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Class 2, Class 1 | AB Municipal Bond Inflation Strategy  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading AB Municipal Bond Inflation Strategy
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Fund’s investment objective is to maximize real after‑tax return for investors subject to federal income taxes, without undue risk to principal.
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)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination January 31, 2023
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 10% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 10.00%
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. The Examples assume that you invest $10,000 in the Fund for the time periods indicated. 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 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 Fund seeks real after‑tax return for investors subject to federal income taxes. Real return is the rate of return after adjusting for inflation. The Fund pursues its objective by investing principally in high-quality, predominantly investment-grade, municipal securities that pay interest exempt from federal taxation. As a fundamental policy, the Fund will invest at least 80% of its net assets in municipal securities. These securities may be subject to the federal alternative minimum tax (“AMT”) for some taxpayers.
  
The Fund will invest at least 80% of its total assets in fixed-income securities rated A or better or the equivalent by one or more national rating agencies (or deemed to be of comparable credit quality by the Adviser). The Fund may invest up to 20% of its total assets in fixed-income securities rated BB or B or the equivalent by one or more national rating agencies (or deemed to be of comparable credit quality by the Adviser), which are not investment-grade (“junk bonds”). If the rating of a fixed-income security falls below investment grade, the Fund will not be obligated to sell the security and may continue to hold it if, in the Adviser’s opinion, the investment is appropriate under the circumstances. 
The Adviser selects securities for purchase or sale based on its assessment of the securities’ risk and return characteristics as well as the securities’ impact on the overall risk and return characteristics of the Fund. In making this assessment, the Adviser takes into account various factors, including the credit quality and sensitivity to interest rates of the securities under consideration and of the Fund’s other holdings. The Fund may invest in fixed-income securities with any maturity and duration. 
To provide inflation protection, the Fund will typically enter into inflation swaps. The Fund may use other inflation-indexed instruments. Payments to the Fund pursuant to swaps will result in taxable income, either ordinary income or capital gains, rather than income exempt from federal income taxation. It is expected that the Fund’s primary use of derivatives will be for the purpose of inflation protection. 
The Fund may also invest in: 
•  
forward commitments; 
•  
zero‑coupon municipal securities and variable, floating and inverse floating-rate municipal securities; 
•  
certain types of mortgage-related securities; and 
•  
derivatives, such as options, futures contracts, forwards and swaps. 
The Fund may utilize leverage for investment purposes through the use of tender option bond (“TOB”) transactions. The Adviser considers the impact of TOB transactions, swaps and other derivatives in making its assessments of the Fund’s risks. The resulting exposures to markets, sectors, issuers or specific securities will be continuously monitored by the Adviser. 
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 bond market fluctuates. The value of the Fund’s 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), that affect large portions of the market. 
•  
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. 
•  
Municipal Market Risk: This is the risk that special factors may adversely affect the value of municipal securities and have a significant effect on the yield or value of the Fund’s investments in municipal securities. These factors include economic conditions, political or legislative changes, public health crises, uncertainties related to the tax status of municipal securities, or the rights of investors in these securities. To the extent that the Fund invests more of its assets in a particular state’s municipal securities, the Fund is vulnerable to events adversely affecting that state, including economic, political and regulatory occurrences, court decisions, terrorism, public health crises (including the occurrence of a contagious disease or illness) and catastrophic natural disasters, such as hurricanes, fires or earthquakes. For example, the novel coronavirus (COVID‑19) pandemic has significantly stressed the financial resources of many issuers of municipal securities, which could impair any such issuer’s ability to meet its financial obligations when due and adversely impact the value of its securities held by the Fund. As the full effects of the COVID‑19 pandemic on state and local economies and on issuers of municipal securities are still uncertain, the financial difficulties of issuers of municipal securities may continue or worsen, adversely affecting the performance of the Fund. The Fund’s investments in certain municipal securities with principal and interest payments that are made from the revenues of a specific project or facility, and not general tax revenues, may have increased risks. Factors affecting the project or facility, such as local business or economic conditions, could have a significant effect on the project’s ability to make payments of principal and interest on these securities. 
Congress has previously considered making changes to the municipal securities provisions of the Internal Revenue Code that could change the U.S. federal income tax treatment of certain types of municipal securities. 
•  
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 current historically low interest rate environment heightens the risks associated with rising interest rates. 
•  
Duration Risk: Duration is a measure that relates the expected price volatility of a fixed-income security to changes in interest rates. The duration of a fixed-income security may be shorter than or equal to full maturity of a fixed-income security. Fixed-income securities with longer durations have more risk and will decrease in price as interest rates rise. 
•  
Inflation Risk: This is the risk that the value of assets or income from investments will be less in the future as inflation decreases the value of money. As inflation increases, the value of the Fund’s assets can decline as can the value of the Fund’s distributions. This risk is significantly greater for fixed-income securities with longer maturities. 
•  
Derivatives Risk: Derivatives may be difficult to price or unwind and leveraged so that small changes may produce disproportionate losses for the Fund. 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: To the extent the Fund uses leveraging techniques, such as TOBs, its net asset value (“NAV”) may be more volatile because leverage tends to exaggerate the effect of changes in interest rates and any increase or decrease in the value of the Fund’s investments. 
•  
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, large positions and heavy redemptions of Fund shares. Illiquid investments risk may be higher in a rising interest rate environment, when the value and liquidity of fixed-income securities generally go down. 
•  
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 intended 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 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 1 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 4.37%, 2nd quarter, 2020; and Worst Quarter was down -6.55%, 1st quarter, 2020.
Performance Table Heading rr_PerformanceTableHeading Performance Table  Average Annual Total Returns (For the periods ended December 31, 2021)
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 1 shares only and will vary for Class 2 shares because Class 2 shares have a different expense ratio;
Class 2, Class 1 | AB Municipal Bond Inflation Strategy | Class 1  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fees rr_ManagementFeesOverAssets 0.50%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.10%
Other Expenses: Transfer Agent rr_Component1OtherExpensesOverAssets none [1]
Other Expenses rr_Component3OtherExpensesOverAssets 0.06%
Total Other Expenses rr_OtherExpensesOverAssets 0.06%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.66%
Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.06%) [2]
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 205
After 5 Years rr_ExpenseExampleYear05 362
After 10 Years rr_ExpenseExampleYear10 $ 817
2012 rr_AnnualReturn2012 5.27%
2013 rr_AnnualReturn2013 (3.54%)
2014 rr_AnnualReturn2014 1.41%
2015 rr_AnnualReturn2015 0.98%
2016 rr_AnnualReturn2016 1.64%
2017 rr_AnnualReturn2017 3.33%
2018 rr_AnnualReturn2018 (0.31%)
2019 rr_AnnualReturn2019 6.10%
2020 rr_AnnualReturn2020 4.53%
2021 rr_AnnualReturn2021 7.16%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 4.37%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (6.55%)
1 Year rr_AverageAnnualReturnYear01 7.16% [3]
5 Years rr_AverageAnnualReturnYear05 4.13% [3]
10 Years rr_AverageAnnualReturnYear10 2.61% [3]
Class 2, Class 1 | AB Municipal Bond Inflation Strategy | Class 2  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fees rr_ManagementFeesOverAssets 0.50%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses: Transfer Agent rr_Component1OtherExpensesOverAssets none [1]
Other Expenses rr_Component3OtherExpensesOverAssets 0.06%
Total Other Expenses rr_OtherExpensesOverAssets 0.06%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.56%
Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.06%) [2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 0.50%
After 1 Year rr_ExpenseExampleYear01 $ 51
After 3 Years rr_ExpenseExampleYear03 173
After 5 Years rr_ExpenseExampleYear05 307
After 10 Years rr_ExpenseExampleYear10 $ 696
1 Year rr_AverageAnnualReturnYear01 7.36%
5 Years rr_AverageAnnualReturnYear05 4.25%
10 Years rr_AverageAnnualReturnYear10 2.71%
Class 2, Class 1 | AB Municipal Bond Inflation Strategy | Return After Taxes on Distributions | Class 1  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 7.13% [3]
5 Years rr_AverageAnnualReturnYear05 4.09% [3]
10 Years rr_AverageAnnualReturnYear10 2.57% [3]
Class 2, Class 1 | AB Municipal Bond Inflation Strategy | Return After Taxes on Distributions and Sale of Fund Shares | Class 1  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 4.90% [3]
5 Years rr_AverageAnnualReturnYear05 3.65% [3]
10 Years rr_AverageAnnualReturnYear10 2.41% [3]
Class 2, Class 1 | AB Municipal Bond Inflation Strategy | Bloomberg TIPS 1-10 Year Index (reflects no deduction for fees, taxes or expenses)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 5.69%
5 Years rr_AverageAnnualReturnYear05 4.46%
10 Years rr_AverageAnnualReturnYear10 2.57%
[1]
Amount is less than .01%.
[2]
The Adviser has contractually agreed to waive its management fees and/or to bear certain expenses of the Fund until January 31, 2023 to the extent necessary to prevent total Fund operating expenses (excluding extraordinary expenses, interest expense, and acquired fund fees and expenses other than the advisory fees of any AB Mutual Funds in which the Fund may invest), on an annualized basis, from exceeding .60% and .50% of average daily net assets, respectively, for Class 1 and Class 2 shares (“expense limitations”). The expense limitations will remain in effect until January 31, 2023 and may only be terminated or changed with the consent of the Fund’s Board of Directors. In addition, the expense limitations will be automatically extended for one‑year terms unless the Adviser provides notice of termination to the Fund at least 60 days prior to the end of the period.
[3] After-tax returns: – Are shown for Class 1 shares only and will vary for Class 2 shares because Class 2 shares have a different expense ratio; – 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.