Earnings Per Common Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings per common share
Net income	$ 6,918	$ 5,337
Preferred stock dividends	(428)	(502)
Net income applicable to common shareholders	$ 6,490	$ 4,835
Average common shares issued and outstanding (in shares)	10,322.4	10,099.6
Earnings per common share (in dollars per share)	$ 0.63	$ 0.48
Diluted earnings per common share
Net income applicable to common shareholders	$ 6,490	$ 4,835
Add preferred stock dividends due to assumed conversions	0	75
Net income allocated to common shareholders	$ 6,490	$ 4,910
Average common shares issued and outstanding (in shares)	10,322.4	10,099.6
Dilutive potential common shares (in shares)	150.3	820.1
Total diluted average common shares issued and outstanding (in shares)	10,472.7	10,919.7
Diluted earnings per common share (in dollars per share)	$ 0.62	$ 0.45