Segment Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments	4
Net financing revenue and other interest income	$ 1,132	$ 1,049
Other revenue	466	354
Net revenue	1,598	1,403
Provision for loan losses	282	261
Noninterest expense	830	814
Income from continuing operations before income tax expense	486	328
Assets	180,117	170,021	$ 178,869
Net financing revenue and other interest income after provision for loan losses	850	788
Corporate and Other
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	36	39
Other revenue	25	33
Net revenue	61	72
Provision for loan losses	(5)	0
Noninterest expense	80	76
Income from continuing operations before income tax expense	(14)	(4)
Assets	34,842	30,375
Automotive Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	980	909
Other revenue	68	66
Net revenue	1,048	975
Provision for loan losses	262	259
Noninterest expense	457	448
Income from continuing operations before income tax expense	329	268
Assets	115,789	114,934
Insurance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	12	12
Other revenue	360	246
Net revenue	372	258
Provision for loan losses	0	0
Noninterest expense	227	231
Income from continuing operations before income tax expense	145	27
Assets	8,179	7,557
Mortgage Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	50	43
Other revenue	2	1
Net revenue	52	44
Provision for loan losses	2	2
Noninterest expense	37	34
Income from continuing operations before income tax expense	13	8
Assets	16,301	12,780
Corporate Finance operations
Segment Reporting Information [Line Items]
Net financing revenue and other interest income	54	46
Other revenue	11	8
Net revenue	65	54
Provision for loan losses	23	0
Noninterest expense	29	25
Income from continuing operations before income tax expense	13	29
Assets	$ 5,006	$ 4,375