Impairments - Impairments by Segment Table (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Impaired Long Lived Assets Held and Used [Line Items]
Total impairments	$ 394	$ 593	$ 514	$ 632
Oil and Gas Exploration and Production Reporting Segment [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Cost-method investment	0	0	2	10
Oil and Gas Exploration and Production Reporting Segment [Member] | U.S. Onshore Properties [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Long-lived assets held for use	387	0	387	0
Oil and Gas Exploration and Production Reporting Segment [Member] | Gulf of Mexico Properties [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Long-lived assets held for use	0	593	115	593
Midstream Reporting Segment [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Long-lived assets held for use	$ 7	$ 0	$ 10	$ 29