Loans - Consumer Banking Portfolio by Credit Quality Indicator (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 261,390	$ 251,624
Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term loans by vintage year one	31,147	29,724
Term loans by vintage year two	21,365	18,253
Term loans by vintage year three	12,388	10,209
Term loans by vintage year four	6,472	6,191
Term loans by vintage year five	3,490	2,717
Term loans by vintage after year five	1,714	1,102
Total term loans	76,576	68,196
Revolving loans	528	683
Revolving loans converted to term	8	9
Total	77,112	68,888
Auto \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term loans by vintage year one	30,727	28,683
Term loans by vintage year two	21,039	18,020
Term loans by vintage year three	12,204	9,995
Term loans by vintage year four	6,286	5,967
Term loans by vintage year five	3,302	2,542
Term loans by vintage after year five	1,158	555
Total term loans	74,716	65,762
Revolving loans	0	0
Revolving loans converted to term	0	0
Total	74,716	65,762
Retail banking \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term loans by vintage year one	420	1,041
Term loans by vintage year two	326	233
Term loans by vintage year three	184	214
Term loans by vintage year four	186	224
Term loans by vintage year five	188	175
Term loans by vintage after year five	556	547
Total term loans	1,860	2,434
Revolving loans	528	683
Revolving loans converted to term	8	9
Total	2,396	3,126
PPP loans	538	919
Current \| Retail banking \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term loans by vintage year one	420	1,041
Term loans by vintage year two	324	233
Term loans by vintage year three	184	206
Term loans by vintage year four	185	222
Term loans by vintage year five	187	167
Term loans by vintage after year five	544	537
Total term loans	1,844	2,406
Revolving loans	497	651
Revolving loans converted to term	6	7
Total	2,347	3,064
30-59 days \| Retail banking \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term loans by vintage year one	0	0
Term loans by vintage year two	1	0
Term loans by vintage year three	0	7
Term loans by vintage year four	0	1
Term loans by vintage year five	0	2
Term loans by vintage after year five	4	2
Total term loans	5	12
Revolving loans	20	15
Revolving loans converted to term	1	1
Total	26	28
60-89 days \| Retail banking \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term loans by vintage year one	0	0
Term loans by vintage year two	0	0
Term loans by vintage year three	0	1
Term loans by vintage year four	0	0
Term loans by vintage year five	0	5
Term loans by vintage after year five	3	4
Total term loans	3	10
Revolving loans	2	8
Revolving loans converted to term	0	1
Total	5	19
Greater than 90 days \| Retail banking \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term loans by vintage year one	0	0
Term loans by vintage year two	1	0
Term loans by vintage year three	0	0
Term loans by vintage year four	1	1
Term loans by vintage year five	1	1
Term loans by vintage after year five	5	4
Total term loans	8	6
Revolving loans	9	9
Revolving loans converted to term	1	0
Total	18	15
Greater than 660 \| Auto \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term loans by vintage year one	16,685	13,352
Term loans by vintage year two	9,696	8,091
Term loans by vintage year three	5,448	4,675
Term loans by vintage year four	2,860	2,810
Term loans by vintage year five	1,475	1,168
Term loans by vintage after year five	462	203
Total term loans	36,626	30,299
Revolving loans	0	0
Revolving loans converted to term	0	0
Total	36,626	30,299
621-660 \| Auto \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term loans by vintage year one	6,093	5,781
Term loans by vintage year two	4,212	3,631
Term loans by vintage year three	2,435	2,003
Term loans by vintage year four	1,276	1,172
Term loans by vintage year five	666	488
Term loans by vintage after year five	231	109
Total term loans	14,913	13,184
Revolving loans	0	0
Revolving loans converted to term	0	0
Total	14,913	13,184
620 or below \| Auto \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term loans by vintage year one	7,949	9,550
Term loans by vintage year two	7,131	6,298
Term loans by vintage year three	4,321	3,317
Term loans by vintage year four	2,150	1,985
Term loans by vintage year five	1,161	886
Term loans by vintage after year five	465	243
Total term loans	23,177	22,279
Revolving loans	0	0
Revolving loans converted to term	0	0
Total	$ 23,177	$ 22,279

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