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Derivative Financial Instruments - Collateral Held and Pledged (Parenthetical) (Detail) - USD ($) $ in Millions | Sep. 30, 2016 | Dec. 31, 2015
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Derivative Instruments and Hedging Activities Disclosure [Abstract] |  |
Collateral held in restricted cash account | $ 0 | $ 2

X
- Definition Collateral held in restricted cash accounts. + References No definition available. + Details
Name: | navi_CollateralInRestrictedCashAccounts
Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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