Earnings Per Common Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings per common share
Net income	$ 4,010	$ 7,311
Preferred stock dividends	(469)	(442)
Net income applicable to common shareholders	$ 3,541	$ 6,869
Average common shares issued and outstanding (in shares)	8,815.6	9,725.9
Earnings per common share (in dollars per share)	$ 0.40	$ 0.71
Diluted earnings per common share
Net income applicable to common shareholders	$ 3,541	$ 6,869
Average common shares issued and outstanding (in shares)	8,815.6	9,725.9
Dilutive potential common shares (in shares)	47.1	61.4
Total diluted average common shares issued and outstanding (in shares)	8,862.7	9,787.3
Diluted earnings per common share (in dollars per share)	$ 0.40	$ 0.70