Loans - Credit Card Loan Portfolio, Delinquency Information (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,052,390	$ 1,010,206	$ 963,665
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	164,667	153,309
Revolving loans converted to term loans	827	987
Total retained loans	$ 165,494	$ 154,296
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	1.01%	0.99%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	9.31%	8.71%
% of 30 plus days past due to total retained loans	1.05%	1.04%
% of 90 plus days past due to total retained loans, Revolving loans within the revolving period	0.50%	0.48%
% of 90 plus days past due to total retained loans, Revolving loans converted to term loans	3.14%	2.74%
% of 90 plus days past due to total retained loans	0.51%	0.50%
Credit card | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	$ 163,010	$ 151,798
Revolving loans converted to term loans	750	901
Total retained loans	163,760	152,699
Credit card | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	841	770
Revolving loans converted to term loans	51	59
Total retained loans	892	829
Credit card | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	816	741
Revolving loans converted to term loans	26	27
Total retained loans	$ 842	$ 768