Objective, Primary [Text Block]

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Fund Overview Key Facts About BlackRock Sustainable Balanced Fund, Inc.

Objective [Heading]

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Investment Objective

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The investment objective of BlackRock Sustainable Balanced Fund, Inc. (the “Fund”) is to seek the highest total investment return through a fully managed investment policy utilizing equity, debt (including money market) and convertible securities.

Expense [Heading]

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Fees and Expenses of the Fund

Expense Narrative [Text Block]

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This table describes the fees and expenses that you may pay if you buy, hold and sell Class K Shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to your financial professional or your selected securities dealer, broker, investment adviser, service provider or industry professional (including BlackRock Advisors, LLC (“BlackRock”) and its affiliates) (each, a “Financial Intermediary”), which are not reflected in the table and example below.

Operating Expenses Caption [Text]

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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

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June 30, 2025

Portfolio Turnover [Heading]

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Portfolio Turnover:

Portfolio Turnover [Text Block]

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The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s turnover rate was 152% of the average value of its portfolio.

Portfolio Turnover, Rate

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152.00%

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

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The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Fund’s most recent annual report, which does not include Acquired Fund Fees and Expenses.

Expense Example [Heading]

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Example:

Expense Example Narrative [Text Block]

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This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes 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. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Strategy [Heading]

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Principal Investment Strategies of the Fund

Strategy Narrative [Text Block]

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The Fund invests in a combination of equity securities, fixed-income securities and derivatives. The proportion the Fund invests in each category at any given time depends on Fund management’s view of how attractive that category appears relative to the others. The Fund intends to invest at least 25% of its assets in equity securities and at least 25% of its assets in senior fixed income securities, such as U.S. government debt securities, corporate debt securities, and mortgage-backed and asset-backed securities.

The Fund seeks to maintain certain ESG characteristics, climate risk exposure and climate opportunities relative to the blended benchmark, which is comprised as follows: 60% MSCI All Country World Index, 40% Bloomberg U.S. Aggregate Bond Index (the “Blended Benchmark”). Specifically, the Fund generally seeks to invest in a portfolio that, in BlackRock’s view, (i) has an aggregate ESG assessment that is better than that of the Blended Benchmark, (ii) has an aggregate carbon emissions assessment that is lower than that of the Blended Benchmark, and (iii) in the aggregate, includes issuers that BlackRock believes are better positioned to capture climate opportunities relative to the issuers in the Blended Benchmark. The Fund may invest in other sectors that are not included in such assessments.

With respect to the Fund’s equity investments, the Fund primarily intends to invest in equity securities or other financial instruments that are components of, or have characteristics similar to, the securities included in the MSCI All Country World Index (the “ACWI”). The ACWI is a capitalization-weighted index from a broad range of industries chosen for market size, liquidity and industry group representation. In selecting equity investments, the Fund primarily uses proprietary return forecast models that incorporate quantitative analysis. Equity securities include common stock, preferred stock and convertible securities. The Fund primarily seeks to buy common stock and may also invest in preferred stock and convertible securities. From time to time, the Fund may invest in shares of companies through “new issues” or initial public offerings (“IPOs”). The Fund may invest in securities of both U.S. or non-U.S. issuers without limit, which can be U.S. dollar based or non-U.S. dollar based and may be currency hedged or unhedged. The Fund may invest in securities of companies of any market capitalization.

With respect to the Fund’s fixed-income investments, the Fund will invest primarily using model-based asset allocation and security selection models. The Fund may invest in obligations issued or guaranteed by the U.S. Government, its agencies or instrumentalities; mortgage-backed securities issued or guaranteed by the U.S. Government or its agencies or instrumentalities, including U.S. agency mortgage pass-through securities; commercial mortgage-backed securities; mortgage to-be-announced (“TBA”) securities; debt obligations of U.S. issuers, including corporate bonds and green bonds (which are bonds with proceeds that are used to fund eligible projects with specific environmental benefits); municipal securities; asset-backed securities; and U.S.-registered dollar-denominated debt obligations of foreign issuers. The Fund may invest in bonds issued by companies located in countries other than the United States, including companies in emerging markets. These securities may have all types of interest rate payment and reset terms, including fixed rate, adjustable rate, floating rate, zero coupon, contingent, deferred, payment in kind and auction rate features. The Fund seeks to invest a substantial portion of its assets in U.S.-registered, dollar-denominated bonds. The Fund may invest up to 10% of its assets in securities rated below investment grade (“high yield” or “junk” bonds). The Fund may invest in bonds of any maturity or duration.

The Fund may invest a significant portion of its fixed income holdings in U.S. agency mortgage pass-through securities, which are securities issued by entities such as the Government National Mortgage Association (“GNMA”) and the Federal National Mortgage Association that are backed by pools of mortgages. Most transactions in mortgage pass-through securities occur through standardized contracts for future delivery in which the exact mortgage-backed securities to be delivered are not specified until a few days prior to settlement. The Fund expects to enter into such contracts on a regular basis. The Fund may also seek to gain exposure to mortgage or government-backed securities that fund societal opportunity projects or environmental development, among other ESG related issues.

The Fund may use derivatives, including options, futures, swaps (including, but not limited to, total return swaps) forward contracts and various other instruments, both to seek to increase the return of the Fund and to hedge (or protect) the value of its assets against adverse movements in currency exchange rates, interest rates and movements in the securities markets. The Fund may also invest in indexed and inverse securities.

To determine the Fund’s investable universe, Fund management will first seek to screen out certain issuers based on ESG criteria determined by BlackRock, subject to the considerations noted below. Such screening criteria principally includes: (i) issuers that derive more than zero percent of revenue from the production of controversial weapons; (ii) issuers that derive more than zero percent of revenue from the production of civilian firearms; (iii) issuers that derive more than zero percent of revenue from the production of tobacco-related products; (iv) issuers that derive more than five percent of revenue from thermal coal generation, unless such issuers either (a) have made certain commitments to reduce climate impact or (b) derive at least fifty percent of revenue from alternative energy sources; (v) issuers that derive more than five percent of revenue from thermal coal mining; (vi) issuers that derive more than

five percent of revenue from oil sands extraction, unless the issuers have set certain targets to reduce climate impact; and (vii) issuers identified as violators of the United Nations Global Compact, which are globally accepted principles covering corporate behavior in the areas of human rights, labor, environment, and anti-corruption. Notwithstanding the foregoing, the Fund may invest in green bonds of issuers that exceed the thresholds stated in (iv), (v) and (vi) above. The Fund relies on one or more third-party ratings agencies to identify issuers for purposes of the above screening criteria. Third-party rating agencies may base the above screening criteria on an estimate when revenue for a covered business activity is not disclosed by the issuer or publicly available.

The Fund’s screening criteria is measured at the time of investment and is dependent upon information and data that may be incomplete, inaccurate, unavailable or estimated. Where the Fund’s criteria looks solely to third-party ratings or data, issuers are only screened to the extent such ratings or data have been assigned or made available by the third parties. This screening criteria is subject to change over time at BlackRock’s discretion. In addition, the Fund may gain indirect exposure (through, including but not limited to, derivatives and investments in other investment companies) to issuers with exposures that are inconsistent with the ESG-related criteria used by Fund management.

Fund management selects and weights securities based on an issuer’s ability to manage the ESG risks to which its business is exposed, as determined by BlackRock. Fund management makes such determinations based on BlackRock’s ESG research, which includes due diligence of the ESG risks and opportunities facing an issuer, as well as third-party ESG ratings. BlackRock researches and develops investment insights related to economic transition, which include target carbon transition readiness and climate opportunities.

While Fund management considers ESG characteristics as well as climate risk exposure and climate opportunities, only one or two of these categories may be considered with respect to a particular investment or sector, and categories may be weighted differently according to the type of investment being considered.

Risk [Heading]

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Principal Risks of Investing in the Fund

Bar Chart and Performance Table [Heading]

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Performance Information

Performance Narrative [Text Block]

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The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. Class K Shares commenced operations on January 25, 2018. As a result, the returns shown below for Class K Shares prior to January 25, 2018 are those of the Fund’s Institutional Shares, which are not offered in this prospectus. The performance of Class K Shares would be substantially similar to Institutional Shares because Class K Shares and Institutional Shares are invested in the same portfolio of securities and performance would differ only to the extent that Institutional Shares and Class K Shares have different expenses. The actual returns of Class K Shares would have been higher than those of Institutional Shares because Class K Shares have lower expenses than Institutional Shares.

Effective April 8, 2022, the Fund changed its name, investment process and investment strategies. Performance for the periods prior to April 8, 2022 shown below is based on the investment process and investment strategies utilized by the Fund under the name “BlackRock Balanced Capital Fund, Inc.” The table compares the Fund’s performance to that of the Bloomberg U.S. Aggregate Bond Index, the MSCI All Country World Index and a customized weighted index comprised of the returns of the MSCI All Country World Index (60%) and the Bloomberg U.S. Aggregate Bond Index (40%). To the extent that dividends and distributions have been paid by the Fund, the performance information for the Fund in the chart and table assumes reinvestment of the dividends and distributions. As with all such investments, past performance (before and after taxes) is not an indication of future results. The table includes all applicable fees. If the Fund’s investment manager and its affiliates had not waived or reimbursed certain Fund expenses during these

periods, the Fund’s returns would have been lower. Updated information on the Fund’s performance, including its current net asset value, can be obtained by visiting http://www.blackrock.com or can be obtained by phone at (800) 882-0052.

Performance Information Illustrates Variability of Returns [Text]

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The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund.

Performance Availability Phone [Text]

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(800) 882-0052

Performance Availability Website Address [Text]

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http://www.blackrock.com

Performance Past Does Not Indicate Future [Text]

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As with all such investments, past performance (before and after taxes) is not an indication of future results.

Bar Chart [Heading]

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Class K Shares ANNUAL TOTAL RETURNS BlackRock Sustainable Balanced Fund, Inc. As of 12/31

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During the ten-year period shown in the bar chart, the highest return for a quarter was 15.52% (quarter ended June 30, 2020) and the lowest return for a quarter was -12.99% (quarter ended March 31, 2020). The year-to-date return as of June 30, 2023 was 10.40%.

Performance Table Heading

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For the periods ended 12/31/22 Average Annual Total Returns

Performance Table Uses Highest Federal Rate

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After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

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Actual after-tax returns depend on the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Performance Table Narrative

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After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Risk Lose Money [Member]

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Equity Securities Risk [Member]

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You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Debt Securities Risk [Member]

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■Equity Securities Risk — Stock markets are volatile. The price of equity securities fluctuates based on changes in a company’s financial condition and overall market and economic conditions.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | ESG Investing Risk [Member]

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■Debt Securities Risk — Debt securities, such as bonds, involve interest rate risk, credit risk, extension risk, and prepayment risk, among other things. Interest Rate Risk — The market value of bonds and other fixed-income securities changes in response to interest rate changes and other factors. Interest rate risk is the risk that prices of bonds and other fixed-income securities will increase as interest rates fall and decrease as interest rates rise. The Fund may be subject to a greater risk of rising interest rates due to the recent period of historically low interest rates. For example, if interest rates increase by 1%, assuming a current portfolio duration of ten years, and all other factors being equal, the value of the Fund’s investments would be expected to decrease by 10%. (Duration is a measure of the price sensitivity of a debt security or portfolio of debt securities to relative changes in interest rates.) The magnitude of these fluctuations in the market price of bonds and other fixed-income securities is generally greater for those securities with longer maturities. Fluctuations in the market price of the Fund’s investments will not affect interest income derived from instruments already owned by the Fund, but will be reflected in the Fund’s net asset value. The Fund may lose money if short-term or long-term interest rates rise sharply in a manner not anticipated by Fund management.To the extent the Fund invests in debt securities that may be prepaid at the option of the obligor (such as mortgage-backed securities), the sensitivity of such securities to changes in interest rates may increase (to the detriment of the Fund) when interest rates rise. Moreover, because rates on certain floating rate debt securities typically reset only periodically, changes in prevailing interest rates (and particularly sudden and significant changes) can be expected to cause some fluctuations in the net asset value of the Fund to the extent that it invests in floating rate debt securities.These basic principles of bond prices also apply to U.S. Government securities. A security backed by the “full faith and credit” of the U.S. Government is guaranteed only as to its stated interest rate and face value at maturity, not its current market price. Just like other fixed-income securities, government-guaranteed securities will fluctuate in value when interest rates change.A general rise in interest rates has the potential to cause investors to move out of fixed-income securities on a large scale, which may increase redemptions from funds that hold large amounts of fixed-income securities. Heavy redemptions could cause the Fund to sell assets at inopportune times or at a loss or depressed value and could hurt the Fund’s performance.Credit Risk — Credit risk refers to the possibility that the issuer of a debt security (i.e., the borrower) will not be able to make payments of interest and principal when due. Changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Fund’s investment in that issuer. The degree of credit risk depends on both the financial condition of the issuer and the terms of the obligation. Extension Risk — When interest rates rise, certain obligations will be paid off by the obligor more slowly than anticipated, causing the value of these obligations to fall. Prepayment Risk — When interest rates fall, certain obligations will be paid off by the obligor more quickly than originally anticipated, and the Fund may have to invest the proceeds in securities with lower yields.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Convertible Securities Risk [Member]

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■ESG Investing Risk — The Fund intends to screen out particular issuers pursuant to certain criteria established by BlackRock, and to measure ESG characteristics, including characteristics related to climate, with respect to certain investments pursuant to a methodology determined by BlackRock. This may affect the Fund’s exposure to certain issuers and the Fund may forego certain investment opportunities. The Fund’s results may be lower than other funds that do not seek to invest in issuers based on ESG criteria, or that use a different methodology to screen out issuers or evaluate ESG criteria. The Fund seeks to identify issuers that it believes are better positioned to manage ESG risks and opportunities related to their businesses and to avoid certain companies and industries with ESG related risks, but investors may differ in their views of what constitutes positive or negative ESG criteria. As a result, the Fund may invest in issuers that do not reflect the beliefs and values of any particular investor. In evaluating a security or issuer based on ESG criteria, BlackRock is dependent upon certain information and data from third party providers of ESG research, which may be incomplete, inaccurate or unavailable. As a result, there is a risk that BlackRock may incorrectly assess a security or issuer. There is also a risk that BlackRock may not apply the relevant ESG criteria correctly or that the Fund could have indirect exposure to issuers who do not meet the relevant ESG criteria used by the Fund. Neither the Fund nor BlackRock make any representation or warranty, express or implied, with respect to the fairness, correctness, accuracy, reasonableness or completeness of such ESG assessment. There may be limitations with respect to availability of ESG data in certain sectors, as well as limited availability of investments with positive ESG assessments in certain sectors. BlackRock’s evaluation of ESG criteria is subjective and may change over time.
The Fund may not include all instruments in its ESG-related assessments, and may place weight on other factors when selecting investments. In addition, the Fund may not be successful in its ESG-related objectives. There is no guarantee that these objectives will be achieved, and such assessments are at BlackRock’s discretion.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Corporate Loans Risk [Member]

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■Convertible Securities Risk — The market value of a convertible security performs like that of a regular debt security; that is, if market interest rates rise, the value of a convertible security usually falls. In addition, convertible securities are subject to the risk that the issuer will not be able to pay interest, principal or dividends when due, and their market value may change based on changes in the issuer’s credit rating or the market’s perception of the issuer’s creditworthiness. Since it derives a portion of its value from the common stock into which it may be converted, a convertible security is also subject to the same types of market and issuer risks that apply to the underlying common stock, including the potential for increased volatility in the price of the convertible security.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Derivatives Risk [Member]

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■Corporate Loans Risk — Commercial banks and other financial institutions or institutional investors make corporate loans to companies that need capital to grow or restructure. Borrowers generally pay interest on corporate loans at rates that change in response to changes in market interest rates such as the Secured Overnight Financing Rate (“SOFR”), the London Interbank Offered Rate (“LIBOR”) or the prime rates of U.S. banks. As a result, the value of corporate loan investments is generally less exposed to the adverse effects of shifts in market interest rates than investments that pay a fixed rate of interest. The market for corporate loans may be subject to irregular trading activity and wide bid/ask spreads. In addition, transactions in corporate loans may settle on a delayed basis. As a result, the proceeds from the sale of corporate loans may not be readily available to make additional investments or to meet the Fund’s redemption obligations. To the extent the extended settlement process gives rise to short-term liquidity needs, the Fund may hold additional cash, sell investments or temporarily borrow from banks and other lenders.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Emerging Markets Risk [Member]

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■Derivatives Risk — The Fund’s use of derivatives may increase its costs, reduce the Fund’s returns and/or increase volatility. Derivatives involve significant risks, including: Leverage Risk — The Fund’s use of derivatives can magnify the Fund’s gains and losses. Relatively small market movements may result in large changes in the value of a derivatives position and can result in losses that greatly exceed the amount originally invested. Market Risk — Some derivatives are more sensitive to interest rate changes and market price fluctuations than other securities. The Fund could also suffer losses related to its derivatives positions as a result of unanticipated market movements, which losses are potentially unlimited. Finally, BlackRock may not be able to predict correctly the direction of securities prices, interest rates and other economic factors, which could cause the Fund’s derivatives positions to lose value. Counterparty Risk — Derivatives are also subject to counterparty risk, which is the risk that the other party in the transaction will be unable or unwilling to fulfill its contractual obligation, and the related risks of having concentrated exposure to such a counterparty. Illiquidity Risk — The possible lack of a liquid secondary market for derivatives and the resulting inability of the Fund to sell or otherwise close a derivatives position could expose the Fund to losses and could make derivatives more difficult for the Fund to value accurately. Operational Risk — The use of derivatives includes the risk of potential operational issues, including documentation issues, settlement issues, systems failures, inadequate controls and human error. Legal Risk — The risk of insufficient documentation, insufficient capacity or authority of counterparty, or legality or enforceability of a contract. Volatility and Correlation Risk — Volatility is defined as the characteristic of a security, an index or a market to fluctuate significantly in price within a short time period. A risk of the Fund’s use of derivatives is that the fluctuations in their values may not correlate with the overall securities markets. Valuation Risk — Valuation for derivatives may not be readily available in the market. Valuation may be more difficult in times of market turmoil since many investors and market makers may be reluctant to purchase complex instruments or quote prices for them. Hedging Risk — Hedges are sometimes subject to imperfect matching between the derivative and the underlying security, and there can be no assurance that the Fund’s hedging transactions will be effective. The use of hedging may result in certain adverse tax consequences. Tax Risk — Certain aspects of the tax treatment of derivative instruments, including swap agreements and commodity-linked derivative instruments, are currently unclear and may be affected by changes in legislation, regulations or other legally binding authority. Such treatment may be less favorable than that given to a direct investment in an underlying asset and may adversely affect the timing, character and amount of income the Fund realizes from its investments.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Foreign Securities Risk [Member]

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■Emerging Markets Risk — Emerging markets are riskier than more developed markets because they tend to develop unevenly and may never fully develop. Investments in emerging markets may be considered speculative. Emerging markets are more likely to experience hyperinflation and currency devaluations, which adversely affect returns to U.S. investors. In addition, many emerging securities markets have far lower trading volumes and less liquidity than developed markets.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | High Portfolio Turnover Risk [Member]

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■Foreign Securities Risk — Foreign investments often involve special risks not present in U.S. investments that can increase the chances that the Fund will lose money. These risks include: ■The Fund generally holds its foreign securities and cash in foreign banks and securities depositories, which may be recently organized or new to the foreign custody business and may be subject to only limited or no regulatory oversight.■Changes in foreign currency exchange rates can affect the value of the Fund’s portfolio.■The economies of certain foreign markets may not compare favorably with the economy of the United States with respect to such issues as growth of gross national product, reinvestment of capital, resources and balance of payments position.■The governments of certain countries, or the U.S. Government with respect to certain countries, may prohibit or impose substantial restrictions through capital controls and/or sanctions on foreign investments in the capital markets or certain industries in those countries, which may prohibit or restrict the ability to own or transfer currency, securities, derivatives or other assets.■Many foreign governments do not supervise and regulate stock exchanges, brokers and the sale of securities to the same extent as does the United States and may not have laws to protect investors that are comparable to U.S. securities laws.■Settlement and clearance procedures in certain foreign markets may result in delays in payment for or delivery of securities not typically associated with settlement and clearance of U.S. investments.■The Fund’s claims to recover foreign withholding taxes may not be successful, and if the likelihood of recovery of foreign withholding taxes materially decreases, due to, for example, a change in tax regulation or approach in the foreign country, accruals in the Fund’s net asset value for such refunds may be written down partially or in full, which will adversely affect the Fund’s net asset value.■The European financial markets have recently experienced volatility and adverse trends due to concerns about economic downturns in, or rising government debt levels of, several European countries as well as acts of war in the region. These events may spread to other countries in Europe and may affect the value and liquidity of certain of the Fund’s investments.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Indexed and Inverse Securities Risk [Member]

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■High Portfolio Turnover Risk — The Fund may engage in active and frequent trading of its portfolio securities. High portfolio turnover (more than 100%) may result in increased transaction costs to the Fund, including brokerage commissions, dealer mark-ups and other transaction costs on the sale of the securities and on reinvestment in other securities. The sale of Fund portfolio securities may result in the realization and/or distribution to shareholders of higher capital gains or losses as compared to a fund with less active trading policies. These effects of higher than normal portfolio turnover may adversely affect Fund performance. In addition, investment in mortgage dollar rolls and participation in to-be-announced (“TBA”) transactions may significantly increase the Fund’s portfolio turnover rate. A TBA transaction is a method of trading mortgage-backed securities where the buyer and seller agree upon general trade parameters such as agency, settlement date, par amount, and price at the time the contract is entered into but the mortgage-backed securities are delivered in the future, generally 30 days later.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Junk Bonds Risk [Member]

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■Indexed and Inverse Securities Risk — Indexed and inverse securities provide a potential return based on a particular index of value or interest rates. The Fund’s return on these securities will be subject to risk with respect to the value of the particular index. These securities are subject to leverage risk and correlation risk. Certain indexed and inverse securities have greater sensitivity to changes in interest rates or index levels than other securities, and the Fund’s investment in such instruments may decline significantly in value if interest rates or index levels move in a way Fund management does not anticipate.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Leverage Risk [Member]

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■Junk Bonds Risk — Although junk bonds generally pay higher rates of interest than investment grade bonds, junk bonds are high risk investments that are considered speculative and may cause income and principal losses for the Fund.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Market Risk and Selection Risk [Member]

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■Leverage Risk — Some transactions may give rise to a form of economic leverage. These transactions may include, among others, derivatives, and may expose the Fund to greater risk and increase its costs. The use of leverage may cause the Fund to liquidate portfolio positions when it may not be advantageous to do so to satisfy its obligations or to meet the applicable requirements of the Investment Company Act of 1940, as amended, and the rules thereunder. Increases and decreases in the value of the Fund’s portfolio will be magnified when the Fund uses leverage.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Mid Cap Securities Risk [Member]

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■Market Risk and Selection Risk — Market risk is the risk that one or more markets in which the Fund invests will go down in value, including the possibility that the markets will go down sharply and unpredictably. The value of a security or other asset may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security or other asset, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Local, regional or global events such as war, acts of terrorism, the spread of infectious illness or other public health issues like pandemics or epidemics, recessions, or other events could have a significant impact on the Fund and its investments. Selection risk is the risk that the securities selected by Fund management will underperform the markets, the relevant indices or the securities selected by other funds with similar investment objectives and investment strategies. The Fund seeks to pursue its investment objective by using proprietary models that incorporate quantitative analysis and is subject to “Model Risk” as described below. This means you may lose money. An outbreak of an infectious coronavirus (COVID-19) that was first detected in December 2019 developed into a global pandemic that has resulted in numerous disruptions in the market and has had significant economic impact leaving general concern and uncertainty. Although vaccines have been developed and approved for use by various governments, the duration of the pandemic and its effects cannot be predicted with certainty. The impact of this coronavirus, and other epidemics and pandemics that may arise in the future, could affect the economies of many nations, individual companies and the market in general ways that cannot necessarily be foreseen at the present time.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Model Risk [Member]

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■Mid Cap Securities Risk — The securities of mid cap companies generally trade in lower volumes and are generally subject to greater and less predictable price changes than the securities of larger capitalization companies.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Money Market Securities Risk [Member]

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■Model Risk — The Fund seeks to pursue its investment objective by using proprietary models that incorporate quantitative analysis. Investments selected using these models may perform differently than as forecasted due to the factors incorporated into the models and the weighting of each factor, changes from historical trends, and issues in the construction and implementation of the models (including, but not limited to, software issues and other technological issues). There is no guarantee that BlackRock’s use of these models will result in effective investment decisions for the Fund.The information and data used in the models may be supplied by third parties. Inaccurate or incomplete data may limit the effectiveness of the models. In addition, some of the data that BlackRock uses may be historical data, which may not accurately predict future market movement. There is a risk that the models will not be successful in selecting investments or in determining the weighting of investment positions that will enable the Fund to achieve its investment objective.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Mortgage and Asset Backed Securities Risks [Member]

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■Money Market Securities Risk — If market conditions improve while the Fund has invested some or all of its assets in high quality money market securities, this strategy could result in reducing the potential gain from the market upswing, thus reducing the Fund’s opportunity to achieve its investment objective.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Municipal Securities Risks [Member]

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■Mortgage- and Asset-Backed Securities Risks — Mortgage- and asset-backed securities represent interests in “pools” of mortgages or other assets, including consumer loans or receivables held in trust. Mortgage- and asset-backed securities are subject to credit, interest rate, prepayment and extension risks. These securities also are subject to risk of default on the underlying mortgage or asset, particularly during periods of economic downturn. Small movements in interest rates (both increases and decreases) may quickly and significantly reduce the value of certain mortgage-backed securities.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | New Issues Risk [Member]

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■Municipal Securities Risks — Municipal securities risks include the ability of the issuer to repay the obligation, the relative lack of information about certain issuers of municipal securities, and the possibility of future legislative changes which could affect the market for and value of municipal securities. Budgetary constraints of local, state, and federal governments upon which the issuers may be relying for funding may also impact municipal securities. These risks include: General Obligation Bonds Risks — Timely payments depend on the issuer’s credit quality, ability to raise tax revenues and ability to maintain an adequate tax base. Revenue Bonds Risks — These payments depend on the money earned by the particular facility or class of facilities, or the amount of revenues derived from another source. Private Activity Bonds Risks — Municipalities and other public authorities issue private activity bonds to finance development of industrial facilities for use by a private enterprise. The private enterprise pays the principal and interest on the bond, and the issuer does not pledge its full faith, credit and taxing power for repayment. Moral Obligation Bonds Risks — Moral obligation bonds are generally issued by special purpose public authorities of a state or municipality. If the issuer is unable to meet its obligations, repayment of these bonds becomes a moral commitment, but not a legal obligation, of the state or municipality. Municipal Notes Risks — Municipal notes are shorter term municipal debt obligations. If there is a shortfall in the anticipated proceeds, the notes may not be fully repaid and the Fund may lose money. Municipal Lease Obligations Risks — In a municipal lease obligation, the issuer agrees to make payments when due on the lease obligation. Although the issuer does not pledge its unlimited taxing power for payment of the lease obligation, the lease obligation is secured by the leased property. Tax-Exempt Status Risk — The Fund and its investment manager will rely on the opinion of issuers’ bond counsel and, in the case of derivative securities, sponsors’ counsel, on the tax-exempt status of interest on municipal bonds and payments under derivative securities. Neither the Fund nor its investment manager will independently review the bases for those tax opinions, which may ultimately be determined to be incorrect and subject the Fund and its shareholders to substantial tax liabilities.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Preferred Securities Risk [Member]

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■“New Issues” Risk — “New issues” are IPOs of equity securities. Securities issued in IPOs have no trading history, and information about the companies may be available for very limited periods. In addition, the prices of securities sold in IPOs may be highly volatile or may decline shortly after the IPO.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Sovereign Debt Risk [Member]

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■Preferred Securities Risk — Preferred securities may pay fixed or adjustable rates of return. Preferred securities are subject to issuer-specific and market risks applicable generally to equity securities. In addition, a company’s preferred securities generally pay dividends only after the company makes required payments to holders of its bonds and other debt. For this reason, the value of preferred securities will usually react more strongly than bonds and other debt to actual or perceived changes in the company’s financial condition or prospects. Preferred securities of smaller companies may be more vulnerable to adverse developments than preferred securities of larger companies.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Structured Securities Risk [Member]

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■Sovereign Debt Risk — Sovereign debt instruments are subject to the risk that a governmental entity may delay or refuse to pay interest or repay principal on its sovereign debt, due, for example, to cash flow problems, insufficient foreign currency reserves, political considerations, the relative size of the governmental entity’s debt position in relation to the economy or the failure to put in place economic reforms required by the International Monetary Fund or other multilateral agencies.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | U S Government Issuer Risk [Member]

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■Structured Securities Risk — Because structured securities of the type in which the Fund may invest typically involve no credit enhancement, their credit risk generally will be equivalent to that of the underlying instruments, index or reference obligation and will also be subject to counterparty risk. The Fund may have the right to receive payments only from the structured security, and generally does not have direct rights against the issuer or the entity that sold the assets to be securitized. In addition to the general risks associated with debt securities discussed herein, structured securities carry additional risks, including, but not limited to: the possibility that distributions from collateral securities will not be adequate to make interest or other payments; the quality of the collateral may decline in value or default; and the possibility that the structured securities are subordinate to other classes. The Fund is permitted to invest in a class of structured securities that is either subordinated or unsubordinated to the right of payment of another class. Subordinated structured securities typically have higher yields and present greater risks than unsubordinated structured securities. Structured securities are typically sold in private placement transactions, and there currently is no active trading market for structured securities. Structured securities are based upon the movement of one or more factors, including currency exchange rates, interest rates, reference bonds and stock indices, and changes in interest rates and impact of these factors may cause significant price fluctuations. Additionally, changes in the reference instrument or security may cause the interest rate on the structured security to be reduced to zero. Certain issuers of such structured securities may be deemed to be “investment companies” as defined in the Investment Company Act. As a result, the Fund’s investment in such securities may be limited by certain investment restrictions contained in the Investment Company Act.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | U S Government Mortgage Related Securities Risk [Member]

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■U.S. Government Issuer Risk — Treasury obligations may differ in their interest rates, maturities, times of issuance and other characteristics. Obligations of U.S. Government agencies and authorities are supported by varying degrees of credit but generally are not backed by the full faith and credit of the U.S. Government. No assurance can be given that the U.S. Government will provide financial support to its agencies and authorities if it is not obligated by law to do so.

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Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Class K Shares

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■U.S. Government Mortgage-Related Securities Risk — There are a number of important differences among the agencies and instrumentalities of the U.S. Government that issue mortgage-related securities and among the securities that they issue. Mortgage-related securities guaranteed by the Government National Mortgage Association (“GNMA” or “Ginnie Mae”) are guaranteed as to the timely payment of principal and interest by GNMA and such guarantee is backed by the full faith and credit of the United States. GNMA securities also are supported by the right of GNMA to borrow funds from the U.S. Treasury to make payments under its guarantee. Mortgage-related securities issued by Fannie Mae or Freddie Mac are solely the obligations of Fannie Mae or Freddie Mac, as the case may be, and are not backed by or entitled to the full faith and credit of the United States but are supported by the right of the issuer to borrow from the Treasury.

Distribution and/or Service (12b-1) Fees

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Management Fee

rr_ManagementFeesOverAssets

0.42%

^[1]

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.07%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

^[2]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.50%

^[2]

Fee Waivers and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.01%)

^[1]

Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements

rr_NetExpensesOverAssets

0.49%

^[1]

rr_ExpenseExampleYear01

$ 50

3 Years

rr_ExpenseExampleYear03

159

rr_ExpenseExampleYear05

279

Year to Date Return, Label

rr_ExpenseExampleYear10

$ 627

2013

rr_AnnualReturn2013

20.35%

2014

rr_AnnualReturn2014

10.99%

2015

rr_AnnualReturn2015

0.39%

2016

rr_AnnualReturn2016

8.53%

2017

rr_AnnualReturn2017

14.62%

2018

rr_AnnualReturn2018

(3.10%)

2019

rr_AnnualReturn2019

21.98%

2020

rr_AnnualReturn2020

15.48%

2021

rr_AnnualReturn2021

16.67%

2022

rr_AnnualReturn2022

(15.41%)

rr_YearToDateReturnLabel

year-to-date return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Jun. 30, 2023

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

10.40%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

highest return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2020

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.52%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

lowest return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2020

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(12.99%)

rr_AverageAnnualReturnYear01

(15.41%)

rr_AverageAnnualReturnYear05

6.14%

Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Return After Taxes on Distributions | Class K Shares

rr_AverageAnnualReturnYear10

8.43%

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rr_AverageAnnualReturnYear01

(16.19%)

rr_AverageAnnualReturnYear05

4.04%

Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Return After Taxes on Distributions and Sale of Fund Shares | Class K Shares

rr_AverageAnnualReturnYear10

5.90%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(8.59%)

rr_AverageAnnualReturnYear05

4.29%

Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | MSCI All Country World Index (Reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear10

6.05%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(18.36%)

rr_AverageAnnualReturnYear05

5.23%

Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | Bloomberg U.S. Aggregate Bond Index (Reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear10

7.98%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(13.01%)

rr_AverageAnnualReturnYear05

0.02%

Class K | BLACKROCK SUSTAINABLE BALANCED FUND, INC. | 60% MSCI All Country World Index/ 40% Bloomberg U.S. Aggregate Bond Index (Reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnYear10

1.06%

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

(16.02%)

rr_AverageAnnualReturnYear05

3.45%