Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other, Nonaccrual Loans and Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025	Jun. 30, 2025
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 1,463,808	$ 1,408,905	$ 1,345,473
Consumer, excluding credit card
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	367,128	368,741	$ 371,855
Consumer, excluding credit card \| Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Nonaccrual loans	228	243
Total retained loans	66,464	65,210
Consumer, excluding credit card \| Auto and other \| California
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	10,111	9,926
Consumer, excluding credit card \| Auto and other \| Texas
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	8,271	7,940
Consumer, excluding credit card \| Auto and other \| Florida
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	5,561	5,382
Consumer, excluding credit card \| Auto and other \| New York
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	4,812	4,771
Consumer, excluding credit card \| Auto and other \| Illinois
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,845	2,804
Consumer, excluding credit card \| Auto and other \| New Jersey
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,370	2,347
Consumer, excluding credit card \| Auto and other \| Pennsylvania
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,167	2,066
Consumer, excluding credit card \| Auto and other \| Georgia
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,704	1,682
Consumer, excluding credit card \| Auto and other \| North Carolina
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,618	1,578
Consumer, excluding credit card \| Auto and other \| Arizona
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,608	1,583
Consumer, excluding credit card \| Auto and other \| All other
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 25,397	$ 25,131