Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income		$ 923	$ 618	$ 2,572	$ 1,757	[1]
Preferred stock dividends and other	[2]	(38)	(43)	(128)	(127)
Net Income Available to Common Stockholders		$ 885	$ 575	$ 2,444	$ 1,630
Weighted-average common shares outstanding — basic (shares)		1,351	1,339	1,349	1,338
Common stock equivalent shares related to stock incentive plans (shares)		13	14	14	14
Weighted-average common shares outstanding — diluted (shares)	[3]	1,364	1,353	1,363	1,352
Basic EPS (USD per share)		$ 0.66	$ 0.43	$ 1.81	$ 1.22
Diluted EPS (USD per share)		$ 0.65	$ 0.42	$ 1.79	$ 1.21
Antidilutive stock options and restricted stock awards excluded from the calculation of diluted EPS (in shares)		11	9	12	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 9 million shares for the third quarters of 2018 and 2017, respectively, and 12 million and 10 million shares for the first nine months of 2018 and 2017, respectively.