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Label Element Value
Small Cap Stock Index Portfolio  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Fund Summary
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The fund seeks to match the performance of the Standard & Poor's® SmallCap 600 Index (S&P SmallCap 600 Index).

Expense [Heading] rr_ExpenseHeading Fees and Expenses
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. These figures do not reflect any fees or charges imposed by participating insurance companies under their Variable Annuity contracts (VA contracts) or Variable Life Insurance policies (VLI policies), and if such fees and/or charges were included, the fees and expenses would be higher.
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)
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 may indicate higher transaction costs. 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 fund's portfolio turnover rate was 16.90% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 16.90%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

The 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 hold or 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. The Example does not reflect fees and expenses incurred under VA contracts and VLI policies; if they were reflected, the figures in the Example would be higher. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategy
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

To pursue its goal, the fund generally is fully invested in all of the stocks that comprise the S&P SmallCap 600. The fund generally invests in all 600 stocks in the index in proportion to their weighting in the index; however, at times, the fund may invest in a representative sample of stocks included in the index. Under these circumstances, the fund expects to invest in approximately 500 or more of the stocks in the index.


The S&P SmallCap 600 Index is an unmanaged index composed of 600 domestic stocks. S&P weights each company's stock in the index by its market capitalization (i.e., the share price times the number of shares outstanding), adjusted by the number of available float shares (i.e., those shares available to public investors). Companies included in the S&P SmallCap 600 Index generally have market capitalizations ranging between approximately $82 million and $13.6 billion, to the extent consistent with market conditions.


"Standard & Poor's®," "S&P®" and "S&P SmallCap 600® Index" are trademarks of Standard & Poor's Financial Services LLC, and have been licensed for use by the fund. The fund is not sponsored, endorsed, sold or promoted by Standard & Poor's and Standard & Poor's makes no representation regarding the advisability of investing in the fund.

Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the fund is not a bank deposit. It is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency. It is not a complete investment program. The fund's share price fluctuates, sometimes dramatically, which means you could lose money.


· Risks of stock investing. Stocks generally fluctuate more in value than bonds and may decline significantly over short time periods. There is the chance that stock prices overall will decline because stock markets tend to move in cycles, with periods of rising prices and falling prices. The market value of a stock may decline due to general market conditions or because of factors that affect the particular company or the company's industry.


· Indexing strategy risk. The fund uses an indexing strategy. It does not attempt to manage market volatility, use defensive strategies or reduce the effects of any long-term periods of poor index performance. The correlation between fund and index performance may be affected by the fund's expenses and use of sampling techniques, changes in securities markets, changes in the composition of the index and the timing of purchases and redemptions of fund shares.


· Small and midsize company risk. Small and midsize companies carry additional risks because the operating histories of these companies tend to be more limited, their earnings and revenues less predictable (and some companies may be experiencing significant losses), and their share prices more volatile than those of larger, more established companies. The shares of smaller companies tend to trade less frequently than those of larger, more established companies, which can adversely affect the pricing of these securities and the fund's ability to sell these securities.
Risk Lose Money [Text] rr_RiskLoseMoney The fund's share price fluctuates, sometimes dramatically, which means you could lose money.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a bank deposit. It is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the performance of the fund's Service shares from year to year. The table compares the average annual total returns of the fund's shares to those of a broad measure of market performance. The fund's past performance is not necessarily an indication of how the fund will perform in the future. More recent performance information may be available at www.dreyfus.com.


Performance information reflects the fund's expenses only and does not reflect the fees and charges imposed by participating insurance companies under their VA contracts or VLI policies. Because these fees and charges will reduce total return, policyowners should consider them when evaluating and comparing the fund's performance. Policyowners should consult the prospectus for their contract or policy for more information.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table provide some indication of the risks of investing in the fund.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.dreyfus.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund's past performance is not necessarily an indication of how the fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Year-by-Year Total Returns as of 12/31 each year (%) Service Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Performance information reflects the fund's expenses only and does not reflect the fees and charges imposed by participating insurance companies under their VA contracts or VLI policies.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Best Quarter
Q2, 2009: 20.83%

 

Worst Quarter
Q4, 2008: -24.87%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 20.83%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (24.87%)
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes reflects no deductions for fees, expenses or taxes
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns (as of 12/31/17)
Small Cap Stock Index Portfolio | S&P SmallCap 600® Index reflects no deductions for fees, expenses or taxes  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 13.23%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 15.99%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 10.43%
Small Cap Stock Index Portfolio | Small Cap Stock Index Portfolio - Service Shares  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.35%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.03%
Total annual fund operating expenses rr_ExpensesOverAssets 0.63%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.03%) [1]
Total annual fund operating expenses (after fee waiver and/or expense reimbursement) rr_NetExpensesOverAssets 0.60%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 61
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 192
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 335
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 750
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 61
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 192
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 335
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 750
Annual Return 2008 rr_AnnualReturn2008 (30.91%)
Annual Return 2009 rr_AnnualReturn2009 25.03%
Annual Return 2010 rr_AnnualReturn2010 25.83%
Annual Return 2011 rr_AnnualReturn2011 0.56%
Annual Return 2012 rr_AnnualReturn2012 15.74%
Annual Return 2013 rr_AnnualReturn2013 40.72%
Annual Return 2014 rr_AnnualReturn2014 5.12%
Annual Return 2015 rr_AnnualReturn2015 (2.33%)
Annual Return 2016 rr_AnnualReturn2016 25.73%
Annual Return 2017 rr_AnnualReturn2017 12.40%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 12.40%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 15.35%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 9.95%
[1] The fund's investment adviser, The Dreyfus Corporation, has agreed in its investment management agreement with the fund to pay all of the fund's expenses, except management fees, Rule 12b-1 fees and certain other expenses, including the fees and expenses of the non-interested board members and their counsel. The Dreyfus Corporation has further agreed to reduce its fees in an amount equal to the fund's allocable portion of the fees and expenses of the non-interested board members and their counsel (in the amount of 0.03% for the past fiscal year). These provisions in the investment management agreement may not be amended without the approval of the fund's shareholders.