Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	BLACKROCK FUNDS
Prospectus Date	rr_ProspectusDate	Nov. 28, 2018
Investor A, Institutional | iShares Russell Mid-Cap Index Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Overview<br/><br/><b>Key Facts About iShares Russell Mid-Cap Index Fund</b>
Objective [Heading]	rr_ObjectiveHeading	<b>Investment Objective </b>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of iShares Russell Mid-Cap Index Fund (the "Fund"), a series of BlackRock FundsSM (the "Trust"), is to seek to track the investment results of an index composed of mid-capitalization U.S. equities.
Expense [Heading]	rr_ExpenseHeading	<b>Fees and Expenses of the Fund </b>
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	<b>Annual Fund Operating Expenses</b><br/><b> (expenses that you pay each year as a percentage of the value of your investment)</b>
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	November 30, 2019
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	<b>Portfolio Turnover: </b>
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. During the most recent fiscal year, the Fund’s portfolio turnover rate was 75% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	75.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	<b>Example: </b>
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in shares of 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	<b>Principal Investment Strategies of the Fund </b>
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund seeks to track the investment results of the Russell Midcap® Index (the “Underlying Index”), which measures the performance of the mid-capitalization sector of the U.S. equity market. The Underlying Index is a float-adjusted, capitalization-weighted index of the 800 smallest issuers in the Russell 1000® Index. The Underlying Index includes equity securities issued by issuers with a median market cap of $7.71 billion as of October 31, 2018. Components primarily include financial services, consumer discretionary and technology companies, and may change over time. BlackRock uses a representative sampling indexing strategy to manage the Fund. “Representative sampling” is an indexing strategy that involves investing in a representative sample of securities that collectively has an investment profile similar to that of the Underlying Index. The securities selected are expected to have, in the aggregate, investment characteristics (based on factors such as market capitalization and industry weightings), fundamental characteristics (such as return variability and yield) and liquidity measures similar to those of the Underlying Index. The Fund may or may not hold all of the securities in the Underlying Index. The Fund generally invests at least 90% of its assets, plus the amount of any borrowing for investment purposes, in securities of the Underlying Index.
Risk [Heading]	rr_RiskHeading	<b>Principal Risks of Investing in the Fund </b>
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. Asset Class Risk — Securities and other assets in the Underlying Index or in the Fund’s portfolio may underperform in comparison to the general financial markets, a particular financial market or other asset classes. Concentration Risk — The Fund reserves the right to concentrate its investments (i.e., invest 25% or more of its total assets in securities of issuers in a particular industry) to approximately the same extent that the Underlying Index concentrates in a particular industry. To the extent the Fund concentrates in a particular industry, it may be more susceptible to economic conditions and risks affecting that industry. Consumer Discretionary Sector Risk — The consumer discretionary sector may be affected by changes in domestic and international economies, exchange and interest rates, competition, consumers’ disposable income, consumer preferences, social trends and marketing campaigns. 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. Financials Sector Risk — Performance of companies in the financials sector may be adversely impacted by many factors, including, among others, changes in government regulations, economic conditions, and interest rates, credit rating downgrades, and decreased liquidity in credit markets. The impact of more stringent capital requirements and recent or future regulation of any individual financial company, or of the financials sector as a whole, cannot be predicted. In recent years, cyber attacks and technology malfunctions and failures have become increasingly frequent in this sector and have caused significant losses to companies in this sector, which may negatively impact the Fund. Index Fund Risk — An index fund has operating and other expenses while an index does not. As a result, while the Fund will attempt to track the Underlying Index as closely as possible, it will tend to underperform the Underlying Index to some degree over time. If an index fund is properly correlated to its stated index, the fund will perform poorly when the index performs poorly. Index-Related Risk — There is no guarantee that the Fund’s investment results will have a high degree of correlation to those of the Underlying Index or that the Fund will achieve its investment objective. Market disruptions and regulatory restrictions could have an adverse effect on the Fund’s ability to adjust its exposure to the required levels in order to track the Underlying Index. Errors in index data, index computations or the construction of the Underlying Index in accordance with its methodology may occur from time to time and may not be identified and corrected by the index provider for a period of time or at all, which may have an adverse impact on the Fund and its shareholders. Issuer Risk — Fund performance depends on the performance of individual securities to which the Fund has exposure. Changes in the financial condition or credit rating of an issuer of those securities may cause the value of the securities to decline. Management Risk — As the Fund may not fully replicate the Underlying Index, it is subject to the risk that BlackRock’s investment strategy may not produce the intended results. 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. 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. Technology Sector Risk — Technology companies, including information technology companies, may have limited product lines, markets, financial resources or personnel. Technology companies typically face intense competition and potentially rapid product obsolescence. They are also heavily dependent on intellectual property rights and may be adversely affected by the loss or impairment of those rights.
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	<b>Performance Information </b>
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The information shows you how the performance of the Fund has varied for the periods since inception and provides some indication of the risks of investing in the Fund. The table compares the Fund’s performance to that of the Russell Midcap® Index. Prior to the Investor A Shares inception date of November 30, 2015, the returns for the Investor A Shares are based on the Fund’s Institutional Shares, as adjusted to reflect the applicable distribution and service (12b-1) fees. 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. 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. 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 performance of the Fund has varied for the periods since inception 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	<b>iShares Russell Mid-Cap Index Fund<br/>Investor A Shares<br/>ANNUAL TOTAL RETURNS<br/>As of 12/31 </b>
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the periods shown in the bar chart, the highest return for a quarter was 5.96% (quarter ended December 31, 2017) and the lowest return for a quarter was 2.25% (quarter ended March 31, 2016). The year-to-date return as of September 30, 2018 was 7.11%.
Performance Table Heading	rr_PerformanceTableHeading	<b>As of 12/31/17<br/>Average Annual Total Returns </b>
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 Institutional 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 Institutional Shares will vary.
Investor A, Institutional | iShares Russell Mid-Cap Index Fund | Investor A Shares
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.02%	[1]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.08%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.35%
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets		[1],[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.35%	[1],[2]
1 Year	rr_ExpenseExampleYear01	$ 36
3 Years	rr_ExpenseExampleYear03	113
5 Years	rr_ExpenseExampleYear05	197
10 Years	rr_ExpenseExampleYear10	$ 443
2016	rr_AnnualReturn2016	13.52%
2017	rr_AnnualReturn2017	18.05%
Year to Date Return, Label	rr_YearToDateReturnLabel	year-to-date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2018
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	7.11%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2017
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	5.96%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Mar. 31, 2016
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	2.25%
1 Year	rr_AverageAnnualReturnYear01	18.05%
Since Inception	rr_AverageAnnualReturnSinceInception	9.19%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 13, 2015
Investor A, Institutional | iShares Russell Mid-Cap Index Fund | Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.02%	[1]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.11%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.13%
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.01%)	[1],[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.12%	[1],[2]
1 Year	rr_ExpenseExampleYear01	$ 12
3 Years	rr_ExpenseExampleYear03	41
5 Years	rr_ExpenseExampleYear05	72
10 Years	rr_ExpenseExampleYear10	$ 165
1 Year	rr_AverageAnnualReturnYear01	18.30%
Since Inception	rr_AverageAnnualReturnSinceInception	9.46%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 13, 2015
Investor A, Institutional | iShares Russell Mid-Cap Index Fund | Return After Taxes on Distributions | Investor A Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	12.38%
Since Inception	rr_AverageAnnualReturnSinceInception	6.81%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 13, 2015
Investor A, Institutional | iShares Russell Mid-Cap Index Fund | Return After Taxes on Distributions and Sale of Fund Shares | Investor A Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	13.07%
Since Inception	rr_AverageAnnualReturnSinceInception	6.63%
Inception Date	rr_AverageAnnualReturnInceptionDate	May 13, 2015
Investor A, Institutional | iShares Russell Mid-Cap Index Fund | Russell Midcap® Index (Reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	18.52%
Since Inception	rr_AverageAnnualReturnSinceInception	9.45%

[1] As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 26, BlackRock Advisors, LLC (“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 November 30, 2019. The contractual 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 Fund” section of the Fund’s prospectus beginning on page 26, BlackRock has contractually agreed to waive and/or reimburse fees or expenses in order to limit Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements (excluding Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses) to 0.37% of average daily net assets (for Investor A Shares) and 0.12% of average daily net assets (for Institutional Shares) through November 30, 2019. The Fund may have to repay some of these waivers and/or reimbursements to BlackRock in the following two years. The contractual 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.