Consolidated Statements Of Changes In Shareholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Cumulative effect of change in accounting principle	Common Stock	Capital Surplus	Capital Surplus Cumulative effect of change in accounting principle	Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Cumulative effect of change in accounting principle	Retained Earnings	Retained Earnings Cumulative effect of change in accounting principle	Treasury Stock
BALANCE at Dec. 31, 2016	$ 7,796	$ 1	$ 1,141	$ 2,135	$ 3	$ (383)		$ 7,331	$ (2)	$ (2,428)
BALANCE (in shares) at Dec. 31, 2016			175.3
Net income	631							631
Other comprehensive income, net of tax	24					24
Cash dividends declared on common stock	(141)							(141)
Purchase of common stock	(396)									(396)
Purchase of common stock (in shares)			(5.7)
Net issuance of common stock under employee stock plans	90			(26)				(22)		138
Net issuance of common stock under employee stock plans (in shares)			3.0
Net issuance of common stock for warrants	0			(28)				(51)		79
Net issuance of common stock for warrants (in shares)			1.7
Share-based compensation	29			29
Other	0			(1)						1
Other (in shares)			0.0
BALANCE at Sep. 30, 2017	8,034		$ 1,141	2,112		(359)		7,746		(2,606)
BALANCE (in shares) at Sep. 30, 2017			174.3
BALANCE at Dec. 31, 2017	7,963	$ 15	$ 1,141	2,122		(451)	$ 1	7,887	$ 14	(2,736)
BALANCE (in shares) at Dec. 31, 2017			172.9
Net income	925							925
Other comprehensive income, net of tax	(161)					(161)
Cash dividends declared on common stock	(210)							(210)
Purchase of common stock	(828)			(7)						(821)
Purchase of common stock (in shares)			(8.7)
Net issuance of common stock under employee stock plans	41			(9)				(24)		74
Net issuance of common stock under employee stock plans (in shares)			1.5
Net issuance of common stock for warrants	0			(3)				(5)		8
Net issuance of common stock for warrants (in shares)			0.2
Share-based compensation	41			41
BALANCE at Sep. 30, 2018	$ 7,786		$ 1,141	$ 2,144		$ (611)		$ 8,587		$ (3,475)
BALANCE (in shares) at Sep. 30, 2018			165.9