Acquisitions and Divestitures - Summary of Sales and Other Operating Revenue and Loss From Discontinued Operation Related to Disposition - Australia Divestitures (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Jun. 30, 2015	Sep. 30, 2016	Sep. 30, 2015		Sep. 30, 2016	Sep. 30, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments		$ (836)	$ (3,903)	[1]	$ (1,009)	$ (6,327)	[1],[2]
Loss from Australian discontinued operations, net of tax		(33)	(17)	[1]	(33)	(135)	[1]
Australia [Member] | Divestiture [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues and other from discontinued operations						288
Income from divested Australian operations						28
Income tax benefit (expense)			(17)			25
Loss from Australian discontinued operations, net of tax		(23)	$ (17)		(23)	(135)
Woodside Sale [Member] | Australia [Member] | Divestiture [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairments						(49)
Gain (loss) on disposal		$ (23)			$ (23)
Consortium Sale [Member] | Australia [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposal	$ (139)
Consortium Sale [Member] | Australia [Member] | Divestiture [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposal						$ (139)

[1] Financial information for 2015 has been recast to reflect retrospective application of the successful efforts method of accounting. See Note 1.

[2] Financial information for 2015 has been recast to reflect retrospective application of the successful efforts method of accounting. See Note 1.