Segment Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments	4
Net financing revenue and other interest income	$ 1,146	$ 1,132
Other revenue	266	466
Total net revenue	1,412	1,598
Provision for credit losses	903	282
Noninterest expense	920	830
Income (loss) from continuing operations before income tax expense	(411)	486
Assets	182,527	180,117	$ 180,644
Net financing revenue and other interest income after provision for loan losses	243	850
Operating Segments | Automotive Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	1,040	980
Other revenue	47	68
Total net revenue	1,087	1,048
Provision for credit losses	766	262
Noninterest expense	494	457
Income (loss) from continuing operations before income tax expense	(173)	329
Assets	111,554	115,789
Operating Segments | Insurance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	14	12
Other revenue	137	360
Total net revenue	151	372
Provision for credit losses	0	0
Noninterest expense	256	227
Income (loss) from continuing operations before income tax expense	(105)	145
Assets	8,420	8,179
Operating Segments | Mortgage Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	38	50
Other revenue	10	2
Total net revenue	48	52
Provision for credit losses	1	2
Noninterest expense	35	37
Income (loss) from continuing operations before income tax expense	12	13
Assets	16,135	16,301
Operating Segments | Corporate Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	68	54
Other revenue	13	11
Total net revenue	81	65
Provision for credit losses	114	23
Noninterest expense	35	29
Income (loss) from continuing operations before income tax expense	(68)	13
Assets	6,572	5,006
Corporate and Other
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	(14)	36
Other revenue	59	25
Total net revenue	45	61
Provision for credit losses	22	(5)
Noninterest expense	100	80
Income (loss) from continuing operations before income tax expense	(77)	(14)
Assets	$ 39,846	$ 34,842