Earnings per Share (details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings per Share disclosure
Net income	$ 1,038	$ 919	$ 683	$ 1,052	$ 988	$ 864	$ 925	$ 896	$ 3,692	$ 3,673	$ 2,473
Participating share-based awards - allocated income									(27)	(27)	(19)
Net income available to common shareholders -- basic									3,665	3,646	2,454
Net income available to common shareholders -- diluted									$ 3,665	$ 3,646	$ 2,454
Weighted average shares outstanding, basic									338.8	370.3	386.2
Weighted average effects of dilutive securities, stock options and performance shares (in shares)									3.7	4.0	3.6
Weighted average shares outstanding, diluted									342.5	374.3	389.8
Net income per common share, basic	$ 3.15	$ 2.72	$ 1.98	$ 2.98	$ 2.73	$ 2.33	$ 2.44	$ 2.36	$ 10.82	$ 9.84	$ 6.35
Net income per common share, diluted	$ 3.11	$ 2.69	$ 1.95	$ 2.95	$ 2.70	$ 2.30	$ 2.41	$ 2.33	$ 10.70	$ 9.74	$ 6.30