Earnings per Share (details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings per Share disclosure
Net income	$ 812	$ 683	$ 1,645	$ 1,735
Participating share-based awards - allocated income	(6)	(5)	(12)	(12)
Net income available to common shareholders -- basic	806	678	1,633	1,723
Net income available to common shareholders -- diluted	$ 806	$ 678	$ 1,633	$ 1,723
Weighted average shares outstanding, basic	314.8	343.0	317.7	346.9
Weighted average effects of dilutive securities, stock options and performance shares (in shares)	3.2	3.7	3.5	3.6
Weighted average shares outstanding, diluted	318.0	346.7	321.2	350.5
Net income per common share, basic	$ 2.56	$ 1.98	$ 5.14	$ 4.97
Net income per common share, diluted	$ 2.53	$ 1.95	$ 5.08	$ 4.91