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 (loss) income	1,479				1,479
Other comprehensive income	73					73
Purchases of treasury stock	(948)						(948)
Common stock issued under employee benefit plans (in shares)			51,000
Common stock issued under employee benefit plans	3		$ 0	3
Common stock issued and stock-based compensation expense (in shares)			1,116,000
Common stock issued and stock-based compensation expense	34		$ 0	34
Dividends — common stock	(262)				(262)
Dividends — preferred stock	(16)							$ (16)
Preferred stock, shares outstanding, balance at end of period (in shares) at Jun. 30, 2019		6,000
Common stock, shares outstanding, balance at end of period (in shares) at Jun. 30, 2019			566,019,000
Stockholders' equity, balance at end of period at Jun. 30, 2019	11,493	$ 563	$ 6	4,167	20,107	(83)	(13,267)
Preferred stock, shares outstanding, balance at beginning of period (in shares) at Mar. 31, 2019		6,000
Common stock, shares outstanding, balance at beginning of period (in shares) at Mar. 31, 2019			565,973,000
Stockholders' equity, balance at beginning of period at Mar. 31, 2019	11,259	$ 563	$ 6	4,148	19,484	(136)	(12,806)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	753				753
Other comprehensive income	53					53
Purchases of treasury stock	(461)						(461)
Common stock issued under employee benefit plans (in shares)			24,000
Common stock issued under employee benefit plans	1		$ 0	1
Common stock issued and stock-based compensation expense (in shares)			22,000
Common stock issued and stock-based compensation expense	18		$ 0	18
Dividends — common stock	(130)				(130)
Dividends — preferred stock	0
Preferred stock, shares outstanding, balance at end of period (in shares) at Jun. 30, 2019		6,000
Common stock, shares outstanding, balance at end of period (in shares) at Jun. 30, 2019			566,019,000
Stockholders' equity, balance at end of period at Jun. 30, 2019	$ 11,493	$ 563	$ 6	4,167	20,107	(83)	(13,267)
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]
Cumulative effect of ASU No. 2016-13 adoption	(1,902)				(1,902)
Net (loss) income	(429)				(429)
Other comprehensive income	241					241
Purchases of treasury stock	(343)						(343)
Common stock issued under employee benefit plans (in shares)			113,000
Common stock issued under employee benefit plans	4		$ 0	4
Common stock issued and stock-based compensation expense (in shares)			886,000
Common stock issued and stock-based compensation expense	6		$ 0	6
Stock Issued During Period, Shares, New Issues		5,000
Stock Issued During Period, Value, New Issues	493	$ 493
Dividends — common stock	(270)				(270)
Dividends — preferred stock	$ (16)							$ (16)
Preferred stock, shares outstanding, balance at end of period (in shares) at Jun. 30, 2020	10,700	11,000
Common stock, shares outstanding, balance at end of period (in shares) at Jun. 30, 2020			567,653,000
Stockholders' equity, balance at end of period at Jun. 30, 2020	$ 9,643	$ 1,056	$ 6	4,216	18,673	122	(14,430)
Preferred stock, shares outstanding, balance at beginning of period (in shares) at Mar. 31, 2020		6,000
Common stock, shares outstanding, balance at beginning of period (in shares) at Mar. 31, 2020			567,530,000
Stockholders' equity, balance at beginning of period at Mar. 31, 2020	9,665	$ 563	$ 6	4,217	19,175	134	(14,430)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(368)				(368)
Other comprehensive income	(12)					(12)
Common stock issued under employee benefit plans (in shares)			49,000
Common stock issued under employee benefit plans	2		$ 0	2
Common stock issued and stock-based compensation expense (in shares)			74,000
Common stock issued and stock-based compensation expense	(3)		$ 0	(3)
Stock Issued During Period, Shares, New Issues		5,000
Stock Issued During Period, Value, New Issues	493	$ 493
Dividends — common stock	(134)				(134)
Dividends — preferred stock	$ 0
Preferred stock, shares outstanding, balance at end of period (in shares) at Jun. 30, 2020	10,700	11,000
Common stock, shares outstanding, balance at end of period (in shares) at Jun. 30, 2020			567,653,000
Stockholders' equity, balance at end of period at Jun. 30, 2020	$ 9,643	$ 1,056	$ 6	$ 4,216	$ 18,673	$ 122	$ (14,430)