Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Treasury Stock [Member]	Series C Preferred Stock [Member] Retained Earnings [Member]
Preferred stock, shares outstanding, balance at beginning of period (in shares) at Dec. 31, 2018		6,000
Common stock, shares outstanding, balance at beginning of period (in shares) at Dec. 31, 2018			564,852,000
Stockholders' equity, balance at beginning of period at Dec. 31, 2018	$ 11,130	$ 563	$ 6	$ 4,130	$ 18,906	$ (156)	$ (12,319)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,249				2,249
Other comprehensive income	82					82
Purchases of treasury stock	(1,367)						(1,367)
Common stock issued under employee benefit plans (in shares)			76,000
Common stock issued under employee benefit plans	6		$ 0	6
Common stock issued and stock-based compensation expense (in shares)			1,676,000
Common stock issued and stock-based compensation expense	52		$ 0	52
Dividends — common stock	(404)				(404)
Dividends — preferred stock	(31)							$ (31)
Preferred stock, shares outstanding, balance at end of period (in shares) at Sep. 30, 2019		6,000
Common stock, shares outstanding, balance at end of period (in shares) at Sep. 30, 2019			566,604,000
Stockholders' equity, balance at end of period at Sep. 30, 2019	11,717	$ 563	$ 6	4,188	20,720	(74)	(13,686)
Preferred stock, shares outstanding, balance at beginning of period (in shares) at Jun. 30, 2019		6,000
Common stock, shares outstanding, balance at beginning of period (in shares) at Jun. 30, 2019			566,019,000
Stockholders' equity, balance at beginning of period at Jun. 30, 2019	11,493	$ 563	$ 6	4,167	20,107	(83)	(13,267)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	770				770
Other comprehensive income	9					9
Purchases of treasury stock	(419)						(419)
Common stock issued under employee benefit plans (in shares)			25,000
Common stock issued under employee benefit plans	3		$ 0	3
Common stock issued and stock-based compensation expense (in shares)			560,000
Common stock issued and stock-based compensation expense	18		$ 0	18
Dividends — common stock	(142)				(142)
Dividends — preferred stock	(15)				(15)
Preferred stock, shares outstanding, balance at end of period (in shares) at Sep. 30, 2019		6,000
Common stock, shares outstanding, balance at end of period (in shares) at Sep. 30, 2019			566,604,000
Stockholders' equity, balance at end of period at Sep. 30, 2019	$ 11,717	$ 563	$ 6	4,188	20,720	(74)	(13,686)
Preferred stock, shares outstanding, balance at beginning of period (in shares) at Dec. 31, 2019	5,700	6,000
Common stock, shares outstanding, balance at beginning of period (in shares) at Dec. 31, 2019			566,654,000
Stockholders' equity, balance at beginning of period at Dec. 31, 2019	$ 11,859	$ 563	$ 6	4,206	21,290	(119)	(14,087)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	342				342
Other comprehensive income	212					212
Purchases of treasury stock	(343)						(343)
Common stock issued under employee benefit plans (in shares)			163,000
Common stock issued under employee benefit plans	7		$ 0	7
Common stock issued and stock-based compensation expense (in shares)			927,000
Common stock issued and stock-based compensation expense	22		$ 0	22
Dividends — common stock	(407)				(407)
Dividends — preferred stock	(31)							(31)
Stock Issued During Period, Shares, New Issues		5,000
Stock Issued During Period, Value, New Issues	493	$ 493
Cumulative effect of ASU No. 2016-13 adoption	$ (1,902)				(1,902)
Preferred stock, shares outstanding, balance at end of period (in shares) at Sep. 30, 2020	5,700	11,000
Common stock, shares outstanding, balance at end of period (in shares) at Sep. 30, 2020			567,744,000
Stockholders' equity, balance at end of period at Sep. 30, 2020	$ 10,252	$ 1,056	$ 6	4,235	19,292	93	(14,430)
Preferred stock, shares outstanding, balance at beginning of period (in shares) at Jun. 30, 2020		11,000
Common stock, shares outstanding, balance at beginning of period (in shares) at Jun. 30, 2020			567,653,000
Stockholders' equity, balance at beginning of period at Jun. 30, 2020	9,643	$ 1,056	$ 6	4,216	18,673	122	(14,430)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	771				771
Other comprehensive income	(29)					(29)
Common stock issued under employee benefit plans (in shares)			50,000
Common stock issued under employee benefit plans	3		$ 0	3
Common stock issued and stock-based compensation expense (in shares)			41,000
Common stock issued and stock-based compensation expense	16		$ 0	16
Dividends — common stock	(137)				(137)
Dividends — preferred stock	(15)							$ (15)
Stock Issued During Period, Value, New Issues	$ 0
Preferred stock, shares outstanding, balance at end of period (in shares) at Sep. 30, 2020	5,700	11,000
Common stock, shares outstanding, balance at end of period (in shares) at Sep. 30, 2020			567,744,000
Stockholders' equity, balance at end of period at Sep. 30, 2020	$ 10,252	$ 1,056	$ 6	$ 4,235	$ 19,292	$ 93	$ (14,430)