Loans - Credit Card Loan Portfolio, Delinquency Information (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,018,397	$ 1,010,206	$ 948,642
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	151,382	153,309
Revolving loans converted to term loans	901	987
Total retained loans	$ 152,283	$ 154,296
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	1.04%	0.99%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	9.32%	8.71%
% of 30 plus days past due to total retained loans	1.09%	1.04%
% of 90 plus days past due to total retained loans, Revolving loans within the revolving period	0.52%	0.48%
% of 90 plus days past due to total retained loans, Revolving loans converted to term loans	3.22%	2.74%
% of 90 plus days past due to total retained loans	0.54%	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	$ 149,811	$ 151,798
Revolving loans converted to term loans	817	901
Total retained loans	150,628	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	780	770
Revolving loans converted to term loans	55	59
Total retained loans	835	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	791	741
Revolving loans converted to term loans	29	27
Total retained loans	$ 820	$ 768