Summary of Significant Accounting Policies (Details 5) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net income									$ 1,877	$ 2,171	$ 2,850
Less: Preferred stock dividends									116	116	104
Net income applicable to common shareholders	$ 811	$ 491	$ 242	$ 217	$ 460	$ 621	$ 326	$ 648	$ 1,761	$ 2,055	$ 2,746
Denominator:
Weighted average common shares outstanding									372.8	401.1	431.4
Effect of dilutive potential common shares:
Stock options (in shares)									3.2	4.0	4.7
Restricted stock units(non-participating) and performance stock awards (in shares)									1.3	1.7	2.1
Weighted average common and dilutive potential common shares outstanding									377.3	406.8	438.2
Earnings per common share - Basic (in dollars per share)	$ 2.20	$ 1.32	$ 0.65	$ 0.57	$ 1.19	$ 1.56	$ 0.80	$ 1.56	$ 4.72	$ 5.12	$ 6.37
Earnings per common share - Diluted (in dollars per share)	$ 2.18	$ 1.31	$ 0.64	$ 0.57	$ 1.18	$ 1.54	$ 0.79	$ 1.53	$ 4.67	$ 5.05	$ 6.27
Other Earnings Per Share Disclosures
Antidilutive stock options, exercise price exceeds market price (in shares)									3.8	2.2	3.0
Antidilutive stock options, exercise price exceeds market price, exercise price range, low end of range (in dollars per share)									$ 53.91	$ 57.98	$ 49.96
Antidilutive stock options, exercise price exceeds market price, exercise price range, high end of range (in dollars per share)									$ 71.29	$ 71.29	$ 67.61