Loans - Credit Card Loan Portfolio, Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025	Jun. 30, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,463,808	$ 1,408,905	$ 1,345,473
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 249,876	$ 247,797
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Equal to or greater than 660	84.90%	84.60%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Less than 660	14.80%	15.20%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, No FICO available	0.30%	0.20%
Credit card \| California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 38,965	$ 38,702
Credit card \| Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	26,582	26,313
Credit card \| New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	19,655	19,488
Credit card \| Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	18,823	18,622
Credit card \| Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	13,295	13,160
Credit card \| New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	10,388	10,282
Credit card \| Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	7,580	7,384
Credit card \| Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	7,381	7,326
Credit card \| Pennsylvania
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,943	6,921
Credit card \| Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,292	6,295
Credit card \| All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 93,972	$ 93,304