Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	AB CAP FUND, INC.
Prospectus Date	rr_ProspectusDate	Mar. 14, 2017
AB Performance Fee Series - Large Cap Growth Portfolio
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SUMMARY INFORMATION AB Performance Fee Series - Large Cap Growth Portfolio
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund's investment objective is 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.
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	December 31 , 2018
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 Fund 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.
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	Total Other Expenses are estimated for the current fiscal year.
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 expense limitation and fee waiver are in effect through the date indicated above . 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 Fund invests primarily in equity securities of a limited number of large, carefully selected, high-quality U.S. companies. The Fund invests primarily in the domestic equity securities of companies selected by the Fund's Adviser for their growth potential within various market sectors. The Fund emphasizes investments in large, seasoned companies. Under normal circumstances, the Fund will invest at least 80% of its net assets in common stocks of large-capitalization companies. For these purposes, "large-capitalization companies" are those that, at the time of investment, have market capitalizations within the range of market capitalizations of companies appearing in the Russell 1000® Growth Index. While the market capitalizations of companies in the Russell 1000® Growth Index ranged from approximately $1.00 billion to $561.53 billion as of June 30, 2016, the Fund normally will invest in common stocks of companies with market capitalizations of at least $5 billion at the time of purchase. The Adviser expects that normally the Fund's portfolio will tend to emphasize investments in securities issued by U.S. companies, although it may invest in foreign securities. The investment team allocates the Fund's investments among broad sector groups based on the fundamental company research conducted by the Adviser's internal research staff, assessing the current and forecasted investment opportunities and conditions, as well as diversification and risk considerations. The investment team may vary the percentage allocations among market sectors and may change the market sectors in which the Fund invests as companies' potential for growth within a sector matures and new trends for growth emerge. The Adviser's research focus is in companies with high sustainable growth prospects, high or improving return on invested capital, transparent business models, and strong and lasting competitive advantages. The Fund may enter into derivatives transactions, such as options, futures contracts, forwards and swaps. The Fund may use options strategies involving the purchase and/or writing of various combinations of call and/or put options, including on individual securities and stock indices, futures contracts (including futures contracts on individual securities and stock indices) or shares of ETFs. These transactions may be used, for example, in an effort to earn extra income, to adjust exposure to individual securities or markets, or to protect all or a portion of the Fund's portfolio from a decline in value, sometimes within certain ranges.
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 or bond 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 growth 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 less liquid due to adverse market, economic, political, regulatory or other factors. Derivatives Risk: 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. 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.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	BAR CHART AND 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.
AB Performance Fee Series - Large Cap Growth 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_ExchangeFeeOverRedemption	none
Management Fees	rr_ManagementFeesOverAssets	0.55%	[1]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.07%
Other Expenses	rr_Component2OtherExpensesOverAssets	0.39%
Total Other Expenses	rr_OtherExpensesOverAssets	0.46%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.01%	[3]
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.41%)	[4]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	0.60%
After 1 Year	rr_ExpenseExampleYear01	$ 61
After 3 Years	rr_ExpenseExampleYear03	$ 281

[1] The management fee paid to the Adviser consists of a base fee at an annualized rate of 0.55% of the Fund's average daily net assets and a positive or negative performance adjustment of up to an annualized rate of 0.50% based upon the Fund's performance relative to the Russell 1000 Growth Index, resulting in a minimum total fee of 0.05% and a maximum total fee of 1.05%.

[2] Total Other Expenses are estimated for the current fiscal year.

[3] Before Waiver

[4] The Adviser has contractually agreed to waive fees and/or to bear expenses of the Fund through December 31 , 2018 to the extent necessary to prevent Total Other 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 0.05% of average daily net assets ("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 Total Other Expenses to exceed the expense limitations.