Loans - Consumer Banking Portfolio by Credit Quality Indicator (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 320,472	$ 312,331
Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	23,828	31,969
2022	22,721	25,937
2021	17,192	11,591
2020	6,876	6,039
2019	3,053	2,589
Prior	1,380	1,372
Total Term Loans	75,050	79,497
Revolving Loans	382	422
Revolving Loans Converted to Term	5	6
Total	75,437	79,925
Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	23,729	31,801
2022	22,564	25,807
2021	17,134	11,509
2020	6,810	5,906
2019	2,936	2,459
Prior	902	891
Total Term Loans	74,075	78,373
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	74,075	78,373
Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	99	168
2022	157	130
2021	58	82
2020	66	133
2019	117	130
Prior	478	481
Total Term Loans	975	1,124
Revolving Loans	382	422
Revolving Loans Converted to Term	5	6
Total	1,362	1,552
Current | Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	98	166
2022	157	128
2021	57	82
2020	65	133
2019	117	127
Prior	468	470
Total Term Loans	962	1,106
Revolving Loans	363	408
Revolving Loans Converted to Term	4	4
Total	1,329	1,518
30-59 days | Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	1	2
2022	0	1
2021	1	0
2020	1	0
2019	0	0
Prior	1	2
Total Term Loans	4	5
Revolving Loans	11	8
Revolving Loans Converted to Term	0	0
Total	15	13
60-89 days | Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0	0
2022	0	1
2021	0	0
2020	0	0
2019	0	0
Prior	1	1
Total Term Loans	1	2
Revolving Loans	2	2
Revolving Loans Converted to Term	0	0
Total	3	4
Greater than 90 days | Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0	0
2022	0	0
2021	0	0
2020	0	0
2019	0	3
Prior	8	8
Total Term Loans	8	11
Revolving Loans	6	4
Revolving Loans Converted to Term	1	2
Total	15	17
Greater than 660 | Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	12,219	17,872
2022	12,593	14,246
2021	9,505	5,354
2020	3,124	2,595
2019	1,213	1,032
Prior	309	328
Total Term Loans	38,963	41,427
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	38,963	41,427
621-660 | Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	4,863	6,212
2022	4,432	5,060
2021	3,346	2,257
2020	1,337	1,167
2019	592	513
Prior	192	185
Total Term Loans	14,762	15,394
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	14,762	15,394
620 or below | Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	6,647	7,717
2022	5,539	6,501
2021	4,283	3,898
2020	2,349	2,144
2019	1,131	914
Prior	401	378
Total Term Loans	20,350	21,552
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	$ 20,350	$ 21,552