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ORGANIZATION AND BUSINESS (Additional Information) (Details) (USD $) | 1 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Nov. 30, 2009 | Nov. 18, 2009 | Dec. 31, 2014 Contracts | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items] |  |  |  |  |  |  |
Fee paid by Authorized Purchasers for each order placed to create one or more Creation Baskets or to redeem one or more baskets |  |  | $ 350 unl_FeePaidPerOrder |  |  |  |
Number of initially registered units on Form S-1 with the U.S. Securities and Exchange Commission | 30,000,000 unl_NumberOfUnitsRegisteredInPeriod |  |  |  |  |  |
Net asset value per share |  | $ 50.00 unl_NetAssetValuePerUnit | $ 13.69 unl_NetAssetValuePerUnit | $ 18.32 unl_NetAssetValuePerUnit | $ 17.23 unl_NetAssetValuePerUnit | $ 21.21 unl_NetAssetValuePerUnit | $ 21.21 unl_NetAssetValuePerUnit
Number of units issued |  | 200,000 unl_UnitsIssuedDuringPeriodUnitsNewIssues |  |  |  |  |
Value of unit issued |  | 10,000,000 unl_UnitsIssuedDuringPeriodValueNewIssues |  |  |  |  |
Commenced investment operations date | Nov. 18, 2009 |  |  |  |  |  |
Number of registered units |  |  | 25,600,000 unl_NumberOfRegisteredUnits |  |  |  |
Derivative, Number of Instruments Held |  |  | 537 us-gaap_DerivativeNumberOfInstrumentsHeld |  |  |  |
Creation Baskets [Member] |  |  |  |  |  |  |
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items] |  |  |  |  |  |  |
Number of units per basket |  |  | 50,000 unl_NumberOfUnitsPerBasket / invest_InvestmentSecuritiesClassAxis = unl_CreationBasketsMember |  |  |  |
Prior to July 1, 2011 [Member] |  |  |  |  |  |  |
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items] |  |  |  |  |  |  |
Fee paid by Authorized Purchasers for each order placed to create one or more Creation Baskets or to redeem one or more baskets |  |  | $ 1,000 unl_FeePaidPerOrder / unl_PeriodAxis = unl_PriorToJuly12011Member |  |  |  |

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