Loans - Consumer Banking Portfolio by Credit Quality Indicator (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 318,186	$ 320,472
Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year, Year 1	15,290	23,828
Term Loans by Vintage Year, Year 2	20,194	22,721
Term Loans by Vintage Year, Year 3	18,586	17,192
Term Loans by Vintage Year, Year 4	13,497	6,876
Term Loans by Vintage Year, Year 5	4,988	3,053
Prior	2,735	1,380
Total Term Loans	75,290	75,050
Revolving Loans	368	382
Revolving Loans Converted to Term	5	5
Total	75,663	75,437
Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year, Year 1	15,204	23,729
Term Loans by Vintage Year, Year 2	20,114	22,564
Term Loans by Vintage Year, Year 3	18,492	17,134
Term Loans by Vintage Year, Year 4	13,442	6,810
Term Loans by Vintage Year, Year 5	4,930	2,936
Prior	2,203	902
Total Term Loans	74,385	74,075
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	74,385	74,075
Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year, Year 1	86	99
Term Loans by Vintage Year, Year 2	80	157
Term Loans by Vintage Year, Year 3	94	58
Term Loans by Vintage Year, Year 4	55	66
Term Loans by Vintage Year, Year 5	58	117
Prior	532	478
Total Term Loans	905	975
Revolving Loans	368	382
Revolving Loans Converted to Term	5	5
Total	1,278	1,362
Current | Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year, Year 1	85	98
Term Loans by Vintage Year, Year 2	80	157
Term Loans by Vintage Year, Year 3	94	57
Term Loans by Vintage Year, Year 4	55	65
Term Loans by Vintage Year, Year 5	57	117
Prior	513	468
Total Term Loans	884	962
Revolving Loans	355	363
Revolving Loans Converted to Term	4	4
Total	1,243	1,329
30-59 days | Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year, Year 1	0	1
Term Loans by Vintage Year, Year 2	0	0
Term Loans by Vintage Year, Year 3	0	1
Term Loans by Vintage Year, Year 4	0	1
Term Loans by Vintage Year, Year 5	0	0
Prior	14	1
Total Term Loans	14	4
Revolving Loans	8	11
Revolving Loans Converted to Term	0	0
Total	22	15
60-89 days | Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year, Year 1	0	0
Term Loans by Vintage Year, Year 2	0	0
Term Loans by Vintage Year, Year 3	0	0
Term Loans by Vintage Year, Year 4	0	0
Term Loans by Vintage Year, Year 5	0	0
Prior	1	1
Total Term Loans	1	1
Revolving Loans	3	2
Revolving Loans Converted to Term	0	0
Total	4	3
Greater than 90 days | Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year, Year 1	1	0
Term Loans by Vintage Year, Year 2	0	0
Term Loans by Vintage Year, Year 3	0	0
Term Loans by Vintage Year, Year 4	0	0
Term Loans by Vintage Year, Year 5	1	0
Prior	4	8
Total Term Loans	6	8
Revolving Loans	2	6
Revolving Loans Converted to Term	1	1
Total	9	15
Greater than 660 | Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year, Year 1	8,444	12,219
Term Loans by Vintage Year, Year 2	10,154	12,593
Term Loans by Vintage Year, Year 3	10,305	9,505
Term Loans by Vintage Year, Year 4	7,455	3,124
Term Loans by Vintage Year, Year 5	2,227	1,213
Prior	823	309
Total Term Loans	39,408	38,963
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	39,408	38,963
621-660 | Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year, Year 1	2,848	4,863
Term Loans by Vintage Year, Year 2	4,175	4,432
Term Loans by Vintage Year, Year 3	3,639	3,346
Term Loans by Vintage Year, Year 4	2,625	1,337
Term Loans by Vintage Year, Year 5	974	592
Prior	452	192
Total Term Loans	14,713	14,762
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	14,713	14,762
620 or below | Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
Term Loans by Vintage Year, Year 1	3,912	6,647
Term Loans by Vintage Year, Year 2	5,785	5,539
Term Loans by Vintage Year, Year 3	4,548	4,283
Term Loans by Vintage Year, Year 4	3,362	2,349
Term Loans by Vintage Year, Year 5	1,729	1,131
Prior	928	401
Total Term Loans	20,264	20,350
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	$ 20,264	$ 20,350