Segment Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments			4
Net financing revenue and other interest income	$ 1,054	$ 1,157	$ 2,200	$ 2,289
Other revenue	555	395	821	861
Total net revenue	1,609	1,552	3,021	3,150
Provision for credit losses	287	177	1,190	459
Total noninterest expense	985	881	1,905	1,711
Income (loss) from continuing operations before income tax expense	337	494	(74)	980
Total assets	184,061	180,448	184,061	180,448	$ 180,644
Net financing revenue and other interest income after the provision for credit losses	767	980	1,000	1,800
Operating Segments | Automotive Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	989	1,022	2,029	2,002
Other revenue	40	61	87	129
Total net revenue	1,029	1,083	2,116	2,131
Provision for credit losses	256	180	1,022	442
Total noninterest expense	444	444	938	901
Income (loss) from continuing operations before income tax expense	329	459	156	788
Total assets	102,016	114,955	102,016	114,955
Operating Segments | Insurance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	12	15	26	27
Other revenue	438	286	575	646
Total net revenue	450	301	601	673
Provision for credit losses	0	0	0	0
Total noninterest expense	322	301	578	528
Income (loss) from continuing operations before income tax expense	128	0	23	145
Total assets	8,740	8,241	8,740	8,241
Operating Segments | Mortgage Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	30	46	68	96
Other revenue	19	4	29	6
Total net revenue	49	50	97	102
Provision for credit losses	3	0	4	2
Total noninterest expense	38	36	73	73
Income (loss) from continuing operations before income tax expense	8	14	20	27
Total assets	16,669	16,584	16,669	16,584
Operating Segments | Corporate Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	77	61	145	115
Other revenue	6	10	19	21
Total net revenue	83	71	164	136
Provision for credit losses	25	3	139	26
Total noninterest expense	26	22	61	51
Income (loss) from continuing operations before income tax expense	32	46	(36)	59
Total assets	6,206	4,980	6,206	4,980
Corporate and Other
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	(54)	13	(68)	49
Other revenue	52	34	111	59
Total net revenue	(2)	47	43	108
Provision for credit losses	3	(6)	25	(11)
Total noninterest expense	155	78	255	158
Income (loss) from continuing operations before income tax expense	(160)	(25)	(237)	(39)
Total assets	$ 50,430	$ 35,688	$ 50,430	$ 35,688