CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - 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]	Student Loan [Member] Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-13 [Member]	$ 0	[1]				$ 0				$ 0
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-02 [Member]						27
Cumulative effect of new accounting principle in period of adoption, reclassification | Accounting Standards Update 2016-13 [Member]						0	$ 0
Balance at beginning of period at Dec. 31, 2018			$ 1,265
Balance at beginning of period at Dec. 31, 2018				$ 0	$ 18,136	1,498	(366)	$ 1,471	$ (366)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Return of capital to parent					(2,400)
Employee benefit plans					0
Net income (loss)	109					109
Other comprehensive income, net of tax	79						79
Balance at end of period at Mar. 31, 2019	17,056			0	15,736	1,607	(287)
Balance at end of period at Mar. 31, 2019	18,321		1,265
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of new accounting principle in period of adoption	(170)
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-13 [Member]	2	[1]				84				$ 2
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-02 [Member]						0
Cumulative effect of new accounting principle in period of adoption, reclassification | Accounting Standards Update 2016-13 [Member]						(2)	2
Balance at beginning of period at Dec. 31, 2019	18,256		1,265
Balance at beginning of period at Dec. 31, 2019	16,991			0	15,736	1,618	(277)	$ 1,534	$ (279)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Return of capital to parent					0
Employee benefit plans					5
Net income (loss)	(1,283)					(1,283)
Other comprehensive income, net of tax	1,255						1,255
Balance at end of period at Mar. 31, 2020	17,054			$ 0	$ 15,741	$ 335	$ 978
Balance at end of period at Mar. 31, 2020	$ 18,319		$ 1,265

[1] See Note 21, "New Accounting Pronouncements," for additional discussion.