| **Financial Instruments and Commodity Contracts - Narrative (Details) (USD $)** |           |           |        |              |              | 3 Months Ended |              |              |             |             |              |
|---------------------------------------------------------------------------------|-----------|-----------|--------|--------------|--------------|----------------|--------------|--------------|-------------|-------------|--------------|
||
| **Derivative [Line Items]**                                                     |      |      |   |         |         |           |         |         |        |        |         |   |
| Payments for Derivative Instrument, Investing Activities                        |      |      |   |         |         | $ 125,000,000  |         |         |        |        |         |   |
| Derivative, Amount of Hedged Item                                               | 0         |      |   |         |         |           |         |         |        |        |         |   |
| Derivative, Collateral, Obligation to Return Cash                               |      |      | 0      |         |         |           |         |         |        |        |         |   |
| Exposure to Credit Risk                                                         | 3,000,000 | 5,000,000 |   |         |         |           |         |         |        |        |         |   |
| Derivative, Notional Amount                                                     |      |      |   | $ 30,000,000 | $ 45,000,000 |           | $ 11,000,000 | $ 11,000,000 | $ 6,000,000 | $ 2,000,000 | $ 78,000,000 | $ 135,000,000 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B
+ Details**Name:**invest_DerivativeNotionalAmount**Namespace Prefix:**invest_**Data Type:**xbrli:monetaryItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Exposure to Credit Risk
+ References
No definition available.
+ Details**Name:**nav_ExposureToCreditRisk**Namespace Prefix:**nav_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of the hedged item as of the balance sheet date related to the derivative. For example, the hedged balance on a debt instrument.
+ References
No definition available.
+ Details**Name:**us-gaap_DerivativeAmountOfHedgedItem**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226016-175313Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=20225523&loc=SL20225862-175312Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=d3e41678-113959
+ Details**Name:**us-gaap_DerivativeCollateralObligationToReturnCash**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The cash outflow for derivative instruments during the period, which are classified as investing activities, excluding those designated as hedging instruments.
+ References
No definition available.
+ Details**Name:**us-gaap_PaymentsForDerivativeInstrumentInvestingActivities**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |