Earnings per Common Share - Computation earnings per common share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net income	$ 1,292	$ 1,006
Less: Preferred stock dividends	31	29
Net income applicable to common shareholders	$ 1,261	$ 977
Denominator:
Weighted average common shares outstanding (in shares)	332.6	354.1
Effect of dilutive potential common shares:
Stock options (in shares)	3.1	4.1
Restricted stock units (non-participating) and performance stock awards (in shares)	1.8	1.7
Weighted average common and dilutive potential common shares outstanding (in shares)	337.5	359.9
Earnings per common share - Basic (in dollars per share)	$ 3.79	$ 2.76
Earnings per common share - Diluted (in dollars per share)	$ 3.74	$ 2.71