Stockholders' Equity - Reconciliation between Basic and Diluted EPS Table (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Net income (loss)
Net income (loss) attributable to common stockholders	$ 2,391		$ (2,649)		$ 761
Less distributions on participating securities	1				1
Less undistributed income allocated to participating securities	14				4
Basic	2,376		(2,649)		756
Diluted	$ 2,376		$ (2,649)		$ 756
Shares
Average number of common shares outstanding - basic	500		498		495
Dilutive effect of stock options and performance-based stock awards	2				2
Average number of common shares outstanding - diluted	502		498		497
Excluded	6	[1]	12	[1]	6	[1]
Net income (loss) per common share
Basic	$ 4.76		$ (5.32)		$ 1.53
Diluted	$ 4.74		$ (5.32)		$ 1.52
Dividends per common share	$ 0.36		$ 0.36		$ 0.36

[1] Inclusion of certain shares would have had an anti-dilutive effect.