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Allowance for Loan Losses - Receivable for Partially Charged-Off Loans (Parenthetical) (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Jun. 30, 2015 | Mar. 31, 2015 | Sep. 30, 2015
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |
Net adjustment resulting from the change in the charge-off rate |  |  | $ 330
Private Education Loans [Member] |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |
Portion of loan amount charged off at default | 79.00% | 73.00% |
Net adjustment resulting from the change in the charge-off rate | $ 330 |  | $ 330

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- Definition Net adjustment from change in charge off rate. + References No definition available. + Details
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Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Portion of loan amount charged off at default. + References No definition available. + Details
Name: | navi_PortionOfLoanAmountChargedOffAtDefault
Namespace Prefix: | navi_
Data Type: | num:percentItemType
Balance Type: | na
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
Name: | us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems
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: |