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Financial Highlights (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jun. 02, 2010
Per Share Operating Performance:        
Net asset value, beginning of year $ 43.81bno_NetAssetValuePerUnit $ 40.98bno_NetAssetValuePerUnit [1] $ 37.27bno_NetAssetValuePerUnit [1] $ 50.00bno_NetAssetValuePerUnit
Total income (loss) $ (21.06)bno_TotalIncomePerUnit $ 3.24bno_TotalIncomePerUnit $ 4.10bno_TotalIncomePerUnit [1]  
Net expenses $ (0.36)bno_TotalExpensePerUnit $ (0.41)bno_TotalExpensePerUnit $ (0.39)bno_TotalExpensePerUnit [1]  
Net increase (decrease) in Net Asset Value $ (21.42)bno_NetIncreaseDecreaseInNetAssetValue $ 2.83bno_NetIncreaseDecreaseInNetAssetValue $ 3.71bno_NetIncreaseDecreaseInNetAssetValue [1]  
Net asset value, end of year $ 22.39bno_NetAssetValuePerUnit $ 43.81bno_NetAssetValuePerUnit $ 40.98bno_NetAssetValuePerUnit [1] $ 50.00bno_NetAssetValuePerUnit
Total Return (48.89%)bno_PercentageOfTotalReturn 6.91%bno_PercentageOfTotalReturn 9.95%bno_PercentageOfTotalReturn  
Ratios to Average Net Assets        
Total income (loss) (68.25%)bno_PercentageOfTotalIncomeOnNetAssets 6.66%bno_PercentageOfTotalIncomeOnNetAssets 9.44%bno_PercentageOfTotalIncomeOnNetAssets  
Management fees 0.75%bno_PercentageOfManagementFeesOnNetAssets 0.75%bno_PercentageOfManagementFeesOnNetAssets 0.75%bno_PercentageOfManagementFeesOnNetAssets  
Total expenses excluding management fees 0.56%bno_PercentageOfTotalExpensesExcludingManagementFeesOnNetAssets 0.45%bno_PercentageOfTotalExpensesExcludingManagementFeesOnNetAssets 0.32%bno_PercentageOfTotalExpensesExcludingManagementFeesOnNetAssets  
Expenses waived (0.39%)bno_PercentageOfExpensesWaivedOnNetAssets (0.20%)bno_PercentageOfExpensesWaivedOnNetAssets (0.09%)bno_PercentageOfExpensesWaivedOnNetAssets  
Net expenses excluding management fees 0.17%bno_PercentageOfNetExpensesExcludingManagementFeeOnNetAssets 0.25%bno_PercentageOfNetExpensesExcludingManagementFeeOnNetAssets 0.23%bno_PercentageOfNetExpensesExcludingManagementFeeOnNetAssets  
Net income (loss) (69.17%)bno_PercentageOfNetIncomeOnNetAssets 5.66%bno_PercentageOfNetIncomeOnNetAssets 8.46%bno_PercentageOfNetIncomeOnNetAssets  
[1] On August 26, 2013, BNO executed a 2-for-1 forward share split for all shareholders of record as of the close of markets on August 26, 2013. The 2-for-1 forward share split was payable after the close of markets on August 28, 2013. BNO began trading at its post split price on August 29, 2013. The Financial Highlights have been adjusted for the periods shown to reflect the 2-for-1 forward share split on a retroactive basis.