Summary of Significant Accounting Policies (Details 5) (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
Numerator:
Net income									$ 2,850	$ 2,280	$ 2,306
Less: Preferred stock dividends									104	17
Net income available to common shareholders	$ 795	$ 750	$ 614	$ 587	$ 810	$ 310	$ 434	$ 709	$ 2,746	$ 2,263	$ 2,306
Denominator:
Weighted average common shares outstanding									431.4	464.4	489.4
Effect of dilutive potential common shares:
Stock options (in shares)									4.7	4.1	2.4
Restricted stock units(non-participating) and performance stock awards (in shares)									2.1	1.8	1.2
Weighted average common and dilutive potential common shares outstanding									438.2	470.3	493.0
Earnings per common share - Basic (in dollars per share)	$ 1.89	$ 1.77	$ 1.41	$ 1.31	$ 1.79	$ 0.67	$ 0.93	$ 1.49	$ 6.37	$ 4.87	$ 4.71
Earnings per common share - Diluted (in dollars per share)	$ 1.86	$ 1.74	$ 1.39	$ 1.30	$ 1.76	$ 0.66	$ 0.92	$ 1.47	$ 6.27	$ 4.81	$ 4.68
Other Earnings Per Share Disclosures
Antidilutive stock options, exercise price exceeds market price (in shares)									3.0	8.8	20.4
Antidilutive stock options, exercise price exceeds market price, exercise price range, low end of range (in dollars per share)									$ 49.96	$ 40.49	$ 26.56
Antidilutive stock options, exercise price exceeds market price, exercise price range, high end of range (in dollars per share)									$ 67.61	$ 62.42	$ 62.84