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v3.25.2

Allowance for Loan Losses - Additional Information (Detail) | 6 Months Ended
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Jun. 30, 2025
Receivables [Abstract] |
Period of hardship forbearance of payments | 12 months
Period of hardship forbearance of payments for borrowers of substantial payments | 24 months
Percentage guaranteed as to principal and accrued interest by federal goverment in event of default | 97.00%

X
- Definition Percentage guaranteed as to principal and accrued interest by federal goverment in event of default. + References No definition available. + Details
Name: | navi_PercentageGuaranteedAsToPrincipalAndAccruedInterestByFederalGovermentInEventOfDefault
Namespace Prefix: | navi_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period of hardship forbearance of payments. + References No definition available. + Details
Name: | navi_PeriodOfHardshipForbearanceOfPayments
Namespace Prefix: | navi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period of hardship forbearance of payments for borrowers of substantial payments. + References No definition available. + Details
Name: | navi_PeriodOfHardshipForbearanceOfPaymentsForBorrowersOfSubstantialPayments
Namespace Prefix: | navi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_ReceivablesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration