Consolidated Statements Of Changes In Shareholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Nonredeemable Preferred Stock	Common Stock	Capital Surplus	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
BALANCE (in shares) at Dec. 31, 2018			160.1
BALANCE at Dec. 31, 2018	$ 7,507		$ 1,141	$ 2,148	$ (609)	$ 8,781	$ (3,954)
Net income	929					929
Other comprehensive income (loss), net of tax	273				273
Cash dividends declared on common stock	(302)					(302)
Purchase of common stock	1,229			0			1,229
Purchase of common stock (in shares)			(16.6)
Issuance of preferred stock	0
Net issuance of common stock under employee stock plans	1			13		25	37
Net issuance of common stock under employee stock plans (in shares)			0.6
Share-based compensation	37			37
BALANCE at Sep. 30, 2019	7,200		$ 1,141	2,172	(336)	9,369	(5,146)
BALANCE (in shares) at Sep. 30, 2019			144.1
BALANCE (in shares) at Jun. 30, 2019			149.8
BALANCE at Jun. 30, 2019	7,323		$ 1,141	2,168	(382)	9,176	(4,780)
Net income	292					292
Other comprehensive income (loss), net of tax	46				46
Cash dividends declared on common stock	(97)					(97)
Purchase of common stock	370						370
Purchase of common stock (in shares)			(5.7)
Net issuance of common stock under employee stock plans	1			1		2	4
Net issuance of common stock under employee stock plans (in shares)			0.0
Share-based compensation	5			5
BALANCE at Sep. 30, 2019	7,200		$ 1,141	2,172	(336)	9,369	(5,146)
BALANCE (in shares) at Sep. 30, 2019			144.1
BALANCE (in shares) at Dec. 31, 2019			142.1
BALANCE at Dec. 31, 2019	7,327		$ 1,141	2,174	(235)	9,538	(5,291)
Net income	259					259
Other comprehensive income (loss), net of tax	351				351
Cash dividends declared on common stock	(284)					(284)
Cash dividends declared on preferred stock	(8)					(8)
Purchase of common stock	194			0			194
Purchase of common stock (in shares)			(3.4)
Issuance of preferred stock	394	$ 394
Net issuance of common stock under employee stock plans	2			13		7	18
Net issuance of common stock under employee stock plans (in shares)			0.4
Share-based compensation	18			18
BALANCE at Sep. 30, 2020	7,874	394	$ 1,141	2,179	116	9,511	(5,467)
BALANCE (in shares) at Sep. 30, 2020			139.1
BALANCE (in shares) at Jun. 30, 2020			139.0
BALANCE at Jun. 30, 2020	7,802	395	$ 1,141	2,173	158	9,404	(5,469)
Net income	211					211
Other comprehensive income (loss), net of tax	(42)				(42)
Cash dividends declared on common stock	(94)					(94)
Cash dividends declared on preferred stock	(8)					(8)
Issuance of preferred stock	(1)	(1)
Net issuance of common stock under employee stock plans	0			0		2	2
Net issuance of common stock under employee stock plans (in shares)			0.1
Share-based compensation	6			6
BALANCE at Sep. 30, 2020	$ 7,874	$ 394	$ 1,141	$ 2,179	$ 116	$ 9,511	$ (5,467)
BALANCE (in shares) at Sep. 30, 2020			139.1