Consolidated Statement of Income Consolidated Statement of Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Revenue and Other Income [Line Items]
Interest and fees on finance receivables and loans									$ 6,688	$ 5,819	$ 5,162
Interest on loans held-for-sale									15	0	0
Interest and dividends on investment securities and other earning assets									788	599	418
Interest on cash and cash equivalents									72	37	14
Operating leases									1,489	1,867	2,711
Total financing revenue and other interest income									9,052	8,322	8,305
Interest Expense [Abstract]
Interest on deposits									1,735	1,077	830
Interest on short-term borrowings									149	127	57
Interest on long-term debt									1,753	1,653	1,742
Total interest expense									3,637	2,857	2,629
Net depreciation expense on operating lease assets									1,025	1,244	1,769
Net financing revenue and other interest income	$ 1,140	$ 1,107	$ 1,094	$ 1,049	$ 1,094	$ 1,081	$ 1,067	$ 979	4,390	4,221	3,907
Other revenue [Abstract]
Insurance premiums and service revenue earned									1,022	973	945
Gain on mortgage and automotive loans, net									25	68	11
Other (loss) gain on investments, net									(50)	102	185
Other income, net of losses									417	401	389
Total other revenue	298	398	364	354	379	381	388	396	1,414	1,544	1,530
Total net revenue									5,804	5,765	5,437
Provision for loan losses									918	1,148	917
Noninterest Expense [Abstract]
Compensation and benefits expense									1,155	1,095	992
Insurance losses and loss adjustment expenses									295	332	342
Other operating expenses									1,814	1,683	1,605
Total noninterest expense	804	807	839	814	769	753	810	778	3,264	3,110	2,939
Income from continuing operations before income tax expense	368	465	461	328	410	395	376	326	1,622	1,507	1,581
Income tax expense from continuing operations	79	91	113	76	231	115	122	113	359	581	470
Net income from continuing operations	289	374	348	252	179	280	254	213	1,263	926	1,111
Net income	290	374	349	250	181	282	252	214	1,263	929	1,067
Income (loss) from discontinued operations, net of tax	$ 1	$ 0	$ 1	$ (2)	$ 2	$ 2	$ (2)	$ 1	$ 0	$ 3	$ (44)
Earnings Per Share, Basic [Abstract]
Net income from continuing operations, basic earnings per common share	$ 0.70	$ 0.89	$ 0.81	$ 0.58	$ 0.40	$ 0.62	$ 0.55	$ 0.46	$ 2.97	$ 2.04	$ 2.25
Income (loss) from discontinued operations, net of tax, basic earnings per common share									0.00	0.01	(0.09)
Net income, basic earnings per common share	0.70	0.89	0.81	0.57	0.41	0.63	0.55	0.46	2.97	2.05	2.15
Earnings Per Share, Diluted [Abstract]
Net income from continuing operations, diluted earnings per common share	0.70	0.88	0.80	0.57	0.40	0.62	0.55	0.46	2.95	2.03	2.24
Income (loss) from discontinued operations, net of tax, diluted earnings per common share									0.00	0.01	(0.09)
Net income, diluted earnings per common share	0.70	0.88	0.81	0.57	0.41	0.63	0.55	0.46	2.95	2.04	2.15
Cash dividends declared per common share	$ 0.15	$ 0.15	$ 0.13	$ 0.13	$ 0.12	$ 0.12	$ 0.08	$ 0.08	$ 0.56	$ 0.40	$ 0.16
Retained earnings
Net income									$ 1,263	$ 929	$ 1,067