Earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basic earnings per share
Net income	$ 6,804	$ 5,565	$ 19,008	$ 16,814
Less: Preferred stock dividends	393	304	1,097	799
Net income applicable to common equity	6,411	5,261	17,911	16,015
Less: Dividends and undistributed earnings allocated to participating securities	141	133	413	427
Net income applicable to common stockholders	$ 6,270	$ 5,128	$ 17,498	$ 15,588
Total weighted-average basic shares outstanding (in shares)	3,694.4	3,755.4	3,709.2	3,774.4
Net income per share (in dollars per share)	$ 1.70	$ 1.37	$ 4.72	$ 4.13
Diluted earnings per share
Net income applicable to common stockholders	$ 6,270	$ 5,128	$ 17,498	$ 15,588
Total weighted-average basic shares outstanding (in shares)	3,694.4	3,755.4	3,709.2	3,774.4
Add: Employee stock options, SARs and warrants (in shares)	31.2	33.3	33.0	33.9
Total weighted-average diluted shares outstanding (in shares)	3,725.6	3,788.7	3,742.2	3,808.3
Net income per share (in dollars per share)	$ 1.68	$ 1.35	$ 4.68	$ 4.09
Earnings Per Share, Diluted, Other Disclosures [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)		1.0		1.0