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Allowance for Loan Losses - Amount of Loans Modified for Borrowers Financial Difficulty and Payment Default (Details) - Private Education Loans [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Accounts Notes And Loans Receivable [Line Items]
Modified Loans (Amortized Cost)	$ 109	$ 128	$ 179	$ 163
Payment Default (Par)	111	131	183	167
Charge-offs (par)	$ 15	$ 10	$ 25	$ 12

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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.

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Amortized cost of financing receivable with payment default in current period and modified within previous 12 months preceding payment default for debtor experiencing financial difficulty.

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