v3.26.3
Allowance for Loan Losses - Education Loans - Allowance for Credit Losses and Recorded Investments in Loans (Detail) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Allowance for Loan Losses        
Beginning balance $ 426 $ 530 $ 537 $ 621
Provision:        
Total provision 227 168 281 236
Charge-offs:        
Gross charge-offs (79) (121) (271) (310)
Expected future recoveries on current period gross charge-offs 9 16 31 39
Net charge-offs (70) (105) (240) (271)
Write off in connection with classification of loans as held for sale (121) 0 (121)  
Decrease in expected future recoveries on previously fully charged-off loans 6 (1) 13 6
Allowance at end of period 464 592 464 592
Private Education Loans [Member]        
Allowance for Loan Losses        
Beginning balance 263 348 364 441
Provision:        
Total provision 210 155 245 207
Charge-offs:        
Gross charge-offs (68) (112) (233) (287)
Expected future recoveries on current period gross charge-offs 9 16 31 39
Net charge-offs (59) (96) (202) (248)
Write off in connection with classification of loans as held for sale (121) 0 (121)  
Decrease in expected future recoveries on previously fully charged-off loans 6 (1) 13 6
Allowance at end of period $ 299 $ 406 $ 299 $ 406
Net charge-offs as a percentage of average loans in repayment 1.49% 2.50% 1.65% 2.16%
Ending total loans $ 12,979 $ 15,862 $ 12,979 $ 15,862
Average loans in repayment 12,613 15,259 12,450 15,368
Ending loans in repayment 12,519 15,221 12,519 15,221
Provision For Education Loans [Member]        
Provision:        
Total provision 223 168 275 236
FFELP Loans [Member]        
Allowance for Loan Losses        
Beginning balance 163 182 173 180
Provision:        
Total provision 13 13 30 29
Charge-offs:        
Gross charge-offs (11) (9) (38) (23)
Expected future recoveries on current period gross charge-offs 0 0 0 0
Net charge-offs (11) (9) (38) (23)
Write off in connection with classification of loans as held for sale 0 0 0  
Decrease in expected future recoveries on previously fully charged-off loans 0 0 0 0
Allowance at end of period $ 165 $ 186 $ 165 $ 186
Net charge-offs as a percentage of average loans in repayment 0.20% 0.15% 0.23% 0.13%
Ending total loans $ 26,063 $ 29,138 $ 26,063 $ 29,138
Average loans in repayment 22,022 24,527 22,571 25,036
Ending loans in repayment $ 21,872 $ 24,136 $ 21,872 $ 24,136