Segment Information - Identifiable Assets by Operating Segment (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Assets	$ 41,896	$ 43,441
Continuing operations [Member]
Segment Reporting Information [Line Items]
Assets	37,766	38,500
Continuing operations [Member] | Exploration and Production [Member]
Segment Reporting Information [Line Items]
Assets	37,059	37,687
Continuing operations [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Assets	707	813
Discontinued operations-Downstream businesses [Member]
Segment Reporting Information [Line Items]
Assets	$ 4,130	$ 4,941