Earnings per Share (details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings per Share disclosure
Net income	$ 928	$ 919	$ 2,573	$ 2,654
Participating share-based awards - allocated income	(6)	(7)	(18)	(19)
Net income available to common shareholders -- basic	922	912	2,555	2,635
Net income available to common shareholders -- diluted	$ 922	$ 912	$ 2,555	$ 2,635
Weighted average shares outstanding, basic	307.6	335.1	314.3	342.9
Weighted average effects of dilutive securities, stock options and performance shares (in shares)	3.4	3.8	3.4	3.6
Weighted average shares outstanding, diluted	311.0	338.9	317.7	346.5
Net income per common share, basic	$ 3.00	$ 2.72	$ 8.13	$ 7.68
Net income per common share, diluted	$ 2.97	$ 2.69	$ 8.04	$ 7.60