v3.26.1
Allowance for Loan Losses - Education Loans - Allowance for Credit Losses and Recorded Investments in Loans (Parenthetical) (Detail) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Accounts Notes And Loans Receivable [Line Items]        
Charge-offs (as a result of lower recovery expectations) $ (92) $ (101) $ (192) $ (189)
Change in balance during period (3) (2) (7) (8)
Loans held for sale 528   528  
Private Education Loans [Member]        
Accounts Notes And Loans Receivable [Line Items]        
Charge-offs (as a result of lower recovery expectations) (82) (93) (165) (175)
Change in balance during period (3) (2) (7) (8)
Loans held for sale 528   528  
Private Education Loans [Member] | Loans Receivable For Previously Fully Charged Off Loans [Member]        
Accounts Notes And Loans Receivable [Line Items]        
Beginning of period expected future recoveries on previously fully charged-off loans 166 174 170 179
Expected future recoveries of current period defaults 11 13 22 23
Recoveries (cash collected) (10) (11) (20) (21)
Charge-offs (as a result of lower recovery expectations) (4) (4) (9) (10)
End of period expected future recoveries on previously fully charged-off loans 163 172 163 172
Change in balance during period $ (3) $ (2) $ (7) $ (8)