v3.26.3
Fair Value Measurements - Fair Values of Financial Assets and Liabilities, Including Derivative Financial Instruments (Detail) - USD ($)
$ in Millions
Sep. 30, 2026
Jun. 30, 2026
Dec. 31, 2025
Sep. 30, 2025
Jun. 30, 2025
Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Total earning assets, Carrying Value $ 43,285   $ 45,862      
Short-term borrowings, Carrying Value 5,751   5,073      
Long-term borrowings, Carrying Value 37,429   40,633      
Total 43,180   45,706      
Financing Receivable, Held-for-Sale 2,400          
Financing Receivable, Allowance for Credit Loss 464 $ 426 537 $ 592 $ 530 $ 621
Total earning assets, Fair Value 42,489   45,417      
Short-term borrowings, Fair Value 5,758   5,084      
Long-term borrowings, Fair Value 36,586   40,120      
Total interest-bearing liabilities, Fair Value 42,344   45,204      
Private Education Loans [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Loans, Carrying Value 12,680   15,451      
Loans receivable, Fair Value 235   0      
Financing Receivable, Held-for-Sale 2,339   0      
FFELP Loans [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Loans, Carrying Value 25,898   28,141      
Loans receivable, Fair Value     28,096      
Financing Receivable, Allowance for Credit Loss 165 163 173 $ 186 $ 182 $ 180
Interest Rate Swaps [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Derivative financial instruments, Carrying Value (6)   39      
Derivative financial instruments, Fair Value (6)   39      
Cross-Currency Interest Rate Swaps [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Derivative financial instruments, Carrying Value (95)   (76)      
Derivative financial instruments, Fair Value (95)   (76)      
Legacy Private Education Loans [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Loans, Carrying Value 15,254          
Loans receivable, Fair Value 235          
Financing Receivable, Held-for-Sale 2,339 $ 5,700        
Financing Receivable, Allowance for Credit Loss 12,680          
Difference [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Cash and investments 0   0      
Total earning assets, Fair Value (796)   (445)      
Short-term borrowings, Fair Value (7)   (11)      
Long-term borrowings, Fair Value 843   513      
Total interest-bearing liabilities, Fair Value 836   502      
Excess of net asset fair value over carrying value 40   57      
Difference [Member] | FFELP Loans [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Loans receivable, Fair Value (72)   (45)      
Difference [Member] | Interest Rate Swaps [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Derivative financial instruments, Fair Value 0   0      
Difference [Member] | Cross-Currency Interest Rate Swaps [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Derivative financial instruments, Fair Value 0   0      
Difference [Member] | Private Education Loans [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Amortized cost (733)   (400)      
Loans receivable, Fair Value 0   0      
Financing Receivable, Held-for-Sale 9   0      
Carrying Value [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Cash and investments 2,133   2,270      
Carrying Value [Member] | Private Education Loans [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Amortized cost 12,680   15,451      
Loans receivable, Fair Value 235   0      
Financing Receivable, Held-for-Sale 2,339   0      
Fair Value [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Cash and investments 2,133   2,270      
Fair Value [Member] | FFELP Loans [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Loans receivable, Fair Value 25,826          
Fair Value [Member] | Private Education Loans [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Amortized cost 11,947   15,051      
Loans receivable, Fair Value 235   0      
Financing Receivable, Held-for-Sale $ 2,348   $ 0