Properties and Equipment - Additional Information (Detail) (USD $)	9 Months Ended				3 Months Ended	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011 Oil and Gas Exploration and Production Reporting Segment [Member] Fair Value, Inputs, Level 3 [Member]	Sep. 30, 2011 Midstream Reporting Segment [Member] Fair Value, Inputs, Level 3 [Member]	Sep. 30, 2012 Assets Held For Sale [Member] Oil and Gas Exploration and Production Reporting Segment [Member]	Sep. 30, 2012 Assets Held For Sale [Member] Oil and Gas Exploration and Production Reporting Segment [Member]
Property, Plant, and Equipment [Abstract]
Suspended exploratory well costs	$ 1,900,000,000	$ 1,400,000,000
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year [Abstract]
Exploratory well costs previously capitalized as suspended exploratory well costs for greater than one year as of December 31, 2011, charged to dry hole expense	41,000,000
Property, Plant, and Equipment [Line Items]
Losses on assets held for sale					5,000,000	35,000,000
Losses on assets held for sale			268,000,000	31,000,000
Remaining balance of assets associated with assets held for sale
Remaining balance of liabilities associated with assets held for sale