Property, Plant and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Cost	$ 21,150,193		$ 17,336,643
Property, plant and equipment, Net	13,011,606		10,475,149
Exploration and Production Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Cost	18,408,904	[1]	14,766,637	[1]
Property, plant and equipment, Net	11,294,933	[1],[2]	8,730,124	[1],[2]
Refining and Marketing
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Cost	2,619,844		2,456,822
Property, plant and equipment, Net	1,661,081		1,688,709
Corporate and Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Cost	121,445		113,184
Property, plant and equipment, Net	$ 55,592		$ 56,316

[1] Includes mineral rights as follows: $ 1,051,153 556,399 1,078,770 619,950

[2] Includes $26,611 in 2012 and $21,154 in 2011 related to administrative assets and support equipment.