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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Additional Information) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014
Significant Accounting Policies [Line Items]
Minimum likelihood of tax benefits being recognized upon ultimate settlement	50.00%unl_PercentageOfIncomeTaxExaminationMinimumLikelihoodOfTaxBenefitsBeingRealizedUponSettlement
Recognized interest income expense and penalties related to unrecognized tax benefits	$ 0unl_RecognizedInterestIncomeExpenseAndPenaltiesRelatedToUnrecognizedTaxBenefits
Redemption Baskets [Member]
Significant Accounting Policies [Line Items]
Number of units per basket	50,000unl_NumberOfUnitsPerBasket / invest_InvestmentSecuritiesClassAxis = unl_RedemptionBasketsMember
Maximum [Member]
Significant Accounting Policies [Line Items]
Cash equivalents maturity period	6 months

X

- Definition

Cash Equivalents, Maturity Period

+ References

No definition available.

+ Details

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X

- Definition

Number of Units per Basket

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

X

- Definition

Percentage of income tax examination minimum likelihood of tax benefits being realized upon settlement.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

X

- Definition

Recognized interest income expense and penalties related to unrecognized tax benefits.

+ References

No definition available.

+ Details

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- Details

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- Details

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X

- Details

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