Loans and Related Allowance for Credit Losses (Credit Quality Indicators for Automobile, Credit Card, Education and Other Consumer Loan Classes) (Details) - USD ($) $ in Millions		Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	[1]	$ 290,230	$ 241,928
Automobile | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		5,517	3,714
Financing receivable, originated in year one		3,878	5,494
Financing receivable, originated in year two		4,360	2,878
Financing receivable, originated in year three		2,234	1,361
Financing receivable, originated in year four		925	609
Prior		351	162
Total Loans		17,265	14,218
Automobile | Greater than or equal to 780 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		2,828	1,807
Financing receivable, originated in year one		1,638	1,915
Financing receivable, originated in year two		1,551	807
Financing receivable, originated in year three		624	452
Financing receivable, originated in year four		281	246
Prior		116	58
Total Loans		7,038	5,285
Automobile | 720 to 779 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		1,694	1,098
Financing receivable, originated in year one		1,157	1,581
Financing receivable, originated in year two		1,225	789
Financing receivable, originated in year three		595	381
Financing receivable, originated in year four		248	167
Prior		91	44
Total Loans		5,010	4,060
Automobile | 660 to 719 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		730	617
Financing receivable, originated in year one		705	1,222
Financing receivable, originated in year two		913	684
Financing receivable, originated in year three		505	288
Financing receivable, originated in year four		195	109
Prior		65	31
Total Loans		3,113	2,951
Automobile | Less than 660 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		220	192
Financing receivable, originated in year one		349	776
Financing receivable, originated in year two		658	598
Financing receivable, originated in year three		504	240
Financing receivable, originated in year four		198	87
Prior		79	29
Total Loans		2,008	1,922
Automobile | No FICO score available or required | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		45
Financing receivable, originated in year one		29
Financing receivable, originated in year two		13
Financing receivable, originated in year three		6
Financing receivable, originated in year four		3
Total Loans		96
Credit card | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans		6,396	6,120
Revolving Loans Converted to Term		70	95
Total Loans		6,466	6,215
Credit card | Greater than or equal to 780 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans		1,718	1,635
Revolving Loans Converted to Term		2	3
Total Loans		1,720	1,638
Credit card | 720 to 779 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans		1,796	1,724
Revolving Loans Converted to Term		10	11
Total Loans		1,806	1,735
Credit card | 660 to 719 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans		1,836	1,765
Revolving Loans Converted to Term		22	26
Total Loans		1,858	1,791
Credit card | Less than 660 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans		925	902
Revolving Loans Converted to Term		33	51
Total Loans		958	953
Credit card | No FICO score available or required | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans		121	94
Revolving Loans Converted to Term		3	4
Total Loans		124	98
Education
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		45	92
Financing receivable, originated in year one		115	163
Financing receivable, originated in year two		143	135
Financing receivable, originated in year three		115	101
Financing receivable, originated in year four		83	78
Prior		2,152	2,377
Total Loans		2,653	2,946
Education | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		45	92
Financing receivable, originated in year one		115	163
Financing receivable, originated in year two		143	135
Financing receivable, originated in year three		115	101
Financing receivable, originated in year four		83	78
Prior		690	746
Total Loans		1,191	1,315
Education | Greater than or equal to 780 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		12	34
Financing receivable, originated in year one		63	90
Financing receivable, originated in year two		81	74
Financing receivable, originated in year three		66	59
Financing receivable, originated in year four		51	50
Prior		412	428
Total Loans		685	735
Education | 720 to 779 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		11	24
Financing receivable, originated in year one		31	46
Financing receivable, originated in year two		39	38
Financing receivable, originated in year three		31	28
Financing receivable, originated in year four		22	20
Prior		175	190
Total Loans		309	346
Education | 660 to 719 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		8	15
Financing receivable, originated in year one		9	15
Financing receivable, originated in year two		12	14
Financing receivable, originated in year three		12	9
Financing receivable, originated in year four		7	6
Prior		75	90
Total Loans		123	149
Education | Less than 660 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		2	3
Financing receivable, originated in year one		1	2
Financing receivable, originated in year two		2	3
Financing receivable, originated in year three		2	2
Financing receivable, originated in year four		2	2
Prior		27	37
Total Loans		36	49
Education | No FICO score available or required | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		12	16
Financing receivable, originated in year one		11	10
Financing receivable, originated in year two		9	6
Financing receivable, originated in year three		4	3
Financing receivable, originated in year four		1
Prior		1	1
Total Loans		38	36
Education | Other internal credit metrics
Financing Receivable, Credit Quality Indicator [Line Items]
Prior		1,462	1,631
Total Loans		1,462	1,631
Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		720	581
Financing receivable, originated in year one		647	763
Financing receivable, originated in year two		695	304
Financing receivable, originated in year three		339	95
Financing receivable, originated in year four		96	75
Prior		193	161
Revolving Loans		3,245	2,713
Revolving Loans Converted to Term		31	6
Total Loans		5,966	4,698
Other consumer | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		656	514
Financing receivable, originated in year one		631	730
Financing receivable, originated in year two		669	267
Financing receivable, originated in year three		320	69
Financing receivable, originated in year four		74	15
Prior		85	86
Revolving Loans		628	379
Revolving Loans Converted to Term		4	3
Total Loans		3,067	2,063
Other consumer | Greater than or equal to 780 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		181	162
Financing receivable, originated in year one		172	187
Financing receivable, originated in year two		162	63
Financing receivable, originated in year three		62	21
Financing receivable, originated in year four		18	5
Prior		38	42
Revolving Loans		203	86
Revolving Loans Converted to Term		2	1
Total Loans		838	567
Other consumer | 720 to 779 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		229	197
Financing receivable, originated in year one		209	247
Financing receivable, originated in year two		209	82
Financing receivable, originated in year three		85	22
Financing receivable, originated in year four		21	5
Prior		23	22
Revolving Loans		200	123
Total Loans		976	698
Other consumer | 660 to 719 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		179	127
Financing receivable, originated in year one		170	210
Financing receivable, originated in year two		201	81
Financing receivable, originated in year three		105	17
Financing receivable, originated in year four		21	3
Prior		14	14
Revolving Loans		144	117
Revolving Loans Converted to Term		1	1
Total Loans		835	570
Other consumer | Less than 660 | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		47	28
Financing receivable, originated in year one		73	86
Financing receivable, originated in year two		96	41
Financing receivable, originated in year three		67	9
Financing receivable, originated in year four		14	2
Prior		9	8
Revolving Loans		57	53
Revolving Loans Converted to Term		1	1
Total Loans		364	228
Other consumer | No FICO score available or required | Using FICO Credit Metric
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		20
Financing receivable, originated in year one		7
Financing receivable, originated in year two		1
Financing receivable, originated in year three		1
Prior		1
Revolving Loans		24
Total Loans		54
Other consumer | Other internal credit metrics
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		64	67
Financing receivable, originated in year one		16	33
Financing receivable, originated in year two		26	37
Financing receivable, originated in year three		19	26
Financing receivable, originated in year four		22	60
Prior		108	75
Revolving Loans		2,617	2,334
Revolving Loans Converted to Term		27	3
Total Loans		$ 2,899	$ 2,635

[1] Our consolidated assets included the following for which we have elected the fair value option: Loans held for sale of $2.0 billion, Loans held for investment of $1.6 billion and Other assets of $0.1 billion at September 30, 2021. Comparable amounts at December 31, 2020 were $1.2 billion, $1.4 billion and $0.1 billion, respectively.