Condensed Consolidated Statement of Comprehensive Income Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Revenue and Other Income [Abstract]
Interest and fees on finance receivables and loans	$ 1,859	$ 1,708	$ 5,526	$ 4,898
Interest on loans held-for-sale	8	4	13	10
Interest and dividends on investment securities and other earning assets	237	198	721	562
Interest on cash and cash equivalents	19	18	63	50
Operating leases	368	368	1,092	1,124
Total financing revenue and other interest income	2,491	2,296	7,415	6,644
Interest Expense [Abstract]
Interest on deposits	658	462	1,901	1,212
Interest on short-term borrowings	33	29	114	101
Interest on long-term debt	378	451	1,204	1,296
Total interest expense	1,069	942	3,219	2,609
Net depreciation expense on operating lease assets	234	247	719	785
Net financing revenue and other interest income	1,188	1,107	3,477	3,250
Other revenue [Abstract]
Insurance premiums and service revenue earned	280	258	802	753
Gain on mortgage and automotive loans, net	10	17	22	19
Other gain on investments, net	27	22	174	37
Other income, net of losses	96	101	276	307
Total 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 [Abstract]
Compensation and benefits expense	296	274	910	872
Insurance losses and loss adjustment expenses	74	77	260	241
Other operating expenses	468	456	1,379	1,347
Total noninterest expense	838	807	2,549	2,460
Income from continuing operations before income tax expense	500	465	1,480	1,254
Statement [Abstract]
Income tax expense from continuing operations	119	91	140	280
Net income from continuing operations	381	374	1,340	974
Loss from discontinued operations, net of tax	0	0	(3)	(1)
Net income	381	374	1,337	973
Other comprehensive income (loss), net of tax	106	(133)	721	(531)
Comprehensive income	$ 487	$ 241	$ 2,058	$ 442
Earnings Per Share, Basic [Abstract]
Net income from continuing operations, basic earnings per common share	$ 0.98	$ 0.89	$ 3.37	$ 2.27
Loss from discontinued operations, net of tax, basic earnings per common share	0	0	(0.01)	0
Net income, basic earnings per common share	0.97	0.89	3.36	2.26
Earnings Per Share, Diluted [Abstract]
Net income from continuing operations, diluted earnings per common share	0.97	0.88	3.35	2.25
Loss from discontinued operations, net of tax, diluted earnings per common share	0	0	(0.01)	0
Net income, diluted earnings per common share	0.97	0.88	3.35	2.25
Cash dividends declared per common share	$ 0.17	$ 0.15	$ 0.51	$ 0.41