Loans - Credit Card Loan Portfolio, Delinquency Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,265,941	$ 1,068,073	$ 1,089,598
Total gross charge-offs	5,096	$ 3,116
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	196,006		184,379
Revolving loans converted to term loans	929		796
Total retained loans	$ 196,935		$ 185,175
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	1.89%		1.40%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	12.38%		12.56%
% of 30 plus days past due to total retained loans	1.94%		1.45%
% of 90 plus days past due to total retained loans, Revolving loans within the revolving period	0.92%		0.67%
% of 90 plus days past due to total retained loans, Revolving loans converted to term loans	4.20%		4.52%
% of 90 plus days past due to total retained loans	0.94%		0.68%
Gross charge-offs originated within the revolving period	$ 3,737
Gross charge-offs originated converted to term loans	115
Total gross charge-offs	3,852
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	192,295		$ 181,793
Revolving loans converted to term loans	814		696
Total retained loans	193,109		182,489
Credit card | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	1,901		1,356
Revolving loans converted to term loans	76		64
Total retained loans	1,977		1,420
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	1,810		1,230
Revolving loans converted to term loans	39		36
Total retained loans	$ 1,849		$ 1,266