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Investor A, C, Institutional and Class R | BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Overview Key Facts About BlackRock Health Sciences Opportunities Portfolio
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The investment objective of BlackRock Health Sciences Opportunities Portfolio (the “Fund”), a series of BlackRock FundsSM (the “Trust”), is to provide long-term growth of capital.
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 shares of the 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. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock or its affiliates. More information about these and other discounts is available from your Financial Intermediary and in the “Details About the Share Classes” and the “Intermediary-Defined Sales Charge Waiver Policies” sections on pages 24 and A-1, respectively, of the Fund’s prospectus and in the “Purchase of Shares” section on page II-87 of Part II of the Fund’s Statement of Additional Information.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
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
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover:
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance.
On April 7, 2021, the Board of Trustees of the Trust approved a change of the fiscal year end of the Fund from September 30 to May 31. During the fiscal year ended September 30, 2020, the Fund’s portfolio turnover rate was 28% of the average value of its portfolio. For the period October 1, 2020 to May 31, 2021, the Fund’s portfolio turnover rate was 19% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 19.00%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock A contingent deferred sales charge (“CDSC”) of 1.00% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock or its affiliates.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 25,000
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:
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption You would pay the following expenses if you did not redeem your shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies of the Fund
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
Under normal market conditions, the Fund invests at least 80% of its total assets in equity securities, primarily common stock, of companies in health sciences and related industries. The health sciences sector can include companies in health care equipment and supplies, health care providers and services, biotechnology, and pharmaceuticals. Health sciences and related industries can include, but are not limited to, businesses involved in the development, production, and distribution or delivery of medical and pharmaceutical products and services, companies engaged in biotechnology and medical research and development, companies that may design, manufacture or distribute medical, dental and optical equipment and supplies, including diagnostic equipment, and companies that may also provide diagnostic services or operate health facilities and hospitals, or provide related administrative, management and financial support. The Fund will concentrate its investments (i.e., invest more than 25% of its assets) in health sciences or related industries, and may invest in companies located in non-U.S. countries.
The Fund reserves the right to invest up to 20% of its total assets in other types of securities. These may include stocks of companies not associated with health sciences.
Strategy Portfolio Concentration [Text] rr_StrategyPortfolioConcentration The Fund will concentrate its investments (i.e., invest more than 25% of its assets) in health sciences or related industries, and may invest in companies located in non-U.S. countries.
Risk [Heading] rr_RiskHeading Principal Risks of Investing in the Fund
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
Risk is inherent in all investing. The value of your investment in the Fund, as well as the amount of return you receive on your investment, may fluctuate significantly from day to day and over time. You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments. The following is a summary description of the principal risks of investing in the Fund. The order of the below risk factors does not indicate the significance of any particular risk factor. 
Concentration Risk The Fund’s strategy of concentrating in health sciences and related companies means that its performance will be closely tied to the performance of a particular market segment. The Fund’s concentration in these companies may present more risks than if it were broadly diversified over numerous industries and sectors of the economy. A downturn in these companies would have a larger impact on the Fund than on a mutual fund that does not concentrate in such companies. At times, the performance of these companies will lag the performance of other industries or the broader market as a whole.
Equity Securities Risk — Stock markets are volatile. The price of equity securities fluctuates based on changes in a company’s financial condition and overall market and economic conditions.
Foreign Securities Risk — Foreign investments often involve special risks not present in U.S. investments that can increase the chances that the Fund will lose money. These risks include: 
The Fund generally holds its foreign securities and cash in foreign banks and securities depositories, which may be recently organized or new to the foreign custody business and may be subject to only limited or no regulatory oversight.
Changes in foreign currency exchange rates can affect the value of the Fund’s portfolio.
The economies of certain foreign markets may not compare favorably with the economy of the United States with respect to such issues as growth of gross national product, reinvestment of capital, resources and balance of payments position.
The governments of certain countries, or the U.S. Government with respect to certain countries, may prohibit or impose substantial restrictions through capital controls and/or sanctions on foreign investments in the capital markets or certain industries in those countries, which may prohibit or restrict the ability to own or transfer currency, securities, derivatives or other assets.
Many foreign governments do not supervise and regulate stock exchanges, brokers and the sale of securities to the same extent as does the United States and may not have laws to protect investors that are comparable to U.S. securities laws.
Settlement and clearance procedures in certain foreign markets may result in delays in payment for or delivery of securities not typically associated with settlement and clearance of U.S. investments.
The Fund’s claims to recover foreign withholding taxes may not be successful, and if the likelihood of recovery of foreign withholding taxes materially decreases, due to, for example, a change in tax regulation or approach in the foreign country, accruals in the Fund’s net asset value for such refunds may be written down partially or in full, which will adversely affect the Fund’s net asset value.
The European financial markets have recently experienced volatility and adverse trends due to concerns about economic downturns in, or rising government debt levels of, several European countries. These events may spread to other countries in Europe. These events may affect the value and liquidity of certain of the Fund’s investments. 
Geographic Concentration Risk — From time to time the Fund may invest a substantial amount of its assets in issuers located in a single country or a limited number of countries. If the Fund concentrates its investments in this manner, it assumes the risk that economic, political and social conditions in those countries will have a significant impact on its investment performance. The Fund’s investment performance may also be more volatile if it concentrates its investments in certain countries, especially emerging market countries.
Healthcare-Related Securities Risk Healthcare companies are strongly affected by worldwide scientific or technological developments. Their products may rapidly become obsolete. Many healthcare companies are also subject to significant government regulation and may be affected by changes in governmental policies.
Investment Style Risk Under certain market conditions, growth investments have performed better during the later stages of economic expansion. Therefore, this investment style may over time go in and out of favor. At times when the investment style used by the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.
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. 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.
Mid Cap Securities Risk — The securities of mid cap companies generally trade in lower volumes and are generally subject to greater and less predictable price changes than the securities of larger capitalization companies. 
Small Cap Securities Risk Small cap companies may have limited product lines or markets. They may be less financially secure than larger, more established companies. They may depend on a more limited management group than larger capitalized companies. 
Risk Lose Money [Text] rr_RiskLoseMoney You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
Class R Shares commenced operations on September 12, 2011, therefore the returns in the table for Class R Shares prior to commencement date are based on the Fund’s Investor A Shares, adjusted to reflect the fees and expenses applicable to Class R Shares and do not reflect any Investor A Shares front-end sales charges, which are not applicable to Class R Shares. This information may be considered when assessing the Fund’s performance, but does not represent the actual performance of these share classes.
The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. The table compares the Fund’s performance to that of the Russell 3000® Health Care Index. To the extent that dividends and distributions have been paid by the Fund, the performance information for the Fund in the chart and table assumes reinvestment of the dividends and distributions. As with all such investments, past performance (before and after taxes) is not an indication of future results. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. However, the table includes all applicable fees and sales charges. If BlackRock and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund’s returns would have been lower. Updated information on the Fund’s performance, including its current net asset value, can be obtained by visiting http://www.blackrock.com or can be obtained by phone at (800) 882-0052.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The information shows you how the 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) 882-0052
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress http://www.blackrock.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture As with all such investments, past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading Investor A Shares ANNUAL TOTAL RETURNS BlackRock Health Sciences Opportunities Portfolio As of 12/31
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
During the ten-year period shown in the bar chart, the highest return for a quarter was 17.54% (quarter ended March 31, 2013) and the lowest return for a quarter was -12.11% (quarter ended September 30, 2011). The year-to-date return as of June 30, 2021 was 7.48%.
Performance Table Heading rr_PerformanceTableHeading For the periods ended 12/31/20 Average Annual Total Returns
Performance Table Does Reflect Sales Loads rr_PerformanceTableDoesReflectSalesLoads However, the table includes all applicable fees and sales charges.
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns are shown for Investor A Shares only, and the after-tax returns for Investor C, Institutional and Class R Shares will vary.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock
After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns are shown for Investor A Shares only, and the after-tax returns for Investor C, Institutional and Class R Shares will vary.
Investor A, C, Institutional and Class R | BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO | Investor A Shares  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.25%
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Management Fees rr_ManagementFeesOverAssets 0.67% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.18%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.10%
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets [2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 1.10% [2]
1 Year rr_ExpenseExampleYear01 $ 631
3 Years rr_ExpenseExampleYear03 856
5 Years rr_ExpenseExampleYear05 1,099
10 Years rr_ExpenseExampleYear10 $ 1,795
2011 rr_AnnualReturn2011 5.97%
2012 rr_AnnualReturn2012 18.39%
2013 rr_AnnualReturn2013 44.15%
2014 rr_AnnualReturn2014 28.86%
2015 rr_AnnualReturn2015 11.00%
2016 rr_AnnualReturn2016 (6.05%)
2017 rr_AnnualReturn2017 24.82%
2018 rr_AnnualReturn2018 7.97%
2019 rr_AnnualReturn2019 25.28%
2020 rr_AnnualReturn2020 19.47%
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Jun. 30, 2021
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 7.48%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2013
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 17.54%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (12.11%)
1 Year rr_AverageAnnualReturnYear01 13.20%
5 Years rr_AverageAnnualReturnYear05 12.42%
10 Years rr_AverageAnnualReturnYear10 16.60%
Investor A, C, Institutional and Class R | BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO | Investor C Shares  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [3]
Management Fees rr_ManagementFeesOverAssets 0.67% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.84%
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets [2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 1.84% [2]
1 Year rr_ExpenseExampleYear01 $ 287
3 Years rr_ExpenseExampleYear03 579
5 Years rr_ExpenseExampleYear05 995
10 Years rr_ExpenseExampleYear10 1,965
1 Year rr_ExpenseExampleNoRedemptionYear01 187
3 Years rr_ExpenseExampleNoRedemptionYear03 579
5 Years rr_ExpenseExampleNoRedemptionYear05 995
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,965
1 Year rr_AverageAnnualReturnYear01 17.60%
5 Years rr_AverageAnnualReturnYear05 12.81%
10 Years rr_AverageAnnualReturnYear10 16.55%
Investor A, C, Institutional and Class R | BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO | Institutional Shares  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fees rr_ManagementFeesOverAssets 0.67% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.17%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.84%
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets [2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 0.84% [2]
1 Year rr_ExpenseExampleYear01 $ 86
3 Years rr_ExpenseExampleYear03 268
5 Years rr_ExpenseExampleYear05 466
10 Years rr_ExpenseExampleYear10 $ 1,037
1 Year rr_AverageAnnualReturnYear01 19.78%
5 Years rr_AverageAnnualReturnYear05 13.95%
10 Years rr_AverageAnnualReturnYear10 17.56%
Investor A, C, Institutional and Class R | BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO | Class R Shares  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fees rr_ManagementFeesOverAssets 0.67% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.27%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.44%
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets [2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 1.44% [2]
1 Year rr_ExpenseExampleYear01 $ 147
3 Years rr_ExpenseExampleYear03 456
5 Years rr_ExpenseExampleYear05 787
10 Years rr_ExpenseExampleYear10 $ 1,724
1 Year rr_AverageAnnualReturnYear01 19.07%
5 Years rr_AverageAnnualReturnYear05 13.26%
10 Years rr_AverageAnnualReturnYear10 16.85%
Investor A, C, Institutional and Class R | BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO | Return After Taxes on Distributions | Investor A Shares  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 12.00%
5 Years rr_AverageAnnualReturnYear05 11.26%
10 Years rr_AverageAnnualReturnYear10 14.76%
Investor A, C, Institutional and Class R | BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO | Return After Taxes on Distributions and Sale of Fund Shares | Investor A Shares  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 8.55%
5 Years rr_AverageAnnualReturnYear05 9.68%
10 Years rr_AverageAnnualReturnYear10 13.31%
Investor A, C, Institutional and Class R | BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO | Russell 3000® Health Care Index (Reflects no deduction for fees, expenses or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 19.34%
5 Years rr_AverageAnnualReturnYear05 12.87%
10 Years rr_AverageAnnualReturnYear10 16.63%
[1] A contingent deferred sales charge (“CDSC”) of 1.00% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.
[2] As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 40, BlackRock has contractually agreed to waive the management fee with respect to any portion of the Fund’s assets estimated to be attributable to investments in other equity and fixed-income mutual funds and exchange-traded funds managed by BlackRock or its affiliates that have a contractual management fee, through June 30, 2023. In addition, BlackRock has contractually agreed to waive its management fees by the amount of investment advisory fees the Fund pays to BlackRock indirectly through its investment in money market funds managed by BlackRock or its affiliates, through June 30, 2023. The contractual agreements 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.
[3] There is no CDSC on Investor C Shares after one year.