Properties and Equipment (Detail) (USD $)	Dec. 31, 2012		Dec. 31, 2011
Property, Plant, and Equipment [Line Items]
Cost of properties and equipment	$ 63,598,000,000		$ 60,081,000,000
Oil and Gas Exploration and Production Reporting Segment [Member]
Property, Plant, and Equipment [Line Items]
Cost of properties and equipment	55,095,000,000	[1]	52,711,000,000	[1]
Table Text Block Supplement [Abstract]
Costs associated with unproved properties	7,100,000,000		8,300,000,000
Midstream Reporting Segment [Member]
Property, Plant, and Equipment [Line Items]
Cost of properties and equipment	6,032,000,000		4,837,000,000
Marketing Reporting Segment [Member]
Property, Plant, and Equipment [Line Items]
Cost of properties and equipment	94,000,000		9,000,000
Other and Intersegment Eliminations [Member]
Property, Plant, and Equipment [Line Items]
Cost of properties and equipment	$ 2,377,000,000		$ 2,524,000,000

[1] Includes costs associated with unproved properties of $7.1 billion at December 31, 2012, and $8.3 billion at December 31, 2011.