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iShares Enhanced Roll Yield Index Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Overview Key Facts About iShares Enhanced Roll Yield Index Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The investment objective of iShares Enhanced Roll Yield Index Fund (the “Fund”), a series of BlackRock FundsSM (the “Trust”), is to seek to track the investment results of an index composed of a broad range of commodity exposures.
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 shares of the 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 June 30, 2035
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. There has been no portfolio turnover because the Fund has not commenced operations as of the date of this prospectus.
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
The Fund seeks to track the investment results of the Bloomberg Enhanced Roll Yield Total Return Index (the “Underlying Index”), which is a broad-based, long-only commodity benchmark. The Underlying Index aims to mitigate the effects of negative roll yield. Roll yield is the difference between the prices of the shorter term and the longer term futures contracts when they are rolled. The Underlying Index is rebalanced on an annual basis.
In seeking to achieve its investment objective, the Fund will invest in a combination of exchange-traded commodity futures contracts, exchange traded options on commodity-related futures contracts and exchange-cleared commodity related swaps (together, “Commodity-Linked Investments”), thereby obtaining exposure to the commodities markets. Commodity-Linked Investments may also include exchange-cleared swaps on commodities and exchange-traded options on futures that provide exposure to the investment returns of the commodities markets, without investing directly in physical commodities. Investing in Commodity-Linked Investments may have a leveraging effect on the Fund. The Fund also seeks to generate interest income and capital appreciation on the cash balances arising from its investment in Commodity-Linked Investments through a cash management strategy consisting primarily of investments in short-term, investment-grade fixed-income securities that include U.S. government and agency securities, treasury inflation-protected securities, sovereign debt obligations of non‑U.S. countries, and repurchase agreements, money market instruments and cash and other cash equivalents (collectively, “Fixed-Income Investments”). The Fund uses Fixed-Income Investments as investments and to provide sufficient assets to account for (or “cover”) mark to‑market changes and to collateralize the Subsidiary’s (as defined below) Commodity-Linked Investments exposure on a day‑to‑day basis.
The Fund generally will invest at least 80% of its assets, plus the amount of any borrowings for investment purposes, in securities or other financial instruments that are components of or have economic characteristics similar to the securities in the Underlying Index. The Fund may invest a portion of the remainder of its assets in securities not included in the Underlying Index, but which BFA believes will help the Fund track the Underlying Index.
The Fund will concentrate its investments (i.e., hold 25% or more of its total assets) in a particular industry or group of industries to approximately the same extent that the Underlying Index is concentrated.
BFA 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 and/or other instruments that collectively has an investment profile similar to that of an applicable underlying index. The securities and/or other instruments selected are expected to have, in the aggregate, investment characteristics (based on factors such as market value and industry weightings), fundamental characteristics (such as return variability, duration, maturity, credit ratings and yield) and liquidity measures similar to those of an applicable underlying index. The Fund may or may not hold all of the securities and/or other instruments in the Underlying Index.
The Fund will seek to gain exposure to Commodity-Linked Investments by investing through the Subsidiary, a wholly-owned subsidiary organized in the Cayman Islands. The Subsidiary is advised by BFA and has the same investment objective as the Fund. BFA has entered into a sub-advisory agreement with BlackRock International Limited with respect to the Subsidiary. Unlike the Fund, the Subsidiary is not an investment company registered under the Investment Company Act of 1940, as amended (the “Investment Company Act”). The Subsidiary will invest solely in Commodity-Linked Investments and cash. The Fund may invest up to 25% of its total assets in the Subsidiary.
The remainder of the Fund’s assets will be invested directly by the Fund, primarily in Fixed-Income Investments. The Fund or the Subsidiary may from time to time invest in other exchange traded funds (“ETFs”), exchange-traded notes or commodity-linked notes.
The Fund is classified as non‑diversified under the Investment Company Act.
Risk [Heading] rr_RiskHeading Principal Risks of Investing in the Fund
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
Because the Fund has not commenced operations as of the date of this prospectus, it does not have performance information an investor would find useful in evaluating the risks of investing in the Fund. The Fund’s benchmarks are the S&P Total Market Index and the Bloomberg Enhanced Roll Yield Total Return Index.
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess Because the Fund has not commenced operations as of the date of this prospectus, it does not have performance information an investor would find useful in evaluating the risks of investing in the Fund.
iShares Enhanced Roll Yield Index Fund | Risk Nondiversified Status [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Non‑Diversification Risk — The Fund is a non‑diversified fund. Because the Fund may invest in securities of a smaller number of issuers, it may be more exposed to the risks associated with and developments affecting an individual issuer than a fund that invests more widely.
iShares Enhanced Roll Yield Index Fund | Risk Lose Money [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments.
iShares Enhanced Roll Yield Index Fund | Commodities Investment Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Commodities Investment Risk — Investing in commodity-linked derivative instruments and equity securities of commodity-related companies may subject the Fund to greater volatility than investments in traditional securities. The commodities markets have experienced periods of extreme volatility. Similar future market conditions may result in rapid and substantial valuation increases or decreases in the Fund’s holdings.
The commodities markets may fluctuate widely based on a variety of factors. Movements in commodity investment prices are outside of the Fund’s control and may not be anticipated by Fund management. Price movements may be influenced by, among other things: governmental, agricultural, trade, fiscal, monetary and exchange control programs and policies; changing market and economic conditions; market liquidity; weather and climate conditions;
changing supply and demand relationships and levels of domestic production and imported commodities; the availability of local, intrastate and interstate transportation systems; energy conservation; the success of exploration projects; changes in international balances of payments and trade; domestic and foreign rates of
inflation; currency devaluations and revaluations; domestic and foreign political and economic events; domestic and foreign interest rates and/or investor expectations concerning interest rates; foreign currency/exchange rates; domestic and foreign governmental regulation and taxation; war, acts of terrorism and other political upheaval and conflicts; governmental expropriation; investment and trading activities of mutual funds, hedge funds and commodities funds; changes in philosophies and emotions of market participants. The frequency and magnitude of such changes cannot be predicted.
The commodity markets are subject to temporary distortions and other disruptions due to, among other factors, lack of liquidity, the participation of speculators, and government regulation and other actions. U.S. futures exchanges and some foreign exchanges limit the amount of fluctuation in futures contract prices which may occur in a single business day (generally referred to as “daily price fluctuation limits”). The maximum or minimum price of a contract as a result of these limits is referred to as a “limit price.” If the limit price has been reached in a particular contract, no trades may be made beyond the limit price. Limit prices have the effect of precluding trading in a particular contract or forcing the liquidation of contracts at disadvantageous times or prices.
iShares Enhanced Roll Yield Index Fund | Commodities Related Investments Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Commodities Related Investments Risk — Exposure to the commodities markets may subject the Fund to greater volatility than investments in traditional securities. The value of commodity-linked derivative investments may be affected by changes in overall market movements, commodity index volatility, changes in inflation, interest rates, or factors affecting a particular industry or commodity, such as drought, floods, weather, embargoes, tariffs and international economic, political and regulatory developments.
iShares Enhanced Roll Yield Index Fund | Commodities Market Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Commodities Market Risk — Stocks of companies engaged in commodities related industries, such as energy or natural resources companies, are especially affected by variations in the commodities markets (that may be due to market events, regulatory developments or other factors that the Fund cannot control) and these companies may lack the resources and the broad business lines to weather hard times.
iShares Enhanced Roll Yield Index Fund | Index Related Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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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 or high volatility, other unusual market circumstances 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. Unusual market conditions or other unforeseen circumstances (such as natural disasters, political unrest or war) may impact the index provider or a third-party data provider, and could cause the index provider to postpone a scheduled rebalance. This could cause the Underlying Index to vary from its normal or expected composition.
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.
iShares Enhanced Roll Yield Index Fund | Passive Investment Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Passive Investment Risk — Because BFA does not select individual companies in the index that the Fund tracks, the Fund may hold securities of companies that present risks that an investment adviser researching individual securities might seek to avoid.
iShares Enhanced Roll Yield Index Fund | Tracking Error Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Tracking Error Risk — The Fund may be subject to tracking error, which is the divergence of the Fund’s performance from that of the Underlying Index. Tracking error may occur because of differences between the securities and other instruments held in the Fund’s portfolio and those included in the Underlying Index, pricing differences (including, as applicable, differences between a security’s price at the local market close and the Fund’s valuation of a security at the time of calculation of the Fund’s net asset value), differences in transaction costs incurred by the Fund, the Fund’s holding of uninvested cash, differences in timing of the accrual of or the valuation of dividends or other distributions, interest, the requirements to maintain pass-through tax treatment, portfolio transactions carried out to minimize the distribution of capital gains to shareholders, changes to the Underlying Index or the cost to the Fund of complying with various new or existing regulatory requirements, among other reasons. These risks may be heightened during times of increased market volatility or other unusual market conditions. In addition, tracking error may result because the Fund incurs fees and expenses, while the Underlying Index does not.
iShares Enhanced Roll Yield Index Fund | Commodities Regulatory Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Commodities Regulatory Risk — Commodity-related companies are subject to significant federal, state and local government regulation in virtually every aspect of their operations, including how facilities are constructed, maintained and operated, environmental and safety controls, and the prices they may charge for the products and services they provide. The Commodity Futures Trading Commission (“CFTC”) and the U.S. commodities exchanges are authorized to take extraordinary actions in the event of a market emergency, including, for example, the imposition of higher margin requirements, the establishment of daily limits and the suspension of trading. Any of these actions, if taken, could adversely affect the returns of the Fund by limiting or precluding investment decisions the Fund might otherwise make.
The CFTC and the U.S. commodities exchanges impose limits referred to as “speculative position limits” on the maximum net long or net short speculative positions that any person may hold or control in any particular futures, options contracts or swaps traded on U.S. commodities exchanges, including with respect to futures and options on futures on many physical commodities, such as energy, metals and agricultural commodities (the “core referenced futures contracts”), and on economically equivalent swaps. Certain position limits include an exemption from limits for bona fide hedging transactions or positions. As a consequence of these position limits, the size or duration of positions available to the Fund may be severely limited.
In addition, the Internal Revenue Service will no longer issue private letter rulings on the tax treatment of a mutual fund investment in commodity-linked derivatives if the ruling would depend on whether the investment is a security under the Investment Company Act.
iShares Enhanced Roll Yield Index Fund | Concentration Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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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.
iShares Enhanced Roll Yield Index Fund | Debt Securities Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Debt Securities Risk — Debt securities, such as bonds, involve risks, such as credit risk, interest rate risk, extension risk, and prepayment risk, each of which are described in further detail below:
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. The degree of credit risk depends on both the financial condition of the issuer and the terms of the obligation.
Interest Rate Risk — The market value of bonds and other fixed-income securities changes in response to interest rate changes and other factors. Interest rate risk is the risk that prices of bonds and other fixed-income securities will increase as interest rates fall and decrease as interest rates rise.
The Fund may be subject to a greater risk of rising interest rates during a period of historically low interest rates. For example, if interest rates increase by 1%, assuming a current portfolio duration of ten years, and all other factors being equal, the value of the Fund’s investments would be expected to decrease by 10%. (Duration is a measure of the price sensitivity of a debt security or portfolio of debt securities to relative changes in interest rates.) The magnitude of these fluctuations in the market price of bonds and other fixed-income securities is generally greater for those securities with longer maturities. Fluctuations in the market price of the Fund’s investments will not affect interest income derived from instruments already owned by the Fund, but will be reflected in the Fund’s net asset value. The Fund may lose money if short-term or long-term interest rates rise sharply in a manner not anticipated by Fund management.
To the extent the Fund invests in debt securities that may be prepaid at the option of the obligor (such as mortgage-backed securities), the sensitivity of such securities to changes in interest rates may increase (to the detriment of the Fund) when interest rates rise. Moreover, because rates on certain floating rate debt securities typically reset only periodically, changes in prevailing interest rates (and particularly sudden and significant changes) can be expected to cause some fluctuations in the net asset value of the Fund to the extent that it invests in floating rate debt securities.
These basic principles of bond prices also apply to U.S. Government securities. A security backed by the “full faith and credit” of the U.S. Government is guaranteed only as to its stated interest rate and face value at maturity, not its current market price. Just like other fixed-income securities, government-guaranteed securities will fluctuate in value when interest rates change.
A general rise in interest rates has the potential to cause investors to move out of fixed-income securities on a large scale, which may increase redemptions from funds that hold large amounts of fixed-income securities. Heavy redemptions could cause the Fund to sell assets at inopportune times or at a loss or depressed value and could hurt the Fund’s performance.
Extension Risk — When interest rates rise, certain obligations will be paid off by the obligor more slowly than anticipated, causing the value of these obligations to fall.
Prepayment Risk — When interest rates fall, certain obligations will be paid off by the obligor more quickly than originally anticipated, and the Fund may have to invest the proceeds in securities with lower yields.
iShares Enhanced Roll Yield Index Fund | Market Risk and Selection Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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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.
An outbreak of an infectious coronavirus (COVID‑19) that was first detected in December 2019 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. Although vaccines have been developed and approved for use by various governments, the duration of the pandemic and its effects cannot be predicted with certainty. 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.
iShares Enhanced Roll Yield Index Fund | Money Market Securities Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Money Market Securities Risk — If market conditions improve while the Fund has invested some or all of its assets in high quality money market securities, this strategy could result in reducing the potential gain from the market upswing, thus reducing the Fund’s opportunity to achieve its investment objective.
iShares Enhanced Roll Yield Index Fund | Representative Sampling Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Representative Sampling Risk — Representative sampling is a method of indexing that involves investing in a representative sample of securities that collectively have a similar investment profile to the Underlying Index and resemble the Underlying Index in terms of risk factors and other key characteristics. The Fund may or may not hold every security in the Underlying Index. When the Fund deviates from a full replication indexing strategy to utilize a representative sampling strategy, the Fund is subject to an increased risk of tracking error, in that the securities selected in the aggregate for the Fund may not have an investment profile similar to those of the Underlying Index.
iShares Enhanced Roll Yield Index Fund | Repurchase Agreements Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Repurchase Agreements Risk — If the other party to a repurchase defaults on its obligation under the agreement, the Fund may suffer delays and incur costs or lose money in exercising its rights under the agreement. If the seller fails to repurchase the security in either situation and the market value of the security declines, the Fund may lose money.
iShares Enhanced Roll Yield Index Fund | Sovereign Debt Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Sovereign Debt Risk — Sovereign debt instruments are subject to the risk that a governmental entity may delay or refuse to pay interest or repay principal on its sovereign debt, due, for example, to cash flow problems, insufficient foreign currency reserves, political considerations, the relative size of the governmental entity’s debt position in relation to the economy or the failure to put in place economic reforms required by the International Monetary Fund or other multilateral agencies.
iShares Enhanced Roll Yield Index Fund | Subsidiary Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Subsidiary Risk — By investing in the Subsidiary, the Fund is indirectly exposed to the risks associated with the Subsidiary’s investments. The commodity-related instruments held by the Subsidiary are generally similar to those that are permitted to be held by the Fund and are subject to the same risks that apply to similar investments if held directly by the Fund (see “Commodities Related Investments Risk” above). There can be no assurance that the investment objective of the Subsidiary will be achieved. The Subsidiary is not registered under the Investment Company Act, and, unless otherwise noted in this prospectus, is not subject to all the investor protections of the Investment Company Act. However, the Fund wholly owns and controls the Subsidiary, and the Fund and the Subsidiary are both managed by BFA, making it unlikely that the Subsidiary will take action contrary to the interests of the Fund and its shareholders. The Board has oversight responsibility for the investment activities of the Fund, including its investment in the Subsidiary, and the Fund’s role as sole shareholder of the Subsidiary. The Subsidiary is subject to the same investment restrictions and limitations, and follows the same compliance policies and procedures, as the Fund, except that the Subsidiary will invest solely in Commodity-Linked Investments and cash. Changes in the laws of the United States and/or the Cayman Islands could result in the inability of the Fund and/or the Subsidiary to operate as described in this prospectus and the Statement of Additional Information (“SAI”) and could adversely affect the Fund.
iShares Enhanced Roll Yield Index Fund | Tax Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Tax Risk — The Fund invests in commodity-related instruments indirectly through the Subsidiary because income from these investments, if made directly, might not be treated as “qualifying income” for purposes of the Fund qualifying as a regulated investment company for U.S. federal income tax purposes. Based on final regulations issued by the U.S. Internal Revenue Service (“IRS”) on which taxpayers may rely for taxable years beginning after September 28, 2016, the Fund expects its income with respect to the Subsidiary to be qualifying income. In the future, if the IRS issues new regulations or other guidance, or Congress enacts legislation, limiting the circumstances in which the Fund’s income with respect to the Subsidiary will be considered “qualifying income,” the Fund might be required to make changes to its operations, which could reduce the Fund’s ability to gain investment exposure to commodities. Fund shareholders could also experience adverse tax consequences in such circumstances.
iShares Enhanced Roll Yield Index Fund | Treasury Obligations Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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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. In addition, notwithstanding that U.S. Treasury obligations are backed by the full faith and credit of the United States, circumstances could arise that could prevent the timely payment of interest or principal, such as reaching the legislative “debt ceiling.” Such non‑payment could result in losses to the Fund and substantial negative consequences for the U.S. economy and the global financial system.
iShares Enhanced Roll Yield Index Fund | U S Government Obligations Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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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. In addition, circumstances could arise that could prevent the timely payment of interest or principal on U.S. Government obligations, such as reaching the legislative “debt ceiling.” Such non‑payment could result in losses to the Fund and substantial negative consequences for the U.S. economy and the global financial system.
iShares Enhanced Roll Yield Index Fund | Derivatives Risks [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
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Derivatives Risk — The Fund’s use of derivatives may increase its costs, reduce the Fund’s returns and/or increase volatility. Derivatives involve significant risks, including:
Leverage Risk — The Fund’s use of derivatives can magnify the Fund’s gains and losses. Relatively small market movements may result in large changes in the value of a derivatives position and can result in losses that greatly exceed the amount originally invested.
Market Risk — Some derivatives are more sensitive to interest rate changes and market price fluctuations than other securities. The Fund could also suffer losses related to its derivatives positions as a result of unanticipated market movements, which losses are potentially unlimited. Finally, BFA may not be able to predict correctly the direction of securities prices, interest rates and other economic factors, which could cause the Fund’s derivatives positions to lose value.
Counterparty Risk — Derivatives are also subject to counterparty risk, which is the risk that the other party in the transaction will be unable or unwilling to fulfill its contractual obligation, and the related risks of having concentrated exposure to such a counterparty.
Illiquidity Risk — The possible lack of a liquid secondary market for derivatives and the resulting inability of the Fund to sell or otherwise close a derivatives position could expose the Fund to losses and could make derivatives more difficult for the Fund to value accurately.
Operational Risk — The use of derivatives includes the risk of potential operational issues, including documentation issues, settlement issues, systems failures, inadequate controls and human error.
Legal Risk — The risk of insufficient documentation, insufficient capacity or authority of counterparty, or legality or enforceability of a contract.
Volatility and Correlation Risk — Volatility is defined as the characteristic of a security, an index or a market to fluctuate significantly in price within a short time period. A risk of the Fund’s use of derivatives is that the fluctuations in their values may not correlate with the overall securities markets.
Valuation Risk — Valuation for derivatives may not be readily available in the market. Valuation may be more difficult in times of market turmoil since many investors and market makers may be reluctant to purchase complex instruments or quote prices for them.
Hedging Risk — Hedges are sometimes subject to imperfect matching between the derivative and the underlying security, and there can be no assurance that the Fund’s hedging transactions will be effective. The use of hedging may result in certain adverse tax consequences.
Tax Risk — Certain aspects of the tax treatment of derivative instruments, including swap agreements and commodity-linked derivative instruments, are currently unclear and may be affected by changes in legislation, regulations or other legally binding authority. Such treatment may be less favorable than that given to a direct investment in an underlying asset and may adversely affect the timing, character and amount of income the Fund realizes from its investments.
iShares Enhanced Roll Yield Index Fund | iShares Enhanced Roll Yield Index Fund  
Risk/Return: rr_RiskReturnAbstract  
Management Fee rr_ManagementFeesOverAssets 0.15% [1]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Administration Fee rr_Component1OtherExpensesOverAssets 0.15% [1]
Independent Expenses rr_Component2OtherExpensesOverAssets [2]
Other Expenses rr_OtherExpensesOverAssets 0.15% [1],[2]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.30%
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.30%) [1],[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets none [1],[2]
1 Year rr_ExpenseExampleYear01 none
3 Years rr_ExpenseExampleYear03 none
[1]
As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 25, BlackRock Fund Advisors (“BFA”) and BlackRock Advisors, LLC (“BAL”), the Fund’s administrator, have contractually agreed to waive their management fee and administration fee, as applicable, through June 30, 2035. On July 1 of each year, the waiver agreement will renew automatically for an additional one year so that the agreement will have a perpetual ten‑year term. 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]
Independent Expenses consist of the Fund’s allocable portion of the fees and expenses of the independent trustees of the Trust, counsel to such independent trustees and the independent registered public accounting firm that provides audit services to the Fund. BAL and BFA have contractually agreed to reimburse, or provide offsetting credits to, the Fund for Independent Expenses through June 30, 2035. On July 1 of each year, the waiver agreement will renew automatically for an additional one year so that the agreement will have a perpetual ten‑year term. After giving effect to such contractual arrangements, Independent Expenses will be 0.00%. Such contractual arrangements 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.