Earnings per Share (details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Earnings per Share disclosure
Net income	$ 806	$ 839
Participating share-based awards - allocated income	(6)	(7)
Preferred stock dividends		(1)
Net income available to common shareholders -- basic	800	831
Effect of dilutive securities, convertible preferred stock		1
Net income available to common shareholders -- diluted	$ 800	$ 832
Weighted average shares outstanding, basic	392.0	428.2
Weighted average effects of dilutive securities, stock options and performance shares (in shares)	3.8	4.6
Weighted average effects of dilutive securities, convertible preferred stock (in shares)		1.6
Weighted average shares outstanding, diluted	395.8	434.4
Net income per common share, basic	$ 2.04	$ 1.94
Net income per common share, diluted	$ 2.02	$ 1.92