CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (UNAUDITED) - USD ($) $ in Millions	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	As Previously Reported [Member] Retained Earnings [Member]	As Previously Reported [Member] Accumulated Other Comprehensive Loss [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Student Loan [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Reclassification [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Reclassification [Member] Accumulated Other Comprehensive Loss [Member]
Balance at beginning of period at Dec. 31, 2019		$ 1,265
Balance at beginning of period, common equity at Dec. 31, 2019			$ 0	$ 15,736	$ 1,618	$ (277)	$ 1,534	$ (279)
Balance at beginning of period, common equity (Accounting Standards Update 2016-13 [Member]) at Dec. 31, 2019									$ 84	$ 2	$ (2)	$ 2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee benefit plans				14
Net income (loss)	$ (1,088)				(1,088)
Cash dividends declared on preferred stock					(39)
Other comprehensive income (loss), net of tax	1,111					1,111
Balance at end of period, common equity at Sep. 30, 2020	17,075		0	15,750	491	834	491	834
Balance at end of period at Sep. 30, 2020	18,340	1,265
Balance at beginning of period at Jun. 30, 2020		1,265
Balance at beginning of period, common equity at Jun. 30, 2020			0	15,746	303	830
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee benefit plans				4
Net income (loss)	188				188
Other comprehensive income (loss), net of tax	4					4
Balance at end of period, common equity at Sep. 30, 2020	17,075		0	15,750	491	834	491	834
Balance at end of period at Sep. 30, 2020	18,340	1,265
Balance at beginning of period at Dec. 31, 2020	18,291	1,265
Balance at beginning of period, common equity at Dec. 31, 2020	17,026		0	15,746	601	679	$ 601	$ 679
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee benefit plans				(3)
Net income (loss)	669				669
Cash dividends declared on preferred stock					(38)
Other comprehensive income (loss), net of tax	(682)					(682)
Balance at end of period, common equity at Sep. 30, 2021	16,972		0	15,743	1,232	(3)
Balance at end of period at Sep. 30, 2021	18,237	1,265
Balance at beginning of period at Jun. 30, 2021		1,265
Balance at beginning of period, common equity at Jun. 30, 2021			0	15,743	1,095	81
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee benefit plans				0
Net income (loss)	137				137
Other comprehensive income (loss), net of tax	(84)					(84)
Balance at end of period, common equity at Sep. 30, 2021	16,972		$ 0	$ 15,743	$ 1,232	$ (3)
Balance at end of period at Sep. 30, 2021	$ 18,237	$ 1,265