Value of input used to measure net derivative asset (liability).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
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-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

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- Definition

Indicates valuation technique for measuring net derivative asset (liability).

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- Definition

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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Fair Value Measurements - Unobservable Data Used in Recurring Valuations of Level 3 (Detail) $ in Millions	Sep. 30, 2026 USD ($)	Dec. 31, 2025 USD ($)
Interest Rate Swaps [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	$ (6)	$ 39
Private Education Loans Commitments [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	247
Cross-Currency Interest Rate Swaps [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	$ (95)	$ (76)
Level 3 [Member] \| Private Education Loans Commitments [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative Asset (Liability) Net, Valuation Technique [Extensible List]	us-gaap:ValuationTechniqueDiscountedCashFlowMember
Level 3 [Member] \| Private Education Loans Commitments [Member] \| Constant Prepayment Rate [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivatives	12.7
Level 3 [Member] \| Private Education Loans Commitments [Member] \| Measurement Input, Discount Rate [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivatives	6.7
Level 3 [Member] \| Private Education Loans Commitments [Member] \| Constant Default Rate [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivatives	0.9
Level 3 [Member] \| Cross-Currency Interest Rate Swaps [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	$ (95)
Derivative Asset (Liability) Net, Valuation Technique [Extensible List]	us-gaap:ValuationTechniqueDiscountedCashFlowMember
Level 3 [Member] \| Cross-Currency Interest Rate Swaps [Member] \| Constant Prepayment Rate [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivatives	4
Level 3 [Member] \| Other [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Derivative financial instruments, Fair Value	$ 152