Loans - Credit Card Loan Portfolio, Delinquency and Gross Charge-offs (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,369,785	$ 1,285,370	$ 1,299,590
Total gross charge-offs	8,941	$ 7,674
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	233,251		231,414
Revolving loans converted to term loans	2,224		1,446
Total retained loans	$ 235,475		$ 232,860
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	2.06%		2.11%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	11.15%		11.20%
% of 30 plus days past due to total retained loans	2.14%		2.17%
% of 90 plus days past due to total retained loans, Revolving loans within the revolving period	1.05%		1.12%
% of 90 plus days past due to total retained loans, Revolving loans converted to term loans	3.69%		3.67%
% of 90 plus days past due to total retained loans	1.07%		1.14%
Gross charge-offs originated within the revolving period	$ 6,621		$ 7,951
Gross charge-offs originated converted to term loans	244		247
Total gross charge-offs	6,865		8,198
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	228,457		226,532
Revolving loans converted to term loans	1,976		1,284
Total retained loans	230,433		227,816
Credit card | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	2,353		2,291
Revolving loans converted to term loans	166		109
Total retained loans	2,519		2,400
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	2,441		2,591
Revolving loans converted to term loans	82		53
Total retained loans	$ 2,523		$ 2,644