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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Additional Information) (Details) - $ / Units | Dec. 31, 2018 | Jun. 30, 2011
--- | --- | ---
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 | 1,000
Creation Baskets |  |
Significant Accounting Policies [Line Items] |  |
Number of Shares per basket | 50,000 |

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- Definition Fee Paid Per Order + References No definition available. + Details
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Namespace Prefix: | usl_
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Period Type: | instant

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

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

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |