Income Taxes - Income (Loss) From Continuing Operations Before Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income (Loss) From Continuing Operations Before Income Taxes - United States	$ (2,784)	$ (2,431)	$ (2,728)
Income (Loss) From Continuing Operations Before Income Taxes - Foreign	(2,994)	(1,423)	(1,530)
Income (Loss) from Continuing Operations Before Income Taxes	$ (5,778)	$ (3,854)	$ (4,258)