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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	$ 1,708	$ 1,486	$ 4,898	$ 4,301
Interest on loans held-for-sale	4	0	10	0
Interest and dividends on investment securities and other earning assets	198	157	562	437
Interest on cash and cash equivalents	18	11	50	23
Operating leases	368	434	1,124	1,465
Financing revenue and other interest income	2,296	2,088	6,644	6,226
Interest on deposits	462	285	1,212	766
Interest on short-term borrowings	29	34	101	94
Interest on long-term debt	451	416	1,296	1,257
Interest on intercompany debt	0	0	0	0
Interest expense	942	735	2,609	2,117
Net depreciation expense on operating lease assets	247	272	785	982
Net financing (loss) revenue	1,107	1,081	3,250	3,127
Cash dividends from bank subsidiaries	0	0	0	0
Cash dividends from nonbank subsidiaries	0	0	0	0
Insurance premiums and service revenue earned	258	252	753	720
Gain on mortgage and automotive loans, net	17	15	19	65
Other gain on investments, net	22	23	37	73
Other income, net of losses	101	91	307	307
Other revenue	398	381	1,116	1,165
Net revenue	1,505	1,462	4,366	4,292
Provision for loan losses	233	314	652	854
Compensation and benefits expense	274	264	872	814
Insurance losses and loss adjustment expenses	77	65	241	278
Other operating expenses	456	424	1,347	1,249
Noninterest expense	807	753	2,460	2,341
Income (loss) from continuing operations before tax	465	395	1,254	1,097
Income tax (benefit) expense from continuing operations	91	115	280	350
Net (loss) income from continuing operations	374	280	974	747
Income (loss) from discontinued operations, net of tax	0	2	(1)	1
Undistributed income of bank subsidiary	0	0	0	0
Undistributed income of nonbank subsidiaries	0	0	0	0
Net Income (Loss) Attributable to Parent	374	282	973	748
Other comprehensive income (loss), attributable to parent	(133)	48	(531)	144
Comprehensive income	241	330	442	892
Parent
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	(4)	13	6	(57)
Interest on loans held-for-sale	0		0
Interest and dividends on investment securities and other earning assets	0	0	0	0
Interest on cash and cash equivalents	2	2	6	6
Operating leases	1	3	4	9
Financing revenue and other interest income	3	21	30	(31)
Interest on deposits	0	0	0	2
Interest on short-term borrowings	12	16	32	52
Interest on long-term debt	250	278	765	834
Interest on intercompany debt	5	3	12	12
Interest expense	267	297	809	900
Net depreciation expense on operating lease assets	2	3	7	8
Net financing (loss) revenue	(266)	(279)	(786)	(939)
Cash dividends from bank subsidiaries	550	2,900	2,050	2,900
Cash dividends from nonbank subsidiaries	88	101	389	528
Insurance premiums and service revenue earned	0	0	0	0
Gain on mortgage and automotive loans, net	16	9	44	39
Other gain on investments, net	0	0	0	0
Other income, net of losses	105	137	301	568
Other revenue	121	146	345	607
Net revenue	493	2,868	1,998	3,096
Provision for loan losses	30	161	143	350
Compensation and benefits expense	19	17	67	157
Insurance losses and loss adjustment expenses	0	0	0	0
Other operating expenses	175	208	530	709
Noninterest expense	194	225	597	866
Income (loss) from continuing operations before tax	269	2,482	1,258	1,880
Income tax (benefit) expense from continuing operations	(88)	(135)	(210)	(362)
Net (loss) income from continuing operations	357	2,617	1,468	2,242
Income (loss) from discontinued operations, net of tax	0	4	(2)	6
Undistributed income of bank subsidiary	(31)	(2,524)	(576)	(1,760)
Undistributed income of nonbank subsidiaries	48	185	83	260
Net Income (Loss) Attributable to Parent	374	282	973	748
Other comprehensive income (loss), attributable to parent	(133)	48	(531)	144
Comprehensive income	241	330	442	892
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
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	550	2,900	2,050	2,900
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
Other revenue	0	0	0	0
Net revenue	550	2,900	2,050	2,900
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
Noninterest expense	0	0	0	0
Income (loss) from continuing operations before tax	550	2,900	2,050	2,900
Income tax (benefit) expense from continuing operations	0	0	0	0
Net (loss) income from continuing operations	550	2,900	2,050	2,900
Income (loss) from discontinued operations, net of tax	0	0	0	0
Undistributed income of bank subsidiary	(31)	(2,524)	(576)	(1,760)
Undistributed income of nonbank subsidiaries	0	0	0	0
Net Income (Loss) Attributable to Parent	519	376	1,474	1,140
Other comprehensive income (loss), attributable to parent	(104)	36	(436)	91
Comprehensive income	415	412	1,038	1,231
Nonguarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	1,712	1,473	4,892	4,358
Interest on loans held-for-sale	4		10
Interest and dividends on investment securities and other earning assets	198	157	563	439
Interest on cash and cash equivalents	16	9	44	17
Operating leases	367	431	1,120	1,456
Financing revenue and other interest income	2,302	2,073	6,640	6,280
Interest on deposits	462	286	1,212	765
Interest on short-term borrowings	17	18	69	42
Interest on long-term debt	201	138	531	423
Interest on intercompany debt	4	2	14	10
Interest expense	684	444	1,826	1,240
Net depreciation expense on operating lease assets	245	269	778	974
Net financing (loss) revenue	1,373	1,360	4,036	4,066
Cash dividends from bank subsidiaries	0	0	0	0
Cash dividends from nonbank subsidiaries	0	0	0	0
Insurance premiums and service revenue earned	258	252	753	720
Gain on mortgage and automotive loans, net	1	6	3	26
Other gain on investments, net	22	23	37	73
Other income, net of losses	187	196	593	630
Other revenue	468	477	1,386	1,449
Net revenue	1,841	1,837	5,422	5,515
Provision for loan losses	203	153	537	504
Compensation and benefits expense	255	247	805	657
Insurance losses and loss adjustment expenses	77	65	241	278
Other operating expenses	472	459	1,404	1,431
Noninterest expense	804	771	2,450	2,366
Income (loss) from continuing operations before tax	834	913	2,435	2,645
Income tax (benefit) expense from continuing operations	179	250	490	712
Net (loss) income from continuing operations	655	663	1,945	1,933
Income (loss) from discontinued operations, net of tax	0	(2)	1	(5)
Undistributed income of bank subsidiary	0	0	0	0
Undistributed income of nonbank subsidiaries	0	0	0	0
Net Income (Loss) Attributable to Parent	655	661	1,946	1,928
Other comprehensive income (loss), attributable to parent	(133)	51	(546)	140
Comprehensive income	522	712	1,400	2,068
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
Affiliated entity | Parent
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	3	2	9	10
Interest on cash and cash equivalents	1	1	5	1
Gain on mortgage and automotive loans, net			45	2,159
Affiliated entity | Guarantors
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
Affiliated entity | Nonguarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	2	1	4	5
Interest on cash and cash equivalents	3	2	7	5
Gain on mortgage and automotive loans, net			(6)	232
Consolidating adjustments
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
Interest and dividends on investment securities and other earning assets	0	0	(1)	(2)
Interest on cash and cash equivalents	0	0	0	0
Operating leases	0	0	0	0
Financing revenue and other interest income	(9)	(6)	(26)	(23)
Interest on deposits	0	(1)	0	(1)
Interest on short-term borrowings	0	0	0	0
Interest on long-term debt	0	0	0	0
Interest on intercompany debt	(9)	(5)	(26)	(22)
Interest expense	(9)	(6)	(26)	(23)
Net depreciation expense on operating lease assets	0	0	0	0
Net financing (loss) revenue	0	0	0	0
Cash dividends from bank subsidiaries	(1,100)	(5,800)	(4,100)	(5,800)
Cash dividends from nonbank subsidiaries	(88)	(101)	(389)	(528)
Insurance premiums and service revenue earned	0	0	0	0
Gain on mortgage and automotive loans, net	0	0	(28)	0
Other gain on investments, net	0	0	0	0
Other income, net of losses	(191)	(242)	(587)	(891)
Other revenue	(191)	(242)	(615)	(891)
Net revenue	(1,379)	(6,143)	(5,104)	(7,219)
Provision for loan losses	0	0	(28)	0
Compensation and benefits expense	0	0	0	0
Insurance losses and loss adjustment expenses	0	0	0	0
Other operating expenses	(191)	(243)	(587)	(891)
Noninterest expense	(191)	(243)	(587)	(891)
Income (loss) from continuing operations before tax	(1,188)	(5,900)	(4,489)	(6,328)
Income tax (benefit) expense from continuing operations	0	0	0	0
Net (loss) income from continuing operations	(1,188)	(5,900)	(4,489)	(6,328)
Income (loss) from discontinued operations, net of tax	0	0	0	0
Undistributed income of bank subsidiary	62	5,048	1,152	3,520
Undistributed income of nonbank subsidiaries	(48)	(185)	(83)	(260)
Net Income (Loss) Attributable to Parent	(1,174)	(1,037)	(3,420)	(3,068)
Other comprehensive income (loss), attributable to parent	237	(87)	982	(231)
Comprehensive income	(937)	(1,124)	(2,438)	(3,299)
Consolidating adjustments | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	(5)	(3)	(13)	(15)
Interest on cash and cash equivalents	$ (4)	$ (3)	(12)	(6)
Gain on mortgage and automotive loans, net			$ (39)	$ (2,391)