Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	BLACKROCK LIQUIDITY FUNDS
Prospectus Date	rr_ProspectusDate	Feb. 28, 2020
Institutional | BLACKROCK LIQUIDITY MUNICASH
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Overview Key Facts About MuniCash
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of MuniCash (the “Fund”), a series of BlackRock Liquidity Funds (the “Trust”), is to seek as high a level of current income exempt from federal income tax 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 and hold Institutional Shares of MuniCash.
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	February 28, 2021
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	Under normal circumstances, MuniCash invests: (i) at least 80% of its net assets, plus the amount of any borrowings for investment purposes, in a broad range of short-term obligations issued by or on behalf of states, territories and possessions of the United States, the District of Columbia, and their respective authorities, agencies, instrumentalities and political subdivisions and derivative securities, such as beneficial interests in municipal trust certificates and partnership trusts (“Municipal Obligations”), the interest on which, in the opinion of counsel to the issuer of the obligation, is exempt from regular federal income tax; or (ii) so that at least 80% of the income distributed by the Fund will be exempt from regular federal income tax. Municipal Obligations in which the Fund may invest will also not be subject to the federal alternative minimum tax. 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 also invest in variable and floating rate instruments, and transact in securities on a when-issued, delayed delivery or forward commitment basis. 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 (the “Board”).
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. Because the share price of the Fund will fluctuate, when you sell your shares they may be worth more or less than what you originally paid for them. The Fund may impose a fee upon the sale of your shares or may temporarily suspend your ability to sell shares if the Fund’s liquidity falls below required minimums because of market conditions or other factors. 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. 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. Foreign Exposure Risk — Securities issued or supported by foreign entities, including foreign banks and corporations, may involve additional risks and considerations. Extensive public information about the foreign issuer may not be available, and unfavorable political, economic or governmental developments in the foreign country involved could affect the payment of principal and interest. 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. 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. Liquidity Fee and Redemption Gate Risk — The Board has discretion to impose a liquidity fee of up to 2% upon sale of your shares or may temporarily suspend your ability to sell shares if the Fund’s liquidity falls below required minimums because of market conditions or other factors. Accordingly, you may not be able to sell your shares or your redemptions may be subject to a liquidity fee when you sell your shares at certain times. 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. 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. Municipal Securities Concentration Risk — From time to time the Fund may invest a substantial amount of its assets in municipal securities whose interest is paid solely from revenues of similar projects. If the Fund concentrates its investments in this manner, it assumes the legal and economic risks relating to such projects and this may have a significant impact on the Fund’s investment performance. Municipal Securities Risks — Municipal securities risks include the ability of the issuer to repay the obligation, the relative lack of information about certain issuers of municipal securities, and the possibility of future legislative changes which could affect the market for and value of municipal securities. These risks include: General Obligation Bonds Risks — Timely payments depend on the issuer’s credit quality, ability to raise tax revenues and ability to maintain an adequate tax base. Revenue Bonds Risks — These payments depend on the money earned by the particular facility or class of facilities, or the amount of revenues derived from another source. Private Activity Bonds Risks — Municipalities and other public authorities issue private activity bonds to finance development of industrial facilities for use by a private enterprise. The private enterprise pays the principal and interest on the bond, and the issuer does not pledge its faith, credit and taxing power for repayment. Moral Obligation Bonds Risks — Moral obligation bonds are generally issued by special purpose public authorities of a state or municipality. If the issuer is unable to meet its obligations, repayment of these bonds becomes a moral commitment, but not a legal obligation, of the state or municipality. Municipal Notes Risks — Municipal notes are shorter term municipal debt obligations. If there is a shortfall in the anticipated proceeds, the notes may not be fully repaid and the Fund may lose money. Municipal Lease Obligations Risks — In a municipal lease obligation, the issuer agrees to make payments when due on the lease obligation. Although the issuer does not pledge its unlimited taxing power for payment of the lease obligation, the lease obligation is secured by the leased property. Tax-Exempt Status Risk — The Fund and its investment manager will rely on the opinion of issuers’ bond counsel and, in the case of derivative securities, sponsors’ counsel, on the tax-exempt status of interest on municipal bonds and payments under derivative securities. Neither the Fund nor its investment manager will independently review the bases for those tax opinions, which may ultimately be determined to be incorrect and subject the Fund and its shareholders to substantial tax liabilities. Taxability Risk — Future laws, regulations, rulings or court decisions may cause interest on municipal securities to be subject, directly or indirectly, to U.S. federal income taxation, or interest on state municipal securities to be subject to state or local income taxation, or the value of state municipal securities to be subject to state or local intangible personal property tax, or may otherwise prevent the Fund from realizing the full current benefit of the tax-exempt status of such securities. Any such change could also affect the market price of such securities, and thus the value of an investment in the Fund. 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. U.S. Government Obligations Risk — Certain securities in which the Fund may invest, including securities issued by certain U.S. Government agencies and U.S. Government sponsored enterprises, are not guaranteed by the U.S. Government or supported by the full faith and credit of the United States. Variable and Floating Rate Instrument Risk — Variable and floating rate securities provide for periodic adjustment in the interest rate paid on the securities. Certain of 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. 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 Price Fluctuates [Text]	rr_RiskMoneyMarketFundPriceFluctuates	Because the share price of the Fund will fluctuate, when you sell your shares they may be worth more or less than what you originally paid for them.
Risk Money Market Fund May Impose Fees or Suspend Sales [Text]	rr_RiskMoneyMarketFundMayImposeFeesOrSuspendSales	The Fund may impose a fee upon the sale of your shares or may temporarily suspend your ability to sell shares if the Fund’s liquidity falls below required minimums because of market conditions or other factors.
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 MuniCash’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. Effective May 28, 2010, Rule 2a-7 was amended to impose new liquidity, credit quality and maturity requirements on all money market funds. Effective October 11, 2016, the Fund implemented additional amendments to Rule 2a-7, including the adoption of a floating net asset value (“NAV”) per Fund share. Fund performance shown prior to May 28, 2010 and October 11, 2016 is based on 1940 Act rules then in effect and is not an indication of future returns. 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 MuniCash’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	MuniCash Institutional Shares ANNUAL TOTAL RETURNS As of 12/31
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the ten-year period shown in the bar chart, the highest return for a quarter was 0.38% (quarter ended December 31, 2018) and the lowest return for a quarter was 0.00% (quarter ended September 30, 2015).
Performance Table Heading	rr_PerformanceTableHeading	As of 12/31/19 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
Institutional | BLACKROCK LIQUIDITY MUNICASH | Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.26%
Distribution (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Miscellaneous/Other Expenses	rr_Component2OtherExpensesOverAssets	0.02%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.28%
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.08%)	[1]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.20%	[1]
1 Year	rr_ExpenseExampleYear01	$ 20
3 Years	rr_ExpenseExampleYear03	82
5 Years	rr_ExpenseExampleYear05	149
10 Years	rr_ExpenseExampleYear10	$ 348
2010	rr_AnnualReturn2010	0.17%
2011	rr_AnnualReturn2011	0.10%
2012	rr_AnnualReturn2012	0.10%
2013	rr_AnnualReturn2013	0.03%
2014	rr_AnnualReturn2014	0.02%
2015	rr_AnnualReturn2015	0.02%
2016	rr_AnnualReturn2016	0.38%
2017	rr_AnnualReturn2017	0.68%
2018	rr_AnnualReturn2018	1.25%
2019	rr_AnnualReturn2019	1.29%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2018
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	0.38%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2015
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	none
1 Year	rr_AverageAnnualReturnYear01	1.29%
5 Years	rr_AverageAnnualReturnYear05	0.72%
10 Years	rr_AverageAnnualReturnYear10	0.40%
7-Day Yield As of December 31, 2019	rr_MoneyMarketSevenDayYield	1.37%

[1] As described in the “Management of the Funds” section of the Fund’s prospectus beginning on page 70, BlackRock Advisors, LLC (“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 0.20% of average daily net assets through February 28, 2021. 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.