v3.26.1
Allowance for Loan Losses - Education Loans - Private Education Loan Portfolio Stratified by Key Credit Quality Indicators (Parenthetical) (Detail) - USD ($)
$ in Millions
Jun. 30, 2026
Jun. 30, 2025
Accounts Notes And Loans Receivable [Line Items]    
Loans held for sale $ 528  
Private Education Loans [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Loans held for sale $ 528  
With Cosigner [Member]    
Accounts Notes And Loans Receivable [Line Items]    
Total Private Education Loan Credit Quality Indicators, Excluding Refinance Loans, Percent 66.00% 66.00%