Stockholders' Equity - Reconciliation between Basic and Diluted EPS Table (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income (loss)
Net income (loss) attributable to common stockholders	$ (456)	$ (3,071)	$ (6,692)
Income (loss) effect of TEUs	(7)	(6)	0
Less distributions on participating securities	1	1	3
Basic	(464)	(3,078)	(6,695)
Income (loss) effect of TEUs	(2)	(1)	0
Diluted	$ (466)	$ (3,079)	$ (6,695)
Shares
Average number of common shares outstanding—basic	548	522	508
Average number of common shares outstanding—diluted	548	522	508
Excluded due to anti-dilutive effect	11	11	11
Net income (loss) per common share
Basic (in usd per share)	$ (0.85)	$ (5.90)	$ (13.18)
Diluted (in usd per share)	$ (0.85)	$ (5.90)	$ (13.18)