Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	AB CAP FUND, INC.
Prospectus Date	rr_ProspectusDate	Oct. 31, 2018
AB Concentrated International Growth Portfolio
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	AB CONCENTRATED INTERNATIONAL GROWTH 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 Funds--Sales Charge Reduction Programs for Class A Shares on page 66 of this Prospectus, in Appendix B--Financial Intermediary Waivers of this Prospectus and in Purchase of Shares--Sales Charge Reduction Programs on page 130 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 of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	October 31, 2019
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. During the most recent fiscal year, the Fund's portfolio turnover rate was 34% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	34.00%
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. For Class C shares, the CDSC is 0% after the first year. Class C shares automatically convert to Class A shares after ten years.
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	EXAMPLE
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 these 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 any fee waiver remains 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, primarily in common stocks of non-U.S. companies, and in companies in at least three countries other than the United States. The Fund will invest in companies that are determined by the Adviser to offer favorable long-term growth potential and that are trading at attractive valuations. The Adviser will employ an appraisal method which attempts to measure each prospective company's quality and growth rate by numerous factors. Such factors will include: a company's record and projections of profit and earnings growth, accuracy and availability of information with respect to the company, success and experience of management, accessibility of management to the Adviser, product lines and competitive position both in the United States and abroad, lack of cyclicality, large market capitalization and liquidity of the company's securities. The Adviser will compare these results to the characteristics of the general stock markets to determine the relative attractiveness of each company at a given time. The Adviser will weigh economic, political and market factors in making investment decisions; this appraisal technique attempts to measure each investment candidate not only against other stocks of the same industry and region, but also against a broad spectrum of investments. The Fund will invest in a relatively small number of individual stocks, generally 25 to 35 companies. The Fund will primarily invest in mid- and large-capitalization companies, which are currently defined for the Fund as companies that have market capitalizations of $2.0 billion or more. The Fund's holdings of non-U.S. companies may include some companies located in emerging markets, and at times emerging market companies may make up a significant portion of the Fund. Fluctuations in currency exchange rates can have a dramatic impact of the returns of equity securities. While the Adviser may hedge the foreign currency exposure resulting from the Fund's security positions through the use of currency-related derivatives, it is not required to do so.
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. FOCUSED PORTFOLIO RISK: Investments in a limited number of companies may have more risk because 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. SECTOR RISK: The Fund may have more risk because of concentrated investments in a particular market sector, such as the technology or financial services sector. Market or economic factors affecting that sector could have a major effect on the value of the Fund’s investments. 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. EMERGING MARKET RISK: Investments in emerging market countries may have more risk because the markets are less developed and less liquid, and because these investments may be subject to increased economic, political, regulatory or other uncertainties. CURRENCY RISK: Fluctuations in currency exchange rates may negatively affect the value of the Fund’s investments or reduce its returns. CAPITALIZATION RISK: Investments in mid-capitalization companies may be more volatile than investments in large-capitalization companies. Investments in mid-capitalization companies may have additional risks because these companies have limited product lines, markets or financial resources. 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	The bar chart and performance information provide an indication of the historical risk of an investment in the Fund by showing: how the Fund’s performance changed from year to year over the life of the Fund; and how the Fund’s average annual returns for one year and since inception compare to those of a broad-based securities market index. You may obtain updated performance information on the Fund’s website at www.abfunds.com (click on “Investments--Mutual Funds”). The Fund’s past performance before and after taxes, of course, does not necessarily indicate how it will perform in the future.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	<ul type="square"><li> how the Fund’s performance changed from year to year over the life of the Fund; and</li></ul><ul type="square"><li> how the Fund’s average annual returns for one year and since inception compare to those of a broad-based securities market index. </li></ul>
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.abfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The Fund's past performance before and after taxes, of course, does not necessarily indicate how it will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	BAR CHART
Bar Chart Narrative [Text Block]	rr_BarChartNarrativeTextBlock	The annual returns in the bar chart are for the Fund's Class A shares and do not reflect sales loads. If sales loads were reflected, returns would be less than those shown. Through September 30, 2018, the year-to-date unannualized return for Class A shares was -1.13%.
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The annual returns in the bar chart are for the Fund's Class A shares and do not reflect sales loads. If sales loads were reflected, returns would be less than those shown.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the period shown in the bar chart, the Fund's: BEST QUARTER WAS UP 10.69%, 1ST QUARTER, 2017; AND WORST QUARTER WAS DOWN -6.07%, 4TH QUARTER, 2016.
Performance Table Heading	rr_PerformanceTableHeading	PERFORMANCE TABLE<br/>AVERAGE ANNUAL TOTAL RETURNS <br/>(For the period ended December 31, 2017)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax Returns: -Are an estimate, which is based on the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes;
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	actual after-tax returns depend on an individual investor's tax situation and are likely to differ from those shown; and -Are not relevant to investors who hold Fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax Returns: -Are shown for Class A shares only and will vary for the other Classes of shares because these Classes have different expense ratios;
AB Concentrated International Growth 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_ExchangeFeeOverRedemption	none
Management Fees	rr_ManagementFeesOverAssets	0.85%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.05%
Other Expenses	rr_Component2OtherExpensesOverAssets	0.93%
Total Other Expenses	rr_OtherExpensesOverAssets	0.98%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.09%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.79%)	[2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	1.30%
After 1 Year	rr_ExpenseExampleYear01	$ 552
After 3 Years	rr_ExpenseExampleYear03	979
After 5 Years	rr_ExpenseExampleYear05	1,431
After 10 Years	rr_ExpenseExampleYear10	$ 2,683
2008	rr_AnnualReturn2008
2009	rr_AnnualReturn2009
2010	rr_AnnualReturn2010
2011	rr_AnnualReturn2011
2012	rr_AnnualReturn2012
2013	rr_AnnualReturn2013
2014	rr_AnnualReturn2014
2015	rr_AnnualReturn2015
2016	rr_AnnualReturn2016	(5.97%)
2017	rr_AnnualReturn2017	37.49%
Year to Date Return, Label	rr_YearToDateReturnLabel	year-to-date
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2018
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	(1.13%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	BEST QUARTER
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2017
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	10.69%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	WORST QUARTER
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2016
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(6.07%)
1 YEAR	rr_AverageAnnualReturnYear01	31.68%	[3]
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	4.97%	[3],[4]
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Apr. 15, 2015	[3]
AB Concentrated International Growth 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%	[5]
Exchange Fee	rr_ExchangeFeeOverRedemption	none
Management Fees	rr_ManagementFeesOverAssets	0.85%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.08%
Other Expenses	rr_Component2OtherExpensesOverAssets	0.96%
Total Other Expenses	rr_OtherExpensesOverAssets	1.04%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.90%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.85%)	[2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	2.05%
After 1 Year	rr_ExpenseExampleYear01	$ 308	[6]
After 3 Years	rr_ExpenseExampleYear03	818
After 5 Years	rr_ExpenseExampleYear05	1,453
After 10 Years	rr_ExpenseExampleYear10	$ 3,163
1 YEAR	rr_AverageAnnualReturnYear01	35.55%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	5.88%	[4]
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Apr. 15, 2015
AB Concentrated International 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	0.85%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses: Transfer Agent	rr_Component1OtherExpensesOverAssets	0.05%
Other Expenses	rr_Component2OtherExpensesOverAssets	0.90%
Total Other Expenses	rr_OtherExpensesOverAssets	0.95%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.81%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(0.76%)	[2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	1.05%
After 1 Year	rr_ExpenseExampleYear01	$ 107
After 3 Years	rr_ExpenseExampleYear03	495
After 5 Years	rr_ExpenseExampleYear05	909
After 10 Years	rr_ExpenseExampleYear10	$ 2,064
1 YEAR	rr_AverageAnnualReturnYear01	37.85%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	6.93%	[4]
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Apr. 15, 2015
AB Concentrated International Growth Portfolio | Return After Taxes on Distributions | CLASS A
Risk/Return:	rr_RiskReturnAbstract
1 YEAR	rr_AverageAnnualReturnYear01	30.33%	[3]
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	4.56%	[3],[4]
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Apr. 15, 2015	[3]
AB Concentrated International Growth Portfolio | Return After Taxes on Distributions and Sale of Fund Shares | CLASS A
Risk/Return:	rr_RiskReturnAbstract
1 YEAR	rr_AverageAnnualReturnYear01	18.33%	[3]
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	3.74%	[3],[4]
INCEPTION DATE	rr_AverageAnnualReturnInceptionDate	Apr. 15, 2015	[3]
AB Concentrated International Growth Portfolio | MSCI EAFE Index (reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 YEAR	rr_AverageAnnualReturnYear01	25.03%
SINCE INCEPTION	rr_AverageAnnualReturnSinceInception	5.58%	[4]

[1] 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.

[2] The Adviser has contractually agreed to waive its management fees and/or to bear expenses of the Fund until October 31, 2019 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 and extraordinary expenses), on an annualized basis, from exceeding 1.30%, 2.05% and 1.05% of average daily net assets, respectively, for Class A, Class C and Advisor Class shares ("expense limitations"). The expense limitations will remain in effect until October 31, 2019 and will continue thereafter from year to year unless the Adviser provides notice of termination to the Fund at least 60 days prior to the end of the period. 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, as included in "Acquired Fund Fees and Expenses".

[3] After-tax Returns: -Are shown for Class A shares only and will vary for the other Classes of shares because these Classes have different expense ratios; -Are an estimate, which is based on the highest historical individual federal marginal income tax rates and do not reflect the impact of state and local taxes; actual after-tax returns depend on an individual investor's tax situation and are likely to differ from those shown; and -Are not relevant to investors who hold Fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts.

[4] Inception date for all Classes: 4/15/15.

[5] For Class C shares, the CDSC is 0% after the first year. Class C shares automatically convert to Class A shares after ten years.

[6] If you did not redeem your shares at the end of the period, your expenses would be decreased by approximately $100.