| **Allowance for Doubtful Accounts - Narrative (Details) $ in Millions** | 3 Months Ended |
|-------------------------------------------------------------------------|----------------|
||
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**        |           |   |
| Number of Portfolio Segments for Finance Receivables | segments         | 2              |   |
| Classes Of Receivables In Each Portfolio | class                        | 1              |   |
| Retail Portfolio [Member]                                               |           |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**        |           |   |
| Impaired Financing Receivable, Average Recorded Investment | $          | $ 13           | $ 20 |

| X                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Classes Of Receivables In Each Portfolio
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of Portfolio Segments for Finance Receivables
+ References
No definition available.
+ Details**Name:**nav_NumberofPortfolioSegmentsforFinanceReceivables**Namespace Prefix:**nav_**Data Type:**xbrli:integerItemType**Balance Type:**na**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_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5258-111524
+ Details**Name:**us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**nav_ReceivableInformationByPortfolioSegmentAxis=nav_RetailPortfolioMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |