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]
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	726				726
Other comprehensive income	20					20
Purchases of treasury stock	(487)						(487)
Common stock issued under employee benefit plans (in shares)			27,000
Common stock issued under employee benefit plans	2		$ 0	2
Common stock issued and stock-based compensation expense (in shares)			1,094,000
Common stock issued and stock-based compensation expense	16		$ 0	16
Dividends — common stock	(132)				(132)
Dividends — preferred stock	(16)				(16)
Preferred stock, shares outstanding, balance at end of period (in shares) at Mar. 31, 2019		6,000
Common stock, shares outstanding, balance at end of period (in shares) at Mar. 31, 2019			565,973,000
Stockholders' equity, balance at end of period at Mar. 31, 2019	$ 11,259	$ 563	$ 6	4,148	19,484	(136)	(12,806)
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	(61)				(61)
Other comprehensive income	253					253
Purchases of treasury stock	(343)						(343)
Common stock issued under employee benefit plans (in shares)			64,000
Common stock issued under employee benefit plans	2		$ 0	2
Common stock issued and stock-based compensation expense (in shares)			812,000
Common stock issued and stock-based compensation expense	9		$ 0	9
Dividends — common stock	(136)				(136)
Dividends — preferred stock	$ (16)				(16)
Preferred stock, shares outstanding, balance at end of period (in shares) at Mar. 31, 2020	5,700	6,000
Common stock, shares outstanding, balance at end of period (in shares) at Mar. 31, 2020			567,530,000
Stockholders' equity, balance at end of period at Mar. 31, 2020	$ 9,665	$ 563	$ 6	$ 4,217	$ 19,175	$ 134	$ (14,430)