Stockholders' Equity - Earnings Per Share Reconciliation (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net income (loss)
Net income (loss) attributable to common stockholders	$ 121	$ (318)
Income (loss) effect of TEUs	(3)	(2)
Less distributions on participating securities	1	0
Basic	117	(320)
Net Income Loss Effect Of Tangible Equity Units Diluted	(1)	0
Diluted	$ 116	$ (320)
Shares
Average number of common shares outstanding—basic	518	551
Dilutive effect of stock options	1	0
Average number of common shares outstanding—diluted	519	551
Excluded due to anti-dilutive effect	10	11
Net income (loss) per common share
Basic (in usd per share)	$ 0.23	$ (0.58)
Diluted (in usd per share)	$ 0.22	$ (0.58)