v3.26.1
Allowance for Credit Losses and Unfunded Loan Commitments - Narrative (Details)
 3 Months Ended 6 Months Ended 12 Months Ended 15 Months Ended
Jun. 30, 2026
USD ($)
Jun. 30, 2026
USD ($)
payment
Jun. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Jun. 30, 2026
USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Monthly payment that is smaller than the interest accrued on the loan in that month   $ 25      
Financing receivable allowance period increase (decrease)   $ 58,000,000      
Loan sale reduction to provision     $ 116,000,000    
Criteria for loans to be considered as nonperforming (greater than)   90 days      
Maximum amount of forbearance granted   12 months      
Number of monthly payments required by a borrower between successive grants of forbearance | payment   12      
Financing receivable, modified in period, subsequently charged off, amount   $ 28,200,000   $ 39,100,000 $ 42,100,000
Period of loans past due that have accrued interest   90 days      
Contractual obligation $ 1,700,000,000 $ 1,700,000,000     $ 1,700,000,000
Private Education Loans          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Loan sale reduction to provision 10,826,000 130,912,000 116,459,000    
Loans sold   $ 3,750,000,000 $ 2,000,000,000.00    
Threshold period when delinquent loans are written off   120 days      
Financing receivable, modified in period, subsequently charged off, amount $ 16,000,000.0 $ 28,200,000      
Unfunded loan held-for-sale   $ 28,000,000      
Minimum          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Increments in which forbearance is granted   1 month      
Maximum          
Accounts, Notes, Loans and Financing Receivable [Line Items]          
Increments in which forbearance is granted   2 months