Stockholders' Equity - Earnings Per Share Reconciliation (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net income (loss)
Net income (loss) attributable to common stockholders	$ (699)	$ (830)	$ (1,432)	$ (2,556)
Income (loss) effect of TEUs	(2)	(2)	(6)	(5)
Less distributions on participating securities	0	1	0	1
Basic	(701)	(833)	(1,438)	(2,562)
Net Income Loss Effect Of Tangible Equity Units Diluted	0	0	(1)	(1)
Diluted	$ (701)	$ (833)	$ (1,439)	$ (2,563)
Shares
Average number of common shares outstanding—basic	553	517	552	512
Average number of common shares outstanding—diluted	553	517	552	512
Excluded due to anti-dilutive effect	11	11	11	11
Net income (loss) per common share
Basic (in usd per share)	$ (1.27)	$ (1.61)	$ (2.60)	$ (5.00)
Diluted (in usd per share)	$ (1.27)	$ (1.61)	$ (2.61)	$ (5.00)