Loans - Credit Card Loan Portfolio, Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,369,785	$ 1,299,590	$ 1,285,370
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 235,475	$ 232,860
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Equal to or greater than 660	84.40%	85.50%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Less than 660	15.50%	14.30%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, No FICO available	0.10%	0.20%
Credit card | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 36,654	$ 36,385
Credit card | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	24,938	24,423
Credit card | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	18,807	18,525
Credit card | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	17,576	17,236
Credit card | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	12,605	12,442
Credit card | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	9,839	9,644
Credit card | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	7,140	6,962
Credit card | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,945	6,976
Credit card | Pennsylvania
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,520	6,558
Credit card | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	5,957	5,796
Credit card | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 88,494	$ 87,913