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Summary Of Significant Accounting Policies (Details Textual) | Feb. 29, 2012
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Number Rof Shares Per Baskets | 50,000
Redemption Baskets [Member] | Prior to July 1, 2011 [Member] |
Number Rof Shares Per Baskets | 100,000

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- Definition Number rof shares Per Baskets. + References No definition available. + Details
Name: | bno_NumberRofSharesPerBaskets
Namespace Prefix: | bno_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant