Earnings per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Numerator:
Net income	$ 677	$ 600
Less: Preferred stock dividends	29	13
Net income available to common shareholders	$ 648	$ 587
Denominator:
Weighted average common shares outstanding	415.8	446.4
Effect of dilutive potential common shares:
Stock options (in shares)	4.9	4.4
Restricted stock units(non-participating) and performance stock awards (in shares)	1.9	2.0
Weighted average common and dilutive potential common shares outstanding	422.6	452.8
Earnings per common share - Basic (in dollars per share)	$ 1.56	$ 1.31
Earnings per common share - Diluted (in dollars per share)	$ 1.53	$ 1.30
Other Earnings Per Share Disclosures
Antidilutive stock options, exercise price exceeds market price (in shares)	2.1	6.7
Antidilutive stock options, exercise price exceeds market price, exercise price range, low end of range (in dollars per share)	$ 60.81	$ 45.61
Antidilutive stock options, exercise price exceeds market price, exercise price range, high end of range (in dollars per share)	$ 70.91	$ 62.42