Earnings per Common 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
Numerator:
Net income	$ 355	$ 645	$ 1,032	$ 1,245
Less: Preferred stock dividends	29	31	58	44
Net income available to common shareholders	$ 326	$ 614	$ 974	$ 1,201
Denominator:
Weighted average common shares outstanding	407.0	434.3	411.4	440.4
Effect of dilutive potential common shares:
Stock options (in shares)	4.2	4.8	4.5	4.6
Restricted stock units(non-participating) and performance stock awards (in shares)	1.4	1.6	1.7	1.8
Weighted average common and dilutive potential common shares outstanding	412.6	440.7	417.6	446.8
Earnings per common share - Basic (in dollars per share)	$ 0.80	$ 1.41	$ 2.37	$ 2.73
Earnings per common share - Diluted (in dollars per share)	$ 0.79	$ 1.39	$ 2.33	$ 2.69
Other Earnings Per Share Disclosures
Antidilutive stock options, exercise price exceeds market price (in shares)	2.2	4.5	2.2	4.6
Antidilutive stock options, exercise price exceeds market price, exercise price range, low end of range (in dollars per share)	$ 60.81	$ 48.46	$ 60.81	$ 45.61
Antidilutive stock options, exercise price exceeds market price, exercise price range, high end of range (in dollars per share)	$ 71.29	$ 62.42	$ 71.29	$ 62.42