Segment Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments			4
Net financing revenue and other interest income	$ 1,200	$ 1,188	$ 3,400	$ 3,477
Other revenue	484	413	1,305	1,274
Total net revenue	1,684	1,601	4,705	4,751
Provision for credit losses	147	263	1,337	722
Total noninterest expense	905	838	2,810	2,549
Income (loss) from continuing operations before income tax expense	632	500	558	1,480
Total assets	185,270	181,485	185,270	181,485	$ 180,644
Net financing revenue and other interest income after the provision for credit losses	1,100	925	2,100	2,800
Operating Segments | Automotive Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	1,102	1,078	3,131	3,080
Other revenue	61	59	148	188
Total net revenue	1,163	1,137	3,279	3,268
Provision for credit losses	128	265	1,150	707
Total noninterest expense	469	443	1,407	1,344
Income (loss) from continuing operations before income tax expense	566	429	722	1,217
Total assets	103,366	115,096	103,366	115,096
Operating Segments | Insurance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	8	14	34	41
Other revenue	338	289	913	935
Total net revenue	346	303	947	976
Provision for credit losses	0	0	0	0
Total noninterest expense	268	247	846	775
Income (loss) from continuing operations before income tax expense	78	56	101	201
Total assets	8,944	8,478	8,944	8,478
Operating Segments | Mortgage Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	30	39	98	135
Other revenue	36	10	65	16
Total net revenue	66	49	163	151
Provision for credit losses	0	0	4	2
Total noninterest expense	40	38	113	111
Income (loss) from continuing operations before income tax expense	26	11	46	38
Total assets	15,503	16,583	15,503	16,583
Operating Segments | Corporate Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	75	60	220	175
Other revenue	9	9	28	30
Total net revenue	84	69	248	205
Provision for credit losses	1	3	140	29
Total noninterest expense	23	22	84	73
Income (loss) from continuing operations before income tax expense	60	44	24	103
Total assets	5,995	5,275	5,995	5,275
Corporate and Other
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	(15)	(3)	(83)	46
Other revenue	40	46	151	105
Total net revenue	25	43	68	151
Provision for credit losses	18	(5)	43	(16)
Total noninterest expense	105	88	360	246
Income (loss) from continuing operations before income tax expense	(98)	(40)	(335)	(79)
Total assets	$ 51,462	$ 36,053	$ 51,462	$ 36,053