Earnings per Share (details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings per Share disclosure
Net income	$ 896	$ 806
Participating share-based awards - allocated income	(6)	(6)
Net income available to common shareholders -- basic	890	800
Net income available to common shareholders -- diluted	$ 890	$ 800
Weighted average shares outstanding, basic	377.7	392.0
Weighted average effects of dilutive securities, stock options and performance shares (in shares)	4.2	3.8
Weighted average shares outstanding, diluted	381.9	395.8
Net income per common share, basic	$ 2.36	$ 2.04
Net income per common share, diluted	$ 2.33	$ 2.02