Condensed Consolidated Statement of Comprehensive Income Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Revenue and Other Income [Line Items]
Interest and fees on finance receivables and loans	$ 1,708	$ 1,486	$ 4,898	$ 4,301
Interest on loans held-for-sale	4	0	10	0
Interest and dividends on investment securities and other earning assets	198	157	562	437
Interest on cash and cash equivalents	18	11	50	23
Operating leases	368	434	1,124	1,465
Financing revenue and other interest income	2,296	2,088	6,644	6,226
Interest Expense [Abstract]
Interest on deposits	462	285	1,212	766
Interest on short-term borrowings	29	34	101	94
Interest on long-term debt	451	416	1,296	1,257
Interest expense	942	735	2,609	2,117
Net depreciation expense on operating lease assets	247	272	785	982
Net financing revenue and other interest income	1,107	1,081	3,250	3,127
Other revenue [Abstract]
Insurance premiums and service revenue earned	258	252	753	720
Gain on mortgage and automotive loans, net	17	15	19	65
Other gain on investments, net	22	23	37	73
Other income, net of losses	101	91	307	307
Other revenue	398	381	1,116	1,165
Net revenue	1,505	1,462	4,366	4,292
Provision for loan losses	233	314	652	854
Noninterest Expense [Abstract]
Compensation and benefits expense	274	264	872	814
Insurance losses and loss adjustment expenses	77	65	241	278
Other operating expenses	456	424	1,347	1,249
Noninterest expense	807	753	2,460	2,341
Income from continuing operations before income tax expense	465	395	1,254	1,097
Income tax expense from continuing operations	91	115	280	350
Net income from continuing operations	374	280	974	747
Net income	374	282	973	748
Other comprehensive income (loss), attributable to parent	(133)	48	(531)	144
Comprehensive income	241	330	442	892
Income (loss) from discontinued operations, net of tax	$ 0	$ 2	$ (1)	$ 1
Earnings Per Share, Basic [Abstract]
Net income from continuing operations, basic earnings per share	$ 0.89	$ 0.62	$ 2.27	$ 1.63
Loss from discontinued operations, net of tax, basic earnings per share	0.00	0.00	0.00	0.00
Net income, basic earnings per share	0.89	0.63	2.26	1.63
Earnings Per Share, Diluted [Abstract]
Net income from continuing operations, diluted earnings per share	0.88	0.62	2.25	1.63
Loss from discontinued operations, net of tax, diluted earnings per share	0.00	0.00	0.00	0.00
Net income, diluted earnings per share	0.88	0.63	2.25	1.63
Cash dividends declared per common share	$ 0.15	$ 0.12	$ 0.41	$ 0.28
Retained earnings
Net income	$ 374	$ 282	$ 973	$ 748