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, 2019				142.1
BALANCE at Dec. 31, 2019	$ 7,327			$ 1,141	$ 2,174	$ (316)	$ 9,619	$ (5,291)
Cumulative effect of change in accounting principle	13						13
Net income	276	[1]					276
Other comprehensive income (loss), net of tax	334					334
Cash dividends declared on common stock	(284)						(284)
Cash dividends declared on preferred stock	(8)						(8)
Purchase of common stock	(194)							(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	18	9,609	(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	66	9,496	(5,469)
Net income	217	[1]					217
Other comprehensive income (loss), net of tax	(48)					(48)
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						(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	18	9,609	(5,467)
BALANCE (in shares) at Sep. 30, 2020				139.1
BALANCE (in shares) at Dec. 31, 2020				139.2
BALANCE at Dec. 31, 2020	8,050		394	$ 1,141	2,185	64	9,727	(5,461)
Net income	940						940
Other comprehensive income (loss), net of tax	(271)					(271)
Cash dividends declared on common stock	(276)						(276)
Cash dividends declared on preferred stock	(17)						(17)
Purchase of common stock	(673)				(24)			(649)
Purchase of common stock (in shares)				(9.0)
Issuance of preferred stock	0
Net issuance of common stock under employee stock plans	14				(27)		(8)	49
Net issuance of common stock under employee stock plans (in shares)				0.8
Share-based compensation	36				36
BALANCE at Sep. 30, 2021	7,803		394	$ 1,141	2,170	(207)	10,366	(6,061)
BALANCE (in shares) at Sep. 30, 2021				131.0
BALANCE (in shares) at Jun. 30, 2021				133.9
BALANCE at Jun. 30, 2021	7,931		394	$ 1,141	2,163	(120)	10,202	(5,849)
Net income	262						262
Other comprehensive income (loss), net of tax	(87)					(87)
Cash dividends declared on common stock	(89)						(89)
Cash dividends declared on preferred stock	(6)						(6)
Purchase of common stock	(220)							(220)
Purchase of common stock (in shares)				(3.1)
Net issuance of common stock under employee stock plans	5						(3)	8
Net issuance of common stock under employee stock plans (in shares)				0.2
Share-based compensation	7				7
BALANCE at Sep. 30, 2021	$ 7,803		$ 394	$ 1,141	$ 2,170	$ (207)	$ 10,366	$ (6,061)
BALANCE (in shares) at Sep. 30, 2021				131.0

[1] See Defined Benefit Pension and Other Postretirement Costs in Note 1.