Parent Company Condensed Financial Information (Condensed Statement of Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net financing revenue and other interest income	$ 1,303	$ 1,200	$ 1,054	$ 1,146	$ 1,156	$ 1,188	$ 1,157	$ 1,132	$ 4,703	$ 4,633	$ 4,390
Noninterest Income	678	484	555	266	487	413	395	466	1,983	1,761	1,414
Total net revenue	1,981	1,684	1,609	1,412	1,643	1,601	1,552	1,598	6,686	6,394	5,804
Provision for credit losses	102	147	287	903	276	263	177	282	1,439	998	918
Total noninterest expense	1,023	905	985	920	880	838	881	830	3,833	3,429	3,264
Income from continuing operations before income tax expense	856	632	337	(411)	487	500	494	486	1,414	1,967	1,622
Income tax (benefit) expense from continuing operations	169	156	95	(92)	106	119	(90)	111	328	246	359
Net income from continuing operations	687	476	242	(319)	381	381	584	375	1,086	1,721	1,263
Loss from discontinued operations, net of tax	0	0	(1)	0	(3)	0	(2)	(1)	(1)	(6)	0
Net income	$ 687	$ 476	$ 241	$ (319)	$ 378	$ 381	$ 582	$ 374	1,085	1,715	1,263
Other Comprehensive Income (Loss), Net of Tax									508	654	(289)
Comprehensive Income									1,593	2,369	974
Parent company
Net financing revenue and other interest income									(1,049)	(1,116)	(1,083)
Dividends paid to parent company by bank subsidiaries									1,150	1,950	2,600
Dividends paid to parent company by nonbank subsidiaries									66	436	443
Noninterest Income									367	343	481
Total net revenue									534	1,613	2,441
Provision for credit losses									(68)	35	176
Total noninterest expense									693	626	764
Income from continuing operations before income tax expense									(91)	952	1,501
Income tax (benefit) expense from continuing operations									(300)	(566)	(300)
Net income from continuing operations									209	1,518	1,801
Loss from discontinued operations, net of tax									(1)	(6)	(2)
Undistributed income (loss) of subsidiaries									877	203	(536)
Net income									1,085	1,715	1,263
Other Comprehensive Income (Loss), Net of Tax									508	654	(289)
Comprehensive Income									$ 1,593	$ 2,369	$ 974