Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income		$ 575	$ 452	$ 1,139	$ 864
Preferred stock dividends and other	[1]	(45)	(46)	(84)	(66)
Net Income Available to Common Stockholders		$ 530	$ 406	$ 1,055	$ 798
Weighted-average common shares outstanding — basic (shares)		1,338	1,322	1,337	1,322
Common stock equivalent shares related to stock incentive plans (shares)		13	11	14	9
Weighted-average common shares outstanding — diluted (shares)	[2]	1,351	1,333	1,351	1,331
Basic EPS (USD per share)		$ 0.40	$ 0.31	$ 0.79	$ 0.60
Diluted EPS (USD per share)		$ 0.39	$ 0.30	$ 0.78	$ 0.60
Antidilutive stock options and restricted stock awards excluded from the calculation of diluted EPS (in shares)		9	19	10	22

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

[2] Antidilutive stock options and restricted stock awards excluded from the calculation of diluted EPS totaled 9 million and 19 million shares for the second quarters of 2017 and 2016, respectively, and 10 million and 22 million shares for the first halves of 2017 and 2016, respectively.