Parent and Guarantor Condensed Consolidating Financial Statements (Schedule of Condensed Consolidating Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	$ 1,807	$ 1,543
Interest on loans held-for-sale	2	0
Interest and dividends on investment securities and other earning assets	240	176
Interest on cash and cash equivalents	23	15
Operating leases	361	382
Financing revenue and other interest income	2,433	2,116
Interest on deposits	592	351
Interest on short-term borrowings	44	32
Interest on long-term debt	419	411
Interest on intercompany debt	0	0
Interest expense	1,055	794
Net depreciation expense on operating lease assets	246	273
Net financing (loss) revenue	1,132	1,049
Cash dividends from bank subsidiaries	0	0
Cash dividends from nonbank subsidiaries	0	0
Insurance premiums and service revenue earned	261	256
Gain on mortgage and automotive loans, net	10	1
Other (loss) gain on investments, net	108	(12)
Other income, net of losses	87	109
Other revenue	466	354
Net revenue	1,598	1,403
Provision for loan losses	282	261
Compensation and benefits expense	318	306
Insurance losses and loss adjustment expenses	59	63
Other operating expenses	453	445
Noninterest expense	830	814
Income from continuing operations before income tax (benefit) expense and undistributed (loss) income of subsidiaries	486	328
Income tax (benefit) expense from continuing operations	111	76
Net (loss) income from continuing operations	375	252
Income (loss) from discontinued operations, net of tax	(1)	(2)
Undistributed income of bank subsidiary	0	0
Undistributed income of nonbank subsidiaries	0	0
Net income	374	250
Other comprehensive income (loss), net of tax	306	(328)
Comprehensive income	680	(78)
Parent
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	(60)	11
Interest on loans held-for-sale	0
Interest and dividends on investment securities and other earning assets	0	0
Interest on cash and cash equivalents	2	2
Operating leases	2	2
Financing revenue and other interest income	(51)	19
Interest on deposits	0	0
Interest on short-term borrowings	13	10
Interest on long-term debt	211	258
Interest on intercompany debt	5	3
Interest expense	229	271
Net depreciation expense on operating lease assets	1	4
Net financing (loss) revenue	(281)	(256)
Cash dividends from bank subsidiaries	400	1,000
Cash dividends from nonbank subsidiaries	42	169
Insurance premiums and service revenue earned	0	0
Gain on mortgage and automotive loans, net	4	28
Other (loss) gain on investments, net	0	0
Other income, net of losses	103	96
Other revenue	107	124
Net revenue	268	1,037
Provision for loan losses	27	81
Compensation and benefits expense	12	23
Insurance losses and loss adjustment expenses	0	0
Other operating expenses	155	182
Noninterest expense	167	205
Income from continuing operations before income tax (benefit) expense and undistributed (loss) income of subsidiaries	74	751
Income tax (benefit) expense from continuing operations	(61)	(56)
Net (loss) income from continuing operations	135	807
Income (loss) from discontinued operations, net of tax	(1)	(1)
Undistributed income of bank subsidiary	57	(597)
Undistributed income of nonbank subsidiaries	183	41
Net income	374	250
Other comprehensive income (loss), net of tax	306	(328)
Comprehensive income	680	(78)
Guarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	0	0
Interest on loans held-for-sale	0
Interest and dividends on investment securities and other earning assets	0	0
Interest on cash and cash equivalents	0	0
Operating leases	0	0
Financing revenue and other interest income	0	0
Interest on deposits	0	0
Interest on short-term borrowings	0	0
Interest on long-term debt	0	0
Interest on intercompany debt	0	0
Interest expense	0	0
Net depreciation expense on operating lease assets	0	0
Net financing (loss) revenue	0	0
Cash dividends from bank subsidiaries	400	1,000
Cash dividends from nonbank subsidiaries	0	0
Insurance premiums and service revenue earned	0	0
Gain on mortgage and automotive loans, net	0	0
Other (loss) gain on investments, net	0	0
Other income, net of losses	0	0
Other revenue	0	0
Net revenue	400	1,000
Provision for loan losses	0	0
Compensation and benefits expense	0	0
Insurance losses and loss adjustment expenses	0	0
Other operating expenses	0	0
Noninterest expense	0	0
Income from continuing operations before income tax (benefit) expense and undistributed (loss) income of subsidiaries	400	1,000
Income tax (benefit) expense from continuing operations	0	0
Net (loss) income from continuing operations	400	1,000
Income (loss) from discontinued operations, net of tax	0	0
Undistributed income of bank subsidiary	57	(597)
Undistributed income of nonbank subsidiaries	0	0
Net income	457	403
Other comprehensive income (loss), net of tax	229	(276)
Comprehensive income	686	127
Nonguarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	1,867	1,532
Interest on loans held-for-sale	2
Interest and dividends on investment securities and other earning assets	240	176
Interest on cash and cash equivalents	21	14
Operating leases	359	380
Financing revenue and other interest income	2,494	2,105
Interest on deposits	592	354
Interest on short-term borrowings	31	22
Interest on long-term debt	208	153
Interest on intercompany debt	5	2
Interest expense	836	531
Net depreciation expense on operating lease assets	245	269
Net financing (loss) revenue	1,413	1,305
Cash dividends from bank subsidiaries	0	0
Cash dividends from nonbank subsidiaries	0	0
Insurance premiums and service revenue earned	261	256
Gain on mortgage and automotive loans, net	6	1
Other (loss) gain on investments, net	108	(12)
Other income, net of losses	144	221
Other revenue	519	466
Net revenue	1,932	1,771
Provision for loan losses	272	208
Compensation and benefits expense	306	283
Insurance losses and loss adjustment expenses	59	63
Other operating expenses	458	471
Noninterest expense	823	817
Income from continuing operations before income tax (benefit) expense and undistributed (loss) income of subsidiaries	837	746
Income tax (benefit) expense from continuing operations	172	132
Net (loss) income from continuing operations	665	614
Income (loss) from discontinued operations, net of tax	0	(1)
Undistributed income of bank subsidiary	0	0
Undistributed income of nonbank subsidiaries	0	0
Net income	665	613
Other comprehensive income (loss), net of tax	320	(339)
Comprehensive income	985	274
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
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
Interest on cash and cash equivalents	2	2
Gain on mortgage and automotive loans, net	507	(423)
Affiliated entity | Guarantors
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	0	0
Interest on cash and cash equivalents	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
Interest on cash and cash equivalents	3	2
Gain on mortgage and automotive loans, net	290	1
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	0	0
Interest on loans held-for-sale	0
Interest and dividends on investment securities and other earning assets	0	0
Interest on cash and cash equivalents	0	(1)
Operating leases	0	0
Financing revenue and other interest income	(10)	(8)
Interest on deposits	0	(3)
Interest on short-term borrowings	0	0
Interest on long-term debt	0	0
Interest on intercompany debt	(10)	(5)
Interest expense	(10)	(8)
Net depreciation expense on operating lease assets	0	0
Net financing (loss) revenue	0	0
Cash dividends from bank subsidiaries	(800)	(2,000)
Cash dividends from nonbank subsidiaries	(42)	(169)
Insurance premiums and service revenue earned	0	0
Gain on mortgage and automotive loans, net	0	(28)
Other (loss) gain on investments, net	0	0
Other income, net of losses	(160)	(208)
Other revenue	(160)	(236)
Net revenue	(1,002)	(2,405)
Provision for loan losses	(17)	(28)
Compensation and benefits expense	0	0
Insurance losses and loss adjustment expenses	0	0
Other operating expenses	(160)	(208)
Noninterest expense	(160)	(208)
Income from continuing operations before income tax (benefit) expense and undistributed (loss) income of subsidiaries	(825)	(2,169)
Income tax (benefit) expense from continuing operations	0	0
Net (loss) income from continuing operations	(825)	(2,169)
Income (loss) from discontinued operations, net of tax	0	0
Undistributed income of bank subsidiary	(114)	1,194
Undistributed income of nonbank subsidiaries	(183)	(41)
Net income	(1,122)	(1,016)
Other comprehensive income (loss), net of tax	(549)	615
Comprehensive income	(1,671)	(401)
Consolidating adjustments | Affiliated entity
Condensed Income Statements, Captions [Line Items]
Interest and fees on finance receivables and loans	(5)	(3)
Interest on cash and cash equivalents	(5)	(4)
Gain on mortgage and automotive loans, net	$ (797)	$ 422