Income Taxes - Summary of Valuation Allowance Against Certain Foreign Net Deferred Tax Assets and State Net Operating Losses (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 5,434	$ 1,564	$ 598
State	(43)	151	62
U.S.	139	2,159	0
Foreign	129	(1,560)	(1,021)
Discontinued operations	0	0	(117)
Balance at end of year	$ 5,401	$ 5,434	$ 1,564