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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Dec. 31, 2011
Registrant Name dei_EntityRegistrantName BLACKROCK FUNDS
Central Index Key dei_EntityCentralIndexKey 0000844779
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Apr. 27, 2012
Document Effective Date dei_DocumentEffectiveDate Apr. 27, 2012
Prospectus Date rr_ProspectusDate Apr. 27, 2012
Investor A, B, C and Investor Shares | BlackRock Index Equity Portfolio Investor
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading
Fund Overview
Key Facts About BlackRock Index Equity Portfolio
Objective [Heading] rr_ObjectiveHeading
Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The investment objective of BlackRock Index Equity Portfolio (“Index Equity Portfolio” or the “Fund”), a series of BlackRock FundsSM (the “Trust”), is to match the performance of the Standard & Poor’s® 500 Index (the “S&P 500®”) as closely as possible before the deduction of Fund expenses.
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 Index Equity Portfolio. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the fund complex advised by BlackRock Advisors, LLC (“BlackRock”). More information about these and other discounts is available from your financial professional and in the “Details About the Share Classes” section on page 14 of the Fund’s prospectus and in the “Purchase of Shares” section on page II-58 of the Fund’s statement of additional information.
Shareholder Fees: rr_ShareholderFeesAbstract  
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption
Shareholder Fees
(Fees paid directly from your investment)
Operating Expenses: rr_OperatingExpensesAbstract  
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 May 1, 2013
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading
Portfolio Turnover:
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The Series pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover 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 Series’ portfolio turnover rate was 6% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 6.00%
Expenses Represent Both Master and Feeder [Text] rr_ExpensesRepresentBothMasterAndFeeder The fees and expenses shown in the table and the example that follows include both the expenses of the Fund and the Fund's share of the allocated expenses of the Master S&P 500 Index Series (the "Series"), a series of Quantitative Master Series LLC (the "Master LLC"). Management fees are paid by the Series.
Expense Example: rr_ExpenseExampleAbstract  
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: rr_ExpenseExampleNoRedemptionAbstract  
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

Index Equity Portfolio employs a “passive” management approach, attempting to invest in a portfolio of assets whose performance is expected to match approximately the performance of the S&P 500®. The Fund will be substantially invested in securities in the S&P 500®, and will invest, under normal circumstances, at least 80% of its assets in securities or other financial instruments that are components of or have economic characteristics similar to the securities included in the S&P 500®. The Fund may change its target index if Fund management believes a different index would better enable the Fund to match the performance of the market segment represented by the current index.

The Fund will invest in the common stocks represented in the S&P 500® in roughly the same proportions as their weightings in the S&P 500®. The Fund may also invest in derivative instruments linked to the S&P 500®. At times, the Fund may not invest in all of the common stocks in the S&P 500®, or in the same weightings as in the S&P 500®. At those times, the Fund chooses investments so that the market capitalizations, industry weighting and other investment characteristics of the stocks and derivative instruments chosen are similar to the S&P 500® as a whole.

The Fund is a “feeder fund” that invests all of its assets in the Master S&P 500 Index Series (previously defined as the “Series”) of Quantitative Master Series LLC (previously defined as the “Master LLC”) which has the same investment objective and strategies as the Fund. All investments are made at the Series level. This structure is sometimes called a “master/feeder” structure. The Fund’s investment results will correspond directly to the investment results of the Series. For simplicity, this prospectus uses the term “Index Equity Portfolio” or “Fund” to include, where applicable, the Series.
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 Index Equity Portfolio, 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 certain risks of investing in the Fund.

  • 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.
  • 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 S&P 500® as closely as possible, it will tend to underperform the 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.
  • 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.
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 The information shows you how Index Equity Portfolio’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 S&P 500®. 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 can be obtained by visiting www.blackrock.com/funds or can be obtained by phone at (800) 882-0052.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The information shows you how Index Equity Portfolio’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 www.blackrock.com/funds
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 Table: rr_BarChartTableAbstract  
Bar Chart [Heading] rr_BarChartHeading
Investor A Shares
ANNUAL TOTAL RETURNS
BlackRock Index Equity 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 15.93% (quarter ended June 30, 2009) and the lowest return for a quarter was –22.02% (quarter ended December 31, 2008). The year-to-date return as of March 31, 2012 was 12.48%.
Average Annual Return: rr_AverageAnnualReturnAbstract  
Performance Table Heading rr_PerformanceTableHeading
As of 12/31/11
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 B, Investor C and 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 Investor B, Investor C and Institutional Shares will vary.
Investor A, B, C and Investor Shares | BlackRock Index Equity Portfolio Investor | Investor A Shares
  
Shareholder Fees: rr_ShareholderFeesAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 3.00%
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses: rr_OperatingExpensesAbstract  
Management Fee rr_ManagementFeesOverAssets 0.01% [1],[2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.15% [1]
Administration Fees rr_Component1OtherExpensesOverAssets 0.10% [1]
Miscellaneous Other Expenses rr_Component2OtherExpensesOverAssets 0.165% [1]
Other Expenses rr_OtherExpensesOverAssets 0.265% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.425% [1]
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.005%) [1],[2],[3]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 0.42% [1],[2],[3]
Expense Example: rr_ExpenseExampleAbstract  
1 Year rr_ExpenseExampleYear01 342
3 Years rr_ExpenseExampleYear03 432
5 Years rr_ExpenseExampleYear05 531
10 Years rr_ExpenseExampleYear10 820
Bar Chart Table: rr_BarChartTableAbstract  
2002 rr_AnnualReturn2002 (22.70%)
2003 rr_AnnualReturn2003 27.66%
2004 rr_AnnualReturn2004 10.21%
2005 rr_AnnualReturn2005 4.45%
2006 rr_AnnualReturn2006 15.51%
2007 rr_AnnualReturn2007 5.23%
2008 rr_AnnualReturn2008 (37.21%)
2009 rr_AnnualReturn2009 26.08%
2010 rr_AnnualReturn2010 14.64%
2011 rr_AnnualReturn2011 1.68%
Year to Date Return, Label rr_YearToDateReturnLabel The year-to-date return as of March 31, 2012 was
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2012
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 12.48%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel the highest return for a quarter was
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.93%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel the lowest return for a quarter was
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (22.02%)
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (1.37%)
5 Years rr_AverageAnnualReturnYear05 (1.19%)
10 Years rr_AverageAnnualReturnYear10 2.14%
Investor A, B, C and Investor Shares | BlackRock Index Equity Portfolio Investor | Investor B Shares
  
Shareholder Fees: rr_ShareholderFeesAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOther 4.50% [4]
Operating Expenses: rr_OperatingExpensesAbstract  
Management Fee rr_ManagementFeesOverAssets 0.01% [1],[2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.90% [1]
Administration Fees rr_Component1OtherExpensesOverAssets 0.10% [1]
Miscellaneous Other Expenses rr_Component2OtherExpensesOverAssets 0.435% [1]
Other Expenses rr_OtherExpensesOverAssets 0.535% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.445% [1]
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.205%) [1],[2],[3]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 1.24% [1],[2],[3]
Expense Example: rr_ExpenseExampleAbstract  
1 Year rr_ExpenseExampleYear01 576
3 Years rr_ExpenseExampleYear03 787
5 Years rr_ExpenseExampleYear05 970
10 Years rr_ExpenseExampleYear10 1,433
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
1 Year rr_ExpenseExampleNoRedemptionYear01 126
3 Years rr_ExpenseExampleNoRedemptionYear03 437
5 Years rr_ExpenseExampleNoRedemptionYear05 770
10 Years rr_ExpenseExampleNoRedemptionYear10 1,433
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (3.61%)
5 Years rr_AverageAnnualReturnYear05 (1.76%)
10 Years rr_AverageAnnualReturnYear10 1.82%
Investor A, B, C and Investor Shares | BlackRock Index Equity Portfolio Investor | Investor C Shares
  
Shareholder Fees: rr_ShareholderFeesAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOther 1.00% [5]
Operating Expenses: rr_OperatingExpensesAbstract  
Management Fee rr_ManagementFeesOverAssets 0.01% [1],[2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.90% [1]
Administration Fees rr_Component1OtherExpensesOverAssets 0.10% [1]
Miscellaneous Other Expenses rr_Component2OtherExpensesOverAssets 0.235% [1]
Other Expenses rr_OtherExpensesOverAssets 0.335% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.245% [1]
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.005%) [1],[2],[3]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 1.24% [1],[2],[3]
Expense Example: rr_ExpenseExampleAbstract  
1 Year rr_ExpenseExampleYear01 226
3 Years rr_ExpenseExampleYear03 394
5 Years rr_ExpenseExampleYear05 683
10 Years rr_ExpenseExampleYear10 1,505
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
1 Year rr_ExpenseExampleNoRedemptionYear01 126
3 Years rr_ExpenseExampleNoRedemptionYear03 394
5 Years rr_ExpenseExampleNoRedemptionYear05 683
10 Years rr_ExpenseExampleNoRedemptionYear10 1,505
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (0.17%)
5 Years rr_AverageAnnualReturnYear05 (1.38%)
10 Years rr_AverageAnnualReturnYear10 1.65%
Investor A, B, C and Investor Shares | BlackRock Index Equity Portfolio Investor | Institutional Shares
  
Shareholder Fees: rr_ShareholderFeesAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOther none
Operating Expenses: rr_OperatingExpensesAbstract  
Management Fee rr_ManagementFeesOverAssets 0.01% [1],[2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none [1]
Administration Fees rr_Component1OtherExpensesOverAssets 0.10% [1]
Miscellaneous Other Expenses rr_Component2OtherExpensesOverAssets 0.125% [1]
Other Expenses rr_OtherExpensesOverAssets 0.225% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.235% [1]
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.055%) [1],[2],[3]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 0.18% [1],[2],[3]
Expense Example: rr_ExpenseExampleAbstract  
1 Year rr_ExpenseExampleYear01 18
3 Years rr_ExpenseExampleYear03 70
5 Years rr_ExpenseExampleYear05 127
10 Years rr_ExpenseExampleYear10 294
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 1.92%
5 Years rr_AverageAnnualReturnYear05 (0.35%)
10 Years rr_AverageAnnualReturnYear10 2.81%
Investor A, B, C and Investor Shares | BlackRock Index Equity Portfolio Investor | Return After Taxes on Distributions | Investor A Shares
  
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (1.97%)
5 Years rr_AverageAnnualReturnYear05 (1.84%)
10 Years rr_AverageAnnualReturnYear10 1.58%
Investor A, B, C and Investor Shares | BlackRock Index Equity Portfolio Investor | Return After Taxes on Distributions and Sale of Fund Shares | Investor A Shares
  
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (0.89%)
5 Years rr_AverageAnnualReturnYear05 (1.39%)
10 Years rr_AverageAnnualReturnYear10 1.49%
Investor A, B, C and Investor Shares | BlackRock Index Equity Portfolio Investor | S&P 500 Index (Reflects no deduction for fees, expenses or taxes)
  
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.11%
5 Years rr_AverageAnnualReturnYear05 (0.25%)
10 Years rr_AverageAnnualReturnYear10 2.92%
Service | BlackRock Index Equity Portfolio Investor
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading
Fund Overview
Key Facts About BlackRock Index Equity Portfolio
Objective [Heading] rr_ObjectiveHeading
Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The investment objective of BlackRock Index Equity Portfolio (“Index Equity Portfolio” or the “Fund”), a series of BlackRock FundsSM (the “Trust”), is to match the performance of the Standard & Poor’s® 500 Index (the “S&P 500®”) as closely as possible before the deduction of Fund expenses.
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 Service Shares of Index Equity Portfolio.
Operating Expenses: rr_OperatingExpensesAbstract  
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 May 1, 2013
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading
Portfolio Turnover:
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The Series pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover 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 Series’ portfolio turnover rate was 6% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 6.00%
Expenses Represent Both Master and Feeder [Text] rr_ExpensesRepresentBothMasterAndFeeder The fees and expenses shown in the table and the example that follows include both the expenses of the Fund and the Fund's share of the allocated expenses of the Master S&P 500 Index Series (the "Series"), a series of Quantitative Master Series LLC (the "Master LLC"). Management fees are paid by the Series.
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
Strategy [Heading] rr_StrategyHeading
Principal Investment Strategies of the Fund
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Index Equity Portfolio employs a “passive” management approach, attempting to invest in a portfolio of assets whose performance is expected to match approximately the performance of the S&P 500®. The Fund will be substantially invested in securities in the S&P 500®, and will invest, under normal circumstances, at least 80% of its assets in securities or other financial instruments that are components of or have economic characteristics similar to the securities included in the S&P 500®. The Fund may change its target index if Fund management believes a different index would better enable the Fund to match the performance of the market segment represented by the current index.

The Fund will invest in the common stocks represented in the S&P 500® in roughly the same proportions as their weightings in the S&P 500®. The Fund may also invest in derivative instruments linked to the S&P 500®. At times, the Fund may not invest in all of the common stocks in the S&P 500®, or in the same weightings as in the S&P 500®. At those times, the Fund chooses investments so that the market capitalizations, industry weighting and other investment characteristics of the stocks and derivative instruments chosen are similar to the S&P 500® as a whole.

The Fund is a “feeder fund” that invests all of its assets in the Master S&P 500 Index Series (previously defined as the “Series”) of Quantitative Master Series LLC (previously defined as the “Master LLC”) which has the same investment objective and strategies as the Fund. All investments are made at the Series level. This structure is sometimes called a “master/feeder” structure. The Fund’s investment results will correspond directly to the investment results of the Series. For simplicity, this prospectus uses the term “Index Equity Portfolio” or “Fund” to include, where applicable, the Series.
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 Index Equity Portfolio, 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 certain risks of investing in the Fund.

  • 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.
  • 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 S&P 500® as closely as possible, it will tend to underperform the 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.
  • 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.
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 The information shows you how Index Equity Portfolio’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 S&P 500®. 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 can be obtained by visiting www.blackrock.com/funds or can be obtained by phone at (800) 882-0052.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The information shows you how Index Equity Portfolio’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 www.blackrock.com/funds
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 Table: rr_BarChartTableAbstract  
Bar Chart [Heading] rr_BarChartHeading
Service Shares
ANNUAL TOTAL RETURNS
BlackRock Index Equity 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 16.01% (quarter ended June 30, 2009) and the lowest return for a quarter was –22.00% (quarter ended December 31, 2008). The year-to-date return as of March 31, 2012 was 12.51%.
Average Annual Return: rr_AverageAnnualReturnAbstract  
Performance Table Heading rr_PerformanceTableHeading
As of 12/31/11
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 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.
Service | BlackRock Index Equity Portfolio Investor | Service Shares
  
Operating Expenses: rr_OperatingExpensesAbstract  
Management Fee rr_ManagementFeesOverAssets 0.01% [1],[6]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.15% [1]
Administration Fees rr_Component1OtherExpensesOverAssets 0.10% [1]
Miscellaneous Other Expenses rr_Component2OtherExpensesOverAssets 0.135% [1]
Other Expenses rr_OtherExpensesOverAssets 0.235% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.395% [1]
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.005%) [1],[6],[7]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 0.39% [1],[6],[7]
Expense Example: rr_ExpenseExampleAbstract  
1 Year rr_ExpenseExampleYear01 40
3 Years rr_ExpenseExampleYear03 126
5 Years rr_ExpenseExampleYear05 221
10 Years rr_ExpenseExampleYear10 499
Bar Chart Table: rr_BarChartTableAbstract  
2002 rr_AnnualReturn2002 (22.58%)
2003 rr_AnnualReturn2003 27.86%
2004 rr_AnnualReturn2004 10.29%
2005 rr_AnnualReturn2005 4.47%
2006 rr_AnnualReturn2006 15.38%
2007 rr_AnnualReturn2007 5.41%
2008 rr_AnnualReturn2008 (37.20%)
2009 rr_AnnualReturn2009 26.11%
2010 rr_AnnualReturn2010 14.67%
2011 rr_AnnualReturn2011 1.73%
Year to Date Return, Label rr_YearToDateReturnLabel The year-to-date return as of March 31, 2012 was
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2012
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 12.51%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel the highest return for a quarter was
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 16.01%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel the lowest return for a quarter was
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (22.00%)
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 1.73%
5 Years rr_AverageAnnualReturnYear05 (0.53%)
10 Years rr_AverageAnnualReturnYear10 2.51%
Service | BlackRock Index Equity Portfolio Investor | Return After Taxes on Distributions | Service Shares
  
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 1.09%
5 Years rr_AverageAnnualReturnYear05 (1.20%)
10 Years rr_AverageAnnualReturnYear10 1.92%
Service | BlackRock Index Equity Portfolio Investor | Return After Taxes on Distributions and Sale of Fund Shares | Service Shares
  
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 1.13%
5 Years rr_AverageAnnualReturnYear05 (0.85%)
10 Years rr_AverageAnnualReturnYear10 1.80%
Service | BlackRock Index Equity Portfolio Investor | S&P 500 Index (Reflects no deduction for fees, expenses or taxes)
  
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.11%
5 Years rr_AverageAnnualReturnYear05 (0.25%)
10 Years rr_AverageAnnualReturnYear10 2.92%
[1] The fees and expenses shown in the table and the example that follows include both the expenses of the Fund and the Fund's share of the allocated expenses of the Master S&P 500 Index Series (the "Series"), a series of Quantitative Master Series LLC (the "Master LLC"). Management fees are paid by the Series.
[2] As described in the "Management of the Fund" section of the Fund's prospectus on pages 29-34, BlackRock has contractually agreed to waive and/or reimburse fees and/or expenses in order to ensure that management fees payable by the Series will not exceed 0.005% of average daily net assets until May 1, 2013. This agreement may be terminated upon 90 days' notice by a majority of the non-interested directors of the Master LLC or by a vote of a majority of the outstanding voting securities of the Series.
[3] As described in the "Management of the Fund" section of the Fund's prospectus on pages 29-34, 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) as a percentage of average daily net assets to 0.785% (for Investor A Shares), 1.24% (for Investor B and C Shares) and 0.18% (for Institutional Shares) until May 1, 2013. The Fund may have to repay some of these waivers and reimbursements to BlackRock in the following two years. The agreement may be terminated upon 90 days' notice by a majority of the non-interested trustees of the Trust or by vote of a majority of the outstanding voting securities of the Fund.
[4] The contingent deferred sales charge ("CDSC") is 4.50% if shares are redeemed in less than one year. The CDSC for Investor B Shares decreases for redemptions made in subsequent years. After six years there is no CDSC on Investor B Shares. (See the section "Details About the Share Classes - Investor B Shares" in the Fund's prospectus for a complete schedule of CDSCs.) Investor B Shares automatically convert to Investor A Shares approximately eight years after you buy them and will no longer be subject to distribution fees.
[5] There is no CDSC on Investor C Shares after one year.
[6] As described in the "Management of the Fund" section of the Fund's prospectus on pages 19-23, BlackRock has contractually agreed to waive and/or reimburse fees and/or expenses in order to ensure that management fees payable by the Series will not exceed 0.005% of average daily net assets until May 1, 2013. This agreement may be terminated upon 90 days' notice by a majority of the non-interested directors of the Master LLC or by a vote of a majority of the outstanding voting securities of the Series.
[7] As described in the "Management of the Fund" section of the Fund's prospectus on pages 19-23, 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) for Service Shares as a percentage to average daily net assets to 0.615% until May 1, 2013. The Fund may have to repay some of these waivers and reimbursements to BlackRock in the following two years. The agreement may be terminated upon 90 days' notice by a majority of the non-interested trustees of the Trust or by vote of a majority of the outstanding voting securities of the Fund.