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Select | BLACKROCK LIQUIDITY TREASURY TRUST FUND  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Overview Key Facts About Treasury Trust Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The investment objective of Treasury Trust Fund (the “Fund”), a series of BlackRock Liquidity Funds (the “Trust”), is to seek current income as is consistent with liquidity and stability of principal.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
This table describes the fees and expenses that you may pay if you buy, hold and sell Select Shares of Treasury Trust Fund. You may pay other fees, such as brokerage commissions and other fees to your financial professional or your selected securities dealer, broker, investment adviser, service provider or industry professional (including BlackRock Advisors, LLC (“BlackRock”) and its affiliates) (each, a “Financial Intermediary”), which are not reflected in the table and example below.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination June 30, 2023 February 28, 2023
Expense Example [Heading] rr_ExpenseExampleHeading Example:
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
 
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies of the Fund
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
Treasury Trust Fund invests 100% of its total assets in cash, U.S. Treasury bills, notes and other obligations issued or guaranteed as to principal and interest by the U.S. Treasury. The Fund invests in securities maturing in 397 days or less (with certain exceptions) and the portfolio will have a dollar-weighted average maturity of 60 days or less and a dollar-weighted average life of 120 days or less. The Fund may invest in variable and floating rate instruments, and transact in securities on a when-issued, delayed delivery or forward commitment basis.
The Fund will invest, under normal circumstances, at least 80% of its net assets, plus the amount of any borrowings for investment purposes, in U.S. Treasury bills, notes and other obligations of the U.S. Treasury. This policy is a non-fundamental policy of the Fund and the Fund will not change the policy without providing shareholders with at least 60 days’ prior notice of any change in the policy.
The securities purchased by the Fund are subject to the quality, diversification, and other requirements of Rule 2a‑7 under the Investment Company Act of 1940, as amended (the “1940 Act”), and other rules of the Securities and Exchange Commission. The Fund will only purchase securities that present minimal credit risk as determined by BlackRock, the Fund’s investment manager, pursuant to guidelines approved by the Trust’s Board of Trustees.
Risk [Heading] rr_RiskHeading Principal Risks of Investing in the Fund
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
Risk is inherent in all investing. You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund’s sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time. The following is a summary description of principal risks of investing in the Fund. The order of the below risk factors does not indicate the significance of any particular risk factor.
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Credit Risk — Credit risk refers to the possibility that the issuer of a debt security (i.e., the borrower) will not be able to make payments of interest and principal when due. Changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Fund’s investment in that issuer. 
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Income Risk — Income risk is the risk that the Fund’s yield will vary as short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. 
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Interest Rate Risk — Interest rate risk is the risk that the value of a debt security may fall when interest rates rise. In general, the market price of debt securities with longer maturities will go up or down more in response to changes in interest rates than the market price of shorter-term securities. Due to fluctuations in interest rates, the market value of such securities may vary during the period shareholders own shares of the Fund. Very low or negative interest rates may magnify interest rate risk. During periods of very low or negative interest rates, the Fund may be unable to maintain positive returns or pay dividends to Fund shareholders. Changing interest rates, including rates that fall below zero, may have unpredictable effects on markets, may result in heightened market volatility and may detract from the Fund’s ability to achieve its investment objective. 
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Market Risk and Selection Risk — Market risk is the risk that one or more markets in which the Fund invests will go down in value, including the possibility that the markets will go down sharply and unpredictably. The value of a security or other asset may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security or other asset, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Local, regional or global events such as war, acts of terrorism, the spread of infectious illness or other public health issues like pandemics or epidemics, recessions, or other events could have a significant impact on the Fund and its investments. Selection risk is the risk that the securities selected by Fund management will underperform the markets, the relevant indices or the securities selected by other funds with similar investment objectives and investment strategies. This means you may lose money. 
A recent outbreak of an infectious coronavirus has developed into a global pandemic that has resulted in numerous disruptions in the market and has had significant economic impact leaving general concern and uncertainty. Because the Fund invests in short-term instruments these events have caused some instruments to have declining yields, which may impair the results of the Fund if these conditions persisted. The impact of this coronavirus, and other epidemics and pandemics that may arise in the future, could affect the economies of many nations, individual companies and the market in general ways that cannot necessarily be foreseen at the present time. 
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Stable Net Asset Value Risk — The Fund may not be able to maintain a stable net asset value (“NAV”) of $1.00 per share at all times. If the Fund fails to maintain a stable NAV (or if there is a perceived threat of such a failure), the Fund, along with other money market funds, could be subject to increased redemption activity. 
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Trading Risk — In selling securities prior to maturity, the Fund may realize a price higher or lower than that paid to acquire such securities, depending upon whether interest rates have decreased or increased since their acquisition. In addition, shareholders in a state that imposes an income or franchise tax should determine through consultation with their own tax advisors whether the Fund’s interest income, when distributed by the Fund, will be considered by the state to have retained exempt status, and whether the Fund’s capital gain and other income, if any, when distributed, will be subject to the state’s income or franchise tax. 
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Treasury Obligations Risk — Direct obligations of the U.S. Treasury have historically involved little risk of loss of principal if held to maturity. However, due to fluctuations in interest rates, the market value of such securities may vary during the period shareholders own shares of the Fund. 
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Variable and Floating Rate Instrument Risk — Variable and floating rate securities provide for periodic adjustment in the interest rate paid on the securities. These securities may be subject to greater illiquidity risk than other fixed income securities, meaning the absence of an active market for these securities could make it difficult for the Fund to dispose of them at any given time. 
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When-Issued and Delayed Delivery Securities and Forward Commitments Risk — When-issued and delayed delivery securities and forward commitments involve the risk that the security the Fund buys will lose value prior to its delivery. There also is the risk that the security will not be issued or that the other party to the transaction will not meet its obligation. If this occurs, the Fund may lose both the investment opportunity for the assets it set aside to pay for the security and any gain in the security’s price. 
Risk Lose Money [Text] rr_RiskLoseMoney You could lose money by investing in the Fund.
Risk Money Market Fund May Not Preserve Dollar [Text] rr_RiskMoneyMarketFundMayNotPreserveDollar Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so.
Risk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Money Market Fund Sponsor May Not Provide Support [Text] rr_RiskMoneyMarketFundSponsorMayNotProvideSupport The Fund’s sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The information shows you how Treasury Trust Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. As with all such investments, past performance is not an indication of future results. The table includes all applicable fees. If BlackRock and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund’s returns would have been lower. The Fund is a money market fund managed pursuant to the requirements of Rule 2a-7 under the 1940 Act. Updated information on the Fund’s performance can be obtained by visiting www.blackrock.com/cash or can be obtained by phone at (800) 441‑7450.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The information shows you how Treasury Trust Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone (800) 441‑7450
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.blackrock.com/cash
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture As with all such investments, past performance is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Treasury Trust Fund Select Shares ANNUAL TOTAL RETURNS As of 12/31
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
During the periods shown in the bar chart, the highest return for a quarter was 0.36% (quarter ended June 30, 2019) and the lowest return for a quarter was 0.00% (quarter ended December 31, 2021). 
Performance Table Heading rr_PerformanceTableHeading For the periods ended 12/31/21  Average Annual Total Returns
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock
Current Yield: You may obtain the Fund’s current 7‑day yield by calling (800) 441‑7450 or by visiting the Fund’s website at www.blackrock.com/cash.
Money Market Seven Day Yield Phone rr_MoneyMarketSevenDayYieldPhone (800) 441‑7450
Select | BLACKROCK LIQUIDITY TREASURY TRUST FUND | Select Shares  
Risk/Return: rr_RiskReturnAbstract  
Management Fee rr_ManagementFeesOverAssets 0.18%
Distribution (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.35%
Shareholder Servicing Fees rr_Component1OtherExpensesOverAssets 0.50%
Miscellaneous/Other Expenses rr_Component2OtherExpensesOverAssets 0.01%
Other Expenses rr_OtherExpensesOverAssets 0.51%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.04%
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.04%) [1],[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 1.00% [1],[2]
1 Year rr_ExpenseExampleYear01 $ 102
3 Years rr_ExpenseExampleYear03 327
5 Years rr_ExpenseExampleYear05 570
10 Years rr_ExpenseExampleYear10 $ 1,267
2016 rr_AnnualReturn2016 0.02%
2017 rr_AnnualReturn2017 0.05%
2018 rr_AnnualReturn2018 0.87%
2019 rr_AnnualReturn2019 1.20%
2020 rr_AnnualReturn2020 0.13%
2021 rr_AnnualReturn2021 0.01%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2019
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 0.36%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2021
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn none
1 Year rr_AverageAnnualReturnYear01 0.01%
5 Years rr_AverageAnnualReturnYear05 0.45%
Since Inception rr_AverageAnnualReturnSinceInception 0.36%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 28, 2015
7-Day Yield As of December 31, 2021 rr_MoneyMarketSevenDayYield 0.01%
[1]
As described in the “Management of the Funds” section of the Fund’s prospectus beginning on page 26, BlackRock, the Fund’s investment manager, has contractually agreed to waive fees and/or reimburse ordinary operating expenses in order to keep combined Management Fees and Miscellaneous/Other Expenses (excluding Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses) from exceeding 0.17% of average daily net assets through June 30, 2023 . The agreement may be terminated upon 90 days’ notice by a majority of the non‑interested trustees of the Trust or by a vote of a majority of the outstanding voting securities of the Fund.
[2]
As described in the “Management of the Funds” section of the Fund’s prospectus beginning on page 26, the Fund’s distributor and the Financial Intermediary party to the waiver agreement have contractually agreed to waive Distribution Fees and/or Shareholder Servicing Fees so that the Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements of the Select Shares do not exceed 1.00% of average daily net assets through February 28, 2023. The agreement renews automatically for successive one year periods and may be terminated by any party upon written notice 75 days prior to the commencement of a successive one year period.