Segment Reporting Information by Business Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Segment Reporting Disclosure [Line Items]
Total Assets	$ 17,751,685				$ 17,522,643
External Revenues	6,639,954		6,956,936	[1]
Income (Loss)	360,599		290,071	[1]
Exploration and production
Segment Reporting Disclosure [Line Items]
Total Assets	13,195,800	[2]
External Revenues	1,299,000	[2]	1,149,700	[2]
Income (Loss)	231,900	[2]	313,000	[2]
Exploration and production | United States
Segment Reporting Disclosure [Line Items]
Total Assets	3,650,900	[2]
External Revenues	408,900	[2]	221,100	[2]
Income (Loss)	93,800	[2]	50,800	[2]
Exploration and production | Canada
Segment Reporting Disclosure [Line Items]
Total Assets	4,357,600	[2]
External Revenues	260,800	[2]	307,000	[2]
Income (Loss)	13,300	[2]	73,300	[2]
Exploration and production | Malaysia
Segment Reporting Disclosure [Line Items]
Total Assets	4,940,900	[2]
External Revenues	560,000	[2]	564,000	[2]
Income (Loss)	205,200	[2]	224,100	[2]
Exploration and production | Republic of the Congo
Segment Reporting Disclosure [Line Items]
Total Assets	135,600	[2]
External Revenues	69,500	[2]	57,600	[2]
Income (Loss)	(14,800)	[2]	1,600	[2]
Exploration and production | Other Regions
Segment Reporting Disclosure [Line Items]
Total Assets	110,800	[2]
External Revenues	(200)	[2]	0	[2]
Income (Loss)	(65,600)	[2]	(36,800)	[2]
Refining and Marketing
Segment Reporting Disclosure [Line Items]
Total Assets	2,867,800
External Revenues	5,349,000		5,804,200
Income (Loss)	25,300		(4,200)
Refining and Marketing | United States
Segment Reporting Disclosure [Line Items]
Total Assets	1,776,300
External Revenues	4,019,500		4,264,200
Income (Loss)	29,400		(7,200)
Refining and Marketing | United Kingdom
Segment Reporting Disclosure [Line Items]
Total Assets	1,091,500
External Revenues	1,329,500		1,540,000
Income (Loss)	(4,100)		3,000
Total Operating Segments
Segment Reporting Disclosure [Line Items]
Total Assets	16,063,600
External Revenues	6,648,000		6,953,900
Income (Loss)	257,200		308,800
Corporate
Segment Reporting Disclosure [Line Items]
Total Assets	1,634,300
External Revenues	(8,000)		3,000
Income (Loss)	(49,200)		(27,300)
Continuing Operations
Segment Reporting Disclosure [Line Items]
Total Assets	17,697,900
External Revenues	6,640,000		6,956,900
Income (Loss)	208,000		281,500
Discontinued Operations
Segment Reporting Disclosure [Line Items]
Total Assets	53,800
External Revenues	0		0
Income (Loss)	$ 152,600		$ 8,600

[1] Reclassified to conform to current presentation.

[2] Additional details about results of oil and gas operations are presented in the tables on page 21.