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Allowance for Loan Losses - Summary of Performance and Related Loan Status of Loans Modified (Parenthetical) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2023 USD ($)
Private Education Loans [Member] |
Accounts Notes And Loans Receivable [Line Items] |
Loans modified, charged off | $ 15

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- Definition Financing receivable modifications, charged off. + References No definition available. + Details
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Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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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 No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=navi_PrivateEducationLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |