operating Segments | Exploration and production | Other Regions
Segment Reporting Disclosure [Line Items]
Total Assets	94,100	[2]			94,100	[2]
External Revenues	(400)	[2]	100	[2]	(600)	[2]	100	[2]
Income (Loss)	(86,200)	[2]	(34,400)	[2]	(151,800)	[2]	(71,200)	[2]
Operating Segments | Refining and Marketing
Segment Reporting Disclosure [Line Items]
Total Assets	2,965,500				2,965,500
External Revenues	5,885,900		6,068,800		11,234,900		11,873,000
Income (Loss)	72,200		80,500		97,500		76,300
Operating Segments | Refining and Marketing | United States
Segment Reporting Disclosure [Line Items]
Total Assets	1,832,300				1,832,300
External Revenues	4,458,300		4,512,100		8,477,800		8,776,300
Income (Loss)	77,900		73,300		107,300		66,100
Operating Segments | Refining and Marketing | United Kingdom
Segment Reporting Disclosure [Line Items]
Total Assets	1,133,200				1,133,200
External Revenues	1,427,600		1,556,700		2,757,100		3,096,700
Income (Loss)	(5,700)		7,200		(9,800)		10,200
Operating Segments | Corporate
Segment Reporting Disclosure [Line Items]
Total Assets	1,393,900				1,393,900
External Revenues	16,600		10,800		8,600		13,800
Income (Loss)	(30,300)		(15,200)		(79,500)		(42,500)
Operating Segments | Continuing Operations
Segment Reporting Disclosure [Line Items]
Total Assets	18,820,900				18,820,900
External Revenues	7,217,800		7,157,600		13,857,800		14,114,500
Income (Loss)	$ 332,100		$ 291,300		$ 540,100		$ 572,700

[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.