| **Income Taxes - Narrative (Details) (USD $)In Millions, unless otherwise specified** | 3 Months Ended                                                       | 6 Months Ended                      |
|---------------------------------------------------------------------------------------|----------------------------------------------------------------------|-------------------------------------|
||
| **Operating Loss Carryforwards [Line Items]**                                         |                                                                 |                                |   |   |
| Income Tax Expense (Benefit)                                                          | $ 18us-gaap_IncomeTaxExpenseBenefit                                  | $ 23us-gaap_IncomeTaxExpenseBenefit | $ 25us-gaap_IncomeTaxExpenseBenefit | $ 11us-gaap_IncomeTaxExpenseBenefit |
| Income Taxes Percent Likelihood Of Being Realized Upon Settlement                     | 50.00%nav_IncomeTaxesPercentLikelihoodOfBeingRealizedUponSettlement  |                                | 50.00%nav_IncomeTaxesPercentLikelihoodOfBeingRealizedUponSettlement |   |
| Unrecognized Tax Benefits                                                             | 42us-gaap_UnrecognizedTaxBenefits                                    |                                | 42us-gaap_UnrecognizedTaxBenefits |   |
| Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense                  | 1us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense |                                |   |   |
| Other Comprehensive Income (Loss) [Member]                                            |                                                                 |                                |   |   |
| **Operating Loss Carryforwards [Line Items]**                                         |                                                                 |                                |   |   |
| Income Tax Expense (Benefit)                                                          |                                                                 |                                | $ (14)us-gaap_IncomeTaxExpenseBenefit/ us-gaap_InformationByFinancialStatementLineItemAxis= us-gaap_OtherComprehensiveIncomeMember |   |

| X                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Income Taxes Percent Likelihood Of Being Realized Upon Settlement
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Income Tax Expense (or Benefit) -URI http://asc.fasb.org/extlink&oid=6515339Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32639-109319
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| X                                                                                                                                                                       |
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.
+ References
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