Prospectus: Series [Axis] Series S000001870 Member BlackRock Managed Volatility Portfolio BLACKROCK MANAGED VOLATILITY PORTFOLIO. Document [Axis] Prospectus Prospectus One Member Investor A, B, C and Institutional Shares Prospectus One. Risk/Return: Risk/Return [Heading] Objective [Heading] Objective, Primary [Text Block] Expense [Heading] Expense Narrative [Text Block] Shareholder Fees Caption [Text] Shareholder Fees [Table] Operating Expenses Caption [Text] Annual Fund Operating Expenses [Table] Expense Example [Heading] Expense Example Narrative [Text Block] Expense Example, With Redemption [Table] Expense Example, No Redemption [Table] Portfolio Turnover [Heading] Portfolio Turnover [Text Block] Strategy [Heading] Strategy Narrative [Text Block] Risk [Heading] Risk Narrative [Text Block] Bar Chart and Performance Table [Heading] Performance Narrative [Text Block] Bar Chart [Heading] Bar Chart [Table] Bar Chart Closing [Text Block] Performance Table Heading Performance Table Narrative Performance [Table] Share Class [Axis] Share Classes C000004880 Member Investor A Shares BLACKROCK MANAGED VOLATILITY PORTFOLIO, INVESTOR A. C000004881 Member Investor B Shares BLACKROCK MANAGED VOLATILITY PORTFOLIO, INVESTOR B. C000004882 Member Investor C Shares BLACKROCK MANAGED VOLATILITY PORTFOLIO, INVESTOR C. C000004878 Member Institutional Shares BLACKROCK MANAGED VOLATILITY PORTFOLIO, INSTITUTIONAL. Shareholder Fees: Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price) Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower) Maximum Deferred Sales Charge (as a percentage of Offering Price) Operating Expenses: Management Fee Management Fees (as a percentage of Assets) Distribution and/or Service (12b-1) Fees Distribution and Service (12b-1) Fees Component1 Other Expenses Interest Expense Miscellaneous Other Expenses Component2 Other Expenses Other Expenses (as a percentage of Assets): Other Expenses Other Expenses Acquired Fund Fees and Expenses Acquired Fund Fees and Expenses Total Annual Fund Operating Expenses Expenses (as a percentage of Assets) Fee Waiver or Reimbursement Fee Waivers and/or Expense Reimbursements Fee Waivers and/or Expense Reimbursements Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements Net Expenses (as a percentage of Assets) Expense Example: 1 Year 1 Year Expense Example, with Redemption, 1 Year 3 Years 3 Years Expense Example, with Redemption, 3 Years 5 Years 5 Years Expense Example, with Redemption, 5 Years 10 Years 10 Years Expense Example, with Redemption, 10 Years Expense Example, No Redemption: 1 Year 1 Year Expense Example, No Redemption, 1 Year 3 Years 3 Years Expense Example, No Redemption, 3 Years 5 Years 5 Years Expense Example, No Redemption, 5 Years 10 Years 10 Years Expense Example, No Redemption, 10 Years Bar Chart Table: 2002 Annual Return 2002 2003 Annual Return 2003 2004 Annual Return 2004 2005 Annual Return 2005 2006 Annual Return 2006 2007 Annual Return 2007 2008 Annual Return 2008 2009 Annual Return 2009 2010 Annual Return 2010 2011 Annual Return 2011 Performance Measure [Axis] Performance Measure Return After Taxes on Distributions After Taxes on Distributions Return After Taxes on Distributions and Sale of Shares After Taxes on Distributions and Sales S And P Five Zero Zero Index Member S&P 500 Index (Reflects no deduction for fees, expenses or taxes) S And P Five Zero Zero Index. Barclays U S Aggregate Bond Index Member Barclays U.S. Aggregate Bond Index (Reflects no deduction for fees, expenses or taxes) Barclays U S Aggregate Bond Index. Msci Acwi Index Member MSCI ACWI Index (Reflects no deduction for fees, expenses or taxes) Msci Acwi Index. Citigroup Wgbi Hedged Into Usd Member Citigroup WGBI (hedged into USD) (Reflects no deduction for fees, expenses or taxes) Citigroup Wgbi Hedged Into Usd. Six Zero Percentage S And P Five Zero Zero Index Four Zero Percentage Barclays U S Aggregate Bond Index Member 60% S&P 500 Index/40% Barclays U.S. Aggregate Bond Index (Reflects no deduction for fees, expenses or taxes) Six Zero Percentage S And P Five Zero Zero Index Four Zero Percentage Barclays U S Aggregate Bond Index. Six Zero Percentage Msci Acwi Index Four Zero Zero Barclays U S Aggregate Bond Index Member 60% MSCI ACWI Index/40% Barclays U.S. Aggregate Bond Index (Reflects no deduction for fees, expenses or taxes) Six Zero Percentage Msci Acwi Index Four Zero Zero Barclays U S Aggregate Bond Index. Six Zero Percentage Msci Acwi Index Four Zero Percentage Citigroup Wgbi Hedged Into Usd Member 60% MSCI ACWI Index/40% Citigroup WGBI (hedged into USD) (Reflects no deduction for fees, expenses or taxes) Six Zero Percentage Msci Acwi Index Four Zero Percentage Citigroup Wgbi hedged into Usd. Average Annual Return: 1 Year 5 Years 10 Years Document Type Document Period End Date Registrant Name Central Index Key Amendment Flag Document Creation Date Document Effective Date Prospectus Date Fee Waiver or Reimbursement over Assets, Date of Termination Portfolio Turnover, Rate Expense Breakpoint Discounts [Text] Expense Breakpoint, Minimum Investment Required [Amount] Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] Risk Lose Money [Text] Performance Information Illustrates Variability of Returns [Text] Performance Availability Phone [Text] Performance Availability Website Address [Text] Performance Past Does Not Indicate Future [Text] Year to Date Return, Label Bar Chart, Year to Date Return, Date Bar Chart, Year to Date Return Highest Quarterly Return, Label Highest Quarterly Return, Date Highest Quarterly Return Lowest Quarterly Return, Label Lowest Quarterly Return, Date Lowest Quarterly Return Performance Table Uses Highest Federal Rate Performance Table Not Relevant to Tax Deferred Performance Table One Class of after Tax Shown [Text] Prospectus Two Member Service Prospectus Two. C000004879 Member Service Shares Black Rock Managed Volatility Portfolio, Service Shares. Bar Chart Does Not Reflect Sales Loads [Text] Risk Narrative One Text Block Risk Narrative One. Risk Narrative [Text Block] Expense Example, No Redemption, By Year, Caption [Text] Performance Table Does Reflect Sales Loads Expenses Restated to Reflect Current [Text]