| **Allowance for Doubtful Accounts - Narrative (Details) (USD $)In Millions, unless otherwise specified** | 3 Months Ended                                                                                                                               |
|----------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                         |                                                                                                                                         |   |
| Number of Portfolio Segments for Finance Receivables                                                     | 2nav_NumberofPortfolioSegmentsforFinanceReceivables                                                                                          |   |
| Classes Of Receivables In Each Portfolio                                                                 | 1nav_ClassesOfReceivablesInEachPortfolio                                                                                                     |   |
| Retail Portfolio [Member]                                                                                |                                                                                                                                         |   |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                         |                                                                                                                                         |   |
| Impaired Financing Receivable, Average Recorded Investment                                               | $ 19us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment/ nav_ReceivableInformationByPortfolioSegmentAxis= nav_RetailPortfolioMember | $ 14us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment/ nav_ReceivableInformationByPortfolioSegmentAxis= nav_RetailPortfolioMember |

| 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.
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| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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=35738203&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=35738203&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:** |