Stockholders' Equity (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net income (loss)
Net income (loss) attributable to common stockholders	$ (2,235)	$ 1,087	$ (5,442)	$ (1,355)
Less noncontrolling interest effect of TEUs	75	60	154	142
Less distributions on participating securities	1	2	4	3
Less undistributed income allocated to participating securities	0	6	0	0
Basic	(2,239)	1,079	(5,449)	(1,358)
Diluted	$ (2,239)	$ 1,079	$ (5,449)	$ (1,358)
Shares
Average number of common shares outstanding—basic	508	506	508	505
Dilutive effect of stock options	0	2	0	0
Average number of common shares outstanding—diluted	508	508	508	505
Excluded due to anti-dilutive effect	10	3	11	11
Net income (loss) per common share
Basic	$ (4.41)	$ 2.13	$ (10.73)	$ (2.69)
Diluted	$ (4.41)	$ 2.12	$ (10.73)	$ (2.69)
7.50% Tangible Equity Units [Member] | Minimum Settlement Rate Effect On Noncontrolling Interest [Member]
Net income (loss)
Less noncontrolling interest effect of TEUs	$ 3	$ 0	$ 3	$ 0