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Allowance for Loan Losses - Summary of Performance and Related Loan Status of Loans Modified (Details) - Private Education Loans (Details) - Private Education Loans [Member] $ in Millions | Dec. 31, 2023 USD ($)
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Accounts, Notes, Loans and Financing Receivable [Line Items] |
Payment status (Amortized Cost) | $ 2,729
School/Deferment [Member] |
Accounts, Notes, Loans and Financing Receivable [Line Items] |
Payment status (Amortized Cost) | 22
Forbearance [Member] |
Accounts, Notes, Loans and Financing Receivable [Line Items] |
Payment status (Amortized Cost) | 93
Financing Asset, Not Past Due [Member] |
Accounts, Notes, Loans and Financing Receivable [Line Items] |
Payment status (Amortized Cost) | 2,199
Financial Asset, 31 to 60 Days Past Due [Member] |
Accounts, Notes, Loans and Financing Receivable [Line Items] |
Payment status (Amortized Cost) | 160
Financial Asset, 61 to 90 Days Past Due [Member] |
Accounts, Notes, Loans and Financing Receivable [Line Items] |
Payment status (Amortized Cost) | 96
Financial Asset, 90 Days Past Due [Member] |
Accounts, Notes, Loans and Financing Receivable [Line Items] |
Payment status (Amortized Cost) | $ 159

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