Parent and Guarantor Condensed Consolidating Financial Statements (Schedule of Condensed Consolidating Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	$ 1,860	$ 1,647	$ 3,667	$ 3,190
Interest on loans held-for-sale	3	6	5	6
Interest and dividends on investment securities and other earning assets	244	188	484	364
Interest on cash and cash equivalents	21	17	44	32
Operating leases	363	374	724	756
Financing revenue and other interest income	2,491	2,232	4,924	4,348
Interest on deposits	651	399	1,243	750
Interest on short-term borrowings	37	40	81	72
Interest on long-term debt	407	434	826	845
Interest on intercompany debt	0	0	0	0
Interest expense	1,095	873	2,150	1,667
Net depreciation expense on operating lease assets	239	265	485	538
Net financing (loss) revenue	1,157	1,094	2,289	2,143
Cash dividends from bank subsidiaries	0	0	0	0
Cash dividends from nonbank subsidiaries	0	0	0	0
Insurance premiums and service revenue earned	261	239	522	495
Gain on mortgage and automotive loans, net	2	1	12	2
Other gain (loss) on investments, net	39	27	147	15
Other income, net of losses	93	97	180	206
Total other revenue	395	364	861	718
Net revenue	1,552	1,458	3,150	2,861
Provision for loan losses	177	158	459	419
Compensation and benefits expense	296	292	614	598
Insurance losses and loss adjustment expenses	127	101	186	164
Other operating expenses	458	446	911	891
Total noninterest expense	881	839	1,711	1,653
Income from continuing operations before income tax (benefit) expense and undistributed (loss) income of subsidiaries	494	461	980	789
Income tax (benefit) expense from continuing operations	(90)	113	21	189
Net income from continuing operations	584	348	959	600
Income (loss) from discontinued operations, net of tax	(2)	1	(3)	(1)
Undistributed income of bank subsidiary	0	0	0	0
Undistributed income of nonbank subsidiaries	0	0	0	0
Net income	582	349	956	599
Other comprehensive income (loss), net of tax	309	(70)	615	(398)
Comprehensive income	891	279	1,571	201
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	(3)	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	1	0	0
Operating leases	0	0	0	0
Financing revenue and other interest income	(15)	(8)	(25)	(17)
Interest on deposits	0	4	0	0
Interest on short-term borrowings	0	0	0	0
Interest on long-term debt	0	0	0	0
Interest on intercompany debt	(12)	(12)	(22)	(17)
Interest expense	(12)	(8)	(22)	(17)
Net depreciation expense on operating lease assets	0	0	0	0
Net financing (loss) revenue	(3)	0	(3)	0
Cash dividends from bank subsidiaries	(1,000)	(1,000)	(1,800)	(3,000)
Cash dividends from nonbank subsidiaries	(94)	(132)	(136)	(301)
Insurance premiums and service revenue earned	0	0	0	0
Gain on mortgage and automotive loans, net	0	0	0	(28)
Other gain (loss) on investments, net	0	0	0	0
Other income, net of losses	(143)	(188)	(303)	(396)
Total other revenue	(143)	(188)	(303)	(424)
Net revenue	(1,240)	(1,320)	(2,242)	(3,725)
Provision for loan losses	(1)	0	(18)	(28)
Compensation and benefits expense	0	0	0	0
Insurance losses and loss adjustment expenses	0	0	0	0
Other operating expenses	(143)	(188)	(303)	(396)
Total noninterest expense	(143)	(188)	(303)	(396)
Income from continuing operations before income tax (benefit) expense and undistributed (loss) income of subsidiaries	(1,096)	(1,132)	(1,921)	(3,301)
Income tax (benefit) expense from continuing operations	0	0	0	0
Net income from continuing operations	(1,096)	(1,132)	(1,921)	(3,301)
Income (loss) from discontinued operations, net of tax	0	0	0	0
Undistributed income of bank subsidiary	(220)	(104)	(334)	1,090
Undistributed income of nonbank subsidiaries	43	6	(140)	(35)
Net income	(1,273)	(1,230)	(2,395)	(2,246)
Other comprehensive income (loss), net of tax	(548)	130	(1,097)	745
Comprehensive income	(1,821)	(1,100)	(3,492)	(1,501)
Consolidating adjustments | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	(4)	(5)	(9)	(8)
Interest on cash and cash equivalents	(8)	(4)	(13)	(8)
Gain on mortgage and automotive loans, net			(507)	(78)
Parent
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	(60)	(1)	(120)	10
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	4	2	6	4
Operating leases	(1)	1	1	3
Financing revenue and other interest income	(51)	8	(102)	27
Interest on deposits	0	0	0	0
Interest on short-term borrowings	13	10	26	20
Interest on long-term debt	212	257	423	515
Interest on intercompany debt	6	4	11	7
Interest expense	231	271	460	542
Net depreciation expense on operating lease assets	1	1	2	5
Net financing (loss) revenue	(283)	(264)	(564)	(520)
Cash dividends from bank subsidiaries	500	500	900	1,500
Cash dividends from nonbank subsidiaries	94	132	136	301
Insurance premiums and service revenue earned	0	0	0	0
Gain on mortgage and automotive loans, net	(1)	0	3	28
Other gain (loss) on investments, net	0	0	0	0
Other income, net of losses	91	100	194	196
Total other revenue	90	100	197	224
Net revenue	401	468	669	1,505
Provision for loan losses	5	32	32	113
Compensation and benefits expense	9	25	21	48
Insurance losses and loss adjustment expenses	0	0	0	0
Other operating expenses	159	173	314	355
Total noninterest expense	168	198	335	403
Income from continuing operations before income tax (benefit) expense and undistributed (loss) income of subsidiaries	228	238	302	989
Income tax (benefit) expense from continuing operations	(289)	(66)	(350)	(122)
Net income from continuing operations	517	304	652	1,111
Income (loss) from discontinued operations, net of tax	(2)	(1)	(3)	(2)
Undistributed income of bank subsidiary	110	52	167	(545)
Undistributed income of nonbank subsidiaries	(43)	(6)	140	35
Net income	582	349	956	599
Other comprehensive income (loss), net of tax	309	(70)	615	(398)
Comprehensive income	891	279	1,571	201
Parent | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	3	4	6	6
Interest on cash and cash equivalents	3	2	5	4
Gain on mortgage and automotive loans, net			216	83
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 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	500	500	900	1,500
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 (loss) 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	500	500	900	1,500
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 (benefit) expense and undistributed (loss) income of subsidiaries	500	500	900	1,500
Income tax (benefit) expense from continuing operations	0	0	0	0
Net income from continuing operations	500	500	900	1,500
Income (loss) from discontinued operations, net of tax	0	0	0	0
Undistributed income of bank subsidiary	110	52	167	(545)
Undistributed income of nonbank subsidiaries	0	0	0	0
Net income	610	552	1,067	955
Other comprehensive income (loss), net of tax	237	(56)	466	(332)
Comprehensive income	847	496	1,533	623
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	1,923	1,648	3,790	3,180
Interest on loans held-for-sale	3	6	5	6
Interest and dividends on investment securities and other earning assets	244	188	484	365
Interest on cash and cash equivalents	17	14	38	28
Operating leases	364	373	723	753
Financing revenue and other interest income	2,557	2,232	5,051	4,338
Interest on deposits	651	395	1,243	750
Interest on short-term borrowings	24	30	55	52
Interest on long-term debt	195	177	403	330
Interest on intercompany debt	6	8	11	10
Interest expense	876	610	1,712	1,142
Net depreciation expense on operating lease assets	238	264	483	533
Net financing (loss) revenue	1,443	1,358	2,856	2,663
Cash dividends from bank subsidiaries	0	0	0	0
Cash dividends from nonbank subsidiaries	0	0	0	0
Insurance premiums and service revenue earned	261	239	522	495
Gain on mortgage and automotive loans, net	3	1	9	2
Other gain (loss) on investments, net	39	27	147	15
Other income, net of losses	145	185	289	406
Total other revenue	448	452	967	918
Net revenue	1,891	1,810	3,823	3,581
Provision for loan losses	173	126	445	334
Compensation and benefits expense	287	267	593	550
Insurance losses and loss adjustment expenses	127	101	186	164
Other operating expenses	442	461	900	932
Total noninterest expense	856	829	1,679	1,646
Income from continuing operations before income tax (benefit) expense and undistributed (loss) income of subsidiaries	862	855	1,699	1,601
Income tax (benefit) expense from continuing operations	199	179	371	311
Net income from continuing operations	663	676	1,328	1,290
Income (loss) from discontinued operations, net of tax	0	2	0	1
Undistributed income of bank subsidiary	0	0	0	0
Undistributed income of nonbank subsidiaries	0	0	0	0
Net income	663	678	1,328	1,291
Other comprehensive income (loss), net of tax	311	(74)	631	(413)
Comprehensive income	974	604	1,959	878
Nonguarantors | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	1	1	3	2
Interest on cash and cash equivalents	$ 5	$ 2	8	4
Gain on mortgage and automotive loans, net			$ 291	$ (5)