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Allowance for Loan Losses - Receivable for Partially Charged-Off Private Education Loans (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Charge-offs | $ (95) | $ (92) | $ (207) | $ (181)
Private Education Loans [Member] |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Receivable at beginning of period |  |  | 22,245 |
Charge-offs | (87) | (75) | (181) | (153)
Receivable at end of period | 21,564 |  | 21,564 |
Private Education Loans [Member] | Loans Receivable For Partially Charged Off Loans [Member] |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |
Receivable at beginning of period | 657 | 741 | 674 | 760
Expected future recoveries of current period defaults | 18 | 19 | 38 | 38
Recoveries | (33) | (36) | (67) | (74)
Charge-offs | (2) |  | (5) |
Receivable at end of period | $ 640 | $ 724 | $ 640 | $ 724

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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 Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524 + Details
Name: | us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
Namespace Prefix: | us-gaap_
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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- Definition Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes loans held for sale. Excludes loans and leases covered under loss sharing agreements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(a)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
Name: | us-gaap_LoansReceivableNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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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: |