Segment Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) segment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			4
Net financing revenue and other interest income	$ 1,594	$ 1,200	$ 4,513	$ 3,400
Other revenue	391	484	1,494	1,305
Total net revenue	1,985	1,684	6,007	4,705
Provision for credit losses	76	147	31	1,337
Total noninterest expense	1,002	905	3,020	2,810
Income (loss) from continuing operations before income tax expense	907	632	2,956	558
Total assets	179,184	185,270	179,184	185,270	$ 182,165
Net financing revenue and other interest income after the provision for credit losses	1,500	1,100	4,500	2,100
Operating Segments | Automotive Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	1,329	1,102	3,868	3,131
Other revenue	61	61	184	148
Total net revenue	1,390	1,163	4,052	3,279
Provision for credit losses	53	128	8	1,150
Total noninterest expense	512	469	1,499	1,407
Income (loss) from continuing operations before income tax expense	825	566	2,545	722
Total assets	99,617	103,366	99,617	103,366
Operating Segments | Insurance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	14	8	44	34
Other revenue	283	338	1,006	913
Total net revenue	297	346	1,050	947
Provision for credit losses	0	0	0	0
Total noninterest expense	273	268	798	846
Income (loss) from continuing operations before income tax expense	24	78	252	101
Total assets	9,354	8,944	9,354	8,944
Operating Segments | Mortgage Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	36	30	82	98
Other revenue	19	36	81	65
Total net revenue	55	66	163	163
Provision for credit losses	2	0	(2)	4
Total noninterest expense	47	40	136	113
Income (loss) from continuing operations before income tax expense	6	26	29	46
Total assets	16,328	15,503	16,328	15,503
Operating Segments | Corporate Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	77	75	225	220
Other revenue	16	9	75	28
Total net revenue	93	84	300	248
Provision for credit losses	5	1	5	140
Total noninterest expense	27	23	86	84
Income (loss) from continuing operations before income tax expense	61	60	209	24
Total assets	6,729	5,995	6,729	5,995
Corporate and Other
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	138	(15)	294	(83)
Other revenue	12	40	148	151
Total net revenue	150	25	442	68
Provision for credit losses	16	18	20	43
Total noninterest expense	143	105	501	360
Income (loss) from continuing operations before income tax expense	(9)	(98)	(79)	(335)
Total assets	$ 47,156	$ 51,462	$ 47,156	$ 51,462