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Allowance for Loan Losses - Additional Information (Detail) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2022 | Dec. 31, 2021
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Percentage of loans granted forbearance that migrated to TDR classification | 77.00% | 75.00%
Payment default period for TDRs | 60 days past due |
Interest Rate Reduction [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
TDR loans, Unpaid Principal Balance | $ 900 | $ 831

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- Definition Payment default period for troubled debt restructurings. + References No definition available. + Details
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Data Type: | xbrli:stringItemType
Balance Type: | na
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- Definition Percentage of loans granted forbearance that migrated to troubled debt restructuring classification. + References No definition available. + Details
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Namespace Prefix: | navi_
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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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- Definition Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a)(4) -URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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Balance Type: |
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