Loans - Consumer Banking Portfolio by Credit Quality Indicator (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 314,780	$ 312,331
Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	19,132	31,969
2022	24,803	25,937
2021	19,139	11,591
2020	7,894	6,039
2019	3,678	2,589
Prior	1,813	1,372
Total Term Loans	76,459	79,497
Revolving Loans	379	422
Revolving Loans Converted to Term	6	6
Total	76,844	79,925
Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	19,059	31,801
2022	24,650	25,807
2021	19,061	11,509
2020	7,825	5,906
2019	3,557	2,459
Prior	1,304	891
Total Term Loans	75,456	78,373
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	75,456	78,373
Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	73	168
2022	153	130
2021	78	82
2020	69	133
2019	121	130
Prior	509	481
Total Term Loans	1,003	1,124
Revolving Loans	379	422
Revolving Loans Converted to Term	6	6
Total	1,388	1,552
Current | Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	73	166
2022	153	128
2021	78	82
2020	69	133
2019	121	127
Prior	497	470
Total Term Loans	991	1,106
Revolving Loans	361	408
Revolving Loans Converted to Term	5	4
Total	1,357	1,518
30-59 days | Retail banking | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0	2
2022	0	1
2021	0	0
2020	0	0
2019	0	0
Prior	3	2
Total Term Loans	3	5
Revolving Loans	12	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	4	4
Revolving Loans Converted to Term	1	2
Total	13	17
Greater than 660 | Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	9,809	17,872
2022	13,757	14,246
2021	10,562	5,354
2020	3,608	2,595
2019	1,499	1,032
Prior	471	328
Total Term Loans	39,706	41,427
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	39,706	41,427
621-660 | Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	3,891	6,212
2022	4,840	5,060
2021	3,724	2,257
2020	1,535	1,167
2019	713	513
Prior	277	185
Total Term Loans	14,980	15,394
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	14,980	15,394
620 or below | Auto | Consumer Banking:
Financing Receivable, Credit Quality Indicator [Line Items]
2023	5,359	7,717
2022	6,053	6,501
2021	4,775	3,898
2020	2,682	2,144
2019	1,345	914
Prior	556	378
Total Term Loans	20,770	21,552
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total	$ 20,770	$ 21,552