Earnings per Share (details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings per Share disclosure
Net income	$ 925	$ 499	$ 1,821	$ 1,305
Participating share-based awards - allocated income	(7)	(4)	(14)	(10)
Net income available to common shareholders -- basic	918	495	1,807	1,295
Net income available to common shareholders -- diluted	$ 918	$ 495	$ 1,807	$ 1,295
Weighted average shares outstanding, basic	375.9	388.0	376.8	390.0
Weighted average effects of dilutive securities, stock options and performance shares (in shares)	4.0	3.6	4.0	3.5
Weighted average shares outstanding, diluted	379.9	391.6	380.8	393.5
Net income per common share, basic	$ 2.44	$ 1.27	$ 4.80	$ 3.32
Net income per common share, diluted	$ 2.41	$ 1.26	$ 4.75	$ 3.29