Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	AB CAP FUND, INC.
Prospectus Date	rr_ProspectusDate	Feb. 28, 2019
AB All China Equity Portfolio
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	AB All China Equity Portfolio
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund’s investment objective is to seek long-term growth of capital.
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 AB 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 67 of this Prospectus, in Appendix B--Financial Intermediary Waivers of this Prospectus and in Purchase of Shares--Sales Charge Reduction Programs for Class A Shares on page 132 of the Fund’s Statement of Additional Information (“SAI”). You may be required to pay commissions and/or other forms of compensation to a broker for transactions in Advisor Class shares, which are not reflected in the tables or the examples below.
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<br/>of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	February 28, 2020
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 38% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	38.00%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	Purchases of Class A shares in amounts of $1,000,000 or more, or by certain group retirement plans, may be subject to a 1%, 1-year contingent deferred sales charge, or CDSC, which may be subject to waiver in certain circumstances.
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 AB 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 the periods. The Examples also assume that your investment has a 5% return each year, that the Fund’s operating expenses stay the same (except for the exclusion of offering costs after the first year) and that any fee waiver and/or expense limitation is in effect for only the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	PRINCIPAL STRATEGIES
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Adviser seeks to achieve the Fund's investment objective by investing, under normal circumstances, at least 80% of the Fund's net assets in a portfolio of equity securities of companies economically tied to the People's Republic of China ("China") (including Hong Kong). A company will be considered to be economically tied to China if it: (i) is domiciled or organized in China; (ii) has securities that are traded principally in China; or (iii) conducts a substantial part of its economic activities in China. Equity securities may include common stocks, preferred stocks, the equity securities of real estate investment trusts, or REITs, depositary receipts and derivative instruments related to equity securities. The Adviser expects to invest Fund assets both in shares of companies that trade on the Shanghai Stock Exchange or the Shenzhen Stock Exchange ("China A shares") and shares of companies economically tied to China that trade in Hong Kong or outside of China. The Adviser believes that, over time, securities that are undervalued by the market relative to their long-term earnings power can provide high returns. The Adviser will utilize fundamental analysis and its quantitative models to attempt to identify these securities for investment by the Fund, attempting to balance factors relating to valuation, company quality and investor sentiment, and will seek to build a portfolio that delivers attractive risk-adjusted returns. The Adviser may, but frequently will not, hedge the foreign currency exposure resulting from the Fund's security positions through the use of currency-related derivatives. The Fund is "non-diversified".
Risk [Heading]	rr_RiskHeading	PRINCIPAL RISKS
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	MARKET RISK: The value of the Fund's assets will fluctuate as the stock market fluctuates. The value of its investments may decline, sometimes rapidly and unpredictably, simply because of economic changes or other events that affect large portions of the market. It includes the risk that a particular style of investing, such as the Fund's value approach, may underperform the market generally. 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 more difficult to trade or dispose of due to adverse market, economic, political, regulatory or other factors. Investments in emerging market countries such as China may involve more risk than investments in developed countries because the markets in emerging market countries are less developed and less liquid and are subject to increased economic, political, regulatory, or other uncertainties. In addition, the value of the Fund's investments may decline because of factors such as unfavorable or unsuccessful government actions and reduction in government or central bank support. CHINA/SINGLE COUNTRY RISK: Investments in issuers located in a particular country or geographic region may have more risk because of particular market factors affecting that country or region, including political instability or unpredictable economic conditions. Risks of investments in securities of companies in China include the volatility of the Chinese stock market, heavy dependence on exports, which may be affected adversely by trade barriers or disputes or may decrease, sometimes significantly, when the world economy weakens, and the continuing importance of the role of the Chinese Government, which may take actions that affect economic and market practices. While the Chinese economy has grown at a rapid rate in recent years, the rate of growth has been declining, and there can be no assurance that China's economy will continue to grow in the future. Investments in China A shares are subject to quotas that may restrict daily trading and generally are less liquid than shares of companies in developed markets. Risks of investments in companies based in Hong Kong include heavy reliance on the U.S. economy and regional economies, particularly the Chinese economy, which makes these investments vulnerable to changes in these economies. CURRENCY RISK: Fluctuations in currency exchange rates may negatively affect the value of the Fund's investments in equity securities denominated in foreign currencies or reduce the Fund's 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. DEPOSITARY RECEIPTS RISK: Investing in depositary receipts involves risks that are similar to the risks of direct investments in foreign securities. For example, investing in depositary receipts may involve risks relating to political, economic or regulatory conditions in foreign countries. In addition, the issuers of the securities underlying certain depositary receipts are under no obligation to distribute shareholder communications or pass through any voting rights with respect to the deposited securities to the holders of such receipts. ILLIQUID INVESTMENTS RISK: Illiquid investments risk exists when certain investments are or become difficult to purchase or sell. Difficulty in selling such investments may result in sales at disadvantageous prices affecting the value of your investment in the Fund. Causes of illiquid investments risk may include low trading volumes and large positions. Foreign fixed-income securities may have more illiquid investments risk because secondary trading markets for these securities may be smaller and less well-developed and the securities may trade less frequently. Illiquid investments risk may be higher in a rising interest rate environment, when the value and liquidity of fixed-income securities generally go down. NON-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. Accordingly, changes in the value of a single security may have a more significant effect, either negative or positive, on the Fund's net asset value, or NAV. 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 for the Fund, 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	<ul type="square"><li>NON-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. Accordingly, changes in the value of a single security may have a more significant effect, either negative or positive, on the Fund's net asset value, or NAV.</li></ul>
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	BAR CHART AND PERFORMANCE INFORMATION
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	No performance information is presented 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 presented for the Fund because it has not yet been in operation for a full calendar year.
AB All China Equity Portfolio | ADVISOR CLASS SHARES
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_ExchangeFeeOverRedemption	none
Management Fees	rr_ManagementFeesOverAssets	0.95%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.12%
Other Expenses	rr_Component2OtherExpensesOverAssets	3.48%
Total Other Expenses	rr_OtherExpensesOverAssets	3.60%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	4.55%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(3.30%)	[1]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	1.25%
After 1 Year	rr_ExpenseExampleYear01	$ 127
After 3 Years	rr_ExpenseExampleYear03	982
After 5 Years	rr_ExpenseExampleYear05	1,852
After 10 Years	rr_ExpenseExampleYear10	$ 4,098
AB All China Equity Portfolio | CLASS A SHARES
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	[2]
Exchange Fee	rr_ExchangeFeeOverRedemption	none
Management Fees	rr_ManagementFeesOverAssets	0.95%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.08%
Other Expenses	rr_Component2OtherExpensesOverAssets	2.95%
Total Other Expenses	rr_OtherExpensesOverAssets	3.03%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	4.23%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(2.73%)	[1]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	1.50%
After 1 Year	rr_ExpenseExampleYear01	$ 571
After 3 Years	rr_ExpenseExampleYear03	1,326
After 5 Years	rr_ExpenseExampleYear05	2,099
After 10 Years	rr_ExpenseExampleYear10	$ 4,118

[1] The Adviser has contractually agreed to waive its management fee and/or to bear expenses of the Fund until February 28, 2020 to the extent necessary to prevent total Fund operating expenses (excluding acquired fund fees and expenses other than the advisory fees of any AB Mutual Funds in which the Fund may invest, interest expense, taxes, extraordinary expenses, and brokerage commissions and other transaction costs), on an annualized basis, from exceeding 1.50% and 1.25% of average daily net assets, respectively, for Class A and Advisor Class shares ("expense limitations"). Any fees waived and expenses borne by the Adviser may be reimbursed by the Fund until the end of the third fiscal year after the fiscal period in which the fee was waived or the expense was borne, provided that no reimbursement payment will be made that would cause the Fund's covered operating expenses to exceed the applicable expense limitations. In connection with the Fund's investments in AB Government Money Market Portfolio (the "Money Market Portfolio"), the Adviser has contractually agreed to waive its management fee from the Fund and/or reimburse other expenses of the Fund in an amount equal to the Fund's pro rata share of the Money Market Portfolio's effective management fee.

[2] Purchases of Class A shares in amounts of $1,000,000 or more, or by certain group retirement plans, may be subject to a 1%, 1-year contingent deferred sales charge, or CDSC, which may be subject to waiver in certain circumstances.