Consolidated Statement of Income Consolidated Statement of Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Revenue and Other Income [Abstract]
Interest and fees on finance receivables and loans									$ 7,337	$ 6,688	$ 5,819
Interest on loans held-for-sale									17	15	0
Interest and dividends on investment securities and other earning assets									955	788	599
Interest on cash and cash equivalents									78	72	37
Operating leases									1,470	1,489	1,867
Total financing revenue and other interest income									9,857	9,052	8,322
Interest Expense [Abstract]
Interest on deposits									2,538	1,735	1,077
Interest on short-term borrowings									135	149	127
Interest on long-term debt									1,570	1,753	1,653
Total interest expense									4,243	3,637	2,857
Net depreciation expense on operating lease assets									981	1,025	1,244
Net financing revenue and other interest income	$ 1,156	$ 1,188	$ 1,157	$ 1,132	$ 1,140	$ 1,107	$ 1,094	$ 1,049	4,633	4,390	4,221
Other revenue [Abstract]
Insurance premiums and service revenue earned									1,087	1,022	973
Gain on mortgage and automotive loans, net									28	25	68
Other gain on investments, net									243	(50)	102
Other income, net of losses									403	417	401
Total other revenue	487	413	395	466	298	398	364	354	1,761	1,414	1,544
Total net revenue	1,643	1,601	1,552	1,598	1,438	1,505	1,458	1,403	6,394	5,804	5,765
Provision for loan losses	276	263	177	282	266	233	158	261	998	918	1,148
Noninterest Expense [Abstract]
Compensation and benefits expense									1,222	1,155	1,095
Insurance losses and loss adjustment expenses									321	295	332
Other operating expenses									1,886	1,814	1,683
Total noninterest expense	880	838	881	830	804	807	839	814	3,429	3,264	3,110
Income from continuing operations before income tax expense	487	500	494	486	368	465	461	328	1,967	1,622	1,507
Statement [Abstract]
Income tax expense from continuing operations	106	119	(90)	111	79	91	113	76	246	359	581
Net income from continuing operations	381	381	584	375	289	374	348	252	1,721	1,263	926
Loss from discontinued operations, net of tax	(3)	0	(2)	(1)	1	0	1	(2)	(6)	0	3
Net income	$ 378	$ 381	$ 582	$ 374	$ 290	$ 374	$ 349	$ 250	$ 1,715	$ 1,263	$ 929
Earnings Per Share, Basic [Abstract]
Net income from continuing operations, basic earnings per common share	$ 1.00	$ 0.98	$ 1.47	$ 0.93	$ 0.70	$ 0.89	$ 0.81	$ 0.58	$ 4.38	$ 2.97	$ 2.04
Loss from discontinued operations, net of tax, basic earnings per common share									(0.02)	0	0.01
Net income, basic earnings per common share	0.99	0.97	1.46	0.93	0.70	0.89	0.81	0.57	4.36	2.97	2.05
Earnings Per Share, Diluted [Abstract]
Net income from continuing operations, diluted earnings per common share	0.99	0.97	1.46	0.92	0.70	0.88	0.80	0.57	4.35	2.95	2.03
Loss from discontinued operations, net of tax, diluted earnings per common share									(0.02)	0	0.01
Net income, diluted earnings per common share	0.99	0.97	1.46	0.92	0.70	0.88	0.81	0.57	4.34	2.95	2.04
Cash dividends declared per common share	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.15	$ 0.15	$ 0.13	$ 0.13	$ 0.68	$ 0.56	$ 0.40