Loans - Credit Card Loan Portfolio, Delinquency Information (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,285,370	$ 1,265,941	$ 1,280,870
Total gross charge-offs	7,674	$ 5,096
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	218,206		210,117
Revolving loans converted to term loans	1,336		1,006
Total retained loans	$ 219,542		$ 211,123
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	2.14%		2.09%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	11.60%		12.33%
% of 30 plus days past due to total retained loans	2.20%		2.14%
% of 90 plus days past due to total retained loans, Revolving loans within the revolving period	1.08%		1.03%
% of 90 plus days past due to total retained loans, Revolving loans converted to term loans	3.89%		3.98%
% of 90 plus days past due to total retained loans	1.10%		1.05%
Gross charge-offs originated within the revolving period	$ 5,868		$ 5,325
Gross charge-offs originated converted to term loans	176		166
Total gross charge-offs	6,044		5,491
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	213,537		205,731
Revolving loans converted to term loans	1,181		882
Total retained loans	214,718		206,613
Credit card | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	2,305		2,217
Revolving loans converted to term loans	103		84
Total retained loans	2,408		2,301
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	2,364		2,169
Revolving loans converted to term loans	52		40
Total retained loans	$ 2,416		$ 2,209