Consolidated Statement of Changes In Shareholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Preferred Stock	Common Stock	Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2016	$ 21,219	$ 3,196	$ 504	$ 9,782	$ 17,459	$ (2,040)	$ (7,682)
Beginning balance (shares) at Dec. 31, 2016			503,880				121,941
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,807				1,807
Other comprehensive income (loss)	1,056					1,056
Cash dividends declared:
Common stock dividends	(442)				(442)
Preferred stock cash dividend	(146)				(146)
Common stock acquired	(1,100)						$ (1,100)
Common stock acquired (shares)							13,131
Common stock awards vested	106			21			$ 85
Common stock awards vested (shares)							(2,033)
Other	(3)				(3)
Ending balance at Sep. 30, 2017	22,497	3,196	$ 504	9,803	18,675	(984)	$ (8,697)
Ending balance (shares) at Sep. 30, 2017			503,880				133,039
Beginning balance at Dec. 31, 2017	22,317	3,196	$ 504	9,799	18,856	(1,009)	$ (9,029)
Beginning balance (shares) at Dec. 31, 2017			503,880				136,230
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,160				2,160
Other comprehensive income (loss)	(702)					(702)
Preferred stock issued	494	494
Common stock issued	1,150			586			$ 564
Common stock issued (shares)							(13,244)
Cash dividends declared:
Common stock dividends	(486)				(486)
Preferred stock cash dividend	(146)				146
Common stock acquired	(350)						$ (350)
Common stock acquired (shares)							3,324
Common stock awards vested	114			33			$ 81
Common stock awards vested (shares)							(1,931)
Other	2				3		$ (1)
Other (shares)							11
Ending balance at Sep. 30, 2018	$ 24,553	$ 3,690	$ 504	$ 10,418	$ 20,387	$ (1,711)	$ (8,735)
Ending balance (shares) at Sep. 30, 2018			503,880				124,390