Loans - Credit Card Loan Portfolio, Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025	Sep. 30, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,497,159	$ 1,408,905	$ 1,369,785
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 252,697	$ 247,797
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Equal to or greater than 660	84.60%	84.60%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Less than 660	15.10%	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	$ 39,397	$ 38,702
Credit card \| Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	26,910	26,313
Credit card \| New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	19,976	19,488
Credit card \| Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	19,097	18,622
Credit card \| Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	13,466	13,160
Credit card \| New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	10,576	10,282
Credit card \| Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	7,664	7,384
Credit card \| Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	7,417	7,326
Credit card \| Pennsylvania
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,962	6,921
Credit card \| Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,411	6,295
Credit card \| All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 94,821	$ 93,304