Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net income	$ 695	$ 246
Less: Preferred stock dividends	29	29
Net income applicable to common shareholders	$ 666	$ 217
Denominator:
Weighted average common shares outstanding	365.7	378.1
Effect of dilutive potential common shares:
Stock options (in shares)	4.2	3.4
Restricted stock units(non-participating) and performance stock awards (in shares)	1.4	1.4
Weighted average common and dilutive potential common shares outstanding (in shares)	371.3	382.9
Earnings per common share - Basic (in dollars per share)	$ 1.82	$ 0.57
Earnings per common share - Diluted (in dollars per share)	$ 1.79	$ 0.57
Other Earnings Per Share Disclosures
Antidilutive stock options, exercise price exceeds market price (in shares)	2.8	5.0
Antidilutive stock options, exercise price exceeds market price, exercise price range, low end of range (in dollars per share)	$ 67.81	$ 52.18
Antidilutive stock options, exercise price exceeds market price, exercise price range, high end of range (in dollars per share)	$ 81.86	$ 71.29