Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other, Nonaccrual Loans and Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025	Sep. 30, 2025
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 1,497,159	$ 1,408,905	$ 1,369,785
Consumer, excluding credit card
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	367,206	368,741	$ 369,859
Consumer, excluding credit card \| Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Nonaccrual loans	233	243
Total retained loans	67,564	65,210
Consumer, excluding credit card \| Auto and other \| California
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	10,120	9,926
Consumer, excluding credit card \| Auto and other \| Texas
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	8,618	7,940
Consumer, excluding credit card \| Auto and other \| Florida
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	5,674	5,382
Consumer, excluding credit card \| Auto and other \| New York
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	4,829	4,771
Consumer, excluding credit card \| Auto and other \| Illinois
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,903	2,804
Consumer, excluding credit card \| Auto and other \| New Jersey
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,385	2,347
Consumer, excluding credit card \| Auto and other \| Pennsylvania
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,226	2,066
Consumer, excluding credit card \| Auto and other \| Georgia
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,737	1,682
Consumer, excluding credit card \| Auto and other \| North Carolina
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,652	1,578
Consumer, excluding credit card \| Auto and other \| Arizona
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,623	1,583
Consumer, excluding credit card \| Auto and other \| All other
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 25,797	$ 25,131