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        <measure>iso4217:USD</measure>
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        <measure>pure</measure>
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    <dei:EntityRegistrantName contextRef="Trust" id="ixv-6956">Fidelity Union Street Trust II</dei:EntityRegistrantName>
    <oef:RiskReturnHeading contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-204">
     
       
     Fund Summary 
       
     Fund: 
     Fidelity&#xae; Municipal Money Market Fund 
    
   </oef:RiskReturnHeading>
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     Investment Objective 
       
    
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     Fidelity&#xae; Municipal Money Market Fund seeks as high a level of interest income exempt from federal income tax as is consistent with liquidity and stability of principal. 
       
    
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     Fee Table 
       
    
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     The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions, which are not reflected in the tables and examples below. 
    
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     Shareholder fees 
       
    
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      contextRef="Pid_S000007502_contentCd_MMM-PRO"
      decimals="0"
      id="ixv-7211"
      unitRef="usd">0</oef:ShareholderFeeOther>
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     Annual Operating Expenses 
       
    
   </oef:OperatingExpensesCaption>
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      contextRef="Pid_S000007502_Cid_C000020476"
      decimals="6"
      id="ixv-7212"
      unitRef="pure">0.0038</oef:ManagementFeesOverAssets>
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      contextRef="Pid_S000007502_Cid_C000020476"
      decimals="6"
      id="ixv-7213"
      unitRef="pure">0</oef:DistributionAndService12b1FeesOverAssets>
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      contextRef="Pid_S000007502_Cid_C000020476"
      decimals="6"
      id="ixv-7214"
      unitRef="pure">0.0001</oef:OtherExpensesOverAssets>
    <oef:ExpensesOverAssets
      contextRef="Pid_S000007502_Cid_C000020476"
      decimals="6"
      id="ixv-7215"
      unitRef="pure">0.0039</oef:ExpensesOverAssets>
    <oef:ExpenseExampleNarrativeTextBlock contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-302">
     
       
     This  
     example 
       
     helps compare the cost of investing in the fund with the cost of investing in other funds. 
       
     Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated: 
    
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      decimals="0"
      id="ixv-7216"
      unitRef="usd">40</oef:ExpenseExampleYear01>
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      contextRef="Pid_S000007502_Cid_C000020476"
      decimals="0"
      id="ixv-7217"
      unitRef="usd">125</oef:ExpenseExampleYear03>
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      contextRef="Pid_S000007502_Cid_C000020476"
      decimals="0"
      id="ixv-7218"
      unitRef="usd">219</oef:ExpenseExampleYear05>
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      contextRef="Pid_S000007502_Cid_C000020476"
      decimals="0"
      id="ixv-7219"
      unitRef="usd">493</oef:ExpenseExampleYear10>
    <oef:StrategyHeading contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-359">
     
       
     Principal Investment Strategies 
       
    
   </oef:StrategyHeading>
    <oef:StrategyNarrativeTextBlock contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-364">
     
       
      
       
        Normally investing in municipal money market securities. 
      Normally investing at least 80% of assets in municipal securities whose interest is exempt from federal income tax. 
      
     Municipal money market securities are high-quality, short-term debt securities that pay a fixed, variable, or floating interest rate, and include variable rate demand notes, commercial paper, and municipal notes. Municipal securities are issued to raise money for a variety of public and private purposes, including general financing for state and local governments, financing for eligible non-profit organizations, or financing for a specific project or public facility. 
      
      Potentially investing up to 20% of assets in securities subject to state and/or federal income tax. 
      Potentially investing more than 25% of total assets in municipal securities that finance similar types of projects. 
      Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. 
      
    
   </oef:StrategyNarrativeTextBlock>
    <oef:RiskTextBlock
      contextRef="Pid_S000007502_contentCd_MMM-PRO_RiskMember_MunicipalMarketVolatilityMember"
      id="ixv-384">
     
       
      
      Municipal Market Volatility. 
      
     The municipal market is volatile and can be significantly affected by adverse tax, legislative, or political changes and the financial condition of the issuers of municipal securities. 
    
   </oef:RiskTextBlock>
    <oef:RiskTextBlock
      contextRef="Pid_S000007502_contentCd_MMM-PRO_RiskMember_InterestRateChangesMember"
      id="ixv-393">
     
       
      
      Interest Rate Changes. 
      
     Interest rate increases can cause the price of a money market security to decrease. 
    
   </oef:RiskTextBlock>
    <oef:RiskTextBlock
      contextRef="Pid_S000007502_contentCd_MMM-PRO_RiskMember_IncomeRiskMember"
      id="ixv-402">
     
       
      
      Income Risk. 
      
     A low or negative interest rate environment can adversely affect the fund's yield. 
    
   </oef:RiskTextBlock>
    <oef:RiskTextBlock
      contextRef="Pid_S000007502_contentCd_MMM-PRO_RiskMember_ForeignExposureMember"
      id="ixv-411">
     
       
      
      Foreign Exposure. 
      
     Entities providing credit support or a maturity-shortening structure that are located in foreign countries can be affected by adverse political, regulatory, market, or economic developments in those countries . 
    
   </oef:RiskTextBlock>
    <oef:RiskTextBlock
      contextRef="Pid_S000007502_contentCd_MMM-PRO_RiskMember_IssuerSpecificChangesMember"
      id="ixv-422">
     
       
      
      Issuer-Specific Changes. 
      
     A decline in the credit quality of an issuer or a provider of credit support (such as guarantees) or a maturity-shortening structure (such as demand and put features) for a security can cause the price of a money market security to decrease. 
      
       
    
   </oef:RiskTextBlock>
    <oef:RiskTextBlock
      contextRef="Pid_S000007502_contentCd_MMM-PRO_RiskMember_RiskLoseMoneyMember"
      id="ixv-432">
     
       
     &#160; 
       
     You could lose money by investing in the fund. 
       
    
   </oef:RiskTextBlock>
    <oef:RiskTextBlock
      contextRef="Pid_S000007502_contentCd_MMM-PRO_RiskMember_RiskMoneyMarketFundMayNotPreserveDollarMember"
      id="ixv-440">
     
       
     &#160; 
       
     Although the fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. The fund may impose a fee upon the sale of your shares. 
       
    
   </oef:RiskTextBlock>
    <oef:RiskTextBlock
      contextRef="Pid_S000007502_contentCd_MMM-PRO_RiskMember_RiskNotInsuredDepositoryInstitutionMember"
      id="ixv-448">
     
       
     &#160; 
       
     An investment in the fund is not a bank account and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. 
       
    
   </oef:RiskTextBlock>
    <oef:RiskTextBlock
      contextRef="Pid_S000007502_contentCd_MMM-PRO_RiskMember_RiskMoneyMarketFundSponsorMayNotProvideSupportMember"
      id="ixv-458">
     
       
     Fidelity Investments and its affiliates, the fund's sponsor, is not required to reimburse the fund for losses, and you should not expect that the sponsor will provide financial support to the fund at any time, including during periods of market stress. 
       
    
   </oef:RiskTextBlock>
    <oef:BarChartAndPerformanceTableHeading contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-463">
     
       
     Performance 
       
    
   </oef:BarChartAndPerformanceTableHeading>
    <oef:PerformanceNarrativeTextBlock contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-468">
     
       
     The following information is intended to help you understand the risks of investing in the fund. 
      
        
      The information illustrates the changes in the performance of the fund's shares from year to year. 
        
      
       
     &#160; 
       
      
        
      Past performance is not an indication of future performance. 
        
      
     Visit 
       
      
        
      www.fidelity.com  
      
       
     for more recent performance information. 
    
   </oef:PerformanceNarrativeTextBlock>
    <oef:PerformanceInformationIllustratesVariabilityOfReturns contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-473"> 
        
      The information illustrates the changes in the performance of the fund's shares from year to year. 
        
     </oef:PerformanceInformationIllustratesVariabilityOfReturns>
    <oef:PerformancePastDoesNotIndicateFuture contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-480"> 
        
      Past performance is not an indication of future performance. 
        
     </oef:PerformancePastDoesNotIndicateFuture>
    <oef:PerformanceAvailabilityWebSiteAddress contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-486"> 
        
      www.fidelity.com  
     </oef:PerformanceAvailabilityWebSiteAddress>
    <oef:BarChartHeading contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-491">
     
       
     Year-by-Year Returns  
    
   </oef:BarChartHeading>
    <oef:AnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_2016"
      decimals="INF"
      id="ixv-7220"
      unitRef="pure">0.0015</oef:AnnlRtrPct>
    <oef:AnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_2017"
      decimals="INF"
      id="ixv-7221"
      unitRef="pure">0.0052</oef:AnnlRtrPct>
    <oef:AnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_2018"
      decimals="INF"
      id="ixv-7222"
      unitRef="pure">0.0112</oef:AnnlRtrPct>
    <oef:AnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_2019"
      decimals="INF"
      id="ixv-7223"
      unitRef="pure">0.0124</oef:AnnlRtrPct>
    <oef:AnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_2020"
      decimals="INF"
      id="ixv-7224"
      unitRef="pure">0.0038</oef:AnnlRtrPct>
    <oef:AnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_2021"
      decimals="INF"
      id="ixv-7225"
      unitRef="pure">0.0002</oef:AnnlRtrPct>
    <oef:AnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_2022"
      decimals="INF"
      id="ixv-7226"
      unitRef="pure">0.0092</oef:AnnlRtrPct>
    <oef:AnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_2023"
      decimals="INF"
      id="ixv-7227"
      unitRef="pure">0.0313</oef:AnnlRtrPct>
    <oef:AnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_2024"
      decimals="INF"
      id="ixv-7228"
      unitRef="pure">0.0314</oef:AnnlRtrPct>
    <oef:AnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_2025"
      decimals="INF"
      id="ixv-7229"
      unitRef="pure">0.0249</oef:AnnlRtrPct>
    <oef:HighestQuarterlyReturnLabel contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-600">
          &#160;&#160;&#160;Highest Quarter Return
        </oef:HighestQuarterlyReturnLabel>
    <oef:BarChartHighestQuarterlyReturn
      contextRef="Pid_S000007502_contentCd_MMM-PRO"
      decimals="4"
      id="ixv-7230"
      unitRef="pure">0.0090</oef:BarChartHighestQuarterlyReturn>
    <oef:BarChartHighestQuarterlyReturnDate contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-610">2023-12-31</oef:BarChartHighestQuarterlyReturnDate>
    <oef:LowestQuarterlyReturnLabel contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-615">
          &#160;&#160;&#160;Lowest Quarter Return
        </oef:LowestQuarterlyReturnLabel>
    <oef:BarChartLowestQuarterlyReturn
      contextRef="Pid_S000007502_contentCd_MMM-PRO"
      decimals="4"
      id="ixv-7231"
      unitRef="pure">0.0000</oef:BarChartLowestQuarterlyReturn>
    <oef:BarChartLowestQuarterlyReturnDate contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-625">2021-03-31</oef:BarChartLowestQuarterlyReturnDate>
    <oef:YearToDateReturnLabel contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-630">
          &#160;&#160;&#160;Year-to-Date Return
        </oef:YearToDateReturnLabel>
    <oef:BarChartYearToDateReturn
      contextRef="Pid_S000007502_contentCd_MMM-PRO"
      decimals="4"
      id="ixv-7232"
      unitRef="pure">0.0158</oef:BarChartYearToDateReturn>
    <oef:BarChartYearToDateReturnDate contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-640">2026-09-30</oef:BarChartYearToDateReturnDate>
    <oef:PerformanceTableHeading contextRef="Pid_S000007502_contentCd_MMM-PRO" id="ixv-645">
     
       
     Average Annual Returns 
       
    
   </oef:PerformanceTableHeading>
    <oef:AverageAnnualReturnLabel
      contextRef="Pid_S000007502_Cid_C000020476_ReturnBeforeTaxes_01"
      id="ixv-678">
         Fidelity&#xae; Municipal Money Market Fund
        </oef:AverageAnnualReturnLabel>
    <oef:AvgAnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_ReturnBeforeTaxes_01"
      decimals="4"
      id="ixv-7233"
      unitRef="pure">0.0249</oef:AvgAnnlRtrPct>
    <oef:AvgAnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_ReturnBeforeTaxes_05"
      decimals="4"
      id="ixv-7234"
      unitRef="pure">0.0193</oef:AvgAnnlRtrPct>
    <oef:AvgAnnlRtrPct
      contextRef="Pid_S000007502_Cid_C000020476_ReturnBeforeTaxes_10"
      decimals="4"
      id="ixv-7235"
      unitRef="pure">0.0130</oef:AvgAnnlRtrPct>
</xbrl>
