Stockholders' Equity - Reconciliation between Basic and Diluted EPS Table (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net income (loss)
Net income (loss) attributable to common stockholders	$ (6,692)	$ (1,750)	$ 801
Less distributions on participating securities	3	4	2
Less undistributed income allocated to participating securities	0	0	4
Basic	(6,695)	(1,754)	795
Diluted	$ (6,695)	$ (1,754)	$ 795
Shares
Average number of common shares outstanding—basic	508	506	502
Dilutive effect of stock options	0	0	3
Average number of common shares outstanding—diluted	508	506	505
Excluded (1)	11	11	4
Net income (loss) per common share
Basic	$ (13.18)	$ (3.47)	$ 1.58
Diluted	$ (13.18)	$ (3.47)	$ 1.58