Stockholders' Equity (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net income (loss)
Net income (loss) attributable to common stockholders	$ 61	$ 227	$ (3,207)	$ (2,442)
Less distributions on participating securities	1	1	2	1
Basic	60	226	(3,209)	(2,443)
Diluted	$ 60	$ 226	$ (3,209)	$ (2,443)
Shares
Average number of common shares outstanding—basic	508	505	507	505
Dilutive effect of stock options	1	2	0	0
Average number of common shares outstanding—diluted	509	507	507	505
Excluded due to anti-dilutive effect	6	4	11	11
Net income (loss) per common share
Basic	$ 0.12	$ 0.45	$ (6.32)	$ (4.84)
Diluted	$ 0.12	$ 0.45	$ (6.32)	$ (4.84)