Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	BLACKROCK LIQUIDITY FUNDS
Prospectus Date	rr_ProspectusDate	Feb. 28, 2020
Premier | 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 and hold Premier Shares of Treasury Trust Fund.
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	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. 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. 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. 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. 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. 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. 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. 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. 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	Premier Shares of Treasury Trust Fund do not have a full calendar year of operations as of the date of this prospectus. As a result, the chart, the table and the seven-day yield shown below give you a picture of the performance for Institutional Shares of the Fund, which are not offered in this prospectus. The performance of the Fund’s Premier Shares would be substantially similar to Institutional Shares because Premier Shares and Institutional Shares are invested in the same portfolio of securities and performance would only differ to the extent that Premier Shares and Institutional Shares have different expenses. 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. Effective May 28, 2010, Rule 2a-7 was amended to impose new liquidity, credit quality and maturity requirements on all money market funds. Fund performance shown prior to May 28, 2010 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 Treasury Trust Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	Premier Shares of Treasury Trust Fund do not have a full calendar year of operations as of the date of this prospectus.
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 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 0.56% (quarter ended June 30, 2019) and the lowest return for a quarter was 0.00% (quarter ended September 30, 2015).
Bar Chart, Returns for Class Not Offered in Prospectus [Text]	rr_BarChartReturnsForClassNotOfferedInProspectus	Premier Shares of Treasury Trust Fund do not have a full calendar year of operations as of the date of this prospectus. As a result, the chart, the table and the seven-day yield shown below give you a picture of the performance for Institutional Shares of the Fund, which are not offered in this prospectus.
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
Premier | BLACKROCK LIQUIDITY TREASURY TRUST FUND | Premier Shares
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.19%
Distribution (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Miscellaneous/Other Expenses	rr_Component2OtherExpensesOverAssets	0.01%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.20%
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.03%)	[1]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.17%	[1]
1 Year	rr_ExpenseExampleYear01	$ 17
3 Years	rr_ExpenseExampleYear03	61
5 Years	rr_ExpenseExampleYear05	110
10 Years	rr_ExpenseExampleYear10	$ 252
Premier | BLACKROCK LIQUIDITY TREASURY TRUST FUND | Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
2010	rr_AnnualReturn2010	0.01%
2011	rr_AnnualReturn2011	none
2012	rr_AnnualReturn2012	none
2013	rr_AnnualReturn2013	0.01%
2014	rr_AnnualReturn2014	none
2015	rr_AnnualReturn2015	0.01%
2016	rr_AnnualReturn2016	0.17%
2017	rr_AnnualReturn2017	0.72%
2018	rr_AnnualReturn2018	1.71%
2019	rr_AnnualReturn2019	2.04%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2019
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	0.56%
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	2.04%
5 Years	rr_AverageAnnualReturnYear05	0.93%
10 Years	rr_AverageAnnualReturnYear10	0.46%
7-Day Yield As of December 31, 2019	rr_MoneyMarketSevenDayYield	1.53%

[1] As described in the “Management of the Funds” section of the Fund’s prospectus beginning on page 65, 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 0.17% 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.