Parent and Guarantor Condensed Consolidating Financial Statements (Schedule of Condensed Consolidating Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Condensed Income Statements, Captions [Line Items]
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
Financing revenue (loss) and other interest income	2,491	2,296	7,415	6,644
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
Interest on intercompany debt	0	0	0	0
Interest expense	1,069	942	3,219	2,609
Net depreciation expense on operating lease assets	234	247	719	785
Net financing (loss) revenue	1,188	1,107	3,477	3,250
Cash dividends from bank subsidiaries	0	0	0	0
Cash dividends from nonbank subsidiaries	0	0	0	0
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
Net revenue	1,601	1,505	4,751	4,366
Provision for loan losses	263	233	722	652
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 and undistributed (loss) income of subsidiaries	500	465	1,480	1,254
Income tax (benefit) expense from continuing operations	119	91	140	280
Net income from continuing operations	381	374	1,340	974
Income (loss) from discontinued operations, net of tax	0	0	(3)	(1)
Undistributed income (loss) of bank subsidiary	0	0	0	0
Undistributed income (loss) of nonbank subsidiaries	0	0	0	0
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
Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	0	0	0	0
Interest on cash and cash equivalents	0	0	0	0
Gain on mortgage and automotive loans, net			0	0
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	(3)	0	(6)	0
Interest on loans held-for-sale	0	0	0	0
Interest and dividends on investment securities and other earning assets	0	0	0	(1)
Interest on cash and cash equivalents	0	0	0	0
Operating leases	0	0	0	0
Financing revenue (loss) and other interest income	(16)	(9)	(41)	(26)
Interest on deposits	0	0	0	0
Interest on short-term borrowings	0	0	0	0
Interest on long-term debt	0	0	0	0
Interest on intercompany debt	(13)	(9)	(35)	(26)
Interest expense	(13)	(9)	(35)	(26)
Net depreciation expense on operating lease assets	0	0	0	0
Net financing (loss) revenue	(3)	0	(6)	0
Cash dividends from bank subsidiaries	(1,100)	(1,100)	(2,900)	(4,100)
Cash dividends from nonbank subsidiaries	(51)	(88)	(187)	(389)
Insurance premiums and service revenue earned	0	0	0	0
Gain on mortgage and automotive loans, net	0	0	0	(28)
Other gain on investments, net	0	0	0	0
Other income, net of losses	(119)	(191)	(422)	(587)
Total other revenue	(119)	(191)	(422)	(615)
Net revenue	(1,273)	(1,379)	(3,515)	(5,104)
Provision for loan losses	1	0	(17)	(28)
Compensation and benefits expense	0	0	0	0
Insurance losses and loss adjustment expenses	0	0	0	0
Other operating expenses	(119)	(191)	(422)	(587)
Total noninterest expense	(119)	(191)	(422)	(587)
Income from continuing operations before income tax expense and undistributed (loss) income of subsidiaries	(1,155)	(1,188)	(3,076)	(4,489)
Income tax (benefit) expense from continuing operations	0	0	0	0
Net income from continuing operations	(1,155)	(1,188)	(3,076)	(4,489)
Income (loss) from discontinued operations, net of tax	0	0	0	0
Undistributed income (loss) of bank subsidiary	(34)	62	(368)	1,152
Undistributed income (loss) of nonbank subsidiaries	15	(48)	(125)	(83)
Net income	(1,174)	(1,174)	(3,569)	(3,420)
Other comprehensive income (loss), net of tax	(189)	237	(1,286)	982
Comprehensive income	(1,363)	(937)	(4,855)	(2,438)
Consolidating adjustments | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	(5)	(5)	(14)	(13)
Interest on cash and cash equivalents	(8)	(4)	(21)	(12)
Gain on mortgage and automotive loans, net			(1,057)	(39)
Parent
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	(52)	(4)	(172)	6
Interest on loans held-for-sale	0	0	0	0
Interest and dividends on investment securities and other earning assets	0	0	0	0
Interest on cash and cash equivalents	2	2	8	6
Operating leases	0	1	1	4
Financing revenue (loss) and other interest income	(43)	3	(145)	30
Interest on deposits	0	0	0	0
Interest on short-term borrowings	15	12	41	32
Interest on long-term debt	215	250	638	765
Interest on intercompany debt	6	5	17	12
Interest expense	236	267	696	809
Net depreciation expense on operating lease assets	1	2	3	7
Net financing (loss) revenue	(280)	(266)	(844)	(786)
Cash dividends from bank subsidiaries	550	550	1,450	2,050
Cash dividends from nonbank subsidiaries	52	88	188	389
Insurance premiums and service revenue earned	0	0	0	0
Gain on mortgage and automotive loans, net	1	16	4	44
Other gain on investments, net	2	0	2	0
Other income, net of losses	72	105	266	301
Total other revenue	75	121	272	345
Net revenue	397	493	1,066	1,998
Provision for loan losses	3	30	35	143
Compensation and benefits expense	9	19	30	67
Insurance losses and loss adjustment expenses	0	0	0	0
Other operating expenses	124	175	438	530
Total noninterest expense	133	194	468	597
Income from continuing operations before income tax expense and undistributed (loss) income of subsidiaries	261	269	563	1,258
Income tax (benefit) expense from continuing operations	(117)	(88)	(467)	(210)
Net income from continuing operations	378	357	1,030	1,468
Income (loss) from discontinued operations, net of tax	1	0	(2)	(2)
Undistributed income (loss) of bank subsidiary	17	(31)	184	(576)
Undistributed income (loss) of nonbank subsidiaries	(15)	48	125	83
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
Parent | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	4	3	10	9
Interest on cash and cash equivalents	3	1	8	5
Gain on mortgage and automotive loans, net			761	45
Guarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	0	0	0	0
Interest on loans held-for-sale	0	0	0	0
Interest and dividends on investment securities and other earning assets	0	0	0	0
Interest on cash and cash equivalents	0	0	0	0
Operating leases	0	0	0	0
Financing revenue (loss) and other interest income	0	0	0	0
Interest on deposits	0	0	0	0
Interest on short-term borrowings	0	0	0	0
Interest on long-term debt	0	0	0	0
Interest on intercompany debt	0	0	0	0
Interest expense	0	0	0	0
Net depreciation expense on operating lease assets	0	0	0	0
Net financing (loss) revenue	0	0	0	0
Cash dividends from bank subsidiaries	550	550	1,450	2,050
Cash dividends from nonbank subsidiaries	0	0	0	0
Insurance premiums and service revenue earned	0	0	0	0
Gain on mortgage and automotive loans, net	0	0	0	0
Other gain on investments, net	0	0	0	0
Other income, net of losses	0	0	0	0
Total other revenue	0	0	0	0
Net revenue	550	550	1,450	2,050
Provision for loan losses	0	0	0	0
Compensation and benefits expense	0	0	0	0
Insurance losses and loss adjustment expenses	0	0	0	0
Other operating expenses	0	0	0	0
Total noninterest expense	0	0	0	0
Income from continuing operations before income tax expense and undistributed (loss) income of subsidiaries	550	550	1,450	2,050
Income tax (benefit) expense from continuing operations	0	0	0	0
Net income from continuing operations	550	550	1,450	2,050
Income (loss) from discontinued operations, net of tax	0	0	0	0
Undistributed income (loss) of bank subsidiary	17	(31)	184	(576)
Undistributed income (loss) of nonbank subsidiaries	0	0	0	0
Net income	567	519	1,634	1,474
Other comprehensive income (loss), net of tax	80	(104)	546	(436)
Comprehensive income	647	415	2,180	1,038
Guarantors | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	0	0	0	0
Interest on cash and cash equivalents	0	0	0	0
Gain on mortgage and automotive loans, net			0	0
Nonguarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	1,914	1,712	5,704	4,892
Interest on loans held-for-sale	8	4	13	10
Interest and dividends on investment securities and other earning assets	237	198	721	563
Interest on cash and cash equivalents	17	16	55	44
Operating leases	368	367	1,091	1,120
Financing revenue (loss) and other interest income	2,550	2,302	7,601	6,640
Interest on deposits	658	462	1,901	1,212
Interest on short-term borrowings	18	17	73	69
Interest on long-term debt	163	201	566	531
Interest on intercompany debt	7	4	18	14
Interest expense	846	684	2,558	1,826
Net depreciation expense on operating lease assets	233	245	716	778
Net financing (loss) revenue	1,471	1,373	4,327	4,036
Cash dividends from bank subsidiaries	0	0	0	0
Cash dividends from nonbank subsidiaries	(1)	0	(1)	0
Insurance premiums and service revenue earned	280	258	802	753
Gain on mortgage and automotive loans, net	9	1	18	3
Other gain on investments, net	25	22	172	37
Other income, net of losses	143	187	432	593
Total other revenue	457	468	1,424	1,386
Net revenue	1,927	1,841	5,750	5,422
Provision for loan losses	259	203	704	537
Compensation and benefits expense	287	255	880	805
Insurance losses and loss adjustment expenses	74	77	260	241
Other operating expenses	463	472	1,363	1,404
Total noninterest expense	824	804	2,503	2,450
Income from continuing operations before income tax expense and undistributed (loss) income of subsidiaries	844	834	2,543	2,435
Income tax (benefit) expense from continuing operations	236	179	607	490
Net income from continuing operations	608	655	1,936	1,945
Income (loss) from discontinued operations, net of tax	(1)	0	(1)	1
Undistributed income (loss) of bank subsidiary	0	0	0	0
Undistributed income (loss) of nonbank subsidiaries	0	0	0	0
Net income	607	655	1,935	1,946
Other comprehensive income (loss), net of tax	109	(133)	740	(546)
Comprehensive income	716	522	2,675	1,400
Nonguarantors | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	1	2	4	4
Interest on cash and cash equivalents	$ 5	$ 3	13	7
Gain on mortgage and automotive loans, net			$ 296	$ (6)