Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income		$ 783	$ 564	[1]
Preferred stock dividends and other	[2]	(37)	(39)
Net Income Available to Common Stockholders		$ 746	$ 525
Weighted-average common shares outstanding — basic (shares)		1,347	1,336
Common stock equivalent shares related to stock incentive plans (shares)		15	15
Weighted-average common shares outstanding — diluted (shares)	[3]	1,362	1,351
Basic EPS (USD per share)		$ 0.55	$ 0.39
Diluted EPS (USD per share)		$ 0.55	$ 0.39
Antidilutive stock options and restricted stock awards excluded from the calculation of diluted EPS (in shares)		11	10

[1] Adjusted for the retrospective adoption of ASU 2016-18. See Note 2.

[2] Includes preferred stock dividends and undistributed earnings and dividends allocated to non-vested restricted stock units.

[3] Antidilutive stock options and restricted stock units excluded from the calculation of diluted EPS totaled 11 million and 10 million shares for the first quarters of 2018 and 2017, respectively.