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Derivative Financial Instruments - Collateral Held and Pledged (Parenthetical) (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Collateral held in restricted cash account	$ 11	$ 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