Segment Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments			4
Net financing revenue and other interest income	$ 1,188	$ 1,107	$ 3,477	$ 3,250
Other revenue	413	398	1,274	1,116
Total net revenue	1,601	1,505	4,751	4,366
Provision for loan losses	263	233	722	652
Noninterest expense	838	807	2,549	2,460
Income (loss) from continuing operations before income tax expense	500	465	1,480	1,254
Assets	181,485	173,101	181,485	173,101	$ 178,869
Net financing revenue and other interest income after provision for loan losses	925	874	2,800	2,600
Operating Segments | Automotive Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	1,078	956	3,080	2,790
Other revenue	59	80	188	209
Total net revenue	1,137	1,036	3,268	2,999
Provision for loan losses	265	229	707	658
Noninterest expense	443	424	1,344	1,308
Income (loss) from continuing operations before income tax expense	429	383	1,217	1,033
Assets	115,096	114,675	115,096	114,675
Operating Segments | Insurance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	14	14	41	39
Other revenue	289	282	935	794
Total net revenue	303	296	976	833
Provision for loan losses	0	0	0	0
Noninterest expense	247	241	775	740
Income (loss) from continuing operations before income tax expense	56	55	201	93
Assets	8,478	7,776	8,478	7,776
Operating Segments | Mortgage Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	39	44	135	131
Other revenue	10	2	16	5
Total net revenue	49	46	151	136
Provision for loan losses	0	2	2	4
Noninterest expense	38	36	111	102
Income (loss) from continuing operations before income tax expense	11	8	38	30
Assets	16,583	14,896	16,583	14,896
Operating Segments | Corporate Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	60	50	175	153
Other revenue	9	14	30	36
Total net revenue	69	64	205	189
Provision for loan losses	3	8	29	2
Noninterest expense	22	20	73	64
Income (loss) from continuing operations before income tax expense	44	36	103	123
Assets	5,275	4,459	5,275	4,459
Corporate and Other
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	(3)	43	46	137
Other revenue	46	20	105	72
Total net revenue	43	63	151	209
Provision for loan losses	(5)	(6)	(16)	(12)
Noninterest expense	88	86	246	246
Income (loss) from continuing operations before income tax expense	(40)	(17)	(79)	(25)
Assets	$ 36,053	$ 31,295	$ 36,053	$ 31,295