Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	AB CAP FUND, INC.
Prospectus Date	rr_ProspectusDate	Jul. 29, 2016
Supplement [Text Block]	abcfi1_SupplementTextBlock	AB EMERGING MARKETS MULTI-ASSET PORTFOLIO ("EMMA") ----------------------------------------------------------------------------------------------------------------- Supplement dated April 10, 2017 to the following Prospectus and Summary Prospectus, as amended: Prospectus                                  Date -------------                                  ------ EMMA                                  July 29, 2016                                        * * * * * The third sentence of the introductory paragraph in the section "Summary Information--Fees and Expenses of the [Fund/Strategy/Portfolio]" is revised to also include reference to "Appendix [B/C]--Financial Intermediary Waivers". The footnote reading "For Class C shares, the CDSC is 0% after the first year" in the section "Fees and Expenses of the [Fund/Strategy/Portfolio]--Annual [Fund/Strategy/Portfolio] Operating Expenses" is replaced by the following: For Class C shares, the CDSC is 0% after the first year. Class C shares automatically convert to Class A shares after ten years.
AB Emerging Markets Multi-Asset Portfolio
Risk/Return:	rr_RiskReturnAbstract
Supplement [Text Block]	abcfi1_SupplementTextBlock	AB EMERGING MARKETS MULTI-ASSET PORTFOLIO ("EMMA") ----------------------------------------------------------------------------------------------------------------- Supplement dated April 10, 2017 to the following Prospectus and Summary Prospectus, as amended: Prospectus                                  Date -------------                                  ------ EMMA                                  July 29, 2016                                        * * * * * The third sentence of the introductory paragraph in the section "Summary Information--Fees and Expenses of the [Fund/Strategy/Portfolio]" is revised to also include reference to "Appendix [B/C]--Financial Intermediary Waivers". The footnote reading "For Class C shares, the CDSC is 0% after the first year" in the section "Fees and Expenses of the [Fund/Strategy/Portfolio]--Annual [Fund/Strategy/Portfolio] Operating Expenses" is replaced by the following: For Class C shares, the CDSC is 0% after the first year. Class C shares automatically convert to Class A shares after ten years.