Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	ALLIANCEBERNSTEIN CAP FUND, INC.
Prospectus Date	rr_ProspectusDate	Jul. 31, 2012
AllianceBernstein Emerging Markets Multi-Asset Portfolio
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY INFORMATION ALLIANCEBERNSTEIN EMERGING MARKETS MULTI-ASSET PORTFOLIO
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund’s investment objective is to maximize total return. Total return is the sum of capital appreciation and income.
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 reductions if you and members of your family invest, or agree to invest in the future, at least $100,000 in AllianceBernstein Mutual Funds. More information about these and other discounts is available from your financial intermediary and in Investing in the Fund--Sales Charge Reduction Programs for Class A Shares on page 22 of this Prospectus and in Purchase of Shares--Sales Charge Reduction Programs on page 77 of the Fund’s Statement of Additional Information (“SAI”).
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	August 31, 2014
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	PORTFOLIO TURNOVER
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys or 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 transaction costs, which are not reflected in the Annual Fund Operating Expenses or in the Examples, affect the Fund’s performance. During the most recent fiscal period, the Fund’s portfolio turnover rate was 48% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	48.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge reductions if you and members of your family invest, or agree to invest in the future, at least $100,000 in AllianceBernstein Mutual Funds.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	100,000
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLES
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The Examples are intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Examples assume 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 Examples also assume that your investment has a 5% return each year, that the Fund’s operating expenses stay the same and that the fee waiver is in effect for the first three years. 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	For the share class listed below, you would pay the following expenses if you did not redeem your shares at the end of the period.
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund invests at least 80% of its net assets under normal circumstances in securities of emerging market issuers and/or the currencies of emerging market countries. Examples of emerging market countries include Argentina, Brazil, Chile, Croatia, Egypt, Hong Kong, India, Indonesia, Israel, Kazakhstan, Malaysia, Mexico, the People’s Republic of China, Peru, the Philippines, Poland, Russia, South Africa, South Korea, Taiwan, Thailand, Turkey and Venezuela. Investing in emerging markets generally involves risks greater than investing in the markets of developed countries. The Fund may invest up to 20% of its net assets in the securities of developed market issuers. The Fund invests in equity securities, debt securities and currencies, and does not attempt to maintain a constant or relatively constant allocation among these asset classes. Rather, allocations among asset classes are adjusted based on the Adviser’s view of the relative attractiveness of the asset classes. These allocations are informed by the Adviser’s proprietary asset allocation tools, which are comprised of a series of volatility, correlation and expected return forecasts. The Adviser reviews potential Fund investments in each asset class holistically from a country, currency, sector and security standpoint to optimize overall portfolio construction. Under normal circumstances, the Fund will invest between 30% and 95% of its net assets in equity securities, and between 0% and 65% of its net assets in debt securities, with any remainder held in cash (including foreign currency). The Fund is not constrained based on the country, region, market capitalization, credit quality or duration of its investments, and its assets may at times be concentrated in a particular country or region. The process for selecting equity securities for the Fund is primarily bottom-up. The Adviser seeks to identify stocks that are attractive based on valuation, profitability, earnings quality, business trends, price momentum and other measures. The process for selecting debt securities for the Fund is more top-down. The Adviser believes that inefficiencies in the global debt markets arise from investor emotion, market complexity and conflicting investment agendas. The Adviser combines quantitative forecasts with fundamental credit and economic research in seeking to exploit these inefficiencies. The Adviser seeks to generate returns from the Fund’s fixed-income investments through a combination of country selection, currency allocation, sector analysis and security selection. Debt securities may include those of both corporate and governmental issuers, and may include below investment grade debt securities (“junk bonds”). The Fund may invest in debt securities with a range of maturities from short- to long-term. The Adviser considers both quantitative and fundamental factors in adjusting the Fund’s currency exposures. In addition to the Fund’s currency exposure that results from its investments in equity and debt securities denominated in foreign currencies (and any related hedging), the Fund may hold foreign currency (or related derivatives) independently of any such investments, and may hold a currency even if the Fund does not hold any securities denominated in that currency. The Fund expects to utilize derivatives, such as futures, forwards and swaps, and invest in exchange-traded funds, or ETFs, to a significant extent. Derivatives and ETFs may provide more efficient and economical exposure to market segments than direct investments, and may also be a quicker and more efficient way to alter the portfolio’s exposure than buying and selling direct investments. In determining when and to what extent to enter into derivatives transactions or to invest in ETFs, the Adviser will consider factors such as the relative risks and returns expected of potential investments and the cost of such transactions. Derivatives may also be used for hedging purposes, including to hedge against interest rate, credit and currency fluctuations. The Adviser also expects to use derivatives frequently to effectively leverage the Fund by creating aggregate exposure somewhat in excess of the Fund’s net assets. The notional value of derivatives and ETFs linked to emerging market securities or currencies are counted towards meeting the percentage minimums and ranges set forth above, including the requirement that the Fund invest at least 80% of its net assets in the securities of emerging market issuers and/or the currencies of emerging market countries.
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	EMERGING MARKET RISK: Investments in emerging market countries may involve more risk than investments in other foreign countries because the markets in emerging market countries are less developed and less liquid as well as being subject to increased economic, political, regulatory, or other uncertainties. MARKET RISK: The value of the Fund’s assets will fluctuate as the stock, bond or currency markets fluctuate. The value of the Fund’s investments may decline, sometimes rapidly and unpredictably, simply because of economic changes or other events that affect large portions of the market. FOREIGN (NON-U.S.) RISK: Investments in securities of non-U.S. issuers may involve more risk than those of U.S. issuers. These securities may fluctuate more widely in price and may be less liquid due to adverse market, economic, political, regulatory or other factors. CURRENCY RISK: Fluctuations in currency exchange rates may negatively affect the value of the Fund’s investments or reduce its returns. Emerging market currencies may be more volatile and less liquid, and subject to significantly greater risk of currency controls and convertibility restrictions, than currencies of developed countries. COUNTRY CONCENTRATION RISK: The Fund may not always be diversified among countries or geographic regions and the effect on the Fund’s net asset value (“NAV”) of the specific risks identified above, such as political, regulatory and currency risks, may be magnified due to concentration of the Fund’s investments in a particular country or region. ALLOCATION RISK: The allocation of Fund assets among different asset classes, such as equity securities, debt securities and currencies, may have a significant effect on the Fund’s NAV when one of these asset classes is performing better or worse than others. The diversification benefits typically associated with investing in both equity and debt securities may be limited in the emerging markets context, as movements in emerging market equity and emerging market debt markets may be more correlated than movements in the equity and debt markets of developed countries. CAPITALIZATION RISK: Investments in small- and mid-capitalization companies may be more volatile than investments in large-capitalization companies. Investments in small-capitalization companies may have additional risks because these companies have limited product lines, markets or financial resources. INTEREST RATE RISK: Changes in interest rates will affect the value of investments in fixed-income securities. When interest rates rise, the value of existing investments in fixed-income securities tends to fall and this decrease in value may not be offset by higher income from new investments. Interest rate risk is generally greater for fixed-income securities with longer maturities or durations. CREDIT RISK: An issuer or guarantor of a fixed-income security, or the counterparty to a derivatives or other contract, may be unable or unwilling to make timely payments of interest or principal, or to otherwise honor its obligations. The issuer or guarantor may default, causing a loss of the full principal amount of a security. The degree of risk for a particular security may be reflected in its credit rating. There is the possibility that the credit rating of a fixed-income security may be downgraded after purchase, which may adversely affect the value of the security. BELOW INVESTMENT GRADE SECURITIES: Investments in fixed-income securities with lower ratings (commonly known as “junk bonds”) tend to have a higher probability that an issuer will default or fail to meet its payment obligations. These securities may be subject to greater price volatility due to factors such as specific corporate developments, interest rate sensitivity, negative perceptions of the junk bond market generally, and less secondary market liquidity. DERIVATIVES RISK: Investments in derivatives may be illiquid, difficult to price, and leveraged so that small changes may produce disproportionate losses for the Fund, and may be subject to counterparty risk to a greater degree than more traditional investments. LEVERAGE RISK: To the extent the Fund uses leveraging techniques, its NAV may be more volatile because leverage tends to exaggerate the effect of changes in interest rates and any increase or decrease in the value of the Fund’s investments. LIQUIDITY RISK: Liquidity risk exists when particular investments are difficult to purchase or sell, possibly preventing the Fund from selling out of these illiquid securities at an advantageous price. Derivatives and securities involving substantial market and credit risk tend to involve greater liquidity risk. DIVERSIFICATION RISK: The Fund may have more risk because it is “non-diversified”, meaning that it can invest more of its assets in a smaller number of issuers. MANAGEMENT RISK: The Fund is subject to management risk because it is an actively managed investment fund. The Adviser will apply its investment techniques and risk analyses in making investment decisions, but there is no guarantee that its techniques will produce the intended results. As with all investments, you may lose money by investing in the Fund.
Risk Lose Money [Text]	rr_RiskLoseMoney	As with all investments, you may lose money by investing in the Fund.
Risk Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	DIVERSIFICATION RISK: The Fund may have more risk because it is “non-diversified”, meaning that it can invest more of its assets in a smaller number of issuers.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	PERFORMANCE INFORMATION
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	No performance information is available for the Fund because it has not yet been in operation for a full calendar year.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	No performance information is available for the Fund because it has not yet been in operation for a full calendar year.
AllianceBernstein Emerging Markets Multi-Asset Portfolio | CLASS A
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	4.25%
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOther	none	[1]
Exchange Fee	rr_ExchangeFee	none
Management Fees	rr_ManagementFeesOverAssets	1.00%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.30%
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.14%
Other Expenses	rr_Component2OtherExpensesOverAssets	2.88%
Total Other Expenses	rr_OtherExpensesOverAssets	3.02%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	4.32%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(2.67%)	[2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	1.65%
After 1 Year	rr_ExpenseExampleYear01	586
After 3 Years	rr_ExpenseExampleYear03	921
After 5 Years	rr_ExpenseExampleYear05	1,817
After 10 Years	rr_ExpenseExampleYear10	4,110
AllianceBernstein Emerging Markets Multi-Asset Portfolio | CLASS C
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 offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[3]
Exchange Fee	rr_ExchangeFee	none
Management Fees	rr_ManagementFeesOverAssets	1.00%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.14%
Other Expenses	rr_Component2OtherExpensesOverAssets	3.00%
Total Other Expenses	rr_OtherExpensesOverAssets	3.14%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	5.14%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(2.79%)	[2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	2.35%
After 1 Year	rr_ExpenseExampleYear01	338
After 3 Years	rr_ExpenseExampleYear03	720
After 5 Years	rr_ExpenseExampleYear05	1,771
After 10 Years	rr_ExpenseExampleYear10	4,385
After 1 Year	rr_ExpenseExampleNoRedemptionYear01	238
After 3 Years	rr_ExpenseExampleNoRedemptionYear03	720
After 5 Years	rr_ExpenseExampleNoRedemptionYear05	1,771
After 10 Years	rr_ExpenseExampleNoRedemptionYear10	4,385
AllianceBernstein Emerging Markets Multi-Asset Portfolio | ADVISOR CLASS
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 offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOther	none
Exchange Fee	rr_ExchangeFee	none
Management Fees	rr_ManagementFeesOverAssets	1.00%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.13%
Other Expenses	rr_Component2OtherExpensesOverAssets	2.96%
Total Other Expenses	rr_OtherExpensesOverAssets	3.09%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	4.09%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(2.74%)	[2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	1.35%
After 1 Year	rr_ExpenseExampleYear01	137
After 3 Years	rr_ExpenseExampleYear03	420
After 5 Years	rr_ExpenseExampleYear05	1,291
After 10 Years	rr_ExpenseExampleYear10	3,540
AllianceBernstein Emerging Markets Multi-Asset Portfolio | CLASS R
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 offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOther	none
Exchange Fee	rr_ExchangeFee	none
Management Fees	rr_ManagementFeesOverAssets	1.00%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.14%
Other Expenses	rr_Component2OtherExpensesOverAssets	3.07%
Total Other Expenses	rr_OtherExpensesOverAssets	3.21%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	4.71%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(2.86%)	[2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	1.85%
After 1 Year	rr_ExpenseExampleYear01	188
After 3 Years	rr_ExpenseExampleYear03	571
After 5 Years	rr_ExpenseExampleYear05	1,551
After 10 Years	rr_ExpenseExampleYear10	4,026
AllianceBernstein Emerging Markets Multi-Asset Portfolio | CLASS K
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 offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOther	none
Exchange Fee	rr_ExchangeFee	none
Management Fees	rr_ManagementFeesOverAssets	1.00%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.05%
Other Expenses	rr_Component2OtherExpensesOverAssets	3.06%
Total Other Expenses	rr_OtherExpensesOverAssets	3.11%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	4.36%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(2.76%)	[2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	1.60%
After 1 Year	rr_ExpenseExampleYear01	163
After 3 Years	rr_ExpenseExampleYear03	496
After 5 Years	rr_ExpenseExampleYear05	1,415
After 10 Years	rr_ExpenseExampleYear10	3,764
AllianceBernstein Emerging Markets Multi-Asset Portfolio | CLASS I
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 offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOther	none
Exchange Fee	rr_ExchangeFee	none
Management Fees	rr_ManagementFeesOverAssets	1.00%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.03%
Other Expenses	rr_Component2OtherExpensesOverAssets	3.06%
Total Other Expenses	rr_OtherExpensesOverAssets	3.09%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	4.09%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(2.74%)	[2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	1.35%
After 1 Year	rr_ExpenseExampleYear01	137
After 3 Years	rr_ExpenseExampleYear03	420
After 5 Years	rr_ExpenseExampleYear05	1,291
After 10 Years	rr_ExpenseExampleYear10	3,540

[1] In some cases, a 1%, 1-year contingent deferred sales charge, or CDSC, may apply. CDSCs for Class A shares may also be subject to waiver in certain circumstances.

[2] The Adviser has agreed to waive its management fees and/or to bear expenses of the Fund through March 31, 2015 to the extent necessary to prevent total Fund operating expenses, on an annualized basis, from exceeding the net expenses reflected in this table. The fee waiver and expense reimbursement apply to total annual fund operating expenses (excluding interest expense, acquired fund fees and expenses, taxes and extraordinary expenses). Any fees waived and expenses borne by the Adviser may be reimbursed by the Fund until August 31, 2014, provided that no reimbursement payment will be made that would cause the Fund's total annual Fund operating expenses to exceed the Total Annual Fund Operating Expenses After Fee Waiver reflected in the table or cause the total of the payments to exceed the Fund's total initial offering expenses.

[3] For Class C shares, the CDSC is 0% after the first year.