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Allowance for Loan Losses - Accrued Interest Receivable (Detail) - USD ($) $ in Millions | Sep. 30, 2016 | Dec. 31, 2015
--- | --- | ---
Private Education Loans - Traditional [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Accrued Interest Receivable | $ 374 | $ 433
Greater Than 90 Days Past Due | 23 | 27
Allowance for Uncollectible Interest | 26 | 26
Private Education Loans - Non-Traditional [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Accrued Interest Receivable | 48 | 57
Greater Than 90 Days Past Due | 7 | 8
Allowance for Uncollectible Interest | 7 | 9
Private Education Loans [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Accrued Interest Receivable | 422 | 490
Greater Than 90 Days Past Due | 30 | 35
Allowance for Uncollectible Interest | $ 33 | $ 35

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- Definition Accrued interest on loans greater than ninety days past due. + References No definition available. + Details
Name: | navi_AccruedInterestOnLoansGreaterThanNinetyDaysPastDue
Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Represents the allowance for uncollectible accrued interest receivable on Private Education Loans. + References No definition available. + Details
Name: | navi_AllowanceForUncollectibleAccruedInterest
Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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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_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.8) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_InterestReceivable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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

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