3.22.2.2 html 19 85 1 true 13 0 false 2 false false R1.htm 000000 - Document - Document and Entity Information {Elements} Sheet http://www.blackrock.com/role/DocumentDocumentandEntityInformationElements000000 Document and Entity Information 1 false false R2.htm 000021 - Disclosure - Risk/Return Detail Data {Elements} - BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO (Investor A, C, Institutional and Class R) Sheet http://www.blackrock.com/role/DisclosureRiskReturnDetailDataElementsBLACKROCKHEALTHSCIENCESOPPORTUNITIESPORTFOLIOInvestorACInstitutionalandClassR Risk/Return Detail Data- BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO (Investor A, C, Institutional and Class R) 2 false false R3.htm 000041 - Disclosure - Risk/Return Detail Data {Elements} - BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO (Class K) Sheet http://www.blackrock.com/role/DisclosureRiskReturnDetailDataElementsBLACKROCKHEALTHSCIENCESOPPORTUNITIESPORTFOLIOClassK000041 Risk/Return Detail Data- BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO (Class K) 3 false false R4.htm 000061 - Disclosure - Risk/Return Detail Data {Elements} - BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO (Service) Sheet http://www.blackrock.com/role/DisclosureRiskReturnDetailDataElementsBLACKROCKHEALTHSCIENCESOPPORTUNITIESPORTFOLIOService Risk/Return Detail Data- BLACKROCK HEALTH SCIENCES OPPORTUNITIES PORTFOLIO (Service) 4 false false All Reports Book All Reports d300208d485bpos.htm bf12-20220922.xsd bf12-20220922_cal.xml bf12-20220922_def.xml bf12-20220922_lab.xml bf12-20220922_pre.xml d300208dex9910a.htm g300208bar.jpg g300208c000004914_dgf.jpg g300208g1bar.jpg g300208g1cnew_dgf.jpg g300208g1imgbb3060471.gif g300208g2bar.jpg g300208g2c000004913_dgf.jpg g300208g2imgebd8a2441.gif g300208img269909be1.gif http://xbrl.sec.gov/dei/2021 http://xbrl.sec.gov/rr/2021 true true