Segment Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) segment	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			4
Net financing revenue and other interest income	$ 1,547	$ 1,054	$ 2,919	$ 2,200
Other revenue	538	555	1,103	821
Total net revenue	2,085	1,609	4,022	3,021
Provision for credit losses	(32)	287	(45)	1,190
Total noninterest expense	1,075	985	2,018	1,905
Income (loss) from continuing operations before income tax expense	1,042	337	2,049	(74)
Total assets	180,470	184,061	180,470	184,061	$ 182,165
Net financing revenue and other interest income after the provision for credit losses	1,600	767	3,000	1,000
Operating Segments | Automotive Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	1,333	989	2,539	2,029
Other revenue	61	40	123	87
Total net revenue	1,394	1,029	2,662	2,116
Provision for credit losses	(23)	256	(45)	1,022
Total noninterest expense	500	444	987	938
Income (loss) from continuing operations before income tax expense	917	329	1,720	156
Total assets	100,162	102,016	100,162	102,016
Operating Segments | Insurance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	15	12	30	26
Other revenue	344	438	723	575
Total net revenue	359	450	753	601
Provision for credit losses	0	0	0	0
Total noninterest expense	272	322	525	578
Income (loss) from continuing operations before income tax expense	87	128	228	23
Total assets	9,394	8,740	9,394	8,740
Operating Segments | Mortgage Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	23	30	46	68
Other revenue	22	19	62	29
Total net revenue	45	49	108	97
Provision for credit losses	0	3	(4)	4
Total noninterest expense	45	38	89	73
Income (loss) from continuing operations before income tax expense	0	8	23	20
Total assets	13,865	16,669	13,865	16,669
Operating Segments | Corporate Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	77	77	148	145
Other revenue	33	6	59	19
Total net revenue	110	83	207	164
Provision for credit losses	(13)	25	0	139
Total noninterest expense	28	26	59	61
Income (loss) from continuing operations before income tax expense	95	32	148	(36)
Total assets	6,246	6,206	6,246	6,206
Corporate and Other
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	99	(54)	156	(68)
Other revenue	78	52	136	111
Total net revenue	177	(2)	292	43
Provision for credit losses	4	3	4	25
Total noninterest expense	230	155	358	255
Income (loss) from continuing operations before income tax expense	(57)	(160)	(70)	(237)
Total assets	$ 50,803	$ 50,430	$ 50,803	$ 50,430