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, 2017		$ 22,270	$ 3,196	$ 504	$ 9,799	$ 18,809	$ (1,009)	$ (9,029)
Beginning balance (shares) at Dec. 31, 2017				503,880				136,230
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		659				659
Other comprehensive income		(65)					(65)
Cash dividends declared:
Common stock dividends		(154)				(154)
Preferred stock cash dividend		(55)				(55)
Common stock acquired		(350)						$ (350)
Common stock acquired (shares)								3,324
Common stock awards exercised		42			(3)			$ 45
Common stock awards vested (shares)								(1,075)
Other		3				3
Other (shares)								(7)
Ending balance at Mar. 31, 2018		22,350	3,196	$ 504	9,796	19,262	(1,074)	$ (9,334)
Ending balance (shares) at Mar. 31, 2018				503,880				138,472
Beginning balance at Dec. 31, 2017		22,270	3,196	$ 504	9,799	18,809	(1,009)	$ (9,029)
Beginning balance (shares) at Dec. 31, 2017				503,880				136,230
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		2,156
Other comprehensive income		(702)
Cash dividends declared:
Common stock dividends		(486)
Preferred stock cash dividend		(146)
Ending balance at Sep. 30, 2018		24,502	3,690	$ 504	10,418	20,336	(1,711)	$ (8,735)
Ending balance (shares) at Sep. 30, 2018				503,880				124,390
Beginning balance at Mar. 31, 2018		22,350	3,196	$ 504	9,796	19,262	(1,074)	$ (9,334)
Beginning balance (shares) at Mar. 31, 2018				503,880				138,472
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		733				733
Other comprehensive income		(414)					(414)
Cash dividends declared:
Common stock dividends		(153)				(153)
Preferred stock cash dividend		(36)				(36)
Common stock awards exercised		41			24			$ 17
Common stock awards vested (shares)								(423)
Other		0
Other (shares)								3
Ending balance at Jun. 30, 2018		22,521	3,196	$ 504	9,820	19,806	(1,488)	$ (9,317)
Ending balance (shares) at Jun. 30, 2018				503,880				138,052
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		764				764
Other comprehensive income		(223)					(223)
Preferred stock issued		494	494
Common stock issued		1,150			586			$ 564
Common stock issued (in shares)								(13,244)
Cash dividends declared:
Common stock dividends		(179)				(179)
Preferred stock cash dividend		(55)				(55)
Common stock awards exercised		31			12			$ 19
Common stock awards vested (shares)								(433)
Other		(1)						$ (1)
Other (shares)								15
Ending balance at Sep. 30, 2018		24,502	3,690	$ 504	10,418	20,336	(1,711)	$ (8,735)
Ending balance (shares) at Sep. 30, 2018				503,880				124,390
Beginning balance at Dec. 31, 2018		24,737	3,690	$ 504	10,061	20,553	(1,356)	$ (8,715)
Beginning balance (shares) at Dec. 31, 2018				503,880				123,933
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of certain tax effects	[1]					84	(84)
Net income		508				508
Other comprehensive income		260					260
Cash dividends declared:
Common stock dividends		(177)				(177)
Preferred stock cash dividend		(55)				(55)
Common stock acquired		(300)						$ (300)
Common stock acquired (shares)								4,230
Common stock awards exercised		71			26			$ 45
Common stock awards vested (shares)								(1,002)
Other		(6)			(5)	(2)		$ 1
Other (shares)								(2)
Ending balance at Mar. 31, 2019		25,038	3,690	$ 504	10,082	20,911	(1,180)	$ (8,969)
Ending balance (shares) at Mar. 31, 2019				503,880				127,159
Beginning balance at Dec. 31, 2018		24,737	3,690	$ 504	10,061	20,553	(1,356)	$ (8,715)
Beginning balance (shares) at Dec. 31, 2018				503,880				123,933
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of certain tax effects		(84)
Net income		1,678
Other comprehensive income		455
Cash dividends declared:
Common stock dividends		(541)
Preferred stock cash dividend		(160)
Ending balance at Sep. 30, 2019		25,209	3,690	$ 504	10,117	21,612	(985)	$ (9,729)
Ending balance (shares) at Sep. 30, 2019				503,880				140,256
Beginning balance at Mar. 31, 2019		25,038	3,690	$ 504	10,082	20,911	(1,180)	$ (8,969)
Beginning balance (shares) at Mar. 31, 2019				503,880				127,159
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		587				587
Other comprehensive income		306					306
Cash dividends declared:
Common stock dividends		(175)				(175)
Preferred stock cash dividend		(50)				(50)
Common stock acquired		(300)						$ (300)
Common stock acquired (shares)								4,598
Common stock awards exercised		47			27			$ 20
Common stock awards vested (shares)								(452)
Other		1				1
Other (shares)								2
Ending balance at Jun. 30, 2019		25,454	3,690	$ 504	10,109	21,274	(874)	$ (9,249)
Ending balance (shares) at Jun. 30, 2019				503,880				131,307
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		583				583
Other comprehensive income		(111)					(111)
Cash dividends declared:
Common stock dividends		(189)				(189)
Preferred stock cash dividend		(55)				(55)
Common stock acquired		(500)						$ (500)
Common stock acquired (shares)								9,407
Common stock awards exercised		49			29			$ 20
Common stock awards vested (shares)								(443)
Other		(22)			(21)	(1)
Other (shares)								(15)
Ending balance at Sep. 30, 2019		$ 25,209	$ 3,690	$ 504	$ 10,117	$ 21,612	$ (985)	$ (9,729)
Ending balance (shares) at Sep. 30, 2019				503,880				140,256

[1] ⁽¹⁾ Represents the reclassification from accumulated other comprehensive income into retained earnings as a result of our adoption of ASU 2018-02 - Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income in the first quarter of 2019.