Loans - Credit Card Loan Portfolio, Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 1,052,390	$ 1,010,206	$ 963,665
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 165,494	$ 154,296
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Equal to or greater than 660	88.20%	88.50%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Less than 660	11.60%	11.30%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, No FICO available	0.20%	0.20%
Credit card | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 24,954	$ 23,030
Credit card | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	17,138	15,879
Credit card | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,616	12,652
Credit card | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	11,205	10,412
Credit card | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	9,198	8,530
Credit card | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	6,854	6,367
Credit card | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,231	4,923
Credit card | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,029	4,573
Credit card | Pennsylvania
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,943	4,708
Credit card | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,988	3,773
Credit card | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 63,338	$ 59,449