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Derivative Financial Instruments - Collateral Held and Pledged (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Collateral held in restricted cash	$ 0	$ 9

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

- Details

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