| N-2 | 6 Months Ended |
| Apr. 30, 2023 shares | |
| Cover [Abstract] | |
| Entity Central Index Key | 0001562818 |
| Amendment Flag | false |
| Entity Inv Company Type | N-2 |
| Document Type | N-CSRS |
| Entity Registrant Name | BlackRock Multi-Sector Income Trust |
| General Description of Registrant [Abstract] | |
| Investment Objectives and Practices [Text Block] | Investment Objective BlackRock Multi-Sector Income Trust’s (BIT) (the “Trust”) No assurance can be given that the Trust’s investment objective will be achieved. |
| Risk Factors [Table Text Block] | 9. PRINCIPAL RISKS In the normal course of business, the Trust invests in securities or other instruments and may enter into certain transactions, and such activities subject the Trust to various risks, including among others, fluctuations in the market (market risk) or failure of an issuer to meet all of its obligations. The value of securities or other instruments may also be affected by various factors, including, without limitation: (i) the general economy; (ii) the overall market as well as local, regional or global political and/or social instability; (iii) regulation, taxation or international tax treaties between various countries; or (iv) currency, interest rate and price fluctuations. Local, regional or global events such as war, acts of terrorism, the spread of infectious illness or other public health issues, recessions, or other events could have a significant impact on the Trust and its investments. The Trust may invest without limitation in illiquid or less liquid investments or investments in which no secondary market is readily available or which are otherwise illiquid, including private placement securities. The Trust may not be able to readily dispose of such investments at prices that approximate those at which the Trust could sell such investments if they were more widely traded and, as a result of such illiquidity, the Trust may have to sell other investments or engage in borrowing transactions if necessary to raise funds to meet its obligations. Limited liquidity can also affect the market price of investments, thereby adversely affecting the Trust’s NAV and ability to make dividend distributions. Privately issued debt securities are often of below investment grade quality, frequently are unrated and present many of the same risks as investing in below investment grade public debt securities. Market Risk: Infectious Illness Risk: Valuation Risk: conditions in seven calendar days or less without the sale or disposition significantly changing the market value of the investment. The Trust may experience difficulty in selling illiquid investments in a timely manner at the price that it believes the investments are worth. Prices may fluctuate widely over short or extended periods in response to company, market or economic news. Markets also tend to move in cycles, with periods of rising and falling prices. This volatility may cause the Trust’s NAV to experience significant increases or decreases over short periods of time. If there is a general decline in the securities and other markets, the NAV of the Trust may lose value, regardless of the individual results of the securities and other instruments in which the Trust invests. The price the Trust could receive upon the sale of any particular portfolio investment may differ from the Trust’s valuation of the investment, particularly for securities that trade in thin or volatile markets or that are valued using a fair valuation technique or a price provided by an independent pricing service. Changes to significant unobservable inputs and assumptions (i.e., publicly traded company multiples, growth rate, time to exit) due to the lack of observable inputs may significantly impact the resulting fair value and therefore the Trust’s results of operations. As a result, the price received upon the sale of an investment may be less than the value ascribed by the Trust, and the Trust could realize a greater than expected loss or lesser than expected gain upon the sale of the investment. The Trust’s ability to value its investments may also be impacted by technological issues and/or errors by pricing services or other third-party service providers. Counterparty Credit Risk: A derivative contract may suffer a mark‑to‑market loss if the value of the contract decreases due to an unfavorable change in the market rates or values of the underlying instrument. Losses can also occur if the counterparty does not perform under the contract. With exchange-traded futures and centrally cleared swaps, there is less counterparty credit risk to the Trust since the exchange or clearinghouse, as counterparty to such instruments, guarantees against a possible default. The clearinghouse stands between the buyer and the seller of the contract; therefore, credit risk is limited to failure of the clearinghouse. While offset rights may exist under applicable law, the Trust does not have a contractual right of offset against a clearing broker or clearinghouse in the event of a default (including the bankruptcy or insolvency). Additionally, credit risk exists in exchange-traded futures and centrally cleared swaps with respect to initial and variation margin that is held in a clearing broker’s customer accounts. While clearing brokers are required to segregate customer margin from their own assets, in the event that a clearing broker becomes insolvent or goes into bankruptcy and at that time there is a shortfall in the aggregate amount of margin held by the clearing broker for all its clients, typically the shortfall would be allocated on a pro rata basis across all the clearing broker’s customers, potentially resulting in losses to the Trust. Concentration Risk: The Trust invests a significant portion of its assets in high yield securities. High yield securities that are rated below investment-grade (commonly referred to as “junk bonds”) or are unrated may be deemed speculative, involve greater levels of risk than higher-rated securities of similar maturity and are more likely to default. High yield securities may be issued by less creditworthy issuers, and issuers of high yield securities may be unable to meet their interest or principal payment obligations. High yield securities are subject to extreme price fluctuations, may be less liquid than higher rated fixed-income securities, even under normal economic conditions, and frequently have redemption features. The Trust invests a significant portion of its assets in fixed-income securities and/or uses derivatives tied to the fixed-income markets. Changes in market interest rates or economic conditions may affect the value and/or liquidity of such investments. Interest rate risk is the risk that prices of bonds and other fixed-income securities will decrease as interest rates rise and increase as interest rates fall. The Trust may be subject to a greater risk of rising interest rates due to the recent period of historically low interest rates. The Federal Reserve has recently begun to raise the federal funds rate as part of its efforts to address inflation. There is a risk that interest rates will continue to rise, which will likely drive down the prices of bonds and other fixed-income securities, and could negatively impact the Trust’s performance. The Trust invests a significant portion of its assets in securities of issuers located in the United States. A decrease in imports or exports, changes in trade regulations, inflation and/or an economic recession in the United States may have a material adverse effect on the U.S. economy and the securities listed on U.S. exchanges. Proposed and adopted policy and legislative changes in the United States may also have a significant effect on U.S. markets generally, as well as on the value of certain securities. Governmental agencies project that the United States will continue to maintain elevated public debt levels for the foreseeable future which may constrain future economic growth. Circumstances could arise that could prevent the timely payment of interest or principal on U.S. government debt, such as reaching the legislative “debt ceiling.” Such non‑payment would result in substantial negative consequences for the U.S. economy and the global financial system. If U.S. relations with certain countries deteriorate, it could adversely affect issuers that rely on the United States for trade. The United States has also experienced increased internal unrest and discord. If these trends were to continue, they may have an adverse impact on the U.S. economy and the issuers in which the Trust invests. The Trust invests a significant portion of its assets in securities backed by commercial or residential mortgage loans or in issuers that hold mortgage and other asset-backed securities. When a Trust concentrates its investments in this manner, it assumes a greater risk of prepayment or payment extension by securities issuers. Changes in economic conditions, including delinquencies and/or defaults on assets underlying these securities, can affect the value, income and/or liquidity of such positions. Investment percentages in these securities are presented in the Schedule of Investments. LIBOR Transition Risk: mechanism by identifying benchmark rates based on SOFR that will replace LIBOR in certain financial contracts after June 30, 2023. The ultimate effect of the LIBOR transition process on the Trust is uncertain. |
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | |
| Capital Stock [Table Text Block] | 10. CAPITAL SHARE TRANSACTIONS The Trust is authorized to issue an unlimited number of shares, all of which were initially classified as Common Shares. The Board is authorized, however, to reclassify any unissued Common Shares to Preferred Shares without the approval of Common Shareholders. Common Shares For the periods shown, shares issued and outstanding increased by the following amounts as a result of dividend reinvestment: Six Months Ended Year Ended Trust Name 04/30/23 10/31/22 BIT 39,531 74,296 The Trust participates in an open market share repurchase program (the “Repurchase Program”). From December 1, 2021 through November 30, 2022, the Trust may repurchase up to 5% of its outstanding common shares under the Repurchase Program, based on common shares outstanding as of the close of business on November 30, 2021, subject to certain conditions. From December 1, 2022 through November 30, 2023, the Trust may repurchase up to 5% of its outstanding common shares under the Repurchase Program, based on common shares outstanding as of the close of business on November 30, 2022, subject to certain conditions. The Repurchase Program has an accretive effect as shares are purchased at a discount to the Trust’s NAV. There is no assurance that the Trust will purchase shares in any particular amounts. For the six months ended April 30, 2023, the Trust did not repurchase any shares. The Trust has filed a prospectus with the SEC allowing it to issue an additional 15,000,000 Common Shares, through an equity Shelf Offering. Under the Shelf Offering, the Trust, subject to market conditions, may raise additional equity capital from time to time in varying amounts and utilizing various offering methods at a net price at or above the Trust’s NAV per Common Share (calculated within 48 hours of pricing). As of period end, 15,000,000 Common Shares remain available for issuance under the Shelf Offering. For the six months ended April 30, 2023, Common Shares issued and outstanding under the Shelf Offering remained constant. See Additional Information - Shelf Offering Program for additional information. Initial costs incurred by the Trust in connection with its Shelf Offering are recorded as “Deferred offering costs” in the Statement of Assets and Liabilities. As shares are sold, a portion of the costs attributable to the shares sold will be charged against paid‑in‑capital. Any remaining deferred charges at the end of the shelf offering period will be charged to expense. |
| Outstanding Securities [Table Text Block] | The Trust is authorized to issue an unlimited number of shares, all of which were initially classified as Common Shares. |
| Outstanding Security, Held [Shares] | 37,725,451 |
| Market Risk [Member] | |
| General Description of Registrant [Abstract] | |
| Risk [Text Block] | Market Risk: |
| Infectious Illness Risk [Member] | |
| General Description of Registrant [Abstract] | |
| Risk [Text Block] | Infectious Illness Risk: |
| Valuation Risk [Member] | |
| General Description of Registrant [Abstract] | |
| Risk [Text Block] | Valuation Risk: conditions in seven calendar days or less without the sale or disposition significantly changing the market value of the investment. The Trust may experience difficulty in selling illiquid investments in a timely manner at the price that it believes the investments are worth. Prices may fluctuate widely over short or extended periods in response to company, market or economic news. Markets also tend to move in cycles, with periods of rising and falling prices. This volatility may cause the Trust’s NAV to experience significant increases or decreases over short periods of time. If there is a general decline in the securities and other markets, the NAV of the Trust may lose value, regardless of the individual results of the securities and other instruments in which the Trust invests. The price the Trust could receive upon the sale of any particular portfolio investment may differ from the Trust’s valuation of the investment, particularly for securities that trade in thin or volatile markets or that are valued using a fair valuation technique or a price provided by an independent pricing service. Changes to significant unobservable inputs and assumptions (i.e., publicly traded company multiples, growth rate, time to exit) due to the lack of observable inputs may significantly impact the resulting fair value and therefore the Trust’s results of operations. As a result, the price received upon the sale of an investment may be less than the value ascribed by the Trust, and the Trust could realize a greater than expected loss or lesser than expected gain upon the sale of the investment. The Trust’s ability to value its investments may also be impacted by technological issues and/or errors by pricing services or other third-party service providers. |
| Counterparty Credit Risk [Member] | |
| General Description of Registrant [Abstract] | |
| Risk [Text Block] | Counterparty Credit Risk: A derivative contract may suffer a mark‑to‑market loss if the value of the contract decreases due to an unfavorable change in the market rates or values of the underlying instrument. Losses can also occur if the counterparty does not perform under the contract. With exchange-traded futures and centrally cleared swaps, there is less counterparty credit risk to the Trust since the exchange or clearinghouse, as counterparty to such instruments, guarantees against a possible default. The clearinghouse stands between the buyer and the seller of the contract; therefore, credit risk is limited to failure of the clearinghouse. While offset rights may exist under applicable law, the Trust does not have a contractual right of offset against a clearing broker or clearinghouse in the event of a default (including the bankruptcy or insolvency). Additionally, credit risk exists in exchange-traded futures and centrally cleared swaps with respect to initial and variation margin that is held in a clearing broker’s customer accounts. While clearing brokers are required to segregate customer margin from their own assets, in the event that a clearing broker becomes insolvent or goes into bankruptcy and at that time there is a shortfall in the aggregate amount of margin held by the clearing broker for all its clients, typically the shortfall would be allocated on a pro rata basis across all the clearing broker’s customers, potentially resulting in losses to the Trust. |
| Concentration Risk [Member] | |
| General Description of Registrant [Abstract] | |
| Risk [Text Block] | Concentration Risk: The Trust invests a significant portion of its assets in high yield securities. High yield securities that are rated below investment-grade (commonly referred to as “junk bonds”) or are unrated may be deemed speculative, involve greater levels of risk than higher-rated securities of similar maturity and are more likely to default. High yield securities may be issued by less creditworthy issuers, and issuers of high yield securities may be unable to meet their interest or principal payment obligations. High yield securities are subject to extreme price fluctuations, may be less liquid than higher rated fixed-income securities, even under normal economic conditions, and frequently have redemption features. The Trust invests a significant portion of its assets in fixed-income securities and/or uses derivatives tied to the fixed-income markets. Changes in market interest rates or economic conditions may affect the value and/or liquidity of such investments. Interest rate risk is the risk that prices of bonds and other fixed-income securities will decrease as interest rates rise and increase as interest rates fall. The Trust may be subject to a greater risk of rising interest rates due to the recent period of historically low interest rates. The Federal Reserve has recently begun to raise the federal funds rate as part of its efforts to address inflation. There is a risk that interest rates will continue to rise, which will likely drive down the prices of bonds and other fixed-income securities, and could negatively impact the Trust’s performance. The Trust invests a significant portion of its assets in securities of issuers located in the United States. A decrease in imports or exports, changes in trade regulations, inflation and/or an economic recession in the United States may have a material adverse effect on the U.S. economy and the securities listed on U.S. exchanges. Proposed and adopted policy and legislative changes in the United States may also have a significant effect on U.S. markets generally, as well as on the value of certain securities. Governmental agencies project that the United States will continue to maintain elevated public debt levels for the foreseeable future which may constrain future economic growth. Circumstances could arise that could prevent the timely payment of interest or principal on U.S. government debt, such as reaching the legislative “debt ceiling.” Such non‑payment would result in substantial negative consequences for the U.S. economy and the global financial system. If U.S. relations with certain countries deteriorate, it could adversely affect issuers that rely on the United States for trade. The United States has also experienced increased internal unrest and discord. If these trends were to continue, they may have an adverse impact on the U.S. economy and the issuers in which the Trust invests. The Trust invests a significant portion of its assets in securities backed by commercial or residential mortgage loans or in issuers that hold mortgage and other asset-backed securities. When a Trust concentrates its investments in this manner, it assumes a greater risk of prepayment or payment extension by securities issuers. Changes in economic conditions, including delinquencies and/or defaults on assets underlying these securities, can affect the value, income and/or liquidity of such positions. Investment percentages in these securities are presented in the Schedule of Investments. |
| LIBOR Transition Risk [Member] | |
| General Description of Registrant [Abstract] | |
| Risk [Text Block] | LIBOR Transition Risk: mechanism by identifying benchmark rates based on SOFR that will replace LIBOR in certain financial contracts after June 30, 2023. The ultimate effect of the LIBOR transition process on the Trust is uncertain. |
