Acquisitions and Divestitures - Summary of Sales and Other Operating Revenue and Loss From Discontinued Operation Related to Disposition (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss from divestiture									$ (1,300,000,000)		$ 0
Income (loss) from discontinued operations, net of tax	$ 188,000,000	$ (95,000,000)	$ (732,000,000)	$ (132,000,000)	$ (1,072,000,000)	$ (156,000,000)	$ 56,000,000	$ (416,000,000)	$ (771,000,000)	$ (1,588,000,000)	308,000,000
Argentina [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss from divestiture										(539,000,000)
Argentina [Member] | Divestiture [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues and other from discontinued operations										87,000,000	494,000,000
Loss from divestiture										(539,000,000)
Income (loss) from operations in Argentina										(1,000,000)	(192,000,000)
Income tax benefit (expense)										23,000,000
Income (loss) from discontinued operations, net of tax										$ (517,000,000)	$ (192,000,000)