Loans receivable repayment period.

No definition available.

Name:	navi_LoansReceivableRepaymentPeriod
Namespace Prefix:	navi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of education loan portfolio in repayment.

+ References

No definition available.

+ Details

Name:	navi_PercentageOfEducationLoanPortfolioInRepayment
Namespace Prefix:	navi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Reimbursement on all qualifying default claims percentage.

+ References

No definition available.

+ Details

Name:	navi_ReimbursementOnAllQualifyingDefaultClaimsPercentage
Namespace Prefix:	navi_
Data Type:	num:percentItemType
Balance Type:	na
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

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of any significant sales of financing receivables during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableSignificantSales
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The gains (losses) included in earning that represent the difference between the sale price and the carrying value of consumer loans. This element refers to the gain (loss) and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

+ Details

Name:	us-gaap_GainLossOnSalesOfConsumerLoans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis=us-gaap_FederalFamilyEducationLoanProgramFfelpGuaranteedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ClassOfFinancingReceivableTypeOfBorrowerAxis=navi_AfterOctoberOneNineteenNinetyThreeAndBeforeJulyOneTwoThousandSixMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_ClassOfFinancingReceivableTypeOfBorrowerAxis=navi_OnOrAfterJulyOneTwoThousandSixMember
Namespace Prefix:
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Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=navi_StaffordLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=navi_PlusLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=navi_ConsolidationLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_StudentLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Education Loans - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts Notes And Loans Receivable [Line Items]
Percentage of education loan portfolio in repayment	86.00%	86.00%	83.00%
Amount of loan sold	$ 0		$ 0
FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Amount of loan sold				$ 412,000,000
Gain (loss) on sale of loans				12,000,000
After October 1 1993 and before July 1 2006 [Member] \| FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Percentage reimbursement on all qualifying default claims period	98.00%	98.00%
On or After July 1 2006 [Member] \| FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Percentage reimbursement on all qualifying default claims period	97.00%	97.00%
Stafford Loans [Member] \| Minimum [Member] \| FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Repayment term		5 years
Stafford Loans [Member] \| Maximum [Member] \| FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Repayment term		10 years
Plus Loans [Member] \| Minimum [Member] \| FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Repayment term		5 years
Plus Loans [Member] \| Maximum [Member] \| FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Repayment term		10 years
Stafford Loans [Member] \| Minimum [Member] \| FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Repayment term		12 years
Stafford Loans [Member] \| Maximum [Member] \| FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Repayment term		30 years
Plus Loans [Member] \| Weighted Average [Member]
Accounts Notes And Loans Receivable [Line Items]
Estimated weighted average life of education loans		7 years	7 years
Private Education Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Amount of loan sold				178,000,000
Gain (loss) on sale of loans				$ (21,000,000)
Private Education Loans [Member] \| Minimum [Member]
Accounts Notes And Loans Receivable [Line Items]
Repayment term		10 years
Private Education Loans [Member] \| Maximum [Member]
Accounts Notes And Loans Receivable [Line Items]
Repayment term		15 years