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Allowance for Loan Losses - Receivable for Partially Charged-Off Loans (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2016 | Jun. 30, 2015 | Jun. 30, 2016 | Jun. 30, 2015
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Net adjustment resulting from the change in the charge-off rate |  | $ (330) |  | $ (330)
Private Education Loans [Member] |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Receivable at beginning of period | $ 867 | 1,236 | $ 881 | 1,245
Expected future recoveries of current period defaults | 32 | 46 | 68 | 108
Recoveries | (52) | (50) | (102) | (102)
Net adjustment resulting from the change in the charge-off rate |  | (330) |  | (330)
Net charge-offs remaining |  |  |  | (19)
Total net charge-offs |  | (330) |  | (349)
Receivable at end of period | $ 847 | $ 902 | $ 847 | $ 902

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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 net charge offs. + References No definition available. + Details
Name: | navi_FinancingReceivableLoansNetChargeOffs
Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Financing receivable loans net charge offs remaining. + References No definition available. + Details
Name: | navi_FinancingReceivableLoansNetChargeOffsRemaining
Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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 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: |