Segment Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) segment subsegment	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			4
Number of operating subsegments | subsegment			2
Net financing revenue and other interest income	$ 1,488	$ 1,533	$ 4,439	$ 4,708
Other revenue	615	435	1,650	1,439
Total net revenue	2,103	1,968	6,089	6,147
Provision for credit losses	645	508	1,609	1,381
Total noninterest expense	1,225	1,232	3,819	3,747
Income (loss) from continuing operations before income tax (benefit) expense	233	228	661	1,019
Total assets	192,981	195,704	192,981	195,704	$ 196,392
Net financing revenue and other interest income after the provision for credit losses	843	1,000	2,800	3,300
Operating Segments | Automotive Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	1,285	1,360	3,913	4,031
Other revenue	85	79	275	239
Total net revenue	1,370	1,439	4,188	4,270
Provision for credit losses	579	444	1,410	1,126
Total noninterest expense	616	618	1,874	1,824
Income (loss) from continuing operations before income tax (benefit) expense	175	377	904	1,320
Total assets	113,934	114,742	113,934	114,742
Operating Segments | Insurance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	31	29	90	84
Other revenue	437	293	1,159	1,011
Total net revenue	468	322	1,249	1,095
Provision for credit losses	0	0	0	0
Total noninterest expense	366	338	1,119	1,011
Income (loss) from continuing operations before income tax (benefit) expense	102	(16)	130	84
Total assets	9,455	8,736	9,455	8,736
Operating Segments | Mortgage Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	52	53	157	160
Other revenue	6	4	17	13
Total net revenue	58	57	174	173
Provision for credit losses	0	(2)	(1)	(3)
Total noninterest expense	31	33	96	108
Income (loss) from continuing operations before income tax (benefit) expense	27	26	79	68
Total assets	17,594	18,745	17,594	18,745
Operating Segments | Corporate Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	101	97	316	292
Other revenue	37	24	90	81
Total net revenue	138	121	406	373
Provision for credit losses	11	5	13	35
Total noninterest expense	32	32	110	110
Income (loss) from continuing operations before income tax (benefit) expense	95	84	283	228
Total assets	10,398	10,749	10,398	10,749
Corporate and Other
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	19	(6)	(37)	141
Other revenue	50	35	109	95
Total net revenue	69	29	72	236
Provision for credit losses	55	61	187	223
Total noninterest expense	180	211	620	694
Income (loss) from continuing operations before income tax (benefit) expense	(166)	(243)	(735)	(681)
Total assets	$ 41,600	$ 42,732	$ 41,600	$ 42,732