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v3.19.1

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Additional Information) (Details) | Dec. 31, 2018 $ / Basket
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Significant Accounting Policies [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
Redemption Baskets [Member] |
Significant Accounting Policies [Line Items] |
Number of units per basket | 50,000

X
- Definition Fee Paid Per Order + References No definition available. + Details
Name: | unl_FeePaidPerOrder
Namespace Prefix: | unl_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of Units per Basket + References No definition available. + Details
Name: | unl_NumberOfUnitsPerBasket
Namespace Prefix: | unl_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | instant

X
- Definition Significant Accounting Policies [Line Items] + References No definition available. + Details
Name: | unl_SignificantAccountingPoliciesLineItems
Namespace Prefix: | unl_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | invest_InvestmentSecuritiesClassAxis=unl_RedemptionBasketsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |