Acquisitions and Divestitures - Additional Information - 2014 Activity - Anadarko Basin and Southern Louisiana Divestitures (Detail) $ in Millions	1 Months Ended	6 Months Ended
	Dec. 31, 2014 USD ($) a	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of oil and gas assets | $		$ 119	$ 381
Anadarko Basin and Southern Louisiana Divestitures [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of oil and gas assets | $	$ 1,300
Effective date of sale	Oct. 01, 2014
Anadarko Basin [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Oil and gas properties sold	115,000
Southern Louisiana [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Oil and gas properties sold	90,000