v3.26.3
Allowance for Credit Losses and Unfunded Loan Commitments - Narrative (Details)
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
payment
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
Dec. 31, 2025
USD ($)
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)     $ 24,000,000      
Loan sale reduction to provision       $ 235,000,000    
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     $ 40,700,000   $ 45,200,000 $ 39,100,000
Period of loans past due that have accrued interest     90 days      
Contractual obligation $ 3,200,000,000   $ 3,200,000,000   $ 3,200,000,000  
Private Education Loans            
Accounts, Notes, Loans and Financing Receivable [Line Items]            
Loan sale reduction to provision 8,984,000 $ 118,794,000 139,896,000 235,253,000    
Loans sold     $ 4,070,000,000.00 $ 3,940,000,000    
Threshold period when delinquent loans are written off     120 days      
Financing receivable, modified in period, subsequently charged off, amount $ 18,000,000.0   $ 40,700,000      
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