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Allowance for Loan Losses - Accrued Interest Receivable (Detail) - USD ($) $ in Millions | Jun. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Accounts Notes And Loans Receivable [Line Items] |  |
Accrued Interest Receivable | $ 1,994 | $ 1,999
Private Education Loans [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Accrued Interest Receivable | 319 | 354
Accrued Interest Receivable, Allowance for Uncollectible Interest | 28 | 27
Private Education Loans [Member] | TDR [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Accrued Interest Receivable | 191 | 205
Accrued Interest Receivable, Allowance for Uncollectible Interest | 22 | 23
Private Education Loans [Member] | Non-TDR [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Accrued Interest Receivable | 128 | 149
Accrued Interest Receivable, Allowance for Uncollectible Interest | 6 | 4
Accrued Interest Receivable, Greater Than 90 Days Past Due [Member] | Private Education Loans [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Accrued Interest Receivable | 29 | 29
Accrued Interest Receivable, Greater Than 90 Days Past Due [Member] | Private Education Loans [Member] | TDR [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Accrued Interest Receivable | 26 | 26
Accrued Interest Receivable, Greater Than 90 Days Past Due [Member] | Private Education Loans [Member] | Non-TDR [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Accrued Interest Receivable | $ 3 | $ 3

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- Definition Represents the allowance for uncollectible accrued interest receivable on Private Education Loans. + References No definition available. + Details
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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
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
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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://fasb.org/us-gaap/role/ref/legacyRef -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
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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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Namespace Prefix: |
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Balance Type: |
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- Details
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Balance Type: |
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- Details
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Data Type: | na
Balance Type: |
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |