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Allowance for Loan Losses - Receivable for Partially Charged-Off Loans (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2016 | Sep. 30, 2015 | Jun. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Net adjustment resulting from the change in the charge-off rate |  |  |  |  | $ (330)
Net charge-offs remaining |  |  |  |  | (549)
Total net charge-offs | $ (130) | $ (161) |  | $ (434) | 879
Private Education Loans [Member] |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Receivable at beginning of period | 847 | 902 |  | 881 | 1,245
Expected future recoveries of current period defaults | 28 | 38 |  | 96 | 147
Recoveries | (47) | (48) |  | (149) | (151)
Net adjustment resulting from the change in the charge-off rate |  |  | $ (330) |  | (330)
Net charge-offs remaining |  |  |  |  | (517)
Total net charge-offs | (112) | (148) |  | (383) | 847
Receivable at end of period | $ 828 | $ 892 | $ 902 | $ 828 | 892
Private Education Loans [Member] | Loans Receivable For Partially Charged Off Loans [Member] |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Net charge-offs remaining |  |  |  |  | (19)
Total net charge-offs |  |  |  |  | $ (349)

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- Definition Allowance for loan and lease losses write offs net remaining. + References No definition available. + Details
Name: | navi_AllowanceForLoanAndLeaseLossesWriteOffsNetRemaining
Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Represents the difference between the loan balance and the company's estimate of the amount to be collected in the future. + References No definition available. + Details
Name: | navi_FinancingReceivableExpectedFutureRecoveriesOfCurrentPeriodDefaults
Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Financing receivable loans recovered. + References No definition available. + Details
Name: | navi_FinancingReceivableLoansRecovered
Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Loans receivable for partially charged-off loans. + References No definition available. + Details
Name: | navi_LoansReceivableForPartiallyChargedOffLoans
Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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- Definition Amount, after recoveries, of loans and leases that have been written-off. + References No definition available. + Details
Name: | us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet
Namespace Prefix: | us-gaap_
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
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: |

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- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=navi_LoansReceivableForPartiallyChargedOffLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |