| **Debt - Narrative (Details) - USD ($)**                                                                                                                   | 1 Months Ended | 3 Months Ended | 9 Months Ended |               |               |               |
|------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|----------------|---------------|---------------|---------------|
||
| **Debt Instrument [Line Items]**                                                                                                                           |           |           |           |          |          |          |   |
| Line of Credit Facility, Maximum Borrowing Capacity                                                                                                        |           |           |           |          |          | $ 100,000,000 |   |
| Cash Dividends Paid to Parent Company by Consolidated Subsidiaries                                                                                         |           |           | $ 50,000,000   | $ 80,000,000  |          |          |   |
| Financial Services Operations [Member] | VFN Facility [Member]                                                                                             |           |           |           |          |          |          |   |
| **Debt Instrument [Line Items]**                                                                                                                           |           |           |           |          |          |          |   |
| Debt Instrument, Face Amount                                                                                                                               |           |           |           |          |          | $ 375,000,000 | $ 500,000,000 |
| Revolving Credit Facility [Member] | Financial Services Operations [Member] | Bank Facility [Member]                                                       |           |           |           |          |          |          |   |
| **Debt Instrument [Line Items]**                                                                                                                           |           |           |           |          |          |          |   |
| Line of Credit Facility, Maximum Borrowing Capacity                                                                                                        |           | $ 500,000,000  |           |          | $ 400,000,000 |          |   |
| Line of Credit Facility, Fair Value of Amount Outstanding                                                                                                  |           |           | 300,000,000    | 300,000,000   |          |          |   |
| Line of Credit Facility, Accordion Feature, Higher Borrowing Capacity Option                                                                               |           |           |           |          | $ 700,000,000 |          |   |
| Term Loan [Member] | Financial Services Operations [Member] | Bank Facility [Member]                                                                       |           |           |           |          |          |          |   |
| **Debt Instrument [Line Items]**                                                                                                                           |           |           |           |          |          |          |   |
| Line of Credit Facility, Fair Value of Amount Outstanding                                                                                                  |           |           | $ 221,000,000  | $ 221,000,000 |          |          |   |
| Scenario, Forecast [Member] | Revolving Credit Facility [Member] | Financial Services Operations [Member] | Bank Facility [Member]                         |           |           |           |          |          |          |   |
| **Debt Instrument [Line Items]**                                                                                                                           |           |           |           |          |          |          |   |
| Line of Credit Facility, Maximum Borrowing Capacity                                                                                                        | $ 275,000,000  |           |           |          |          |          |   |
| Scenario, Forecast [Member] | Term Loan [Member] | Financial Services Operations [Member] | Bank Facility [Member]                                         |           |           |           |          |          |          |   |
| **Debt Instrument [Line Items]**                                                                                                                           |           |           |           |          |          |          |   |
| Line of Credit Facility, Maximum Borrowing Capacity                                                                                                        | 82,000,000     |           |           |          |          |          |   |
| Installment Payments Set Two [Member] | Term Loan [Member] | Financial Services Operations [Member] | Bank Facility [Member]                               |           |           |           |          |          |          |   |
| **Debt Instrument [Line Items]**                                                                                                                           |           |           |           |          |          |          |   |
| Debt Instrument, Periodic Payment, Principal                                                                                                               |           | $ 9,000,000    |           |          |          |          |   |
| Installment Payments Set Two [Member] | Scenario, Forecast [Member] | Term Loan [Member] | Financial Services Operations [Member] | Bank Facility [Member] |           |           |           |          |          |          |   |
| **Debt Instrument [Line Items]**                                                                                                                           |           |           |           |          |          |          |   |
| Debt Instrument, Periodic Payment, Principal                                                                                                               | $ 2,000,000    |           |           |          |          |          |   |

| X                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line of Credit Facility, Accordion Feature, Higher Borrowing Capacity Option
+ References
No definition available.
+ Details**Name:**nav_LineofCreditFacilityAccordionFeatureHigherBorrowingCapacityOption**Namespace Prefix:**nav_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04.(b)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 235 -Section S99 -Paragraph 2 -Subparagraph (SX 210.9-06) -URI http://asc.fasb.org/extlink&oid=6882215&loc=d3e537971-122884
+ Details**Name:**us-gaap_CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Face (par) amount of debt instrument at time of issuance.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399
+ Details**Name:**us-gaap_DebtInstrumentFaceAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
+ Details**Name:**us-gaap_DebtInstrumentLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of the required periodic payments applied to principal.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682
+ Details**Name:**us-gaap_DebtInstrumentPeriodicPaymentPrincipal**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value of the amount outstanding under the credit facility.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13433-108611Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13476-108611
+ Details**Name:**us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682
+ Details**Name:**us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementBusinessSegmentsAxis=nav_FinancialServicesOperationsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DebtInstrumentAxis=nav_VfnFacilityMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DebtInstrumentAxis=nav_BankFacilityMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_CreditFacilityAxis=nav_TermLoanMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**nav_InstallmentPaymentsBySetAxis=nav_InstallmentPaymentsSetTwoMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |