| Label | Element | Value | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Class Z Shares | Small Cap Core Portfolio | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk/Return [Heading] | rr_RiskReturnHeading | U.S. EQUITY PORTFOLIO Small Cap Core Portfolio of Bernstein Fund, Inc. | |||||||
| Objective [Heading] | rr_ObjectiveHeading | INVESTMENT OBJECTIVE: | |||||||
| Objective, Primary [Text Block] | rr_ObjectivePrimaryTextBlock | The Portfolio’s investment objective is to provide long-term growth of capital.
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| Expense [Heading] | rr_ExpenseHeading | FEES AND EXPENSES OF THE PORTFOLIO: | |||||||
| 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 Portfolio. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.
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| Shareholder Fees Caption [Text] | rr_ShareholderFeesCaption | Shareholder Fees (fees paid directly from your investment) | |||||||
| Operating Expenses Caption [Text] | rr_OperatingExpensesCaption | Annual Portfolio 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 Portfolio 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 Portfolio shares are held in a taxable account. These transaction costs, which are not reflected in the Annual Portfolio Operating Expenses or in the Examples, affect the Portfolio’s performance. For the most recent fiscal year, the Portfolio’s portfolio turnover rate was 63% of the average value of its portfolio.
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| Portfolio Turnover, Rate | rr_PortfolioTurnoverRate | 63.00% | |||||||
| 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 Portfolio with the cost of investing in other mutual funds. The Examples assume that you invest $10,000 in the Portfolio 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 and that the Portfolio’s operating expenses stay the same. Although your actual costs may be higher or lower, based on these assumptions your costs as reflected in the Examples would be:
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| Strategy [Heading] | rr_StrategyHeading | PRINCIPAL STRATEGIES: | |||||||
| Strategy Narrative [Text Block] | rr_StrategyNarrativeTextBlock | The Portfolio invests, under normal circumstances, at least 80% of its net assets (plus any borrowings for investment purposes) in equity securities of small-capitalization companies or other securities or instruments with similar economic characteristics, including derivatives related to equity securities. Equity securities are primarily common stocks, although, for purposes of the 80% policy, equity securities may also include preferred stocks, warrants, convertible securities, sponsored or unsponsored American Depositary Receipts (“ADRs”) and Global Depositary Receipts (“GDRs”) and equity real estate investment trusts (“REITs”). You will be notified at least 60 days prior to any change to the Portfolio’s 80% investment policy. AllianceBernstein L.P. serves as the Portfolio’s investment manager (the “Manager”). The Manager invests the assets of the Portfolio primarily in a diversified portfolio of equity securities of small-capitalization companies located in the U.S. The Portfolio defines small-capitalization companies as those that, at the time of investment, fall within the capitalization range between the smallest company in the Russell 2000 Index (the “Russell 2000”) and the largest company in the Russell 2000. As of August 31, 2024, the market capitalization range of the Russell 2000 was between approximately $11.8 million and $13.1 billion. The market capitalization of the companies included in the Portfolio’s definition of “small-capitalization” companies changes over time as the capitalization of the securities included in the Russell 2000 changes. The Manager utilizes both quantitative analysis and fundamental research to determine which securities will be held by the Portfolio and to manage risk. The Manager applies quantitative analysis to all of the securities in the Portfolio’s research universe, which is composed primarily of securities in the Portfolio’s benchmark (the Russell 2000 Index). Those securities that score highly on this quantitative analysis are then screened to eliminate those securities that the Manager is recommending against purchasing based on its fundamental research. The Manager additionally sources ideas from its fundamental research to complement its quantitative ideas and derive an additional source of investment performance. The Portfolio is ultimately constructed from quantitatively and fundamentally sourced ideas, with holdings weights optimized to maximize risk-adjusted returns. In its quantitative analysis, the Manager considers a number of metrics that have historically provided some indication of favorable future returns, including metrics relating to valuation, quality, investor behavior and earnings growth. In general, stocks are purchased when, in the view of the Manager, they provide the highest expected returns, considering their contribution to the estimated risk of the Portfolio’s existing investments. Typically, growth in the size of a company’s market capitalization relative to other domestically traded companies does not cause the Manager to dispose of the security. The Manager expects to seek to manage the overall portfolio volatility of the Portfolio relative to the Russell 2000 by favoring securities that the Manager believes offer the best balance between return and targeted risk. The Portfolio may also invest in exchange-traded funds (“ETFs”) and other investment companies from time to time. The Portfolio expects to utilize derivatives, such as options, futures contracts, forwards and swaps. For example, the Portfolio may use stock index futures contracts to equitize cash. Derivatives may provide a more efficient and economical exposure to market segments than direct investments, and may also be a more efficient way to alter the Portfolio’s exposure.
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| Risk [Heading] | rr_RiskHeading | PRINCIPAL RISKS: | |||||||
| 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 Portfolio by showing:
You may obtain updated performance information for the Portfolio at www.bernstein.com (at the bottom of the page, click on “Investments,” then “Mutual Fund Performance at a Glance”). The Portfolio’s past performance before and after taxes, of course, does not necessarily indicate how it will perform in the future. As with all investments, you may lose money by investing in the Portfolio.
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| Performance Information Illustrates Variability of Returns [Text] | rr_PerformanceInformationIllustratesVariabilityOfReturns | how the Portfolio’s performance changed from year to year over the life of the Portfolio; andhow the Portfolio’s average annual returns for one year, five years and over the life of the Portfolio compare to those of a broad-based securities market index and an additional index that more closely reflects the market segments in which the Portfolio invests. | |||||||
| Performance Availability Website Address [Text] | rr_PerformanceAvailabilityWebSiteAddress | www.bernstein.com | |||||||
| Performance Past Does Not Indicate Future [Text] | rr_PerformancePastDoesNotIndicateFuture | The Portfolio’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 Portfolio’s Class Z shares.
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| Bar Chart Closing [Text Block] | rr_BarChartClosingTextBlock | Calendar Year End (%) During the period shown in the bar chart, the Portfolio’s: Best Quarter was up 26.77%, 4th quarter, 2020; and Worst Quarter was down -32.51%, 1st quarter, 2020. | |||||||
| Performance Table Heading | rr_PerformanceTableHeading | Performance Table Average Annual Total Returns (For the periods ended December 31, 2024) | |||||||
| Performance Table Market Index Changed | rr_PerformanceTableMarketIndexChanged | Effective July 24, 2024, the primary broad-based index used for comparison with the Portfolio’s performance changed from the Russell 2000 Index to the S&P 500 Index to comply with new regulations that require the Portfolio’s primary benchmark to reflect the overall market in which the Portfolio may invest. The Portfolio’s previous primary benchmark, the Russell 2000 Index, which more closely reflects the market segments in which the Portfolio invests, is the Portfolio’s secondary benchmark. | |||||||
| 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 Portfolio shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts. | |||||||
| Performance Table Narrative | rr_PerformanceTableNarrativeTextBlock | 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 Portfolio shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts.
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| Class Z Shares | Small Cap Core Portfolio | Risk Lose Money [Member] | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk [Text Block] | rr_RiskTextBlock | The share price of the Portfolio will fluctuate and you may lose money. | |||||||
| Class Z Shares | Small Cap Core Portfolio | Market Risk [Member] | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk [Text Block] | rr_RiskTextBlock |
The United States and other countries are periodically involved in disputes over trade and other matters, which may result in tariffs on various categories of goods imported from the other country, restrictions on investment and adverse impacts on affected companies and securities. For example, the current political climate between the United States and China has intensified concerns about protectionist trade policies and a potential trade war between China and the United States. The United States has imposed tariffs and other trade barriers on Chinese exports and placed other restrictions on or barriers to investments in China. Trade disputes, particularly prolonged disputes, may adversely affect the economies of the United States and its trading partners, as well as the companies directly or indirectly affected by the dispute and financial markets generally, and thus may adversely affect the value of the Portfolio’s assets. In addition, an increase in tariffs or trade restrictions, or even the threat of such increased tariffs or restrictions, could lead to a significant reduction in international trade, which could have a negative impact on the global economy and a commensurately negative impact on the Portfolio. The United States government has in the recent past acted to prohibit U.S. persons, such as the Portfolio, from owning, and required them to divest, certain Chinese companies designated as related to the Chinese military. There is no assurance that more such companies will not be so designated in the future, which could limit the Portfolio’s opportunities for investment and require the sale of securities at a loss or make them illiquid. Some countries and regions in which the Portfolio invests have strained international relations due to territorial disputes, historical animosities or other defense concerns. Incidents involving a country’s or region’s security may cause uncertainty in the markets and may adversely affect a Portfolio’s investments. For example, the Chinese government is involved in a territorial dispute with Taiwan as well as other territorial disputes; the risk of a forced unification with Taiwan by the Chinese government may adversely affect securities of Chinese, Taiwan-based and other issuers both in and outside the region. If the political climate between the United States, China and other countries in Asia continues to deteriorate, economies and markets may be adversely affected. Policy and legislative changes in the U.S. and in other countries are affecting many aspects of financial regulation, and these and other events affecting global markets, such as the United Kingdom’s exit from the European Union; potential trade imbalances with China or other countries; or sanctions or other government actions against Russia, other nations, or individuals or companies (or countermeasures taken in response to such sanctions), may contribute to decreased liquidity and increased volatility in the financial markets. The impact of these changes on the markets, and the implications for market participants, may not be fully known for some time. Economies and financial markets throughout the world are highly interconnected. Economic, financial or political events, trading and tariff arrangements, armed conflict, including Russia’s military invasion of Ukraine and the conflict involving Israel and other countries in the Middle East, terrorism, natural disasters (including the spread of infectious illness) and other circumstances in one country or region could have profound impacts on global economies or markets. Following Russia’s invasion of Ukraine commencing in February of 2022, the United States, the European Union and other countries instituted numerous sanctions against Russia and Belarus and certain companies and individuals. Russia in turn has taken a large number of retaliatory actions, some of which effectively froze Russian securities held by U.S. investors (including U.S. funds such as the Portfolio) and investors in other countries viewed as “unfriendly” by Russia, including securities represented by depositary receipts, effectively precluding the Portfolio from buying, selling, receiving or delivering those securities or accessing income received on such securities. Since then, Russian securities held by investors in the U.S. and other jurisdictions viewed as “unfriendly” by Russia have lost all, or nearly all, of their market value, and many other issuers, securities and markets have been adversely affected. The disruption of the Russian economy has had severe adverse effects on the region and beyond, including significant negative impacts on the markets for certain securities and commodities, such as oil and natural gas, as well as other sectors. As a result, whether or not the Portfolio invests in securities of issuers located in or with significant exposure to countries experiencing economic and financial difficulties, the value and liquidity of the Portfolio’s investments may be negatively affected.
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| Class Z Shares | Small Cap Core Portfolio | Sector Risk [Member] | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk [Text Block] | rr_RiskTextBlock |
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| Class Z Shares | Small Cap Core Portfolio | Redemption Risk [Member] | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk [Text Block] | rr_RiskTextBlock |
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| Class Z Shares | Small Cap Core Portfolio | Capitalization Risk [Member] | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk [Text Block] | rr_RiskTextBlock |
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| Class Z Shares | Small Cap Core Portfolio | Allocation Risk [Member] | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk [Text Block] | rr_RiskTextBlock |
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| Class Z Shares | Small Cap Core Portfolio | Derivatives Risks [Member] | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk [Text Block] | rr_RiskTextBlock |
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| Class Z Shares | Small Cap Core Portfolio | Real Estate Related Securities Risk [Member] | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk [Text Block] | rr_RiskTextBlock |
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| Class Z Shares | Small Cap Core Portfolio | Investment in Other Investment Companies Risk [Member] | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk [Text Block] | rr_RiskTextBlock |
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| Class Z Shares | Small Cap Core Portfolio | Illiquid Investments Risk [Member] | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk [Text Block] | rr_RiskTextBlock |
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| Class Z Shares | Small Cap Core Portfolio | Management Risk [Member] | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| Risk [Text Block] | rr_RiskTextBlock |
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| Class Z Shares | Small Cap Core Portfolio | Class Z | |||||||||
| 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 | |||||||
| Maximum Account Fee | rr_MaximumAccountFeeOverAssets | none | |||||||
| Management Fees | rr_ManagementFeesOverAssets | 0.80% | |||||||
| Distribution and/or Service (12b-1) Fees | rr_DistributionAndService12b1FeesOverAssets | none | |||||||
| Other Expenses: Transfer Agent | rr_Component2OtherExpensesOverAssets | 0.03% | |||||||
| Other Expenses | rr_Component3OtherExpensesOverAssets | 0.06% | |||||||
| Total Other Expenses | rr_OtherExpensesOverAssets | 0.09% | |||||||
| Total Annual Portfolio Operating Expenses | rr_ExpensesOverAssets | 0.89% | |||||||
| After 1 Year | rr_ExpenseExampleYear01 | $ 91 | |||||||
| After 3 Years | rr_ExpenseExampleYear03 | 284 | |||||||
| After 5 Years | rr_ExpenseExampleYear05 | 493 | |||||||
| After 10 Years | rr_ExpenseExampleYear10 | $ 1,096 | |||||||
| 2015 | rr_AnnualReturn2015 | ||||||||
| 2016 | rr_AnnualReturn2016 | 20.63% | |||||||
| 2017 | rr_AnnualReturn2017 | 7.43% | |||||||
| 2018 | rr_AnnualReturn2018 | (13.32%) | |||||||
| 2019 | rr_AnnualReturn2019 | 24.28% | |||||||
| 2020 | rr_AnnualReturn2020 | 12.42% | |||||||
| 2021 | rr_AnnualReturn2021 | 23.24% | |||||||
| 2022 | rr_AnnualReturn2022 | (18.87%) | |||||||
| 2023 | rr_AnnualReturn2023 | 20.95% | |||||||
| 2024 | rr_AnnualReturn2024 | 7.65% | |||||||
| Highest Quarterly Return, Label | rr_HighestQuarterlyReturnLabel | Best Quarter | |||||||
| Highest Quarterly Return, Date | rr_BarChartHighestQuarterlyReturnDate | Dec. 31, 2020 | |||||||
| Highest Quarterly Return | rr_BarChartHighestQuarterlyReturn | 26.77% | |||||||
| Lowest Quarterly Return, Label | rr_LowestQuarterlyReturnLabel | Worst Quarter | |||||||
| Lowest Quarterly Return, Date | rr_BarChartLowestQuarterlyReturnDate | Mar. 31, 2020 | |||||||
| Lowest Quarterly Return | rr_BarChartLowestQuarterlyReturn | (32.51%) | |||||||
| 1 Year | rr_AverageAnnualReturnYear01 | 7.65% | |||||||
| 5 Years | rr_AverageAnnualReturnYear05 | 7.91% | |||||||
| Since Inception | rr_AverageAnnualReturnSinceInception | 7.96% | [1] | ||||||
| Inception Date | rr_AverageAnnualReturnInceptionDate | Dec. 29, 2015 | |||||||
| Class Z Shares | Small Cap Core Portfolio | Return After Taxes on Distributions | Class Z | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| 1 Year | rr_AverageAnnualReturnYear01 | 4.36% | |||||||
| 5 Years | rr_AverageAnnualReturnYear05 | 6.10% | |||||||
| Since Inception | rr_AverageAnnualReturnSinceInception | 6.42% | [1] | ||||||
| Inception Date | rr_AverageAnnualReturnInceptionDate | Dec. 29, 2015 | |||||||
| Class Z Shares | Small Cap Core Portfolio | Return After Taxes on Distributions and Sale of Portfolio Shares | Class Z | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| 1 Year | rr_AverageAnnualReturnYear01 | 6.92% | |||||||
| 5 Years | rr_AverageAnnualReturnYear05 | 6.10% | |||||||
| Since Inception | rr_AverageAnnualReturnSinceInception | 6.12% | [1] | ||||||
| Inception Date | rr_AverageAnnualReturnInceptionDate | Dec. 29, 2015 | |||||||
| Class Z Shares | Small Cap Core Portfolio | S&P 500 Index (reflects no deduction for fees, expenses, or taxes) | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| 1 Year | rr_AverageAnnualReturnYear01 | 25.02% | [2] | ||||||
| 5 Years | rr_AverageAnnualReturnYear05 | 14.53% | [2] | ||||||
| Since Inception | rr_AverageAnnualReturnSinceInception | 14.25% | [1],[2] | ||||||
| Class Z Shares | Small Cap Core Portfolio | Russell 2000 Index (reflects no deduction for fees, expenses, or taxes) | |||||||||
| Risk/Return: | rr_RiskReturnAbstract | ||||||||
| 1 Year | rr_AverageAnnualReturnYear01 | 11.54% | |||||||
| 5 Years | rr_AverageAnnualReturnYear05 | 7.40% | |||||||
| Since Inception | rr_AverageAnnualReturnSinceInception | 8.99% | [1] | ||||||
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