| **Allowance for Doubtful Accounts - Schedule of Impaired Finance Receivables (Details) - USD ($) $ in Millions** | 6 Months Ended |        |
|------------------------------------------------------------------------------------------------------------------|----------------|--------|
||
| Retail Portfolio [Member]                                                                                        |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Impaired Financing Receivable, Average Recorded Investment                                                       | $ 21           | $ 25   |   |
| Impaired finance receivables with specific loss reserves [Member]                                                |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Impaired Financing Receivable, Recorded Investment                                                               | 21             |   | $ 21 |
| Impaired finance receivables with specific loss reserves [Member] | Retail Portfolio [Member]                    |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Impaired Financing Receivable, Recorded Investment                                                               | 21             |   | 21 |
| Impaired finance receivables with specific loss reserves [Member] | Wholesale Portfolio [Member]                 |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Impaired Financing Receivable, Recorded Investment                                                               | 0              |   | 0 |
| Impaired financing receivable without specific loss reserves [Member]                                            |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Impaired Financing Receivable, Recorded Investment                                                               | 0              |   | 0 |
| Impaired financing receivable without specific loss reserves [Member] | Retail Portfolio [Member]                |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Impaired Financing Receivable, Recorded Investment                                                               | 0              |   | 0 |
| Impaired financing receivable without specific loss reserves [Member] | Wholesale Portfolio [Member]             |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Impaired Financing Receivable, Recorded Investment                                                               | 0              |   | 0 |
| Specific loss reserves on impaired finance receivables [Member]                                                  |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Specific loss reserves on impaired finance receivables                                                           | 11             |   | 9 |
| Specific loss reserves on impaired finance receivables [Member] | Retail Portfolio [Member]                      |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Specific loss reserves on impaired finance receivables                                                           | 11             |   | 9 |
| Specific loss reserves on impaired finance receivables [Member] | Wholesale Portfolio [Member]                   |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Specific loss reserves on impaired finance receivables                                                           | 0              |   | 0 |
| Finance receivable non-accrual status [Member]                                                                   |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Finance receivables on non-accrual status                                                                        | 21             |   | 21 |
| Finance receivable non-accrual status [Member] | Retail Portfolio [Member]                                       |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Finance receivables on non-accrual status                                                                        | 21             |   | 21 |
| Finance receivable non-accrual status [Member] | Wholesale Portfolio [Member]                                    |           |   |   |
| **Finance Receivable, Impaired [Line Items]**                                                                    |           |   |   |
| Finance receivables on non-accrual status                                                                        | $ 0            |   | $ 0 |

| 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_FinancingReceivableImpairedLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Recorded Investment -URI http://asc.fasb.org/extlink&oid=65880944Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5111-111524
+ Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| 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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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 14A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953550-111524
+ Details**Name:**us-gaap_ImpairedFinancingReceivableRecordedInvestment**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of allowance for credit losses related to recorded investment.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Recorded Investment -URI http://asc.fasb.org/extlink&oid=65880944Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524
+ Details**Name:**us-gaap_ImpairedFinancingReceivableRelatedAllowance**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**nav_ReceivableInformationByPortfolioSegmentAxis=nav_RetailPortfolioMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**nav_ReceivableInformationByPortfolioSegmentAxis=nav_WholesalePortfolioMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=nav_ImpairedFinancingReceivableWithoutSpecificLossReservesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=nav_SpecificLossReservesOnImpairedFinanceReceivablesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=nav_FinanceReceivableNonAccrualStatusMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |