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AB Global Real Estate Investment Fund II  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading SUMMARY INFORMATION AB Global Real Estate Investment Fund II
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Fund’s investment objective is total return from long-term growth of capital 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, hold and sell 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)
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 53% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 53.00%
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. They 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. They also assume that your investment has a 5% return each year and that the Fund’s operating expenses stay the same. 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
Under normal circumstances, the Fund invests at least 80% of its net assets in the equity securities of real estate investment trusts, or REITs, and other real estate industry companies, such as real estate operating companies. The Fund invests in real estate companies that the Adviser believes have strong property fundamentals and management teams. The Fund seeks to invest in real estate companies whose underlying portfolios are diversified geographically and by property type.
The Fund invests in U.S. and non‑U.S. issuers. Under normal circumstances, the Fund invests significantly (at least 40%—unless market conditions are not deemed favorable by the Adviser) in securities of non‑U.S. companies. In addition, the Fund invests, under normal circumstances, in the equity securities of companies located in at least three countries. Equity securities include common stock, shares of beneficial interest of REITs, and securities with common stock characteristics, such as preferred stock or convertible securities (“real estate equity securities”).
  
The Fund’s investment policies emphasize investment in companies determined by the Adviser to be undervalued relative to their peers, using a fundamental value approach. In selecting real estate equity securities, the Adviser’s research and investment process seeks to identify globally those companies where the magnitude and growth of cash flow streams have not been appropriately reflected in the price of the security. These securities may trade at a more attractive valuation than others that may have similar overall fundamentals. The Adviser’s fundamental research efforts are focused on forecasting the short- and long-term normalized cash generation capability of real estate companies by isolating supply and demand for property types in local markets, determining the replacement value of properties, assessing future development opportunities, and normalizing capital structures of real estate companies. 
The Fund may invest in mortgage-backed securities, which are securities that directly or indirectly represent participations in, or are collateralized by and payable from, mortgage loans secured by real property. These securities include mortgage pass-through certificates, real estate mortgage investment conduit certificates, or REMICs, and collateralized mortgage obligations, or CMOs. The Fund may also invest in short-term investment grade debt securities and other fixed-income securities. 
Currency exposures can have a dramatic impact on equity return, significantly adding to returns in some years and greatly diminishing them in others. The Adviser may seek to hedge the currency exposure resulting from a securities position when it finds the currency exposure unattractive. To hedge a portion of its currency risk, the Fund may from time to time invest in currency-related derivatives, including forward currency exchange contracts, futures contracts, options on futures contracts, swaps and options. Equity positions and whether to hedge currency exposure are evaluated separately by the Adviser. The Adviser also may seek investment opportunities by taking long or short positions in currencies through the use of currency-related derivatives. 
The Fund may enter into forward commitments and standby commitment agreements. The Fund may enter into other 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 exchange-traded funds (“ETFs”). These transactions may be used, for example, 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. 
The Fund may, at times, invest in ETFs in lieu of making direct investments in equity securities. ETFs may provide more efficient and economical exposure to the type of companies and geographic locations in which the Fund seeks to invest than direct investments. 
Strategy Portfolio Concentration [Text] rr_StrategyPortfolioConcentration Under normal circumstances, the Fund invests at least 80% of its net assets in the equity securities of real estate investment trusts, or REITs, and other real estate industry companies, such as real estate operating companies.
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, including public health crises (including the occurrence of a contagious disease or illness) and regional and global conflicts, that affect large portions of the market. 
 
Real Estate Risk: The Fund’s investments in real estate securities have many of the same risks as direct ownership of real estate, including the risk that the value of real estate could decline due to a variety of factors affecting the real estate market generally. Investments in REITs may have additional risks. REITs are dependent on the capability of their managers, may have limited diversification, and could be significantly affected by changes in taxes. Some REITs may utilize leverage, which increases investment risk and may potentially increase the Fund’s losses. 
 
Foreign (Non‑U.S.) Risk: Investment 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 due to adverse market, economic, political, regulatory or other factors. 
 
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. The Fund may be subject to a greater risk of rising interest rates than would normally be the case due to the recent end of a period of historically low rates and the effect of potential central bank monetary policy, and government fiscal policy, initiatives and resulting market reactions to those initiatives. 
 
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 and accrued interest. 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. Investments in fixed-income securities with lower ratings tend to have a higher probability that an issuer will default or fail to meet its payment obligations. 
 
Currency Risk: Fluctuations in currency exchange rates may negatively affect the value of the Fund’s investments or reduce its returns. 
 
Mortgage-Related and/or Other Asset-Backed Securities Risk: Investments in mortgage-related and other asset-backed securities are subject to certain additional risks. The value of these securities may be particularly sensitive to changes in interest rates. These risks include “extension risk”, which is the risk that, in periods of rising interest rates, issuers may delay the payment of principal, and “prepayment risk”, which is the risk that in periods of falling interest rates, issuers may pay principal sooner than expected, exposing the Fund to a lower rate of return upon reinvestment of principal. Mortgage-backed securities offered by non‑governmental issuers and other asset-backed securities may be subject to other risks, such as higher rates of default in the mortgages or assets backing the securities or risks associated with the nature and servicing of mortgages or assets backing the securities. 
 
Derivatives Risk: Derivatives may be difficult to price or unwind and leveraged so that small changes may produce disproportionate losses for the Fund. A short position in a derivative instrument involves the risk of a theoretically unlimited increase in the value of the underlying asset, which could cause the Fund to suffer a potentially unlimited loss. Derivatives, especially over‑the‑counter derivatives, are also subject to counterparty risk, which is the risk that the counterparty (the party on the other side of the transaction) on a derivative transaction will be unable or unwilling to honor its contractual obligations to the Fund. 
 
Leverage Risk: When the Fund borrows money or otherwise leverages its portfolio, it may be more volatile because leverage tends to exaggerate the effect of any increase or decrease in the value of the Fund’s investments. The Fund may create leverage through the use of reverse repurchase agreements or forward commitments, or by borrowing money. 
 
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 desired results. Some of these techniques may incorporate, or rely upon, quantitative models, but there is no guarantee that these models will generate accurate forecasts, reduce risk or otherwise perform as expected. 
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 ten years; and
 
how the Fund’s average annual returns for one, five and ten years compare to those of a broad-based securities market index.
You can obtain updated performance information for the Fund at www.bernstein.com (click on “Investments,” then “Mutual Fund Performance at a Glance”). 
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 how the Fund’s performance changed from year to year over ten years; andhow the Fund’s average annual returns for one, five and ten years compare to those of a broad-based securities market index.
Performance Additional Market Index [Text] rr_PerformanceAdditionalMarketIndex The FTSE EPRA/NAREIT Developed Real Estate Index provides information about the performance of REITs in global markets. The MSCI World Index (net) provides broad-based information about the performance of global markets. The FTSE NAREIT Equity REIT Index provides information about the performance of REITs in the U.S.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.bernstein.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 I shares. 
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Calendar Year End (%) During the period shown in the bar chart, the Fund’s: Best Quarter was up 15.18%, 1st quarter, 2019; and Worst Quarter was down -26.82%, 1st quarter, 2020.
Performance Table Heading rr_PerformanceTableHeading Performance Table Average Annual Total Returns (For the periods ended December 31, 2022)
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.
AB Global Real Estate Investment Fund II | Class I  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fees rr_ManagementFeesOverAssets 0.55%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses: Transfer Agent rr_Component1OtherExpensesOverAssets 0.01%
Other Expenses rr_Component2OtherExpensesOverAssets 0.18%
Total Other Expenses rr_OtherExpensesOverAssets 0.19%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.74%
After 1 Year rr_ExpenseExampleYear01 $ 76
After 3 Years rr_ExpenseExampleYear03 237
After 5 Years rr_ExpenseExampleYear05 411
After 10 Years rr_ExpenseExampleYear10 $ 918
2013 rr_AnnualReturn2013 5.91%
2014 rr_AnnualReturn2014 14.56%
2015 rr_AnnualReturn2015 0.38%
2016 rr_AnnualReturn2016 3.44%
2017 rr_AnnualReturn2017 14.43%
2018 rr_AnnualReturn2018 (4.32%)
2019 rr_AnnualReturn2019 23.53%
2020 rr_AnnualReturn2020 (4.62%)
2021 rr_AnnualReturn2021 26.53%
2022 rr_AnnualReturn2022 (25.35%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2019
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.18%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (26.82%)
1 Year rr_AverageAnnualReturnYear01 (25.35%) [1]
5 Years rr_AverageAnnualReturnYear05 1.26% [1]
10 Years rr_AverageAnnualReturnYear10 4.38% [1]
AB Global Real Estate Investment Fund II | Return After Taxes on Distributions | Class I  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (26.56%) [1],[2]
5 Years rr_AverageAnnualReturnYear05 (0.24%) [1],[2]
10 Years rr_AverageAnnualReturnYear10 2.55% [1],[2]
AB Global Real Estate Investment Fund II | Return After Taxes on Distributions and Sale of Fund Shares | Class I  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (14.51%) [1],[2]
5 Years rr_AverageAnnualReturnYear05 0.61% [1],[2]
10 Years rr_AverageAnnualReturnYear10 2.73% [1],[2]
AB Global Real Estate Investment Fund II | S&P 500 Index  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (18.11%)
5 Years rr_AverageAnnualReturnYear05 9.42%
10 Years rr_AverageAnnualReturnYear10 12.56%
AB Global Real Estate Investment Fund II | FTSE EPRA/NAREIT Developed Real Estate Index (net) (reflects no deduction for fees, expenses, or taxes except the reinvestment of dividends net of non-U.S. withholding taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (25.09%) [3]
5 Years rr_AverageAnnualReturnYear05 (0.23%) [3]
10 Years rr_AverageAnnualReturnYear10 2.99% [3]
AB Global Real Estate Investment Fund II | MSCI World Index (net) (reflects no deduction for fees, expenses or taxes except the reinvestment of dividends net of non-U.S. withholding taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (18.14%) [3]
5 Years rr_AverageAnnualReturnYear05 6.14% [3]
10 Years rr_AverageAnnualReturnYear10 8.85% [3]
AB Global Real Estate Investment Fund II | FTSE NAREIT Equity REIT Index (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (24.95%) [3]
5 Years rr_AverageAnnualReturnYear05 4.43% [3]
10 Years rr_AverageAnnualReturnYear10 7.10% [3]
[1] 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; 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.
[2]
After‑tax returns are based on information available to the Fund as of the date of this Prospectus.
[3]
The FTSE EPRA/NAREIT Developed Real Estate Index provides information about the performance of REITs in global markets. The MSCI World Index (net) provides broad-based information about the performance of global markets. The FTSE NAREIT Equity REIT Index provides information about the performance of REITs in the U.S.