Impairments - Impairments Table (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Impaired Long Lived Assets Held and Used [Line Items]
Impairments	$ 389	$ 1,774	$ 216
Oil and Gas Exploration and Production Reporting Segment [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Cost-method investment	13	91	61
Oil and Gas Exploration and Production Reporting Segment [Member] | Onshore Domestic [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Long-lived assets held for use	259	1,063	31
Oil and Gas Exploration and Production Reporting Segment [Member] | Gulf Of Mexico [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Long-lived assets held for use	104	162	114
Midstream Reporting Segment [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Long-lived assets held for use	13	458	2
Marketing Reporting Segment [Member]
Impaired Long Lived Assets Held and Used [Line Items]
Long-lived assets held for use			$ 8