S000069099 [Member] Investment Risks - WESTERN ASSET SMASh SERIES CORE COMPLETION FUND	Feb. 28, 2025
Market events risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Market events risk. The market values of securities or other assets will fluctuate, sometimes sharply and unpredictably, due to factors such as economic events, governmental actions or intervention, actions taken by the U.S. Federal Reserve or foreign central banks, market disruptions caused by trade disputes, labor strikes or other factors, political developments, armed conflicts, economic sanctions and countermeasures in response to sanctions, major cybersecurity events, the global and domestic effects of widespread or local health, weather or climate events, and other factors that may or may not be related to the issuer of the security or other asset. Economies and financial markets throughout the world are increasingly interconnected. Economic, financial or political events, trading and tariff arrangements, public health events, terrorism, wars, natural disasters and other circumstances in one country or region could have profound impacts on global economies or markets. As a result, whether or not the fund invests in securities of issuers located in or with significant exposure to the countries or markets directly affected, the value and liquidity of the fund’s investments may be negatively affected. Ongoing armed conflicts between Russia and Ukraine in Europe and among Israel, Hamas and other militant groups in the Middle East have caused and could continue to cause significant market disruptions and volatility. The hostilities and sanctions resulting from those hostilities have and could continue to have a significant impact on certain fund investments as well as fund performance and liquidity. Following Russia’s invasion of Ukraine in 2022, Russian stocks lost all, or nearly all, of their market value. Other securities or markets could be similarly affected by past or future geopolitical or other events or conditions. Furthermore, events involving limited liquidity, defaults, non-performance or other adverse developments that affect one industry, such as the financial services industry, or concerns or rumors about any events of these kinds, have in the past and may in the future lead to market-wide liquidity problems, may spread to other industries, and could negatively affect the value and liquidity of the fund’s investments. Raising the ceiling on U.S. government debt has become increasingly politicized. Any failure to increase the total amount that the U.S. government is authorized to borrow could lead to a default on U.S. government obligations, with unpredictable consequences for economies and markets in the U.S. and elsewhere. Recently, inflation and interest rates have been volatile and may increase in the future. These circumstances could adversely affect the value and liquidity of the fund’s investments, impair the fund’s ability to satisfy redemption requests, and negatively impact the fund’s performance. The United States and other countries are periodically involved in disputes over trade and other matters, which may result in tariffs, investment restrictions and adverse impacts on affected companies and securities. For example, the United States has imposed tariffs and other trade barriers on Chinese exports, has restricted sales of certain categories of goods to China, and has established barriers to investments in China. Trade disputes may adversely affect the economies of the United States and its trading partners, as well as companies directly or indirectly affected and financial markets generally. The United States government has prohibited U.S. persons from investing in Chinese companies designated as related to the Chinese military. These and possible future restrictions could limit the fund’s opportunities for investment and require the sale of securities at a loss or make them illiquid. Moreover, the Chinese government is involved in a longstanding dispute with Taiwan that has included threats of invasion. If the political climate between the United States and China does not improve or continues to deteriorate, if China were to attempt unification of Taiwan by force, or if other geopolitical conflicts develop or get worse, economies, markets and individual securities may be severely affected both regionally and globally, and the value of the fund’s assets may go down.
Inflation risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Inflation risk. Inflation risk is the risk that the value of assets or income from investments will be worth less in the future as prices go up and the purchasing power of money goes down. The market prices of debt securities generally fall as inflation increases because the purchasing power of the principal and income is expected to be less when paid. Inflation often is accompanied or followed by a recession, or period of decline in economic activity, which may include job loss and other hardships and may cause the value of securities to go down generally.
Credit Risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Credit risk. If an issuer or guarantor of a security held by the fund or a counterparty to a financial contract with the fund defaults or its credit is downgraded, or is perceived to be less creditworthy, or if the value of the assets underlying a security declines, the value of your investment will typically decline. Changes in actual or perceived creditworthiness may occur quickly. The fund could be delayed or hindered in its enforcement of rights against an issuer, guarantor or counterparty. Subordinated securities (meaning securities that rank below other securities with respect to claims on the issuer’s assets) are more likely to suffer a credit loss than non-subordinated securities of the same issuer and will be disproportionately affected by a default, downgrade or perceived decline in creditworthiness.
Leverage risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Leverage risk. The value of your investment may be more volatile if the fund borrows or uses instruments, such as derivatives, that have a leveraging effect on the fund’s portfolio. Other risks described in the Prospectus also will be compounded because leverage generally magnifies the effect of a change in the value of an asset and creates a risk of loss of value on a larger pool of assets than the fund would otherwise have had. The fund may also have to sell assets at inopportune times to satisfy its obligations created by the use of leverage or derivatives. The use of leverage is considered to be a speculative investment practice and may result in the loss of a substantial amount, and possibly all, of the fund’s assets. In addition, the fund’s portfolio will be leveraged if it exercises its right to delay payment on a redemption, and losses will result if the value of the fund’s assets declines between the time a redemption request is deemed to be received by the fund and the time the fund liquidates assets to meet redemption requests.
Commodities risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Commodities risk. Commodity prices can be extremely volatile and are affected by many factors. Exposure to commodities can cause the value of the fund’s shares to decline or fluctuate in a rapid and unpredictable manner. Investments in commodity-linked instruments may subject the fund to greater volatility than investments in traditional securities or the commodity, commodities or commodity index to which they relate. The value of commodities and commodity-linked instruments may be affected, for example, by changes in overall market movements, real or perceived inflationary trends, commodity index volatility, prolonged or intense speculation by investors, changes in interest rates or factors affecting a particular industry or commodity, such as drought, floods, other weather phenomena, livestock disease, embargoes, tariffs, economic sanctions, armed conflicts and international economic, political and regulatory developments. The prices of commodities can also fluctuate widely due to supply and demand disruptions in major producing or consuming regions. The fund’s ability to gain exposure to commodities using derivatives or other means may be limited by tax considerations. If the fund has taken a long or short position in a commodity using futures contracts or other derivatives, it might be required to take or make delivery of the underlying commodity under undesirable circumstances. This would cause the fund to incur a number of costs. To the extent the fund focuses its investments in a particular commodity, the fund will be more susceptible to risks associated with the particular commodity. No active trading market may exist for certain commodities investments.
Commodity regulatory risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Commodity regulatory risk. The fund is a “commodity pool” and the fund’s manager is registered as a “commodity pool operator” under the Commodity Exchange Act with respect to the fund. As a result, additional disclosure, reporting and recordkeeping obligations mandated by the U.S. Commodity Futures Trading Commission (“CFTC”) apply with respect to the fund. The fund’s manager is therefore subject to dual regulation by the Securities and Exchange Commission and the CFTC. Notwithstanding the foregoing, the CFTC has adopted rules that allow for substituted compliance with certain CFTC disclosure and shareholder reporting requirements based on compliance with comparable SEC requirements. This means that for most of the CFTC’s disclosure and shareholder reporting applicable to the manager as the fund’s commodity pool operator, the manager’s and the fund’s compliance with SEC disclosure and shareholder reporting requirements will be deemed to fulfill the manager’s CFTC compliance obligations. The CFTC has neither reviewed nor approved the fund, its investment strategies, or this Prospectus.
Illiquidity risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Illiquidity risk. Some assets held by the fund may be or become impossible or difficult to sell and some assets that the fund wants to invest in may be impossible or difficult to purchase, particularly during times of market turmoil or due to adverse changes in the conditions of a particular issuer. These illiquid assets may also be volatile and difficult to value. Markets may become illiquid quickly. Markets may become illiquid when, for instance, there are few, if any, interested buyers or sellers or when dealers are unwilling or unable to make a market for certain securities. As a general matter, dealers have been less willing to make markets in recent years. Federal banking regulations may also cause certain dealers to reduce their inventories of certain securities, which may further decrease the fund’s ability to buy or sell such securities. During times of market turmoil, there have been, and may be, no buyers or sellers for securities in entire asset classes. If the fund is forced to sell an illiquid asset to meet redemption requests or other cash needs, or to try to limit losses, the fund may be forced to sell at a substantial loss or may not be able to sell at all. The fund may not receive its proceeds from the sale of certain securities for an extended period (for example, several weeks or even longer).
Foreign investments and emerging markets risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Foreign investments and emerging markets risk. The fund’s investments in securities of foreign issuers or issuers with significant exposure to foreign markets involve additional risk as compared to investments in U.S. securities or issuers with predominantly U.S. exposure, such as less liquid, less transparent, less regulated and more volatile markets. The value of the fund’s investments may decline because of factors affecting the particular issuer as well as foreign markets and issuers generally, such as unfavorable or unsuccessful government actions, reduction of government or central bank support, inadequate accounting standards and auditing and financial recordkeeping requirements, lack of information, political, economic, financial or social instability, terrorism, armed conflicts and other geopolitical events, and the impact of tariffs and other restrictions on trade or economic sanctions. Geopolitical or other events such as nationalization or expropriation could even cause the loss of the fund’s entire investment in one or more countries. In addition, there may be significant obstacles to obtaining information necessary for investigations into or litigation against issuers located in or operating in certain foreign markets, particularly emerging market countries, and shareholders may have limited legal remedies. The value of investments in securities denominated in foreign currencies increases or decreases as the rates of exchange between those currencies and the U.S. dollar change. Currency conversion costs and currency fluctuations could erase investment gains or add to investment losses. Currency exchange rates can be volatile, and are affected by factors such as general economic and political conditions, the actions of the U.S. and foreign governments or central banks, the imposition of currency controls and speculation. The fund may be unable or may choose not to hedge its foreign currency exposure. Less developed markets are more likely to experience problems with the clearing and settling of trades and the holding of securities by local banks, agents and depositories. Settlement of trades in these markets can take longer than in other markets and the fund may not receive its proceeds from the sale of certain securities for an extended period (possibly several weeks or even longer). The risks of foreign investments are heightened when investing in issuers in emerging market countries. Emerging market countries tend to have economic, political and legal systems that are less developed and are less stable than those of more developed countries. Their economies tend to be less diversified than those of more developed countries. They typically have fewer medical and economic resources than more developed countries, and thus they may be less able to control or mitigate the effects of a pandemic or a natural disaster. They are often particularly sensitive to market movements because their market prices tend to reflect speculative expectations. Low trading volumes may result in a lack of liquidity and in extreme price volatility.
Valuation risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Valuation risk. The sales price the fund could receive for any particular portfolio investment may differ from the fund’s valuation of the investment, particularly for securities that trade in thin or volatile markets or that are valued using a fair value methodology. These differences may increase significantly and affect fund investments more broadly during periods of market volatility. Investors who purchase or redeem fund shares on days when the fund is holding fair-valued securities may receive fewer or more shares or lower or higher redemption proceeds than they would have received if the fund had not fair-valued securities or had used a different valuation methodology. The fund’s ability to value its investments may be impacted by technological issues and/or errors by pricing services or other third party service providers. The valuation of the fund’s investments involves subjective judgment, which may prove to be incorrect.
Prepayment or call risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Prepayment or call risk. Many issuers have a right to prepay their fixed income securities. Issuers may be more likely to prepay their securities if interest rates fall. If this happens, the fund may not benefit from the rise in the market price of the securities that normally accompanies a decline in interest rates, and will be forced to reinvest prepayment proceeds at a time when yields on securities available in the market are lower than the yield on prepaid securities. The fund may also lose any premium it paid to purchase the securities.
Extension risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Extension risk. When interest rates rise, repayments of fixed income securities, particularly asset- and mortgage-backed securities, may occur more slowly than anticipated, extending the effective duration of these fixed income securities at below market interest rates and causing their market prices to decline more than they would have declined due to the rise in interest rates alone. This may cause the fund’s share price to be more volatile.
Hedging risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Hedging risk. There can be no assurance that the fund will engage in hedging transactions at any given time, even under volatile market conditions, or that any hedging transactions the fund engages in will be successful. Hedging transactions involve costs and may reduce gains or result in losses.
Cash management and defensive investing risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Cash management and defensive investing risk. The value of the investments held by the fund for cash management or defensive investing purposes can fluctuate. Like other fixed income securities, they are subject to risk, including market, interest rate and credit risk. If the fund holds cash uninvested, the cash will be subject to the credit risk of the depository institution holding the cash and the fund will not earn income on the cash. If a significant amount of the fund’s assets is used for cash management or defensive investing purposes, the fund will be less likely to achieve its investment objective. Defensive investing may not work as intended and the value of an investment in the fund may still decline.
Mortgage backed and asset backed securities risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Mortgage-backed and asset-backed securities risk. When market interest rates increase, the market values of mortgage-backed securities decline. At the same time, mortgage refinancings and prepayments slow, which lengthens the effective duration of these securities. As a result, the negative effect of the interest rate increase on the market value of mortgage-backed securities is usually more pronounced than it is for other types of fixed income securities, potentially increasing the volatility of the fund. Conversely, when market interest rates decline, while the value of mortgage-backed securities may increase, the rate of prepayment of the underlying mortgages also tends to increase, which shortens the effective duration of these securities. Mortgage-backed securities are also subject to the risk that underlying borrowers will be unable to meet their obligations and the value of property that secures the mortgage may decline in value and be insufficient, upon foreclosure, to repay the associated loan. Investments in asset-backed securities are subject to similar risks. The ability of an issuer of asset-backed securities to enforce its security interest in the underlying assets may be limited, and therefore certain asset-backed securities present a heightened level of risk.
Portfolio management risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Portfolio management risk. The value of your investment may decrease if the subadvisers’ judgment about the quality, relative yield, value or market trends affecting a particular security, industry, sector or region, or about interest rates or other market factors, is incorrect or does not produce the desired results, or if there are imperfections, errors or limitations in the models, tools and data used by the subadvisers. In addition, the fund’s investment strategies or policies may change from time to time. Those changes may not lead to the results intended by the subadvisers and could have an adverse effect on the value or performance of the fund.
Portfolio turnover risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Portfolio turnover risk. Active and frequent trading will increase the fund’s transaction costs, which could detract from fund performance.
Redemption risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Redemption risk. The fund may experience heavy redemptions that could cause the fund to liquidate its assets at inopportune times or unfavorable prices or increase or accelerate taxable gains or transaction costs and may negatively affect the fund’s net asset value, performance, or ability to satisfy redemptions in a timely manner, which could cause the value of your investment to decline.
Cybersecurity risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Cybersecurity risk. Like other funds and business enterprises, the fund, the manager, the subadvisers and their service providers are subject to the risk of cyber incidents occurring from time to time. Cybersecurity incidents, whether intentionally caused by third parties or otherwise, may allow an unauthorized party to gain access to fund assets, fund or customer data (including private shareholder information) or proprietary information, cause the fund, the manager, the subadvisers and/or their service providers (including, but not limited to, fund accountants, custodians, sub-custodians, transfer agents and financial intermediaries) to suffer data breaches, data corruption or loss of operational functionality, or prevent fund investors from purchasing, redeeming or exchanging shares, receiving distributions or receiving timely information regarding the fund or their investment in the fund. The fund, the manager, and the subadvisers have limited ability to prevent or mitigate cybersecurity incidents affecting third party service providers, and such third party service providers may have limited indemnification obligations to the fund, the manager, and/or the subadvisers. Cybersecurity incidents may result in financial losses to the fund and its shareholders, and substantial costs may be incurred in order to prevent or mitigate any future cybersecurity incidents. Issuers of securities in which the fund invests are also subject to cybersecurity risks, and the value of these securities could decline if the issuers experience cybersecurity incidents. New ways to carry out cyber attacks continue to develop. There is a chance that some risks have not been identified or prepared for, or that an attack may not be detected, which puts limitations on the fund’s ability to plan for or respond to a cyber attack.
Derivatives risks [Member]
Prospectus [Line Items]
Risk [Text Block]	Derivatives risk. Using derivatives can increase fund losses and reduce opportunities for gains, such as when market prices, interest rates, currencies, or the derivatives themselves behave in a way not anticipated by the fund’s subadviser. Using derivatives also can have a leveraging effect and increase fund volatility. Certain derivatives have the potential for unlimited loss, regardless of the size of the initial investment. Derivatives may not be available at the time or price desired, may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. Derivatives are generally subject to the risks applicable to the assets, rates, indices or other indicators underlying the derivative. The value of a derivative may fluctuate more than the underlying assets, rates, indices or other indicators to which it relates. Use of derivatives may have different tax consequences for the fund than an investment in the underlying asset, and those differences may affect the amount, timing and character of income distributed to shareholders. The U.S. government and non-U.S. governments have adopted and implemented regulations governing derivatives markets, including mandatory clearing of certain derivatives, margin and reporting requirements. The ultimate impact of the regulations remains unclear. Additional regulation of derivatives may make derivatives more costly, limit their availability or utility, otherwise adversely affect their performance or disrupt markets. Credit default swap contracts involve heightened risks and may result in losses to the fund. Credit default swaps may be illiquid and difficult to value. When the fund sells credit protection via a credit default swap, credit risk increases since the fund has exposure to both the issuer whose credit is the subject of the swap and the counterparty to the swap.
Market and interest rate risk [Member]
Prospectus [Line Items]
Risk [Text Block]	Market and interest rate risk. The market prices of securities held by the fund may go up or down, sometimes rapidly or unpredictably. If the market prices of the fund’s securities fall, the value of your investment in the fund will decline. The market price of a security may fall due to general market conditions, such as real or perceived adverse economic or political conditions or trends, tariffs and trade disruptions, inflation, substantial economic downturn or recession, changes in interest rates, lack of liquidity in the bond markets or adverse investor sentiment. Changes in market conditions will not typically have the same impact on all types of securities. The value of your investment will generally go down when interest rates rise. A rise in rates tends to have a greater impact on the prices of longer term or duration securities. A general rise in interest rates may cause investors to move out of fixed income securities on a large scale, which could adversely affect the price and liquidity of fixed income securities and could also result in increased redemptions from the fund. Recently, there have been inflationary price movements. As a result, fixed income securities markets may experience heightened levels of interest rate volatility and liquidity risk. The U.S. government and the U.S. Federal Reserve, as well as certain foreign governments and central banks, have from time to time taken steps to support financial markets. The U.S. government and the U.S. Federal Reserve may, conversely, reduce market support activities, including by taking action intended to increase certain interest rates. This and other government intervention may not work as intended, particularly if the efforts are perceived by investors as being unlikely to achieve the desired results. Changes in government activities in this regard, such as changes in interest rate policy, can negatively affect financial markets generally, increase market volatility and reduce the value and liquidity of securities in which the fund invests. The maturity of a security may be significantly longer than its duration. A security’s maturity and other features may be more relevant than its duration in determining the security’s sensitivity to other factors affecting the issuer or markets generally such as changes in credit quality or in the yield premium that the market may establish for certain types of securities.
Risk Lose Money [Member]
Prospectus [Line Items]
Risk [Text Block]	You may lose part or all of your investment in the fund or your investment may not perform as well as other similar investments.
Risk Not Insured Depository Institution [Member]
Prospectus [Line Items]
Risk [Text Block]	An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or by any bank or government agency.
Risk Nondiversified Status [Member]
Prospectus [Line Items]
Risk [Text Block]	Non-diversification risk. The fund is classified as “non-diversified,” which means it may invest a larger percentage of its assets in a smaller number of issuers than a diversified fund. To the extent the fund invests its assets in a smaller number of issuers, the fund will be more susceptible to negative events affecting those issuers than a diversified fund.

S000069099 [Member] Investment Risks - WESTERN ASSET SMASh SERIES CORE COMPLETION FUND

Feb. 28, 2025

Market events risk. The market values of securities or other assets will fluctuate, sometimes sharply and unpredictably, due to factors such as economic events, governmental actions or intervention, actions taken by the U.S. Federal Reserve or foreign central banks, market disruptions caused by trade disputes, labor strikes or other factors, political developments, armed conflicts, economic sanctions and countermeasures in response to sanctions, major cybersecurity events, the global and domestic effects of widespread or local health, weather or climate events, and other factors that may or may not be related to the issuer of the security or other asset. Economies and financial markets throughout the world are increasingly interconnected. Economic, financial or political events, trading and tariff arrangements, public health events, terrorism, wars, natural disasters and other circumstances in one country or region could have profound impacts on global economies or markets. As a result, whether or not the fund invests in securities of issuers located in or with significant exposure to the countries or markets directly affected, the value and liquidity of the fund’s investments may be negatively affected. Ongoing armed conflicts between Russia and Ukraine in Europe and among Israel, Hamas and other militant groups in the Middle East have caused and could continue to cause significant market disruptions and volatility. The hostilities and sanctions resulting from those hostilities have and could continue to have a significant impact on certain fund investments as well as fund performance and liquidity. Following Russia’s invasion of Ukraine in 2022, Russian stocks lost all, or nearly all, of their market value. Other securities or markets could be similarly affected by past or future geopolitical or other events or conditions. Furthermore, events involving limited liquidity, defaults, non-performance or other adverse developments that affect one industry, such as the financial services industry, or concerns or rumors about any events of these kinds, have in the past and may in the future lead to market-wide liquidity problems, may spread to other industries, and could negatively affect the value and liquidity of the fund’s investments.

Raising the ceiling on U.S. government debt has become increasingly politicized. Any failure to increase the total amount that the U.S. government is authorized to borrow could lead to a default on U.S. government obligations, with unpredictable consequences for economies and markets in the U.S. and elsewhere. Recently, inflation and interest rates have been volatile and may increase in the future. These circumstances could adversely affect the value and liquidity of the fund’s investments, impair the fund’s ability to satisfy redemption requests, and negatively impact the fund’s performance.

The United States and other countries are periodically involved in disputes over trade and other matters, which may result in tariffs, investment restrictions and adverse impacts on affected companies and securities. For example, the United States has imposed tariffs and other trade barriers on Chinese exports, has restricted sales of certain categories of goods to China, and has established barriers to investments in China. Trade disputes may adversely affect the economies of the United States and its trading partners, as well as companies directly or indirectly affected and financial markets generally. The United States government has prohibited U.S. persons from investing in Chinese companies designated as related to the Chinese military. These and possible future restrictions could limit the fund’s opportunities for investment and require the sale of securities at a loss or make them illiquid. Moreover, the Chinese government is involved in a longstanding dispute with Taiwan that has included threats of invasion. If the political climate between the United States and China does not improve or continues to deteriorate, if China were to attempt unification of Taiwan by force, or if other geopolitical conflicts develop or get worse, economies, markets and individual securities may be severely affected both regionally and globally, and the value of the fund’s assets may go down.