XML 82 R65.htm IDEA: XBRL DOCUMENT v3.7.0.1

Segment Reporting - Core Earnings Adjustments to GAAP (Parenthetical) (Detail)	3 Months Ended
	Mar. 31, 2017 USD ($)
Segment Reporting [Abstract]
Amount that will be equal to cumulative net unrealized gain or loss over the life of the contract	$ 0

X

- Definition

Cumulative net unrealized gain or loss over the life of the contract.

+ References

No definition available.

+ Details

Name:	navi_CumulativeNetUnrealizedGainOrLossOverLifeOfContract
Namespace Prefix:	navi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- References

No definition available.

+ Details

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