Earnings per Share (details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings per Share disclosure
Net income	$ 864	$ 333	$ 2,169	$ 808
Participating share-based awards - allocated income	(6)	(2)	(17)	(6)
Preferred stock dividends				(1)
Net income available to common shareholders -- basic	858	331	2,152	801
Effect of dilutive securities, convertible preferred stock				1
Net income available to common shareholders -- diluted	$ 858	$ 331	$ 2,152	$ 802
Weighted average shares outstanding, basic	384.0	415.0	388.0	420.4
Weighted average effects of dilutive securities, stock options and performance shares (in shares)	3.9	3.5	3.5	4.3
Weighted average effects of dilutive securities, convertible preferred stock (in shares)				0.9
Weighted average shares outstanding, diluted	387.9	418.5	391.5	425.6
Net income per common share, basic	$ 2.23	$ 0.80	$ 5.55	$ 1.90
Net income per common share, diluted	$ 2.21	$ 0.79	$ 5.50	$ 1.88