Objective, Primary [Text Block]

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Objective [Heading]

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Investment Objective

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The Growth Portfolio (the “Fund”) seeks long-term capital appreciation by investing primarily in growth-oriented equity securities of large capitalization companies.

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. The Fund does not charge any sales loads or other fees when you purchase or redeem Class IR shares. 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.

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 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 39% of the average value of its portfolio.

Portfolio Turnover, Rate

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39.00%

Strategy [Heading]

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Principal Investment Strategies

Strategy Narrative [Text Block]

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Under normal market conditions, the Adviser seeks to achieve the Fund’s investment objective by investing primarily in established and emerging companies, with capitalizations within the range of companies included in the Russell 1000® Growth Index. As of December 31, 2024, these market capitalizations ranged between $1.7 billion and $3.8 trillion.

The Adviser emphasizes a bottom-up stock selection process, seeking attractive investments on an individual company basis. In selecting securities for investment, the Adviser typically invests in unique companies it believes have sustainable competitive advantages with above average business visibility, the ability to deploy capital at high rates of return, strong balance sheets and an

attractive risk/reward. The Adviser typically focuses a significant portion of the Fund’s investments in a limited number of issuers, which may be in the same industry, sector or geographic region.

The Adviser actively integrates sustainability into the investment process by using environmental, social and governance (“ESG”) factors as a lens for additional fundamental research, which can contribute to investment decision-making. The Adviser seeks to understand how environmental and social initiatives within companies can create value by strengthening durable competitive advantages, creating growth opportunities, driving profitability and/or aligning with secular growth trends. The Adviser generally engages with company management teams to discuss their ESG practices, with the aim of identifying how sustainability themes present opportunities and risks that can be material to the value of the security over the long-term. Other aspects of the investment process include a proprietary, systematic evaluation of governance policies, specifically focusing on compensation alignment on long-term value creation. Although consideration of ESG factors is incorporated into the investment process, it is only one of many tools the Adviser utilizes to make investment decisions.

In addition to common stocks, the Fund may invest in other types of equity securities. The Fund may also invest in privately placed and restricted securities.

The Adviser may invest up to 25% of the Fund’s total assets in foreign securities, including emerging market securities and securities classified as American Depositary Receipts (“ADRs”), Global Depositary Receipts (“GDRs”), American Depositary Shares (“ADSs”) or Global Depositary Shares (“GDSs”), foreign U.S. dollar-denominated securities that are traded on a U.S. exchange or local shares of non-U.S. issuers.

Risk [Heading]

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Principal Risks

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 IR 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 and one or more additional indexes. The additional index(es) in the table provides a means to compare the Fund’s average annual total returns to a benchmark that the Adviser believes is representative of the Fund’s investment universe. 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 1-800-869-6397.

Performance Information Illustrates Variability of Returns [Text]

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Performance Availability Phone [Text]

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1-800-869-6397

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 other classes will vary from Class IR shares’ returns.

Performance Table Explanation after Tax Higher

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After-tax returns may be higher than before-tax returns due to 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	58.33%
Low Quarter	06/30/22	-41.18%

Performance Table Heading

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Average Annual Total Returns(for the calendar periods ended December 31, 2024)

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 other classes will vary from Class IR 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 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.

(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Risk Not Insured Depository Institution [Member]

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Risk Lose Money [Member]

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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.

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Equity Securities [Member]

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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.

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Foreign and Emerging Market Securities [Member]

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•

Equity Securities. In general, prices of equity securities are more volatile than those of fixed-income securities. U.S. and foreign stock markets, and equity securities of individual issuers, have experienced periods of substantial price volatility in the past and it is possible that they will do so again in the future. The prices of equity securities fluctuate, sometimes rapidly or widely, 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, political and public health conditions. During periods when equity securities experience heightened volatility, such as during periods of market, economic or financial uncertainty or distress, the Fund’s investments in equity securities are subject to heightened risks.

The value of equity securities declines in response to perceived or actual adverse changes in the economy, economic outlook or financial markets; deterioration in investor sentiment; inflation, interest rate, currency, and commodity price fluctuations; adverse geopolitical, social or environmental developments; issuer- and sector-specific considerations; unexpected trading activity among retail investors; and other factors. Market conditions affect certain types of equity securities to a greater extent than other types of equity securities. If the stock market declines, the value of the Fund’s equity securities will also likely decline, which will result in a decrease in the value of your investment in the Fund. Although prices can rebound, there is no assurance that prices of the Fund’s equity securities will return to previous levels.

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Foreign Currency Forward Exchange Contracts [Member]

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•

Foreign and Emerging Market Securities. Investments in foreign markets entail special risks, such as currency, political (including geopolitical), economic and market risks and heightened risks, that may result in losses to the Fund. There also may be greater market volatility, less reliable financial information, less stringent investor protections and disclosure standards, higher transaction and custody costs and risks, 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 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 (including regional and global, military or other conflicts), the imposition of economic sanctions against a particular country or countries, organizations, companies, entities and/or individuals, changes in international trading patterns, trade barriers (including tariffs) and other protectionist or retaliatory measures. Investments in foreign markets may also be adversely affected by governmental interventions or other 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 and decline in value in response to market developments or adverse investor perceptions, or become illiquid after purchase by the

Fund, particularly during periods of market, economic, political and social 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. Emerging market countries may be subject to increased potential for market manipulation and 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 market 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. Economic sanctions or other similar measures may be, and have been, imposed against certain countries, organizations, companies, entities and/or individuals. Economic sanctions and other similar measures could, among other things, effectively restrict or eliminate the Fund’s ability to purchase or sell securities (in the sanctioned country and other markets), negatively impact the value or liquidity of the Fund’s investments, significantly delay or prevent the settlement of the Fund’s securities transactions, force the Fund to sell or otherwise dispose of investments at inopportune times or prices, or impair the Fund’s ability to meet its investment objective or invest in accordance with its investment strategies.

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Liquidity [Member]

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•

Foreign Currency Forward Exchange Contracts. To the extent the Fund seeks to hedge its foreign currency exposure 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 risks associated with derivatives and 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.

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Focused Investing [Member]

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•

Liquidity. The Fund may make investments that are less liquid, illiquid or restricted or that may become illiquid or 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. 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 and may be unable to sell the security at all.

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Market and Geopolitical Risk [Member]

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•

Focused Investing. Although the Fund is a diversified investment company under the Investment Company Act of 1940 (the “1940 Act”), the Fund typically invests a significant portion of its portfolio in a limited number of issuers, which may be in the same industry, sector or geographic region. As a result, the Fund will be more susceptible to risks associated with, and negative events affecting those issuers, industries, sectors or geographic regions, and a decline in the value of a particular instrument may cause the Fund’s overall value to be more volatile and decline to a greater degree than if the Fund were invested more widely.

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Private Placements and Restricted Securities [Member]

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•

Market and Geopolitical Risk. The value of your investment in the Fund is based on the values of the Fund’s investments, which change due to economic, geopolitical and other events that affect the U.S. and global markets generally, as well as those that affect or are perceived or expected to affect particular regions, countries, industries, companies, issuers, sectors, asset classes or governments. These types of events may be sudden and unexpected, and could adversely affect the value (or income generated by) and liquidity of the Fund’s investments, which may in turn impact 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 or events, epidemics and pandemics, terrorism, conflicts, social unrest, recessions, inflation, interest rate changes, supply chain disruptions and the imposition of tariffs, trade barriers and other protectionist or retaliatory measures) adversely interrupt or otherwise affect the global economy and financial markets. It is difficult to predict when events affecting the U.S. or global financial markets or economies may occur, the effects that such events may have and the duration of those effects (which may last for extended periods). These types of events may negatively impact broad segments of businesses and populations and have a significant and rapid negative impact on the performance or value 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. The frequency and magnitude of resulting changes in the value of the Fund’s investments cannot be predicted.

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Information Technology Sector Risk [Member]

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•

Private Placements and Restricted Securities. The Fund’s investments may include privately placed and restricted securities, which are generally subject to resale or transfer restrictions or prohibitions. Private placements and restricted securities may not be listed on an exchange and may have no active trading market. The Fund may be unable to dispose of privately placed and restricted securities promptly or may be able to sell privately placed and restricted securities only at disadvantageous times or prices, especially under adverse market or economic conditions or in the event of adverse changes in the financial condition of the issuer. There is no assurance that a liquid market will exist for privately placed and restricted securities and these securities could have the effect of increasing the level of Fund illiquidity. In addition, the market for certain investments deemed liquid at the time of purchase may become illiquid under adverse market or economic conditions. Restricted securities, including privately placed

securities, may be difficult to value and may experience significant price volatility, and there is typically less information available about issuers of private placements and restricted securities and there is no assurance that the information obtained by the Adviser is reliable. Private placements and restricted securities may involve a high degree of business and financial risk and may result in substantial losses to the Fund.

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Consumer Discretionary Sector Risk [Member]

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•

Information Technology Sector Risk. To the extent the Fund invests a substantial portion of its assets in the information technology sector, the value of Fund shares may be particularly impacted by events that adversely affect the information technology sector, such as rapid changes in technology product cycles, product obsolescence, government regulation, and competition, and may fluctuate more than that of a fund that does not invest significantly in companies in the technology sector.

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Active Management Risk [Member]

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•

Consumer Discretionary Sector Risk. To the extent that the Fund invests a substantial portion of its assets in the consumer discretionary sector, the Fund will be particularly susceptible to the risks associated with companies operating in such sector. Companies in the consumer discretionary sector are subject to risks, including fluctuations in the performance of the overall domestic and international economy, shipment and supply chain disruptions, interest rate changes, currency exchange rates, increased competition and consumer confidence. Performance of such companies may also be adversely affected by factors such as reduced disposable household income, reduced consumer spending, and changing demographics and consumer tastes.

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(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Russell 1000® Index (reflects no deduction for fees, expenses or taxes)

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•

Active Management Risk. In pursuing the Fund’s investment objective, the Adviser has considerable leeway in deciding which investments to buy, hold or sell on a day-to-day basis, and which trading strategies to use. For example, the Adviser, in its discretion, may determine to use some permitted trading strategies while not using others. The success or failure of such decisions will affect the Fund’s performance.

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rr_AverageAnnualReturnYear01

24.51%

^[1]

rr_AverageAnnualReturnYear05

14.28%

^[1]

(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Russell 1000® Growth Index (reflects no deduction for fees, expenses or taxes)

rr_AverageAnnualReturnSinceInception

13.72%

^[1],[2]

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rr_AverageAnnualReturnYear01

33.36%

^[3]

rr_AverageAnnualReturnYear05

18.96%

^[3]

(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Class IR

rr_AverageAnnualReturnSinceInception

17.67%

^[2],[3]

Management Fees (as a percentage of Assets)

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rr_ManagementFeesOverAssets

0.42%

^[4]

Distribution and Service (12b-1) Fees

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none

Other Expenses (as a percentage of Assets):

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6.37%

^[5]

Total Annual Fund Operating Expenses

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6.79%

^[6]

Fee Waiver or Reimbursement

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6.06%

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Total Annual Fund Operating Expenses After Expense Reimbursement

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0.73%

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Expense Example, with Redemption, 1 Year

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$ 75

Expense Example, with Redemption, 3 Years

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1,465

Expense Example, with Redemption, 5 Years

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2,807

Expense Example, with Redemption, 10 Years

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5,956

Expense Example, No Redemption, 1 Year

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Expense Example, No Redemption, 3 Years

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1,465

Expense Example, No Redemption, 5 Years

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2,807

Expense Example, No Redemption, 10 Years

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$ 5,956

Annual Return 2019

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23.26%

Annual Return 2020

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115.74%

Annual Return 2021

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0.52%

Annual Return 2022

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(60.41%)

Annual Return 2023

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50.33%

Annual Return 2024

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46.81%

Highest Quarterly Return, Label

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High Quarter

Highest Quarterly Return

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58.33%

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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(41.18%)

Lowest Quarterly Return, Date

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Jun. 30, 2022

rr_AverageAnnualReturnYear01

46.81%

rr_AverageAnnualReturnYear05

13.64%

(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Class IR | Return After Taxes on Distributions

rr_AverageAnnualReturnSinceInception

11.35%

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rr_AverageAnnualReturnYear01

46.47%

^[7]

rr_AverageAnnualReturnYear05

11.15%

^[7]

(MSIF - Growth Portfolio - Class IR) | (Growth Portfolio) | Class IR | Return After Taxes on Distributions and Sale of Fund Shares

rr_AverageAnnualReturnSinceInception

8.79%

^[7]

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rr_AverageAnnualReturnYear01

27.73%

rr_AverageAnnualReturnYear05

10.61%