Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other, Nonaccrual Loans and Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024	Jun. 30, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 1,345,473	$ 1,299,590	$ 1,273,047
Consumer, excluding credit card
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	371,855	376,334	$ 382,795
Consumer, excluding credit card \| Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Nonaccrual loans	232	249
Total retained loans	66,794	66,821
Consumer, excluding credit card \| Auto and other \| California
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	10,303	10,321
Consumer, excluding credit card \| Auto and other \| Texas
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	8,002	7,772
Consumer, excluding credit card \| Auto and other \| Florida
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	5,460	5,428
Consumer, excluding credit card \| Auto and other \| New York
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	4,869	4,905
Consumer, excluding credit card \| Auto and other \| Illinois
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,897	2,890
Consumer, excluding credit card \| Auto and other \| New Jersey
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,439	2,468
Consumer, excluding credit card \| Auto and other \| Pennsylvania
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,035	2,012
Consumer, excluding credit card \| Auto and other \| Georgia
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,717	1,716
Consumer, excluding credit card \| Auto and other \| Arizona
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,642	1,643
Consumer, excluding credit card \| Auto and other \| North Carolina
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,610	1,597
Consumer, excluding credit card \| Auto and other \| All other
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 25,820	$ 26,069