| **Postretirement Benefits - Summary of Changes in the Defined Benefit Plans (Details) (USD $)In Millions, unless otherwise specified** | 3 Months Ended                                                                                                                                                                    | 12 Months Ended                                                                                                                                                                   |
|----------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]**                                                                  |                                                                                                                                                                              |                                                                                                                                                                              |   |   |   |
| Curtailments                                                                                                                           | $ 4us-gaap_DefinedBenefitPlanCurtailments                                                                                                                                         |                                                                                                                                                                              |   |   |   |
| Pension Benefits                                                                                                                       |                                                                                                                                                                              |                                                                                                                                                                              |   |   |   |
| **Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]**                                                                  |                                                                                                                                                                              |                                                                                                                                                                              |   |   |   |
| Benefit obligations at beginning of year                                                                                               |                                                                                                                                                                              |                                                                                                                                                                              | 3,943us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 4,492us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Amendments                                                                                                                             |                                                                                                                                                                              |                                                                                                                                                                              | 0us-gaap_DefinedBenefitPlanPlanAmendments/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 3us-gaap_DefinedBenefitPlanPlanAmendments/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Service cost                                                                                                                           |                                                                                                                                                                              |                                                                                                                                                                              | 12us-gaap_DefinedBenefitPlanServiceCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 20us-gaap_DefinedBenefitPlanServiceCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 17us-gaap_DefinedBenefitPlanServiceCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |
| Interest on obligations                                                                                                                |                                                                                                                                                                              |                                                                                                                                                                              | 158us-gaap_DefinedBenefitPlanInterestCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 143us-gaap_DefinedBenefitPlanInterestCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 169us-gaap_DefinedBenefitPlanInterestCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |
| Actuarial loss (gain)                                                                                                                  |                                                                                                                                                                              |                                                                                                                                                                              | (176)us-gaap_DefinedBenefitPlanActuarialGainLoss/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 334us-gaap_DefinedBenefitPlanActuarialGainLoss/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Curtailments                                                                                                                           |                                                                                                                                                                              |                                                                                                                                                                              | 2us-gaap_DefinedBenefitPlanCurtailments/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 33us-gaap_DefinedBenefitPlanCurtailments/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Contractual termination benefits                                                                                                       |                                                                                                                                                                              |                                                                                                                                                                              | 23us-gaap_DefinedBenefitPlanSpecialTerminationBenefits/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 0us-gaap_DefinedBenefitPlanSpecialTerminationBenefits/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Currency translation                                                                                                                   |                                                                                                                                                                              |                                                                                                                                                                              | (49)us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 15us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation/ 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 |   |
| Subsidy receipts                                                                                                                       |                                                                                                                                                                              |                                                                                                                                                                              | 0us-gaap_DefinedBenefitPlanGrossPrescriptionDrugSubsidyReceiptsReceived/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 0us-gaap_DefinedBenefitPlanGrossPrescriptionDrugSubsidyReceiptsReceived/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Benefits paid                                                                                                                          |                                                                                                                                                                              |                                                                                                                                                                              | 318us-gaap_DefinedBenefitPlanBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 333us-gaap_DefinedBenefitPlanBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Benefit obligations at end of year                                                                                                     | 3,943us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                         | 4,041us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                         | 4,041us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 3,943us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 4,492us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |
| **Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]**                                                           |                                                                                                                                                                              |                                                                                                                                                                              |   |   |   |
| Fair value of plan assets at beginning of year                                                                                         |                                                                                                                                                                              |                                                                                                                                                                              | 2,519us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 2,411us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Actual return on plan assets                                                                                                           |                                                                                                                                                                              |                                                                                                                                                                              | 206us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 284us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Currency translation                                                                                                                   |                                                                                                                                                                              |                                                                                                                                                                              | 42us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | (22)us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Employer contributions                                                                                                                 |                                                                                                                                                                              | 164us-gaap_DefinedBenefitPlanContributionsByEmployer/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                     | 164us-gaap_DefinedBenefitPlanContributionsByEmployer/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 165us-gaap_DefinedBenefitPlanContributionsByEmployer/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Benefits paid                                                                                                                          |                                                                                                                                                                              |                                                                                                                                                                              | 304nav_DefinedBenefitPlanChangeInFairValueOfPlanAssetsBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 319nav_DefinedBenefitPlanChangeInFairValueOfPlanAssetsBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Fair value of plan assets at end of year                                                                                               | 2,519us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                     | 2,627us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                     | 2,627us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 2,519us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | 2,411us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |
| Funded status at year end                                                                                                              | (1,424)us-gaap_DefinedBenefitPlanFundedStatusOfPlan/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                      | (1,414)us-gaap_DefinedBenefitPlanFundedStatusOfPlan/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                      | (1,414)us-gaap_DefinedBenefitPlanFundedStatusOfPlan/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember | (1,424)us-gaap_DefinedBenefitPlanFundedStatusOfPlan/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |
| Health and Life Insurance Benefits                                                                                                     |                                                                                                                                                                              |                                                                                                                                                                              |   |   |   |
| **Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]**                                                                  |                                                                                                                                                                              |                                                                                                                                                                              |   |   |   |
| Benefit obligations at beginning of year                                                                                               |                                                                                                                                                                              |                                                                                                                                                                              | 1,674us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 1,866us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Amendments                                                                                                                             |                                                                                                                                                                              |                                                                                                                                                                              | 0us-gaap_DefinedBenefitPlanPlanAmendments/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 0us-gaap_DefinedBenefitPlanPlanAmendments/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Service cost                                                                                                                           |                                                                                                                                                                              |                                                                                                                                                                              | 5us-gaap_DefinedBenefitPlanServiceCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 7us-gaap_DefinedBenefitPlanServiceCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 7us-gaap_DefinedBenefitPlanServiceCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |
| Interest on obligations                                                                                                                |                                                                                                                                                                              |                                                                                                                                                                              | 68us-gaap_DefinedBenefitPlanInterestCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 62us-gaap_DefinedBenefitPlanInterestCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 83us-gaap_DefinedBenefitPlanInterestCost/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |
| Actuarial loss (gain)                                                                                                                  |                                                                                                                                                                              |                                                                                                                                                                              | (319)us-gaap_DefinedBenefitPlanActuarialGainLoss/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 142us-gaap_DefinedBenefitPlanActuarialGainLoss/ 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 |   |
| Contractual termination benefits                                                                                                       |                                                                                                                                                                              |                                                                                                                                                                              | 2us-gaap_DefinedBenefitPlanSpecialTerminationBenefits/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 0us-gaap_DefinedBenefitPlanSpecialTerminationBenefits/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Currency translation                                                                                                                   |                                                                                                                                                                              |                                                                                                                                                                              | 0us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 0us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Plan participants' contributions                                                                                                       |                                                                                                                                                                              |                                                                                                                                                                              | 40us-gaap_DefinedBenefitPlanContributionsByPlanParticipants/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 28us-gaap_DefinedBenefitPlanContributionsByPlanParticipants/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Subsidy receipts                                                                                                                       |                                                                                                                                                                              |                                                                                                                                                                              | 34us-gaap_DefinedBenefitPlanGrossPrescriptionDrugSubsidyReceiptsReceived/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 41us-gaap_DefinedBenefitPlanGrossPrescriptionDrugSubsidyReceiptsReceived/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Benefits paid                                                                                                                          |                                                                                                                                                                              |                                                                                                                                                                              | 185us-gaap_DefinedBenefitPlanBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 188us-gaap_DefinedBenefitPlanBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Benefit obligations at end of year                                                                                                     | 1,674us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember      | 1,957us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember      | 1,957us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 1,674us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 1,866us-gaap_DefinedBenefitPlanBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |
| **Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]**                                                           |                                                                                                                                                                              |                                                                                                                                                                              |   |   |   |
| Fair value of plan assets at beginning of year                                                                                         |                                                                                                                                                                              |                                                                                                                                                                              | 447us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 437us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Actual return on plan assets                                                                                                           |                                                                                                                                                                              |                                                                                                                                                                              | 26us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 66us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Currency translation                                                                                                                   |                                                                                                                                                                              |                                                                                                                                                                              | 0us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 0us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Employer contributions                                                                                                                 |                                                                                                                                                                              |                                                                                                                                                                              | 2us-gaap_DefinedBenefitPlanContributionsByEmployer/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 3us-gaap_DefinedBenefitPlanContributionsByEmployer/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Benefits paid                                                                                                                          |                                                                                                                                                                              |                                                                                                                                                                              | 60nav_DefinedBenefitPlanChangeInFairValueOfPlanAssetsBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 59nav_DefinedBenefitPlanChangeInFairValueOfPlanAssetsBenefitsPaid/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |
| Fair value of plan assets at end of year                                                                                               | 447us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember    | 415us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember    | 415us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 447us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 437us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |
| Funded status at year end                                                                                                              | $ (1,227)us-gaap_DefinedBenefitPlanFundedStatusOfPlan/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | $ (1,542)us-gaap_DefinedBenefitPlanFundedStatusOfPlan/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | $ (1,542)us-gaap_DefinedBenefitPlanFundedStatusOfPlan/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | $ (1,227)us-gaap_DefinedBenefitPlanFundedStatusOfPlan/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |   |

| X                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined Benefit Plan Change In Fair Value Of Plan Assets Benefits Paid
+ References
No definition available.
+ Details**Name:**nav_DefinedBenefitPlanChangeInFairValueOfPlanAssetsBenefitsPaid**Namespace Prefix:**nav_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Actual Return on Plan Assets (Component of Net Periodic Postretirement Benefit Cost) -URI http://asc.fasb.org/extlink&oid=6504192Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Actual Return on Plan Assets (Component of Net Periodic Pension Cost) -URI http://asc.fasb.org/extlink&oid=6504226
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Glossary Gain or Loss -URI http://asc.fasb.org/extlink&oid=6514294Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Glossary Gain or Loss -URI http://asc.fasb.org/extlink&oid=6749293
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date.  2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Projected Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6522206Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Accumulated Postretirement Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6503904
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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
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(4) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920
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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
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(10) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Plan Curtailment -URI http://asc.fasb.org/extlink&oid=6520938Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 15 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=7577095&loc=d3e8001-114927
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of gain (loss) from foreign currency exchange rate changes for benefit obligation for plans of a foreign operation whose functional currency is not the reporting currency.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(5) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of increase or decrease in plan assets attributed to foreign currency changes. The effects of foreign currency exchange rate changes that are to be disclosed are those applicable to plans of a foreign operation whose functional currency is not the reporting currency.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=21915240&loc=d3e1703-114919
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of the period's gross receipts received from the prescription drug subsidy, which is to be used in the roll forward of the accumulated postretirement benefit obligation of an applicable postretirement benefit plan.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(2) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of increase or decrease due to a change in the terms of an existing plan or the initiation of a new plan. A plan amendment may increase or decrease benefits, including those attributed to years of service already rendered.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Glossary Plan Amendment -URI http://asc.fasb.org/extlink&oid=6520743Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Glossary Plan Amendment -URI http://asc.fasb.org/extlink&oid=6520782Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(7) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Service Cost (Component of Net Periodic Pension Cost) -URI http://asc.fasb.org/extlink&oid=6525008Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of increase related to special termination benefits offered to and accepted by employees in connection with their termination of employment that are only offered for a short period of time. A situation involving termination benefits may also involve a curtailment.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(10) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Termination Benefits -URI http://asc.fasb.org/extlink&oid=6526498
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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