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Allowance for Loan Losses - Receivable for Partially Charged-Off Private Education Loans (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Charge-offs	$ (151)	$ (160)
Private Education Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Receivable at beginning of period	23,340
Charge-offs	(137)	(144)
Receivable at end of period	22,552
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	815	881
Expected future recoveries of current period defaults	34	36
Recoveries	(44)	(47)
Charge-offs	(5)	(3)
Receivable at end of period	$ 800	$ 867

X

- 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

X

- Definition

Financing receivable loans recovered.

+ References

No definition available.

+ Details

Name:	navi_FinancingReceivableLoansRecovered
Namespace Prefix:	navi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- 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

X

- 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

X

- 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://www.xbrl.org/2003/role/presentationRef
-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

X

- Details

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

X

- Details

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