Objective, Primary [Text Block]

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Objective [Heading]

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Investment Objective

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The High Yield Portfolio (the “Fund”) seeks total return.

Expense [Heading]

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Fees and Expenses

Expense Narrative [Text Block]

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The table below describes the fees and expenses that you may pay if you buy, hold and sell Class IR shares of the Fund. You may pay fees other than the fees and expenses of the Fund, such as brokerage commissions and other fees charged by financial intermediaries, which are not reflected in the tables and examples below. The Fund does not charge any sales loads or other fees when you purchase or redeem Class IR shares.

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)

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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The example below 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, your investment has a 5% return each year and that the Fund’s operating expenses remain the same (except that the example incorporates the fee waiver and/or expense reimbursement arrangement for only the first year). Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example by, Year, Caption [Text]

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If You SOLD Your Shares

Expense Example, No Redemption, By Year, Caption [Text]

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If You HELD Your Shares

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 Fund shares are held in a taxable account. These costs, which are not reflected in Total Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 54% of the average value of its portfolio.

Portfolio Turnover, Rate

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54.00%

Strategy [Heading]

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Principal Investment Strategies

Strategy Narrative [Text Block]

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Under normal circumstances, at least 80% of the Fund’s assets will be invested in high yield securities (commonly referred to as “junk bonds”). This policy may be changed without shareholder approval; however, you would be notified upon 60 days’ notice in writing of any changes. The Fund seeks to achieve its investment objective by investing primarily in high yield securities which are fixed-income securities rated by one or more rating agencies below Baa3 by Moody’s Investors Service, Inc. (“Moody’s”), below BBB- by S&P Global Ratings Group, a division of S&P Global Inc. (“S&P”), below BBB- by Fitch Ratings, Inc. (“Fitch”) or, if unrated, considered by the Adviser to be of equivalent quality. The average maturity of the Fund’s investments varies, and there is no limit on the maturity or on the credit quality of any security held by the Fund. The Fund’s securities may include distressed and defaulted securities and mezzanine investments. The Fund also may invest in investment grade fixed-income securities, including U.S. and foreign government securities, corporate bonds and collateralized bond obligations. The Fund may also invest in preferred securities, equity securities and convertible securities.

The Fund’s investment process starts with top-down macroeconomic analysis to assess the optimal positioning of the Fund. The team then applies a combination of quantitative and qualitative filters to identify securities that meet the team’s investment criteria in terms of competitive position, franchise value and management quality. The investment team’s credit analysis focuses on financial risk, business risk, management ability and intentions. Valuation analysis is used to narrow the screened investment universe to a pool of investment candidates who are then assessed in order to determine relative valuation. Finally, the Fund is constructed with sector allocation driven primarily from bottom-up security selection. Integral to the Fund construction process is the measurement and monitoring of market risk, duration and volatility and credit risk through the use of proprietary risk measures and models.

The Fund’s investment process incorporates information about environmental, social and governance issues (also referred to as ESG) via an integrated approach within the investment team’s fundamental investment analysis framework. The Adviser may engage with management of certain issuers regarding corporate governance practices as well as what the Adviser deems to be materially important environmental and/or social issues facing a company.

The Fund may also invest in loan-related investments, such as public bank loans made by banks or other financial institutions and loan participations and assignments, which may be rated investment grade or below investment grade.

The Fund may also invest in restricted and illiquid securities.

The Fund may, but it is not required to, use derivative instruments for a variety of purposes, including hedging, risk management, portfolio management or to earn income. The Fund’s use of derivatives may involve the purchase and sale of derivative instruments such as futures, options, swaps and other related instruments and techniques. The Fund may utilize foreign currency forward exchange contracts, which are also derivatives, in connection with its investments in foreign securities. Derivative instruments used by the Fund will be counted toward the Fund’s 80% policy discussed above to the extent they have economic characteristics similar to the securities included within that policy.

Risk [Heading]

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Principal Risks

Risk Narrative [Text Block]

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There is no assurance that the Fund will achieve its investment objective, and you can lose money investing in this Fund. The principal risks of investing in the Fund include:

•

Credit and Interest Rate Risk. Credit risk refers to the possibility that the issuer or guarantor of a security will be unable or unwilling or perceived to be unable to unwilling to make interest payments and/or repay the principal on its debt. In such instances, the value of the Fund could decline and the Fund could lose money. Interest rate risk refers to the decline in the value of a fixed-income security resulting from changes in the general level of interest rates. When the general level of interest rates goes up, the prices of most fixed-income securities go down. When the general level of interest rates goes down, the prices of most fixed-income securities go up. The Fund may invest in variable and floating rate loans and other variable and floating rate securities. Although these instruments are generally less sensitive to interest rate changes than fixed rate instruments, the value of variable and floating rate loans and other securities may decline if their interest rates do not rise as quickly, or as much, as general interest rates. The Fund may face a heightened level of interest rate risk in times of monetary policy change and/or uncertainty, such as when the Federal Reserve Board adjusts a quantitative easing program and/or changes rates. A changing interest rate environment increases certain risks, including the potential for periods of volatility, increased redemptions, shortened durations (i.e., prepayment risk) and extended durations (i.e., extension risk). During periods when interest rates are low or there are negative interest rates, the Fund’s yield (and total return) also may be low or otherwise adversely affected or the Fund may be unable to maintain positive returns. Credit ratings may not be an accurate assessment of liquidity or credit risk. Although credit quality may not accurately reflect the true credit risk of an instrument, a change in the credit rating of an instrument or an issuer can have a rapid, adverse effect on the instrument’s liquidity and make it more difficult for a Fund to sell at an advantageous price or time.

•

Fixed-Income Securities. Fixed-income securities are subject to the risk of the issuer’s inability to meet principal and interest payments on its obligations (i.e., credit risk) and are subject to price volatility resulting from, among other things, interest rate sensitivity (i.e., interest rate risk), market perception of the creditworthiness of the issuer and general market liquidity (i.e., market risk). The Fund may face a heightened level of interest rate risk in times of monetary policy change and/or uncertainty, such as when the Federal Reserve Board adjusts a quantitative easing program and/or changes rates. A changing interest rate environment increases certain risks, including the potential for periods of volatility, increased redemptions, shortened durations (i.e., prepayment risk) and extended durations (i.e., extension risk). The Fund is not limited as to the maturities (when a debt security provides its final payment) or durations (measure of interest rate sensitivity) of the securities in which it may invest. Securities with longer durations are likely to be more sensitive to changes in interest rates, generally making them more volatile than securities with shorter durations. Lower rated fixed-income securities have greater volatility because there is less certainty that principal and interest payments will be made as scheduled. A portion of the Fund’s fixed-income securities may be rated below investment grade. The Fund may be subject to certain liquidity risks that may result from the lack of an active market and the reduced number and capacity of traditional market participants to make a market in fixed-income securities. To the extent that the Fund invests in convertible securities, and the convertible security’s investment value is greater than its conversion value, its

price will be likely to increase when interest rates fall and decrease when interest rates rise. If the conversion value exceeds the investment value, the price of the convertible security will tend to fluctuate directly with the price of the underlying security.

•

High Yield Securities (“Junk Bonds”). High yield securities offer a higher yield than other, higher rated securities, but they carry a greater degree of risk and are considered speculative by the major credit rating agencies. Changes in the value of high yield securities are influenced more by changes in the financial and business position of the issuing company than by changes in interest rates when compared to investment grade securities. Lower rated fixed-income securities have greater volatility because there is less certainty that principal and interest payments will be made as scheduled. Prices of fixed-income securities generally will move in correlation to changes in an issuer’s credit rating and inversely to movements in interest rates. The Fund’s investments in high yield securities expose it to a substantial degree of credit risk. Prices of high yield securities will rise and fall primarily in response to actual or perceived changes in the issuer’s financial health, although changes in market interest rates also will affect prices. High yield securities may be issued by companies that are restructuring, are smaller and less creditworthy or are more highly indebted than other companies, and therefore they may have more difficulty making scheduled payments of principal and interest. High yield securities may experience reduced liquidity, and sudden and substantial decreases in price. An economic downturn affecting an issuer of high yield securities may result in an increased incidence of default. In the event of a default, the Fund may incur additional expenses to seek recovery.

•

Foreign and Emerging Market Securities. Investments in foreign markets entail special risks such as currency, political, economic and market risks. There also may be greater market volatility, less reliable financial information, less stringent investor protections and disclosure standards, higher transaction and custody costs, decreased market liquidity and less government and exchange regulation associated with investments in foreign markets. In addition, investments in certain foreign markets that have historically been considered stable may become more volatile and subject to increased risk due to ongoing developments and changing conditions in such markets. Moreover, the growing interconnectivity of global economies and financial markets has increased the probability that adverse developments and conditions in one country or region will affect the stability of economies and financial markets in other countries or regions. Certain foreign markets may rely heavily on particular industries or foreign capital and are more vulnerable to diplomatic developments, the imposition of economic sanctions against a particular country or countries, organizations, companies, entities and/or individuals, changes in international trading patterns, trade barriers and other protectionist or retaliatory measures. Investments in foreign markets may also be adversely affected by governmental actions such as the imposition of capital controls, nationalization of companies or industries, expropriation of assets or the imposition of punitive taxes. The governments of certain countries may prohibit or impose substantial restrictions on foreign investing in their capital markets or in certain sectors or industries. In addition, a foreign government may limit or cause delay in the convertibility or repatriation of its currency which would adversely affect the U.S. dollar value and/or liquidity of investments denominated in that currency. Certain foreign investments may become less liquid in response to market developments or adverse investor perceptions, or become illiquid after purchase by the Fund, particularly during periods of market turmoil. When the Fund holds illiquid investments, its portfolio may be harder to value. The risks of investing in emerging market countries are greater than the risks associated with investments in foreign developed countries. Certain emerging market countries may be subject to less stringent requirements regarding accounting, auditing, financial reporting and record keeping and therefore, material information related to an investment may not be available or reliable. In addition, the Fund is limited in its ability to exercise its legal rights or enforce a counterparty’s legal obligations in certain jurisdictions outside of the United States, in particular, in emerging markets countries. In addition, the Fund’s investments in foreign issuers may be denominated in foreign currencies and therefore, to the extent unhedged, the value of those investments will fluctuate with U.S. dollar exchange rates. To the extent hedged by the use of foreign currency forward exchange contracts, the precise matching of the foreign currency forward exchange contract amounts and the value of the securities involved will not generally be possible because the future value of such securities in foreign currencies will change as a consequence of market movements in the value of those securities between the date on which the contract is entered into and the date it matures. There is additional risk that such transactions may reduce or preclude the opportunity for gain if the value of the currency should move in the direction opposite to the position taken and that foreign currency forward exchange contracts create exposure to currencies in which the Fund’s securities are not denominated. The use of foreign currency forward exchange contracts involves the risk of loss from the insolvency or bankruptcy of the counterparty to the contract or the failure of the counterparty to make payments or otherwise comply with the terms of the contract. Economic sanctions may be, and have been, imposed against certain countries, organizations, companies, entities and/or individuals. Economic sanctions and other similar governmental actions could, among other things, effectively restrict or eliminate the Fund’s ability to purchase or sell securities or groups of securities, and thus may make the Fund’s investments in such securities less liquid or more difficult to value. In addition, as a result of economic sanctions, the Fund may be forced to sell or otherwise dispose of investments at inopportune times or prices.

•

Loan-Related Investments. In addition to risks generally associated with debt investments, loan-related investments, such as public bank loans and loan participations and assignments, are subject to other risks. Such investments may be subject to additional risks including subordination to other creditors, no collateral or limited rights in collateral, lack of a regular trading market, extended settlement periods, liquidity risks, prepayment risks, potentially less protection under the federal securities laws and lack of publicly available information. Bank loans are subject to the risk of default in the payment of interest or principal on a loan, which will result in a reduction of income to the Fund, and a potential decrease in the Fund’s net asset value per share (“NAV”).

The risk of default will increase in the event of an economic downturn or a substantial increase in interest rates. Because public bank loans usually rank lower in priority of payment to senior loans, they present a greater degree of investment risk. These bank loans may exhibit greater price volatility as well.

•

Equity Securities. In general, prices of equity securities are more volatile than those of fixed-income securities. The prices of equity securities fluctuate, and sometimes widely fluctuate, in response to activities specific to the issuer of the security as well as factors unrelated to the fundamental condition of the issuer, including general market, economic and political conditions. To the extent that the Fund invests in convertible securities, and the convertible security’s investment value is greater than its conversion value, its price will be likely to increase when interest rates fall and decrease when interest rates rise. If the conversion value exceeds the investment value, the price of the convertible security will tend to fluctuate directly with the price of the underlying security.

•

Preferred Securities. Preferred stock is issued with a fixed par value and pays dividends based on a percentage of that par value at a fixed rate. As with fixed-income securities, which also make fixed payments, the market value of preferred stock is sensitive to changes in interest rates. Preferred stock generally decreases in value if interest rates rise and increases in value if interest rates fall.

•

Mezzanine Investments. Mezzanine investments are subordinated debt securities that receive payments of interest and principal after other more senior security holders are paid. Mezzanine investments carry the risk that the issuer will not be able to meet its obligations and that the mezzanine investments may lose value.

•

Distressed and Defaulted Securities. Distressed and defaulted securities are speculative and involve substantial risks in addition to the risks of investing in high yield securities. The Fund will generally not receive interest payments on the distressed securities and the repayment of principal may also be at risk. These securities may present a substantial risk of default or may be in default at the time of investment, requiring the Fund to incur additional costs. The repayment of defaulted securities is also subject to significant uncertainties. The Fund may incur substantial expenses in seeking recovery upon a default in the payment of principal of or interest on its portfolio holdings.

•

Liquidity. The Fund may make investments that are illiquid or restricted or that may become less liquid in response to overall economic conditions or adverse investor perceptions, and which may entail greater risk than investments in other types of securities. These investments may be more difficult to value or sell, particularly in times of market turmoil, and there may be little trading in the secondary market available for particular securities. Liquidity risk may be magnified in a market where credit spread and interest rate volatility is rising and where investor redemptions from fixed-income mutual funds may be higher than normal. If the Fund is forced to sell an illiquid or restricted security to fund redemptions or for other cash needs, it may be forced to sell the security at a loss or for less than its fair value.

•

Derivatives. A derivative instrument often has risks similar to its underlying asset and may have additional risks, including imperfect correlation between the value of the derivative and the underlying asset, risks of default by the counterparty to certain transactions, magnification of losses incurred due to changes in the market value of the securities, instruments, indices or interest rates to which the derivative instrument relates and risks that the transactions may not be liquid. Certain derivative transactions may give rise to a form of leverage. Leverage magnifies the potential for gain and the risk of loss. Investments in currency derivatives may substantially change the Fund’s exposure to currency exchange rates and could result in losses to the Fund if currencies do not perform as the Adviser expects. Foreign currency forward exchange contracts and currency futures and options contracts create exposure to currencies in which the Fund’s securities are not denominated.

•

Market and Geopolitical Risk. The value of your investment in the Fund is based on the values of the Fund’s investments, which may change due to economic and other events that affect markets generally, as well as those that affect particular regions, countries, industries, companies or governments. These events may be sudden and unexpected, and could adversely affect the liquidity of the Fund’s investments, which may in turn impact valuation, the Fund’s ability to sell securities and/or its ability to meet redemptions. The risks associated with these developments may be magnified if certain social, political, economic and other conditions and events (such as war, natural disasters, epidemics and pandemics, terrorism, conflicts and social unrest) adversely interrupt the global economy and financial markets. It is difficult to predict when events affecting the U.S. or global financial markets may occur, the effects that such events may have and the duration of those effects (which may last for extended periods). These events may negatively impact broad segments of businesses and populations and have a significant and rapid negative impact on the performance of the Fund’s investments, adversely affect and increase the volatility of the Fund’s share price and exacerbate pre-existing risks to the Fund.

Shares of the Fund are not bank deposits and are not guaranteed or insured by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

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There is no assurance that the Fund will achieve its investment objective, and you can lose money investing in this Fund.

Risk Not Insured Depository Institution [Text]

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Shares of the Fund are not bank deposits and are not guaranteed or insured by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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Performance Information

Performance Narrative [Text Block]

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The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s Class IS shares’ performance from year-to-year and by showing how the Fund’s average annual returns for the past one and five year periods and since inception compare with those of a broad measure of market performance, as well as an index that represents a group of similar mutual funds, over time. The Fund’s past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future. Updated performance information is available online at www.morganstanley.com/im or by calling toll-free 1-800-548-7786.

Performance Information Illustrates Variability of Returns [Text]

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Performance Availability Phone [Text]

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1-800-548-7786

Performance Availability Website Address [Text]

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www.morganstanley.com/im

Performance Past Does Not Indicate Future [Text]

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The Fund’s past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future.

Bar Chart [Heading]

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Annual Total Returns—Calendar Years

Performance Table Uses Highest Federal Rate

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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 after-tax returns are not relevant to investors who hold their Fund shares through tax deferred arrangements such as 401(k) plans or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

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After-tax returns for the Fund’s Class IR shares will vary from Class IS shares’ returns.

Performance Table Explanation after Tax Higher

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After-tax returns may be higher than before-tax returns due to foreign tax credits and/or an assumed benefit from capital losses that would have been realized had Fund shares been sold at the end of the relevant periods, as applicable.

Bar Chart Closing [Text Block]

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High Quarter

06/30/20

10.18%

Low Quarter

03/31/20

-16.01%

Performance Table Heading

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Average Annual Total Returns(for the calendar periods ended December 31, 2021)

Performance Table Closing [Text Block]

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The after-tax returns shown in the table above are calculated using the historical highest individual federal marginal income tax rates during the period shown and do not reflect the impact of state and local taxes. After-tax returns for the Fund’s Class IR shares will vary from Class IS shares’ returns. Actual after-tax returns depend on the investor’s tax situation and may differ from those shown, and after-tax returns are not relevant to investors who hold their Fund shares through tax deferred arrangements such as 401(k) plans or individual retirement accounts. After-tax returns may be higher than before-tax returns due to foreign tax credits and/or an assumed benefit from capital losses that would have been realized had Fund shares been sold at the end of the relevant periods, as applicable.

(MSIFT High Yield Portfolio - Class IR) | (High Yield Portfolio) | Bloomberg U.S. Corporate High Yield Index (reflects no deduction for fees, expenses or taxes)

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rr_AverageAnnualReturnYear01

5.28%

^[1]

rr_AverageAnnualReturnYear05

6.30%

^[1]

(MSIFT High Yield Portfolio - Class IR) | (High Yield Portfolio) | Lipper High Current Yield Bond Funds Index (reflects no deduction for taxes)

rr_AverageAnnualReturnSinceInception

5.47%

^[1],[2]

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rr_AverageAnnualReturnYear01

5.85%

^[3]

rr_AverageAnnualReturnYear05

5.76%

^[3]

(MSIFT High Yield Portfolio - Class IR) | (High Yield Portfolio) | Class IR

rr_AverageAnnualReturnSinceInception

4.75%

^[2],[3]

Management Fees (as a percentage of Assets)

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rr_ManagementFeesOverAssets

0.60%

Distribution and Service (12b-1) Fees

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none

Other Expenses (as a percentage of Assets):

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18.37%

Total Annual Fund Operating Expenses

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18.97%

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Fee Waiver or Reimbursement

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18.35%

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Total Annual Fund Operating Expenses After Expense Reimbursement

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0.62%

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Expense Example, with Redemption, 1 Year

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$ 63

Expense Example, with Redemption, 3 Years

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3,490

Expense Example, with Redemption, 5 Years

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6,026

Expense Example, with Redemption, 10 Years

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9,844

Expense Example, No Redemption, 1 Year

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Expense Example, No Redemption, 3 Years

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3,490

Expense Example, No Redemption, 5 Years

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6,026

Expense Example, No Redemption, 10 Years

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$ 9,844

rr_AverageAnnualReturnYear01

5.58%

rr_AverageAnnualReturnYear05

(MSIFT High Yield Portfolio - Class IR) | (High Yield Portfolio) | Class IS

rr_AverageAnnualReturnSinceInception

5.19%

Highest Quarterly Return, Label

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Annual Return 2015

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(1.78%)

Annual Return 2016

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15.52%

Annual Return 2017

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8.05%

Annual Return 2018

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(2.17%)

Annual Return 2019

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13.93%

Annual Return 2020

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3.28%

Annual Return 2021

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5.69%

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High Quarter

Highest Quarterly Return

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10.18%

Highest Quarterly Return, Date

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Jun. 30, 2020

Lowest Quarterly Return, Label

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Low Quarter

Lowest Quarterly Return

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(16.01%)

Lowest Quarterly Return, Date

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Mar. 31, 2020

rr_AverageAnnualReturnYear01

5.69%

rr_AverageAnnualReturnYear05

5.62%

(MSIFT High Yield Portfolio - Class IR) | (High Yield Portfolio) | Class IS | Return After Taxes on Distributions

rr_AverageAnnualReturnSinceInception

4.90%

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rr_AverageAnnualReturnYear01

3.33%

^[5]

rr_AverageAnnualReturnYear05

2.92%

^[5]

(MSIFT High Yield Portfolio - Class IR) | (High Yield Portfolio) | Class IS | Return After Taxes on Distributions and Sale of Fund Shares

rr_AverageAnnualReturnSinceInception

2.07%

^[5]

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rr_AverageAnnualReturnYear01

3.34%

rr_AverageAnnualReturnYear05

3.10%