Earnings per Share (details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings per Share disclosure
Net income (loss)	$ 499	$ (364)	$ 1,305	$ 475
Participating share-based awards - allocated income	(4)	(2)	(10)	(4)
Preferred stock dividends				(1)
Net income (loss) available to common shareholders -- basic	495	(366)	1,295	470
Effect of dilutive securities, convertible preferred stock				1
Net income (loss) available to common shareholders -- diluted	495	(366)	1,295	471
Weighted average shares outstanding, basic	388.0	418.6	390.0	423.3
Weighted average effects of dilutive securities, stock options and performance shares (in shares)	3.6		3.5	4.4
Weighted average effects of dilutive securities, convertible preferred stock (in shares)				1.4
Weighted average shares outstanding, diluted	391.6	418.6	393.5	429.1
Net income (loss) per common share, basic	$ 1.27	$ (0.88)	$ 3.32	$ 1.11
Net income (loss) per common share, diluted	$ 1.26	$ (0.88)	$ 3.29	$ 1.10
Amount of allocation of undistributed loss excluded from earnings per share		$ 4.6
Number of stock options and performance shares excluded from the calculation of net loss per share on a diluted basis (in shares)		4.6
Number of shares of convertible preferred stock excluded from the calculation of net loss per share on a diluted basis (converted into common shares)		1.2