Acquisitions and Divestitures - Additional Information - 2014 Activity - Anadarko Basin and Southern Louisiana Divestitures (Detail) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2014 USD ($) a	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) a	Dec. 31, 2013 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of oil and gas assets	$ 1,200	$ 268	$ 470	$ 307
Loss on disposal of assets, before tax	(180)
Loss on disposal of assets, net of tax	(116)
GTP Facilities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of oil and gas assets	72
Anadarko Basin and Southern Louisiana [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 | a	115,000		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 | a	90,000		90,000