Loans - Consumer Banking Portfolio by Credit Quality Indicator (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 249,597	$ 251,624	$ 251,512
Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year One	21,453	29,724
Term Loans by Vintage Year Two	24,359	18,253
Term Loans by Vintage Year Three	14,245	10,209
Term Loans by Vintage Year Four	7,600	6,191
Term Loans by Vintage Year Five	4,272	2,717
Term Loans by Vintage After Year Five	2,255	1,102
Total Term Loans	74,184	68,196
Revolving Loans	566	683
Revolving Loans Converted to Term	9	9
Total Loans	74,759	68,888
Auto \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year One	20,942	28,683
Term Loans by Vintage Year Two	23,614	18,020
Term Loans by Vintage Year Three	14,035	9,995
Term Loans by Vintage Year Four	7,401	5,967
Term Loans by Vintage Year Five	4,074	2,542
Term Loans by Vintage After Year Five	1,647	555
Total Term Loans	71,713	65,762
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total Loans	71,713	65,762
Retail banking \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year One	511	1,041
Term Loans by Vintage Year Two	745	233
Term Loans by Vintage Year Three	210	214
Term Loans by Vintage Year Four	199	224
Term Loans by Vintage Year Five	198	175
Term Loans by Vintage After Year Five	608	547
Total Term Loans	2,471	2,434
Revolving Loans	566	683
Revolving Loans Converted to Term	9	9
Total Loans	3,046	3,126
Loans under Paycheck Protection Program	1,100	919
Current \| Retail banking \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year One	511	1,041
Term Loans by Vintage Year Two	745	233
Term Loans by Vintage Year Three	210	206
Term Loans by Vintage Year Four	198	222
Term Loans by Vintage Year Five	195	167
Term Loans by Vintage After Year Five	597	537
Total Term Loans	2,456	2,406
Revolving Loans	535	651
Revolving Loans Converted to Term	8	7
Total Loans	2,999	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	0	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	3	2
Total Term Loans	3	12
Revolving Loans	18	15
Revolving Loans Converted to Term	0	1
Total Loans	21	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	1	5
Term Loans by Vintage After Year Five	4	4
Total Term Loans	5	10
Revolving Loans	3	8
Revolving Loans Converted to Term	0	1
Total Loans	8	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	0	0
Term Loans by Vintage Year Three	0	0
Term Loans by Vintage Year Four	1	1
Term Loans by Vintage Year Five	2	1
Term Loans by Vintage After Year Five	4	4
Total Term Loans	7	6
Revolving Loans	10	9
Revolving Loans Converted to Term	1	0
Total Loans	18	15
Greater than 660 \| Auto \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year One	11,276	13,352
Term Loans by Vintage Year Two	10,874	8,091
Term Loans by Vintage Year Three	6,258	4,675
Term Loans by Vintage Year Four	3,396	2,810
Term Loans by Vintage Year Five	1,855	1,168
Term Loans by Vintage After Year Five	683	203
Total Term Loans	34,342	30,299
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total Loans	34,342	30,299
621-660 \| Auto \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year One	4,130	5,781
Term Loans by Vintage Year Two	4,752	3,631
Term Loans by Vintage Year Three	2,817	2,003
Term Loans by Vintage Year Four	1,496	1,172
Term Loans by Vintage Year Five	815	488
Term Loans by Vintage After Year Five	326	109
Total Term Loans	14,336	13,184
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total Loans	14,336	13,184
620 or below \| Auto \| Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year One	5,536	9,550
Term Loans by Vintage Year Two	7,988	6,298
Term Loans by Vintage Year Three	4,960	3,317
Term Loans by Vintage Year Four	2,509	1,985
Term Loans by Vintage Year Five	1,404	886
Term Loans by Vintage After Year Five	638	243
Total Term Loans	23,035	22,279
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total Loans	$ 23,035	$ 22,279

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