v3.26.3
Allowance for Loan Losses - Education Loans - Summary of Performance and Related Loan Status of Loans Modified (Details) - Private Education Loans [Member] - USD ($)
$ in Millions
Sep. 30, 2026
Dec. 31, 2025
Accounts Notes And Loans Receivable [Line Items]    
Payment status (Amortized Cost) $ 1,865 $ 2,680
School/Deferment [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Payment status (Amortized Cost) 18 24
Forbearance [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Payment status (Amortized Cost) 81 73
Financing Asset, Not Past Due [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Payment status (Amortized Cost) 1,390 2,056
Financial Asset, 31 to 60 Days Past Due [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Payment status (Amortized Cost) 144 191
Financial Asset, 61 to 90 Days Past Due [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Payment status (Amortized Cost) 89 125
Financial Asset, 90 Days Past Due [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Payment status (Amortized Cost) $ 143 $ 211