Segment Information (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2025 USD ($) subsegment segment	Mar. 31, 2024 USD ($)	Dec. 31, 2024 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment	3
Number of operating subsegments | subsegment	2
Total financing revenue and other interest income	$ 3,393	$ 3,582
Total interest expense	1,675	1,922
Net depreciation expense on operating lease assets	240	192
Net financing revenue and other interest income	1,478	1,468
Other revenue	63	530
Total net revenue	1,541	1,998
Provision for credit losses	191	507
Compensation and benefits expense	505	519
Insurance losses and loss adjustment expenses	161	112
Goodwill impairment	305	0	$ 118
Other operating expenses
Technology and communications	103	106
Other	560	571
Total other operating expenses	663	677
Total noninterest expense	1,634	1,308
(Loss) income from continuing operations before income tax (benefit) expense	(284)	183
Total assets	193,331	192,800	191,836
Net financing revenue and other interest income after the provision for credit losses	1,300	961
Operating Segments | Automotive Finance operations
Segment Reporting Information [Line Items]
Total financing revenue and other interest income	2,571	2,576
Total interest expense	1,065	1,010
Net depreciation expense on operating lease assets	240	192
Net financing revenue and other interest income	1,266	1,374
Other revenue	97	97
Total net revenue	1,363	1,471
Provision for credit losses	434	448
Compensation and benefits expense	183	178
Insurance losses and loss adjustment expenses	0	0
Goodwill impairment	0		0
Other operating expenses
Technology and communications	29	32
Other	342	333
Total other operating expenses	371	365
Total noninterest expense	554	543
(Loss) income from continuing operations before income tax (benefit) expense	375	480
Total assets	111,672	114,464
Operating Segments | Insurance operations
Segment Reporting Information [Line Items]
Total financing revenue and other interest income	44	39
Total interest expense	14	13
Net depreciation expense on operating lease assets	0	0
Net financing revenue and other interest income	30	26
Other revenue	364	384
Total net revenue	394	410
Provision for credit losses	0	0
Compensation and benefits expense	30	28
Insurance losses and loss adjustment expenses	161	112
Goodwill impairment	0		0
Other operating expenses
Technology and communications	5	5
Other	196	195
Total other operating expenses	201	200
Total noninterest expense	392	340
(Loss) income from continuing operations before income tax (benefit) expense	2	70
Total assets	9,489	9,100
Operating Segments | Corporate Finance operations
Segment Reporting Information [Line Items]
Total financing revenue and other interest income	221	269
Total interest expense	117	149
Net depreciation expense on operating lease assets	0	0
Net financing revenue and other interest income	104	120
Other revenue	29	23
Total net revenue	133	143
Provision for credit losses	14	(1)
Compensation and benefits expense	25	27
Insurance losses and loss adjustment expenses	0	0
Goodwill impairment	0
Other operating expenses
Technology and communications	1	1
Other	17	16
Total other operating expenses	18	17
Total noninterest expense	43	44
(Loss) income from continuing operations before income tax (benefit) expense	76	100
Total assets	11,002	10,410
Corporate and Other
Segment Reporting Information [Line Items]
Total financing revenue and other interest income	557	698
Total interest expense	479	750
Net depreciation expense on operating lease assets	0	0
Net financing revenue and other interest income	78	(52)
Other revenue	(427)	26
Total net revenue	(349)	(26)
Provision for credit losses	(257)	60
Compensation and benefits expense	267	286
Insurance losses and loss adjustment expenses	0	0
Goodwill impairment	305		$ 118
Other operating expenses
Technology and communications	68	68
Other	5	27
Total other operating expenses	73	95
Total noninterest expense	645	381
(Loss) income from continuing operations before income tax (benefit) expense	(737)	(467)
Total assets	$ 61,168	$ 58,826