XML 11 R3.htm IDEA: XBRL DOCUMENT v3.8.0.1
Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName BLACKROCK FUNDS
Prospectus Date rr_ProspectusDate Sep. 28, 2017
Supplement [Text Block] bf1_SupplementTextBlock

BLACKROCK FUNDSSM

BlackRock Impact Bond Fund

(the “Fund”)

Supplement dated December 26, 2017 to the Summary Prospectuses, Prospectuses and Statement of Additional Information (“SAI”) of the Fund, dated September 28, 2017

Effective December 29, 2017, BlackRock (as defined below) has agreed contractually to cap net expenses of the Fund at lower levels for the Fund’s Investor A, Investor C, Institutional and Class K Shares. To achieve these expense caps, BlackRock has agreed to waive and/or reimburse fees or expenses if the Fund’s annual fund operating expenses, excluding certain expenses described in the prospectus, exceed a certain limit for the Fund’s Investor A, Investor C, Institutional and Class K Shares. Accordingly, effective December 29, 2017, the Fund’s Summary Prospectuses, Prospectuses and SAI are amended as follows:

The section of the Investor A, Investor C and Institutional Shares Summary Prospectus entitled “Key Facts About BlackRock Impact Bond Fund — Fees and Expenses of the Fund” and the section of the Investor A, Investor C and Institutional Shares Prospectus entitled “Fund Overview — Key Facts About BlackRock Impact Bond Fund — Fees and Expenses of the Fund” are deleted in their entirety and replaced with the following:

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock Advisors, LLC (“BlackRock”) or its affiliates. More information about these and other discounts is available from your financial professional or your selected securities dealer, broker, investment adviser, service provider or industry professional (including BlackRock, The PNC Financial Services Group, Inc. and their respective affiliates) (each a “Financial Intermediary”) and in the “Details About the Share Classes” and the “Intermediary-Defined Sales Charge Waiver Policies” sections on pages 26 and A-1, respectively, of the Fund’s prospectus and in the “Purchase of Shares” section on page II-74 of Part II of the Fund’s Statement of Additional Information.

 

Shareholder Fees
(fees paid directly from your investment)
    Investor A
Shares		   Investor C
Shares		   Institutional
Shares
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)        4.00 %       None       None
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)        None 1       1.00 %2       None
Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your
investment)
    Investor A
Shares		   Investor C
Shares		   Institutional
Shares
Management Fee3        0.30 %       0.30 %       0.30 %
Distribution and/or Service (12b-1) Fees        0.25 %       1.00 %       None
Other Expenses4,5        1.00 %       1.01 %       0.91 %
Acquired Fund Fees and Expenses5        0.01 %       0.01 %       0.01 %
Total Annual Fund Operating Expenses5        1.56 %       2.32 %       1.22 %
Fee Waivers and/or Expense Reimbursements3,6        (0.89 )%       (0.90 )%       (0.80 )%
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements3,6        0.67 %       1.42 %       0.42 %
1  A contingent deferred sales charge (“CDSC”) of 0.50% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.
2  There is no CDSC on Investor C Shares after one year.
3 
As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 41, 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 September 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.
4  Other Expenses have been restated to reflect current fees.
5  The Total Annual Fund Operating Expenses do not correlate to the ratios of expenses to average net assets given in the Fund’s most recent annual report, which do not include Acquired Fund Fees and Expenses or the restatement of Other Expenses to reflect current fees.
6  As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 41, 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 0.66% of average daily net assets (for Investor A Shares), 1.41% of average daily net assets (for Investor C Shares) and 0.41% of average daily net assets (for Institutional Shares) through September 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.

Example:

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:

 

      1 Year        3 Years        5 Years        10 Years  
Investor A Shares    $ 466        $ 789        $ 1,135        $ 2,110  
Investor C Shares    $ 245        $ 638        $ 1,159        $ 2,587  
Institutional Shares    $ 43        $ 308        $ 593        $ 1,406  

You would pay the following expenses if you did not redeem your shares:

 

      1 Year        3 Years        5 Years        10 Years  
Investor C Shares    $ 145        $ 638        $ 1,159        $ 2,587  

Portfolio Turnover:

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. For the period August 23, 2016 (commencement of operations) through May 31, 2017, the Fund’s portfolio turnover rate was 470% of the average value of its portfolio.

The section of the Class K Shares Summary Prospectus entitled “Key Facts About BlackRock Impact Bond Fund — Fees and Expenses of the Fund” and the section of the Class K Shares Prospectus entitled “Fund Overview — Key Facts About BlackRock Impact Bond Fund — Fees and Expenses of the Fund” are deleted in their entirety and replaced with the following:

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold Class K Shares of the Fund.

 

Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your investment)
    Class K
Shares
Management Fee1        0.30 %
Distribution and/or Service (12b-1) Fees        None
Other Expenses2,3        1.02 %
Acquired Fund Fees and Expenses3        0.01 %
Total Annual Fund Operating Expenses3        1.33 %
Fee Waivers and/or Expense Reimbursements1,4        (0.96 )%
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements1,4        0.37 %
1  As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 31, 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 September 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  Other Expenses have been restated to reflect current fees.
3  The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Fund’s most recent annual report, which does not include Acquired Fund Fees and Expenses or the restatement of Other Expenses to reflect current fees.
4  As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 31, 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 0.36% of average daily net assets through September 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.

Example:

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:

 

      1 Year        3 Years        5 Years        10 Years  
Class K Shares    $ 38        $ 326        $ 637        $ 1,517  

Portfolio Turnover:

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. For the period August 23, 2016 (commencement of operations) through May 31, 2017, the Fund’s portfolio turnover rate was 470% of the average value of its portfolio.

Investor A, C and Institutional | BlackRock Impact Bond Fund  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] bf1_SupplementTextBlock

BLACKROCK FUNDSSM

BlackRock Impact Bond Fund

(the “Fund”)

Supplement dated December 26, 2017 to the Summary Prospectuses, Prospectuses and Statement of Additional Information (“SAI”) of the Fund, dated September 28, 2017

Effective December 29, 2017, BlackRock (as defined below) has agreed contractually to cap net expenses of the Fund at lower levels for the Fund’s Investor A, Investor C, Institutional and Class K Shares. To achieve these expense caps, BlackRock has agreed to waive and/or reimburse fees or expenses if the Fund’s annual fund operating expenses, excluding certain expenses described in the prospectus, exceed a certain limit for the Fund’s Investor A, Investor C, Institutional and Class K Shares. Accordingly, effective December 29, 2017, the Fund’s Summary Prospectuses, Prospectuses and SAI are amended as follows:

The section of the Investor A, Investor C and Institutional Shares Summary Prospectus entitled “Key Facts About BlackRock Impact Bond Fund — Fees and Expenses of the Fund” and the section of the Investor A, Investor C and Institutional Shares Prospectus entitled “Fund Overview — Key Facts About BlackRock Impact Bond Fund — Fees and Expenses of the Fund” are deleted in their entirety and replaced with the following:

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock Advisors, LLC (“BlackRock”) or its affiliates. More information about these and other discounts is available from your financial professional or your selected securities dealer, broker, investment adviser, service provider or industry professional (including BlackRock, The PNC Financial Services Group, Inc. and their respective affiliates) (each a “Financial Intermediary”) and in the “Details About the Share Classes” and the “Intermediary-Defined Sales Charge Waiver Policies” sections on pages 26 and A-1, respectively, of the Fund’s prospectus and in the “Purchase of Shares” section on page II-74 of Part II of the Fund’s Statement of Additional Information.

 

Shareholder Fees
(fees paid directly from your investment)
    Investor A
Shares		   Investor C
Shares		   Institutional
Shares
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)        4.00 %       None       None
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)        None 1       1.00 %2       None
Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your
investment)
    Investor A
Shares		   Investor C
Shares		   Institutional
Shares
Management Fee3        0.30 %       0.30 %       0.30 %
Distribution and/or Service (12b-1) Fees        0.25 %       1.00 %       None
Other Expenses4,5        1.00 %       1.01 %       0.91 %
Acquired Fund Fees and Expenses5        0.01 %       0.01 %       0.01 %
Total Annual Fund Operating Expenses5        1.56 %       2.32 %       1.22 %
Fee Waivers and/or Expense Reimbursements3,6        (0.89 )%       (0.90 )%       (0.80 )%
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements3,6        0.67 %       1.42 %       0.42 %
1  A contingent deferred sales charge (“CDSC”) of 0.50% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.
2  There is no CDSC on Investor C Shares after one year.
3 
As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 41, 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 September 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.
4  Other Expenses have been restated to reflect current fees.
5  The Total Annual Fund Operating Expenses do not correlate to the ratios of expenses to average net assets given in the Fund’s most recent annual report, which do not include Acquired Fund Fees and Expenses or the restatement of Other Expenses to reflect current fees.
6  As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 41, 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 0.66% of average daily net assets (for Investor A Shares), 1.41% of average daily net assets (for Investor C Shares) and 0.41% of average daily net assets (for Institutional Shares) through September 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.

Example:

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:

 

      1 Year        3 Years        5 Years        10 Years  
Investor A Shares    $ 466        $ 789        $ 1,135        $ 2,110  
Investor C Shares    $ 245        $ 638        $ 1,159        $ 2,587  
Institutional Shares    $ 43        $ 308        $ 593        $ 1,406  

You would pay the following expenses if you did not redeem your shares:

 

      1 Year        3 Years        5 Years        10 Years  
Investor C Shares    $ 145        $ 638        $ 1,159        $ 2,587  

Portfolio Turnover:

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. For the period August 23, 2016 (commencement of operations) through May 31, 2017, the Fund’s portfolio turnover rate was 470% of the average value of its portfolio.

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. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock Advisors, LLC (“BlackRock”) or its affiliates. More information about these and other discounts is available from your financial professional or your selected securities dealer, broker, investment adviser, service provider or industry professional (including BlackRock, The PNC Financial Services Group, Inc. and their respective affiliates) (each a “Financial Intermediary”) and in the “Details About the Share Classes” and the “Intermediary-Defined Sales Charge Waiver Policies” sections on pages 26 and A-1, respectively, of the Fund’s prospectus and in the “Purchase of Shares” section on page II-74 of Part II of the Fund’s Statement of Additional Information.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees
(fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your
investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination September 30, 2019
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. For the period August 23, 2016 (commencement of operations) through May 31, 2017, the Fund’s portfolio turnover rate was 470% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 470.00%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock A contingent deferred sales charge (“CDSC”) of 0.50% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock Advisors, LLC (“BlackRock”) or its affiliates.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 25,000
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent Other Expenses have been restated to reflect current fees.
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees The Total Annual Fund Operating Expenses do not correlate to the ratios of expenses to average net assets given in the Fund’s most recent annual report, which do not include Acquired Fund Fees and Expenses or the restatement of Other Expenses to reflect current fees.
Expense Example [Heading] rr_ExpenseExampleHeading Example:
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption You would pay the following expenses if you did not redeem your shares:
Investor A, C and Institutional | BlackRock Impact Bond Fund | Investor A Shares  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.00%
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none [1]
Management Fee rr_ManagementFeesOverAssets 0.30% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 1.00% [3],[4]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01% [4]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.56% [4]
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.89%) [2],[5]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 0.67% [2],[5]
1 Year rr_ExpenseExampleYear01 $ 466
3 Years rr_ExpenseExampleYear03 789
5 Years rr_ExpenseExampleYear05 1,135
10 Years rr_ExpenseExampleYear10 $ 2,110
Investor A, C and Institutional | BlackRock Impact Bond Fund | Investor C Shares  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [6]
Management Fee rr_ManagementFeesOverAssets 0.30% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 1.01% [3],[4]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01% [4]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.32% [4]
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.90%) [2],[5]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 1.42% [2],[5]
1 Year rr_ExpenseExampleYear01 $ 245
3 Years rr_ExpenseExampleYear03 638
5 Years rr_ExpenseExampleYear05 1,159
10 Years rr_ExpenseExampleYear10 2,587
1 Year rr_ExpenseExampleNoRedemptionYear01 145
3 Years rr_ExpenseExampleNoRedemptionYear03 638
5 Years rr_ExpenseExampleNoRedemptionYear05 1,159
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,587
Investor A, C and Institutional | BlackRock Impact Bond Fund | Institutional Shares  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fee rr_ManagementFeesOverAssets 0.30% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.91% [3],[4]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01% [4]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.22% [4]
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.80%) [2],[5]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 0.42% [2],[5]
1 Year rr_ExpenseExampleYear01 $ 43
3 Years rr_ExpenseExampleYear03 308
5 Years rr_ExpenseExampleYear05 593
10 Years rr_ExpenseExampleYear10 $ 1,406
Class K | BlackRock Impact Bond Fund  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] bf1_SupplementTextBlock

BLACKROCK FUNDSSM

BlackRock Impact Bond Fund

(the “Fund”)

Supplement dated December 26, 2017 to the Summary Prospectuses, Prospectuses and Statement of Additional Information (“SAI”) of the Fund, dated September 28, 2017

Effective December 29, 2017, BlackRock (as defined below) has agreed contractually to cap net expenses of the Fund at lower levels for the Fund’s Investor A, Investor C, Institutional and Class K Shares. To achieve these expense caps, BlackRock has agreed to waive and/or reimburse fees or expenses if the Fund’s annual fund operating expenses, excluding certain expenses described in the prospectus, exceed a certain limit for the Fund’s Investor A, Investor C, Institutional and Class K Shares. Accordingly, effective December 29, 2017, the Fund’s Summary Prospectuses, Prospectuses and SAI are amended as follows:

The section of the Class K Shares Summary Prospectus entitled “Key Facts About BlackRock Impact Bond Fund — Fees and Expenses of the Fund” and the section of the Class K Shares Prospectus entitled “Fund Overview — Key Facts About BlackRock Impact Bond Fund — Fees and Expenses of the Fund” are deleted in their entirety and replaced with the following:

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold Class K Shares of the Fund.

 

Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your investment)
    Class K
Shares
Management Fee1        0.30 %
Distribution and/or Service (12b-1) Fees        None
Other Expenses2,3        1.02 %
Acquired Fund Fees and Expenses3        0.01 %
Total Annual Fund Operating Expenses3        1.33 %
Fee Waivers and/or Expense Reimbursements1,4        (0.96 )%
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements1,4        0.37 %
1  As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 31, 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 September 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  Other Expenses have been restated to reflect current fees.
3  The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Fund’s most recent annual report, which does not include Acquired Fund Fees and Expenses or the restatement of Other Expenses to reflect current fees.
4  As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 31, 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 0.36% of average daily net assets through September 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.

Example:

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:

 

      1 Year        3 Years        5 Years        10 Years  
Class K Shares    $ 38        $ 326        $ 637        $ 1,517  

Portfolio Turnover:

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. For the period August 23, 2016 (commencement of operations) through May 31, 2017, the Fund’s portfolio turnover rate was 470% of the average value of its portfolio.

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 Class K 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 September 30, 2019
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. For the period August 23, 2016 (commencement of operations) through May 31, 2017, the Fund’s portfolio turnover rate was 470% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 470.00%
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent Other Expenses have been restated to reflect current fees.
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Fund’s most recent annual report, which does not include Acquired Fund Fees and Expenses or the restatement of Other Expenses to reflect current fees.
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:
Class K | BlackRock Impact Bond Fund | Class K Shares  
Risk/Return: rr_RiskReturnAbstract  
Management Fee rr_ManagementFeesOverAssets 0.30% [7]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 1.02% [3],[8]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01% [8]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.33% [8]
Fee Waivers and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.96%) [7],[9]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements rr_NetExpensesOverAssets 0.37% [7],[9]
1 Year rr_ExpenseExampleYear01 $ 38
3 Years rr_ExpenseExampleYear03 326
5 Years rr_ExpenseExampleYear05 637
10 Years rr_ExpenseExampleYear10 $ 1,517
[1] A contingent deferred sales charge (“CDSC”) of 0.50% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.
[2] As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 41, 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 September 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.
[3] Other Expenses have been restated to reflect current fees.
[4] The Total Annual Fund Operating Expenses do not correlate to the ratios of expenses to average net assets given in the Fund’s most recent annual report, which do not include Acquired Fund Fees and Expenses or the restatement of Other Expenses to reflect current fees.
[5] As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 41, 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 0.66% of average daily net assets (for Investor A Shares), 1.41% of average daily net assets (for Investor C Shares) and 0.41% of average daily net assets (for Institutional Shares) through September 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.
[6] There is no CDSC on Investor C Shares after one year.
[7] As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 31, 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 September 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.
[8] The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Fund’s most recent annual report, which does not include Acquired Fund Fees and Expenses or the restatement of Other Expenses to reflect current fees.
[9] As described in the “Management of the Fund” section of the Fund’s prospectus beginning on page 31, 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 0.36% of average daily net assets through September 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.