Debt instrument maturities month year.

No definition available.

Name:	navi_DebtInstrumentMaturitiesMonthYear
Namespace Prefix:	navi_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Total unencumbered loans at the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	navi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of assets pledged to secure a debt instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ 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 210.5-02.19(b),22(b))
-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:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentAxis=navi_PrivateEducationLoanSecuritizationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=navi_PrivateEducationRefinanceLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=navi_PrivateEducationLoanAbcpBorrowingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=navi_FFELPLoansOtherFacilitiesMember
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Period Type:

- Details

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- Details

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Borrowings - Additional Information (Detail) - USD ($)	12 Months Ended
Borrowings - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Outstanding borrowings under facility	$ 105,012,000,000	$ 112,368,000,000
Issuance of unsecured debt	$ 1,600,000,000	$ 1,300,000,000	$ 500,000,000
Private Education Loan Securitizations [Member] \| Asset-backed Securities, Securitized Loans and Receivables [Member]
Debt Instrument [Line Items]
Amount of asset-backed securitization repurchase facility			$ 2,500,000,000
Private Education Refinance Loan [Member] \| Private Education Loan Abcp Borrowings [Member]
Debt Instrument [Line Items]
Facility maturity date	2018-10
Maximum unused capacity	$ 328,000,000
Maximum borrowing capacity	750,000,000
FFELP Loan - Other Facilities [Member]
Debt Instrument [Line Items]
Outstanding borrowings under facility	8,400,000,000
Assets securing facility	9,400,000,000
Maximum unused capacity	2,400,000,000
Unencumbered Loans	700,000,000
Private Education Loan Abcp Borrowings [Member]
Debt Instrument [Line Items]
Outstanding borrowings under facility	2,400,000,000
Assets securing facility	3,100,000,000
Maximum unused capacity	925,000,000
Unencumbered Loans	$ 2,500,000,000
Minimum [Member] \| FFELP Loan - Other Facilities [Member]
Debt Instrument [Line Items]
Facility maturity date	2018-11
Minimum [Member] \| Private Education Loan Abcp Borrowings [Member]
Debt Instrument [Line Items]
Facility maturity date	2018-06
Maximum [Member] \| FFELP Loan - Other Facilities [Member]
Debt Instrument [Line Items]
Facility maturity date	2021-01
Maximum [Member] \| Private Education Loan Abcp Borrowings [Member]
Debt Instrument [Line Items]
Facility maturity date	2020-06