Parent and Guarantor Condensed Consolidating Financial Statements (Schedule of Condensed Consolidating Statement of Income) (Details) - 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
Condensed Income Statements, Captions [Line Items]
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
Financing revenue (loss) and other interest income									9,857	9,052	8,322
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
Interest on intercompany debt									0	0	0
Interest expense									4,243	3,637	2,857
Net depreciation expense on operating lease assets									981	1,025	1,244
Net financing (loss) revenue	$ 1,156	$ 1,188	$ 1,157	$ 1,132	$ 1,140	$ 1,107	$ 1,094	$ 1,049	4,633	4,390	4,221
Cash dividends from bank subsidiaries									0	0	0
Cash dividends from nonbank subsidiaries									0	0	0
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									998	918	1,148
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 and undistributed (loss) income of subsidiaries	487	500	494	486	368	465	461	328	1,967	1,622	1,507
Income tax (benefit) 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
Income (loss) from discontinued operations, net of tax									(6)	0	3
Undistributed income (loss) of bank subsidiary									0	0	0
Undistributed income (loss) of nonbank subsidiaries									0	0	0
Net income	$ 378	$ 381	$ 582	$ 374	$ 290	$ 374	$ 349	$ 250	1,715	1,263	929
Other comprehensive income (loss), net of tax									654	(289)	106
Comprehensive income									2,369	974	1,035
Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									0	0	0
Interest on cash and cash equivalents									0	0	0
Gain on mortgage and automotive loans, net									0	0	0
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									(8)	0	0
Interest on loans held-for-sale									0	0
Interest and dividends on investment securities and other earning assets									0	(1)	(2)
Interest on cash and cash equivalents									0	0	0
Operating leases									0	0	0
Financing revenue (loss) and other interest income									(56)	(35)	(31)
Interest on deposits									0	0	(4)
Interest on short-term borrowings									0	0	0
Interest on long-term debt									0	0	0
Interest on intercompany debt									(48)	(35)	(27)
Interest expense									(48)	(35)	(31)
Net depreciation expense on operating lease assets									0	0	0
Net financing (loss) revenue									(8)	0	0
Cash dividends from bank subsidiaries									(3,900)	(5,200)	(6,600)
Cash dividends from nonbank subsidiaries									(436)	(443)	(752)
Insurance premiums and service revenue earned									0	0	0
Gain on mortgage and automotive loans, net									0	(54)	0
Other gain on investments, net									0	0	0
Other income, net of losses									(545)	(764)	(1,108)
Total other revenue									(545)	(818)	(1,108)
Total net revenue									(4,889)	(6,461)	(8,460)
Provision for loan losses									(18)	(54)	0
Compensation and benefits expense									0	0	0
Insurance losses and loss adjustment expenses									0	0	0
Other operating expenses									(545)	(764)	(1,108)
Total noninterest expense									(545)	(764)	(1,108)
Income from continuing operations before income tax expense and undistributed (loss) income of subsidiaries									(4,326)	(5,643)	(7,352)
Income tax (benefit) expense from continuing operations									0	0	0
Net income from continuing operations									(4,326)	(5,643)	(7,352)
Income (loss) from discontinued operations, net of tax									0	0	0
Undistributed income (loss) of bank subsidiary									(420)	1,228	2,336
Undistributed income (loss) of nonbank subsidiaries									7	(78)	(387)
Net income									(4,739)	(4,493)	(5,403)
Other comprehensive income (loss), net of tax									(1,177)	551	(169)
Comprehensive income									(5,916)	(3,942)	(5,572)
Consolidating adjustments | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									(17)	(17)	(18)
Interest on cash and cash equivalents									(31)	(17)	(11)
Gain on mortgage and automotive loans, net									(1,002)	22	(2,285)
Parent
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									(225)	(40)	(27)
Interest on loans held-for-sale									0	0
Interest and dividends on investment securities and other earning assets									0	0	0
Interest on cash and cash equivalents									10	8	7
Operating leases									2	5	11
Financing revenue (loss) and other interest income									(188)	(7)	7
Interest on deposits									0	0	3
Interest on short-term borrowings									53	44	60
Interest on long-term debt									849	1,009	1,101
Interest on intercompany debt									23	15	15
Interest expense									925	1,068	1,179
Net depreciation expense on operating lease assets									3	8	11
Net financing (loss) revenue									(1,116)	(1,083)	(1,183)
Cash dividends from bank subsidiaries									1,950	2,600	3,300
Cash dividends from nonbank subsidiaries									436	443	752
Insurance premiums and service revenue earned									0	0	0
Gain on mortgage and automotive loans, net									4	70	40
Other gain on investments, net									2	0	0
Other income, net of losses									337	411	675
Total other revenue									343	481	715
Total net revenue									1,613	2,441	3,584
Provision for loan losses									35	176	465
Compensation and benefits expense									36	83	180
Insurance losses and loss adjustment expenses									0	0	0
Other operating expenses									590	681	899
Total noninterest expense									626	764	1,079
Income from continuing operations before income tax expense and undistributed (loss) income of subsidiaries									952	1,501	2,040
Income tax (benefit) expense from continuing operations									(566)	(300)	337
Net income from continuing operations									1,518	1,801	1,703
Income (loss) from discontinued operations, net of tax									(6)	(2)	7
Undistributed income (loss) of bank subsidiary									210	(614)	(1,168)
Undistributed income (loss) of nonbank subsidiaries									(7)	78	387
Net income									1,715	1,263	929
Other comprehensive income (loss), net of tax									654	(289)	106
Comprehensive income									2,369	974	1,035
Parent | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									11	12	12
Interest on cash and cash equivalents									14	8	4
Gain on mortgage and automotive loans, net									718	(20)	2,068
Guarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									0	0	0
Interest on loans held-for-sale										0
Interest and dividends on investment securities and other earning assets									0	0	0
Interest on cash and cash equivalents									0	0	0
Operating leases									0	0	0
Financing revenue (loss) and other interest income									0	0	0
Interest on deposits									0	0	0
Interest on short-term borrowings									0	0	0
Interest on long-term debt									0	0	0
Interest on intercompany debt									0	0	0
Interest expense									0	0	0
Net depreciation expense on operating lease assets									0	0	0
Net financing (loss) revenue									0	0	0
Cash dividends from bank subsidiaries									1,950	2,600	3,300
Cash dividends from nonbank subsidiaries									0	0	0
Insurance premiums and service revenue earned									0	0	0
Gain on mortgage and automotive loans, net									0	0	0
Other gain on investments, net									0	0	0
Other income, net of losses									0	0	0
Total other revenue									0	0	0
Total net revenue									1,950	2,600	3,300
Provision for loan losses									0	0	0
Compensation and benefits expense									0	0	0
Insurance losses and loss adjustment expenses									0	0	0
Other operating expenses									0	0	0
Total noninterest expense									0	0	0
Income from continuing operations before income tax expense and undistributed (loss) income of subsidiaries									1,950	2,600	3,300
Income tax (benefit) expense from continuing operations									0	0	0
Net income from continuing operations									1,950	2,600	3,300
Income (loss) from discontinued operations, net of tax									0	0	0
Undistributed income (loss) of bank subsidiary									210	(614)	(1,168)
Undistributed income (loss) of nonbank subsidiaries									0	0	0
Net income									2,160	1,986	2,132
Other comprehensive income (loss), net of tax									492	(243)	65
Comprehensive income									2,652	1,743	2,197
Guarantors | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans										0	0
Interest on cash and cash equivalents									0	0	0
Gain on mortgage and automotive loans, net									0	0	0
Nonguarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									7,570	6,728	5,846
Interest on loans held-for-sale									17	15
Interest and dividends on investment securities and other earning assets									955	789	601
Interest on cash and cash equivalents									68	64	30
Operating leases									1,468	1,484	1,856
Financing revenue (loss) and other interest income									10,101	9,094	8,346
Interest on deposits									2,538	1,735	1,078
Interest on short-term borrowings									82	105	67
Interest on long-term debt									721	744	552
Interest on intercompany debt									25	20	12
Interest expense									3,366	2,604	1,709
Net depreciation expense on operating lease assets									978	1,017	1,233
Net financing (loss) revenue									5,757	5,473	5,404
Cash dividends from bank subsidiaries									0	0	0
Cash dividends from nonbank subsidiaries									0	0	0
Insurance premiums and service revenue earned									1,087	1,022	973
Gain on mortgage and automotive loans, net									24	9	28
Other gain on investments, net									241	(50)	102
Other income, net of losses									611	770	834
Total other revenue									1,963	1,751	1,937
Total net revenue									7,720	7,224	7,341
Provision for loan losses									981	796	683
Compensation and benefits expense									1,186	1,072	915
Insurance losses and loss adjustment expenses									321	295	332
Other operating expenses									1,841	1,897	1,892
Total noninterest expense									3,348	3,264	3,139
Income from continuing operations before income tax expense and undistributed (loss) income of subsidiaries									3,391	3,164	3,519
Income tax (benefit) expense from continuing operations									812	659	244
Net income from continuing operations									2,579	2,505	3,275
Income (loss) from discontinued operations, net of tax									0	2	(4)
Undistributed income (loss) of bank subsidiary									0	0	0
Undistributed income (loss) of nonbank subsidiaries									0	0	0
Net income									2,579	2,507	3,271
Other comprehensive income (loss), net of tax									685	(308)	104
Comprehensive income									3,264	2,199	3,375
Nonguarantors | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans									6	5	6
Interest on cash and cash equivalents									17	9	7
Gain on mortgage and automotive loans, net									$ 284	$ (2)	$ 217