Loans - Credit Card Loan Portfolio, Delinquency and Gross Charge-offs (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,425,236	$ 1,300,990	$ 1,408,905
Total gross charge-offs	2,911	$ 2,816
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	236,149		245,188
Revolving loans converted to term loans	2,974		2,609
Total retained loans	$ 239,123		$ 247,797
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	2.05%		2.06%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	11.84%		12.27%
% of 30 plus days past due to total retained loans	2.17%		2.16%
% of 90 plus days past due to total retained loans, Revolving loans within the revolving period	1.10%		1.07%
% of 90 plus days past due to total retained loans, Revolving loans converted to term loans	4.47%		4.33%
% of 90 plus days past due to total retained loans	1.15%		1.10%
Gross charge-offs originated within the revolving period	$ 2,353		$ 8,812
Gross charge-offs originated converted to term loans	133		352
Total gross charge-offs	2,486		9,164
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	231,304		240,147
Revolving loans converted to term loans	2,622		2,289
Total retained loans	233,926		242,436
Credit card | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Revolving loans within the revolving period	2,236		2,422
Revolving loans converted to term loans	219		207
Total retained loans	2,455		2,629
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	2,609		2,619
Revolving loans converted to term loans	133		113
Total retained loans	$ 2,742		$ 2,732