Income Taxes - Components of Total Deferred Taxes Table (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets (Liabilities), Net [Line Items]
Total deferred taxes	$ (2,213)	$ (4,310)
Federal [Member]
Deferred Tax Assets (Liabilities), Net [Line Items]
Total deferred taxes	(1,758)	(3,805)
State, net of federal [Member]
Deferred Tax Assets (Liabilities), Net [Line Items]
Total deferred taxes	(200)	(173)
Foreign [Member]
Deferred Tax Assets (Liabilities), Net [Line Items]
Total deferred taxes	$ (255)	$ (332)