Earnings per Common Share - Computation earnings per common share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Numerator:
Net income	$ 549	$ 1,292
Less: Preferred stock dividends	36	31
Net income applicable to common shareholders	$ 513	$ 1,261
Denominator:
Weighted average common shares outstanding (in shares)	317.4	332.6
Effect of dilutive potential common shares:
Stock options (in shares)	3.3	3.1
Restricted stock units (non-participating) and performance stock awards (in shares)	1.7	1.8
Weighted average common and dilutive potential common shares outstanding (in shares)	322.4	337.5
Earnings per common share - Basic (in dollars per share)	$ 1.62	$ 3.79
Earnings per common share - Diluted (in dollars per share)	$ 1.59	$ 3.74
Anti-dilutive options excluded from diluted earnings per common share (in shares)	0.8	4.0