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Derivative Financial Instruments - Additional Information (Detail) $ in Millions | Sep. 30, 2016 USD ($) Counterparty | Dec. 31, 2015 USD ($)
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Derivative Instruments and Hedging Activities Disclosure [Abstract] |  |
Decrease in valuation due to net credit risk adjustments | $ 3 | $ 1
Decrease in valuation due to liquidity adjustments | 30 | $ 31
Derivative liability position including accrued interest, net of premium receivable with counterparty | $ 594 |
Number of counterparties with right to terminate | Counterparty | 2 |

X
- Definition Decrease in valuation due to liquidity adjustments. + References No definition available. + Details
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Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Derivative liability position including accrued interest, net of premium receivable with counterparty. + References No definition available. + Details
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Namespace Prefix: | navi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number of counterparties with right to terminate. + References No definition available. + Details
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Namespace Prefix: | navi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of credit risk valuation adjustment to derivative assets to properly reflect the credit quality of the counterparties. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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