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Commitments, Contingencies and Guarantees - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Commitments And Contingencies Disclosure [Abstract]
Amount reserved for expected compliance remediation	$ 70

X

- Definition

Expected compliance remediation efforts reserve.

+ References

No definition available.

+ Details

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Namespace Prefix:	navi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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- Details

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