Loans - Credit Card Loan Portfolio, Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,425,236	$ 1,408,905	$ 1,300,990
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 239,123	$ 247,797
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Equal to or greater than 660	83.90%	84.60%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Less than 660	15.80%	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	$ 37,362	$ 38,702
Credit card | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	25,640	26,313
Credit card | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	18,793	19,488
Credit card | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	18,095	18,622
Credit card | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	12,707	13,160
Credit card | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	9,898	10,282
Credit card | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	7,205	7,384
Credit card | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	7,016	7,326
Credit card | Pennsylvania
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,602	6,921
Credit card | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,110	6,295
Credit card | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 89,695	$ 93,304