<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.8.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>17</ContextCount>
  <ElementCount>46</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>14</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>2</UnitCount>
  <MyReports>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000000 - Document - Document and Entity Information {Elements}</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DocumentDocumentandEntityInformationElements</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory></MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>000011 - Document - Risk/Return Summary {Unlabeled} - iShares Edge MSCI Multifactor USA Index Fund (Institutional)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DocumentRiskReturnSummaryUnlabelediSharesEdgeMSCIMultifactorUSAIndexFundInstitutional</Role>
      <ShortName>Risk/Return Summary- iShares Edge MSCI Multifactor USA Index Fund (Institutional)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>000019 - Disclosure - Risk/Return Detail Data {Elements} - iShares Edge MSCI Multifactor USA Index Fund (Institutional)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DisclosureRiskReturnDetailDataElementsiSharesEdgeMSCIMultifactorUSAIndexFundInstitutional</Role>
      <ShortName>Risk/Return Detail Data- iShares Edge MSCI Multifactor USA Index Fund (Institutional)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>000021 - Document - Risk/Return Summary {Unlabeled} - iShares Edge MSCI Multifactor Intl Index Fund (Institutional)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DocumentRiskReturnSummaryUnlabelediSharesEdgeMSCIMultifactorIntlIndexFundInstitutional</Role>
      <ShortName>Risk/Return Summary- iShares Edge MSCI Multifactor Intl Index Fund (Institutional)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>000029 - Disclosure - Risk/Return Detail Data {Elements} - iShares Edge MSCI Multifactor Intl Index Fund (Institutional)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DisclosureRiskReturnDetailDataElementsiSharesEdgeMSCIMultifactorIntlIndexFundInstitutional</Role>
      <ShortName>Risk/Return Detail Data- iShares Edge MSCI Multifactor Intl Index Fund (Institutional)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>000031 - Document - Risk/Return Summary {Unlabeled} - iShares Edge MSCI Min Vol USA Index Fund (Institutional)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DocumentRiskReturnSummaryUnlabelediSharesEdgeMSCIMinVolUSAIndexFundInstitutional</Role>
      <ShortName>Risk/Return Summary- iShares Edge MSCI Min Vol USA Index Fund (Institutional)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>000039 - Disclosure - Risk/Return Detail Data {Elements} - iShares Edge MSCI Min Vol USA Index Fund (Institutional)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DisclosureRiskReturnDetailDataElementsiSharesEdgeMSCIMinVolUSAIndexFundInstitutional</Role>
      <ShortName>Risk/Return Detail Data- iShares Edge MSCI Min Vol USA Index Fund (Institutional)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>000041 - Document - Risk/Return Summary {Unlabeled} - iShares Edge MSCI Min Vol EAFE Index Fund (Institutional)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DocumentRiskReturnSummaryUnlabelediSharesEdgeMSCIMinVolEAFEIndexFundInstitutional</Role>
      <ShortName>Risk/Return Summary- iShares Edge MSCI Min Vol EAFE Index Fund (Institutional)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>000049 - Disclosure - Risk/Return Detail Data {Elements} - iShares Edge MSCI Min Vol EAFE Index Fund (Institutional)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DisclosureRiskReturnDetailDataElementsiSharesEdgeMSCIMinVolEAFEIndexFundInstitutional</Role>
      <ShortName>Risk/Return Detail Data- iShares Edge MSCI Min Vol EAFE Index Fund (Institutional)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>000051 - Document - Risk/Return Summary {Unlabeled} - iShares Edge MSCI Multifactor USA Index Fund (Class K)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DocumentRiskReturnSummaryUnlabelediSharesEdgeMSCIMultifactorUSAIndexFundClassK</Role>
      <ShortName>Risk/Return Summary- iShares Edge MSCI Multifactor USA Index Fund (Class K)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>000059 - Disclosure - Risk/Return Detail Data {Elements} - iShares Edge MSCI Multifactor USA Index Fund (Class K)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DisclosureRiskReturnDetailDataElementsiSharesEdgeMSCIMultifactorUSAIndexFundClassK</Role>
      <ShortName>Risk/Return Detail Data- iShares Edge MSCI Multifactor USA Index Fund (Class K)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>000061 - Document - Risk/Return Summary {Unlabeled} - iShares Edge MSCI Multifactor Intl Index Fund (Class K)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DocumentRiskReturnSummaryUnlabelediSharesEdgeMSCIMultifactorIntlIndexFundClassK</Role>
      <ShortName>Risk/Return Summary- iShares Edge MSCI Multifactor Intl Index Fund (Class K)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>000069 - Disclosure - Risk/Return Detail Data {Elements} - iShares Edge MSCI Multifactor Intl Index Fund (Class K)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DisclosureRiskReturnDetailDataElementsiSharesEdgeMSCIMultifactorIntlIndexFundClassK</Role>
      <ShortName>Risk/Return Detail Data- iShares Edge MSCI Multifactor Intl Index Fund (Class K)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>000071 - Document - Risk/Return Summary {Unlabeled} - iShares Edge MSCI Min Vol USA Index Fund (Class K)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DocumentRiskReturnSummaryUnlabelediSharesEdgeMSCIMinVolUSAIndexFundClassK</Role>
      <ShortName>Risk/Return Summary- iShares Edge MSCI Min Vol USA Index Fund (Class K)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>000079 - Disclosure - Risk/Return Detail Data {Elements} - iShares Edge MSCI Min Vol USA Index Fund (Class K)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DisclosureRiskReturnDetailDataElementsiSharesEdgeMSCIMinVolUSAIndexFundClassK</Role>
      <ShortName>Risk/Return Detail Data- iShares Edge MSCI Min Vol USA Index Fund (Class K)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>000081 - Document - Risk/Return Summary {Unlabeled} - iShares Edge MSCI Min Vol EAFE Index Fund (Class K)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DocumentRiskReturnSummaryUnlabelediSharesEdgeMSCIMinVolEAFEIndexFundClassK</Role>
      <ShortName>Risk/Return Summary- iShares Edge MSCI Min Vol EAFE Index Fund (Class K)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>000089 - Disclosure - Risk/Return Detail Data {Elements} - iShares Edge MSCI Min Vol EAFE Index Fund (Class K)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.blackrock.com/role/DisclosureRiskReturnDetailDataElementsiSharesEdgeMSCIMinVolEAFEIndexFundClassK</Role>
      <ShortName>Risk/Return Detail Data- iShares Edge MSCI Min Vol EAFE Index Fund (Class K)</ShortName>
      <MenuCategory></MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="bf1-20171121.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>040000 - Disclosure - Risk/Return Detail Data {Elements}</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/rr/role/RiskReturnDetailData</Role>
      <ShortName>Risk/Return Detail Data</ShortName>
      <MenuCategory></MenuCategory>
      <Position>18</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>bf1-20171121.xml</File>
    <File>bf1-20171121.xsd</File>
    <File>bf1-20171121_cal.xml</File>
    <File>bf1-20171121_def.xml</File>
    <File>bf1-20171121_lab.xml</File>
    <File>bf1-20171121_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://xbrl.sec.gov/rr/2012-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2014-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
