Earnings per 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
Earnings Per Share, Basic, Two Class Method [Abstract]
Net income	$ 6,290	$ 5,980	$ 12,204	$ 11,249
Less: Preferred stock dividends	380	268	704	495
Net income applicable to common equity	5,910	5,712	11,500	10,754
Less: Dividends and undistributed earnings allocated to participating securities	134	144	272	294
Net income applicable to common stockholders	$ 5,776	$ 5,568	$ 11,228	$ 10,460
Weighted-average basic shares (in shares)	3,707.8	3,780.6	3,716.6	3,783.9
Basic earnings per share (in dollars per share)	$ 1.56	$ 1.47	$ 3.02	$ 2.76
Earnings Per Share, Diluted, Two Class Method [Abstract]
Net income applicable to common stockholders	$ 5,776	$ 5,568	$ 11,228	$ 10,460
Weighted-average basic shares (in shares)	3,707.8	3,780.6	3,716.6	3,783.9
Add: Employee stock options, SARs and warrants (in shares)	35.8	31.9	33.9	34.2
Total weighted-average diluted shares (in shares)	3,743.6	3,812.5	3,750.5	3,818.1
Diluted earnings per share (in dollars per share)	$ 1.54	$ 1.46	$ 2.99	$ 2.74
Earnings Per Share, Diluted, Other Disclosures [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)		1.0		1.0