| **Postretirement Benefits - Narrative (Details) (USD $)Share data in Millions, unless otherwise specified**                                            | 3 Months Ended                                                              | 12 Months Ended                                                                                                                                                                                                                         | 3 Months Ended                                                                                                                                                                                                                            | 12 Months Ended                                                                                                                                                                                                                          | 3 Months Ended                                                                                                                                                                                                                                                                                         | 1 Months Ended                                                                                                                                                                   |                                                                                                                                                         |
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| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year                                                                  |                                                                        | $ 148,000,000us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInCurrentFiscalYear                                                                                                                                         |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Benefit Plan, Accumulated Benefit Obligation                                                                                                   | 3,900,000,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation         | 4,000,000,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation                                                                                                                                                                     | 3,900,000,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation                                                                                                                                                                       |                                                                                                                                                                                                                                     | 4,000,000,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation                                                                                                                                                                                                                                    |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Restructuring charges                                                                                                                                  |                                                                        | 42,000,000us-gaap_RestructuringCharges                                                                                                                                                                                                  | 25,000,000us-gaap_RestructuringCharges                                                                                                                                                                                                    | 107,000,000us-gaap_RestructuringCharges                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined benefit plan, weighted average rate of increase in in per capita cost percent of benefit obligation                                            |                                                                        | 8.25%nav_DefinedBenefitPlanWeightedAverageRateOfIncreaseInInPerCapitaCostPercentOfBenefitObligation                                                                                                                                     |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Contribution Plan, Cost Recognized                                                                                                             |                                                                        | 27,000,000us-gaap_DefinedContributionPlanCostRecognized                                                                                                                                                                                 |                                                                                                                                                                                                                                      | 41,000,000us-gaap_DefinedContributionPlanCostRecognized                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Curtailments                                                                                                                                           | 4,000,000us-gaap_DefinedBenefitPlanCurtailments                             |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)                                                                                   | 33,000,000us-gaap_DefinedBenefitPlanBenefitObligationPeriodIncreaseDecrease |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Pension and other postretirment charges due to reduction in workfroce                                                                                  |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      | 7,000,000nav_PensionAndOtherPostretirmentChargesDueToReductionInWorkfroce                                                                                                                                                                |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Equity Method Investments [Member]                                                                                                                     |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Benefit Plan, Target Plan Asset Allocations                                                                                                    |                                                                        | 55.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquityMethodInvestmentsMember                                                                                  |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Fixed Income Investments [Member]                                                                                                                      |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Benefit Plan, Target Plan Asset Allocations                                                                                                    |                                                                        | 30.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_FixedIncomeInvestmentsMember                                                                                   |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Other Investments [Member]                                                                                                                             |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Benefit Plan, Target Plan Asset Allocations                                                                                                    |                                                                        | 10.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_OtherInvestmentsMember                                                                                         |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Cash [Member]                                                                                                                                          |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Benefit Plan, Target Plan Asset Allocations                                                                                                    |                                                                        | 5.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_CashMember                                                                                                      |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| US Large Cap [Member]                                                                                                                                  |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Benefit Plan, Target Plan Asset Allocations                                                                                                    |                                                                        | 15.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= nav_UsLargeCapMember                                                                                                   |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| United States Postretirement Benefit Plan of US Entity [Member]                                                                                        |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Deferred Income Taxes and Other Assets, Noncurrent                                                                                                     |                                                                        | 537,000,000us-gaap_DeferredIncomeTaxesAndOtherAssetsNoncurrent/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_UnitedStatesPostretirementBenefitPlansOfUSEntityDefinedBenefitMember                             |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     | 537,000,000us-gaap_DeferredIncomeTaxesAndOtherAssetsNoncurrent/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_UnitedStatesPostretirementBenefitPlansOfUSEntityDefinedBenefitMember                                                                                            |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Pension Benefits                                                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Employer contributions                                                                                                                                 |                                                                        | 164,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                   | 165,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                     |                                                                                                                                                                                                                                     | 164,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                                                                                  |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax                                              |                                                                        | 71,000,000us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                     | (585,000,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                    | 357,000,000us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Curtailments                                                                                                                                           |                                                                        | 2,000,000us-gaap_DefinedBenefitPlanCurtailments/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                                | 33,000,000us-gaap_DefinedBenefitPlanCurtailments/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                                 |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Plan participants' contributions                                                                                                                       |                                                                        | 0us-gaap_DefinedBenefitPlanContributionsByPlanParticipants/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                     | 0us-gaap_DefinedBenefitPlanContributionsByPlanParticipants/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                       |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Benefits paid                                                                                                                                          |                                                                        | 318,000,000us-gaap_DefinedBenefitPlanBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                              | 333,000,000us-gaap_DefinedBenefitPlanBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                                |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Health and Life Insurance Benefits                                                                                                                     |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Employer contributions                                                                                                                                 |                                                                        | 2,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                                                  | 3,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                                                    |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined benefit plan, weighted average rate of increase in in per capita cost percent of benefit obligation                                            |                                                                        | 91.00%nav_DefinedBenefitPlanWeightedAverageRateOfIncreaseInInPerCapitaCostPercentOfBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember        |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year                                                                         |                                                                        | 7.80%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                              |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Benefit Plan, Ultimate Health Care Cost Trend Rate                                                                                             |                                                                        | 5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                                              |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax                                              |                                                                        | 314,000,000us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | (200,000,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | (88,000,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Curtailments                                                                                                                                           |                                                                        | 0us-gaap_DefinedBenefitPlanCurtailments/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                                                                     | 0us-gaap_DefinedBenefitPlanCurtailments/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                                                                       |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Plan participants' contributions                                                                                                                       |                                                                        | 40,000,000us-gaap_DefinedBenefitPlanContributionsByPlanParticipants/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                                         | 28,000,000us-gaap_DefinedBenefitPlanContributionsByPlanParticipants/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                                           |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year                                                                     |                                                                        | 2,000,000us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Benefits paid                                                                                                                                          |                                                                        | 185,000,000us-gaap_DefinedBenefitPlanBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                                                           | 188,000,000us-gaap_DefinedBenefitPlanBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                                                             |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Defined benefit plan, benefits paid from Company assets                                                                                                |                                                                        | 51,000,000nav_DefinedBenefitPlanBenefitsPaidFromCompanyAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                                               | 60,000,000nav_DefinedBenefitPlanBenefitsPaidFromCompanyAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember                                                 |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Unfunded pension plan [Member]                                                                                                                         |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Benefits paid                                                                                                                                          |                                                                        |                                                                                                                                                                                                                                    | 14,000,000us-gaap_DefinedBenefitPlanBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= nav_UnfundedPensionPlanMember                                                                                            |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Other Pension Plan, Postretirement or Supplemental Plans [Member]                                                                                      |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Contribution To The Trust Shares                                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   | 25.5nav_ContributionToTrustShares/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefitMember |                                                                                                                                                    |   |   |
| Early Retiree Reinsurance Program [Member]                                                                                                             |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Plan participants' contributions                                                                                                                       |                                                                        | 0us-gaap_DefinedBenefitPlanContributionsByPlanParticipants/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= nav_EarlyRetireeReinsuranceProgramMember                                                                     |                                                                                                                                                                                                                                      | 3,000,000us-gaap_DefinedBenefitPlanContributionsByPlanParticipants/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= nav_EarlyRetireeReinsuranceProgramMember                                                              |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Indianapolis and Waukesha Foundry [Member] | North America Truck [Member]                                                                              |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Restructuring charges                                                                                                                                  |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     | 13,000,000us-gaap_RestructuringCharges/ dei_EntityByLocationAxis= nav_IndianapolisandWaukeshaFoundryMember/ us-gaap_StatementBusinessSegmentsAxis= nav_NorthAmericaTruckMember                                                                                                                         |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Indianapolis and Waukesha Foundry [Member] | North America Truck [Member] | Pension And Other Postretirement Contractual Termination Benefits [Member] |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Restructuring charges                                                                                                                                  |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     | 11,000,000us-gaap_RestructuringCharges/ dei_EntityByLocationAxis= nav_IndianapolisandWaukeshaFoundryMember/ us-gaap_RestructuringCostAndReserveAxis= nav_PensionAndOtherPostretirementContractualTerminationBenefitsMember/ us-gaap_StatementBusinessSegmentsAxis= nav_NorthAmericaTruckMember         |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Chatham [Member] | Facility Closing [Member] | Health and Life Insurance Benefits                                                                      |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Postemployment Benefits, Period Expense                                                                                                                |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     | 14,000,000us-gaap_PostemploymentBenefitsPeriodExpense/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember/ dei_EntityByLocationAxis= nav_ChathamMember/ us-gaap_RestructuringCostAndReserveAxis= us-gaap_FacilityClosingMember |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Chatham [Member] | North America Truck [Member]                                                                                                        |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Restructuring charges                                                                                                                                  |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             | 14,000,000us-gaap_RestructuringCharges/ dei_EntityByLocationAxis= nav_ChathamMember/ us-gaap_StatementBusinessSegmentsAxis= nav_NorthAmericaTruckMember |   |   |
| Effect Of Remeasurement On Plan [Member]                                                                                                               |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax                                              |                                                                        | 10,000,000us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax/ nav_DefinedBenefitPlanRemeasurementAxis= nav_EffectOfRemeasurementOnPlanMember                                              |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Call Option [Member]                                                                                                                                   |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Derivative, Notional Amount                                                                                                                            |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   | $ 183,000,000invest_DerivativeNotionalAmount/ us-gaap_InvestmentTypeAxis= us-gaap_CallOptionMember |
| Designated as Hedging Instrument [Member] | Put Option [Member]                                                                                        |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                       |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    |   |   |
| Derivative, Term of Contract                                                                                                                           |                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                             |                                                                                                                                                    | 3 years |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.
+ References
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| - Definition
Contribution To The Trust Shares
+ References
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| X                                                                                                                                                                                                                                                                                           |
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| - Definition
Defined benefit plan, benefits paid from Company assets
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No definition available.
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| - Definition
Defined benefit plan, weighted average rate of increase in in per capita cost percent of benefit obligation
+ References
No definition available.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Pension and other postretirment charges due to reduction in workfroce
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No definition available.
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| - Definition
Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and other assets expected to be realized or consumed after one year or normal operating cycle, if longer.
+ References
No definition available.
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| - Definition
For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.
+ References
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| - Definition
Net increase or decrease in the plan benefit obligation during the reporting period.
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The increase in the fair value of plan assets from contributions made by the employer.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of contributions made by plan participants. This item represents a periodic increase to the plan obligation and an increase to plan assets.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of decrease that is related to an event that significantly reduces the expected years of future service of present employees or eliminates for a significant number of employees the accrual of defined benefits for some or all of their future services.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.
+ References
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| - Definition
Amount of employer's best estimate of contributions expected to be paid to the plan in the current remaining fiscal period.
+ References
No definition available.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Target allocation of investments of this type to total plan assets presented on a weighted average basis.
+ References
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| - Definition
The ultimate trend rate for health care costs.
+ References
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| - Definition
The amount of the cost recognized during the period for defined contribution plans.
+ References
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| - Definition
Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
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No definition available.
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| - Definition
Amount before tax, after reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.
+ References
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| - Definition
Period expense related to postemployment benefits.
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No definition available.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.
+ References
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