Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other, Nonaccrual Loans and Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 1,425,236	$ 1,408,905	$ 1,300,990
Consumer, excluding credit card
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	367,274	368,741	$ 372,892
Consumer, excluding credit card | Auto and other
Financing Receivable, Credit Quality Indicator [Line Items]
Nonaccrual loans	236	243
Total retained loans	65,327	65,210
Consumer, excluding credit card | Auto and other | California
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	9,965	9,926
Consumer, excluding credit card | Auto and other | Texas
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	8,008	7,940
Consumer, excluding credit card | Auto and other | Florida
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	5,421	5,382
Consumer, excluding credit card | Auto and other | New York
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	4,766	4,771
Consumer, excluding credit card | Auto and other | Illinois
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,806	2,804
Consumer, excluding credit card | Auto and other | New Jersey
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,331	2,347
Consumer, excluding credit card | Auto and other | Pennsylvania
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	2,091	2,066
Consumer, excluding credit card | Auto and other | Georgia
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,677	1,682
Consumer, excluding credit card | Auto and other | North Carolina
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,583	1,578
Consumer, excluding credit card | Auto and other | Arizona
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	1,582	1,583
Consumer, excluding credit card | Auto and other | All other
Financing Receivable, Credit Quality Indicator [Line Items]
Total retained loans	$ 25,097	$ 25,131