Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other, Nonaccrual Loans and Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 1,369,785	$ 1,299,590	$ 1,285,370
Consumer, excluding credit card
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	369,859	376,334	$ 377,938
Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Nonaccrual loans	243	249
Total retained loans	66,023	66,821
Consumer, excluding credit card | Auto and other | California
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	10,101	10,321
Consumer, excluding credit card | Auto and other | Texas
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	7,996	7,772
Consumer, excluding credit card | Auto and other | Florida
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	5,429	5,428
Consumer, excluding credit card | Auto and other | New York
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	4,833	4,905
Consumer, excluding credit card | Auto and other | Illinois
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,867	2,890
Consumer, excluding credit card | Auto and other | New Jersey
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,399	2,468
Consumer, excluding credit card | Auto and other | Pennsylvania
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,043	2,012
Consumer, excluding credit card | Auto and other | Georgia
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,707	1,716
Consumer, excluding credit card | Auto and other | Arizona
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,614	1,643
Consumer, excluding credit card | Auto and other | North Carolina
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,590	1,597
Consumer, excluding credit card | Auto and other | All other
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 25,444	$ 26,069