Earnings per Share (details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings per Share disclosure
Net income	$ 864	$ 864	$ 2,685	$ 2,169
Participating share-based awards - allocated income	(6)	(6)	(20)	(17)
Net income available to common shareholders -- basic	858	858	2,665	2,152
Net income available to common shareholders -- diluted	$ 858	$ 858	$ 2,665	$ 2,152
Weighted average shares outstanding, basic	368.9	384.0	374.1	388.0
Weighted average effects of dilutive securities, stock options and performance shares (in shares)	4.0	3.9	4.0	3.5
Weighted average shares outstanding, diluted	372.9	387.9	378.1	391.5
Net income per common share, basic	$ 2.33	$ 2.23	$ 7.12	$ 5.55
Net income per common share, diluted	$ 2.30	$ 2.21	$ 7.05	$ 5.50