Stockholders' Equity (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Net income (loss)
Net income (loss) attributable to common stockholders	$ (1,034)	$ (3,268)
Income (loss) effect of TEUs	36	32
Less distributions on participating securities	0	1
Basic	(1,035)	(3,269)
Diluted	$ (1,035)	$ (3,269)
Shares
Average number of common shares outstanding—basic	509	507
Average number of common shares outstanding—diluted	509	507
Excluded due to anti-dilutive effect	10	11
Net income (loss) per common share
Basic	$ (2.03)	$ (6.45)
Diluted	$ (2.03)	$ (6.45)
7.50% Tangible Equity Units [Member] | Minimum Settlement Rate Effect On Noncontrolling Interest [Member]
Net income (loss)
Income (loss) effect of TEUs	$ (1)	$ 0