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Label Element Value
(MSIF Active International Allocation Portfolio - Class IS) | (Active International Allocation Portfolio)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Active International Allocation Portfolio (the "Fund") seeks long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The table below describes the fees and expenses that you may pay if you buy and hold Class IS shares of the Fund. The Fund does not charge any sales loads or other fees when you purchase Class IS shares.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates Other Expenses have been estimated for the current fiscal year.
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
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] rr_ExpenseExampleByYearCaption If You SOLD Your Shares
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If You HELD Your Shares
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
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 Fund performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 43% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 43.00%
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
The Fund's Adviser actively selects among developed and emerging countries applying its investment process to determine a country's future economic growth and equity return potential. The Adviser utilizes a proprietary top-down framework to quantitatively and qualitatively rank countries relative to one another and relative to their own history. The Adviser's approach combines a top-down country process with sector allocation and bottom-up stock selection. Under normal market conditions, the Fund invests at least 40% of its total assets in the securities of issuers located outside of the United States.
The Adviser analyzes the global economic environment and each country's fundamentals and actively allocate the Fund's assets among countries and sectors located throughout the world (the investment universe is developed markets, including the United States, and emerging markets, including frontier markets). Investment decisions may be implemented through sector, industry and stock-specific allocations within and across markets that best capture the top-down view. Country and sector weightings are based on relative economic, political and social fundamentals, stock valuations and investor sentiment and are a function of the Adviser's conviction levels, the size of the economy and liquidity. The investment process considers analysis of sustainability with respect to financial strength, environmental and social factors and governance (also referred to as ESG).
Investments are based on fundamental analysis in an effort to identify those equities that stand to benefit most from the Adviser's current and prospective macro views and that are likely to experience attractive earnings growth prospects as a result of exposure and gearing to those top-down conditions. Investment decisions are implemented by equity positions in sectors, industries, customized baskets and/or individual stocks. The equity securities in which the Fund may invest include common stock, preferred stock, convertible securities, depositary receipts, rights and warrants. The Adviser generally considers selling a portfolio holding when they determine that the position no longer satisfies their investment criteria.
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, contracts for difference ("CFDs") 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 exposure in the types of securities listed above to the extent they have economic characteristics similar to such securities.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
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:
  • 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.
  • 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, 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, entities and/or individuals, changes in international trading patterns, trade barriers and other protectionist or retaliatory measures. Economic sanctions could, among other things, effectively restrict or eliminate the Fund's ability to purchase or sell securities or groups of securities for a substantial period of time, and may make the Fund's investments in such securities harder to value. The risks of investing in emerging market countries are greater than the risks associated with investments in foreign developed 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 could reduce or preclude the opportunity for gain if the value of the currency moves 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.
  • 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. 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.
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] rr_RiskLoseMoney 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] rr_RiskNotInsuredDepositoryInstitution 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] rr_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
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 I shares' performance from year-to-year and by showing how the Fund's average annual returns for the past one, five and 10 year periods 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 (800) 548-7786.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns—Calendar Years
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

High Quarter

06/30/09

24.16%

Low Quarter

09/30/11

-20.43%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the calendar periods ended December 31, 2018)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
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 IS shares will vary from Class I 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.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses or taxes)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate 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.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred 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 Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher 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.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund's past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns 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 I shares' performance from year-to-year and by showing how the Fund's average annual returns for the past one, five and 10 year periods 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.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns for the Fund's Class IS shares will vary from Class I shares' returns.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.morganstanley.com/im
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone (800) 548-7786
(MSIF Active International Allocation Portfolio - Class IS) | (Active International Allocation Portfolio) | MSCI All Country World ex USA Index (reflects no deduction for fees, expenses or taxes)  
Prospectus: rr_ProspectusTable  
Past One Year rr_AverageAnnualReturnYear01 (14.20%) [1]
Past Five Years rr_AverageAnnualReturnYear05 0.68% [1]
Past Ten Years rr_AverageAnnualReturnYear10 6.57% [1]
(MSIF Active International Allocation Portfolio - Class IS) | (Active International Allocation Portfolio) | Active International Allocation Blend Index (reflects no deduction for fees, expenses or taxes)  
Prospectus: rr_ProspectusTable  
Past One Year rr_AverageAnnualReturnYear01 (14.20%) [2]
Past Five Years rr_AverageAnnualReturnYear05 0.78% [2]
Past Ten Years rr_AverageAnnualReturnYear10 6.45% [2]
(MSIF Active International Allocation Portfolio - Class IS) | (Active International Allocation Portfolio) | Lipper International Multi-Cap Growth Funds Index (reflects no deduction for taxes)  
Prospectus: rr_ProspectusTable  
Past One Year rr_AverageAnnualReturnYear01 (14.74%) [3]
Past Five Years rr_AverageAnnualReturnYear05 0.60% [3]
Past Ten Years rr_AverageAnnualReturnYear10 7.62% [3]
(MSIF Active International Allocation Portfolio - Class IS) | (Active International Allocation Portfolio) | Class I  
Prospectus: rr_ProspectusTable  
Annual Return 2009 rr_AnnualReturn2009 27.26%
Annual Return 2010 rr_AnnualReturn2010 8.95%
Annual Return 2011 rr_AnnualReturn2011 (14.56%)
Annual Return 2012 rr_AnnualReturn2012 17.30%
Annual Return 2013 rr_AnnualReturn2013 21.38%
Annual Return 2014 rr_AnnualReturn2014 (6.37%)
Annual Return 2015 rr_AnnualReturn2015 (1.63%)
Annual Return 2016 rr_AnnualReturn2016 (0.67%)
Annual Return 2017 rr_AnnualReturn2017 24.76%
Annual Return 2018 rr_AnnualReturn2018 (15.14%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel High Quarter
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 24.16%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Low Quarter
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (20.43%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Past One Year rr_AverageAnnualReturnYear01 (15.14%) [4]
Past Five Years rr_AverageAnnualReturnYear05 (0.64%) [4]
Past Ten Years rr_AverageAnnualReturnYear10 5.03% [4]
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 17, 1992 [4]
(MSIF Active International Allocation Portfolio - Class IS) | (Active International Allocation Portfolio) | Class I | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past One Year rr_AverageAnnualReturnYear01 (15.47%) [4],[5]
Past Five Years rr_AverageAnnualReturnYear05 (1.00%) [4],[5]
Past Ten Years rr_AverageAnnualReturnYear10 4.65% [4],[5]
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 17, 1992 [4],[5]
(MSIF Active International Allocation Portfolio - Class IS) | (Active International Allocation Portfolio) | Class I | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past One Year rr_AverageAnnualReturnYear01 (8.72%) [4]
Past Five Years rr_AverageAnnualReturnYear05 (0.39%) [4]
Past Ten Years rr_AverageAnnualReturnYear10 4.12% [4]
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 17, 1992 [4]
(MSIF Active International Allocation Portfolio - Class IS) | (Active International Allocation Portfolio) | Class IS  
Prospectus: rr_ProspectusTable  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage based on the lesser of the offering price or net asset value per share ("NAV") at redemption) rr_MaximumDeferredSalesChargeOverOther none
Redemption Fee (as a percentage of the amount redeemed on redemptions made within 30 days of purchase) rr_RedemptionFeeOverRedemption 2.00%
Advisory Fee rr_ManagementFeesOverAssets 0.65%
Distribution and/or Shareholder Service (12b-1) Fee rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 14.10% [6]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 14.75% [7]
Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets 13.90% [7]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 0.85% [7]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 87
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 2,867
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 87
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 $ 2,867
Past One Year rr_AverageAnnualReturnYear01 [4]
Past Five Years rr_AverageAnnualReturnYear05 [4]
Past Ten Years rr_AverageAnnualReturnYear10 [4]
(MSIF Active International Allocation Portfolio - Class IR) | (Active International Allocation Portfolio)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Active International Allocation Portfolio (the "Fund") seeks long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The table below describes the fees and expenses that you may pay if you buy and hold Class IR shares of the Fund. The Fund does not charge any sales loads or other fees when you purchase Class IR shares.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates Other Expenses have been estimated for the current fiscal year.
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
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] rr_ExpenseExampleByYearCaption If You SOLD Your Shares
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If You HELD Your Shares
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
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 Fund performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 43% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 43.00%
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
The Fund's Adviser actively selects among developed and emerging countries applying its investment process to determine a country's future economic growth and equity return potential. The Adviser utilizes a proprietary top-down framework to quantitatively and qualitatively rank countries relative to one another and relative to their own history. The Adviser's approach combines a top-down country process with sector allocation and bottom-up stock selection. Under normal market conditions, the Fund invests at least 40% of its total assets in the securities of issuers located outside of the United States.
The Adviser analyzes the global economic environment and each country's fundamentals and actively allocate the Fund's assets among countries and sectors located throughout the world (the investment universe is developed markets, including the United States, and emerging markets, including frontier markets). Investment decisions may be implemented through sector, industry and stock-specific allocations within and across markets that best capture the top-down view. Country and sector weightings are based on relative economic, political and social fundamentals, stock valuations and investor sentiment and are a function of the Adviser's conviction levels, the size of the economy and liquidity. The investment process considers analysis of sustainability with respect to financial strength, environmental and social factors and governance (also referred to as ESG).
Investments are based on fundamental analysis in an effort to identify those equities that stand to benefit most from the Adviser's current and prospective macro views and that are likely to experience attractive earnings growth prospects as a result of exposure and gearing to those top-down conditions. Investment decisions are implemented by equity positions in sectors, industries, customized baskets and/or individual stocks. The equity securities in which the Fund may invest include common stock, preferred stock, convertible securities, depositary receipts, rights and warrants. The Adviser generally considers selling a portfolio holding when they determine that the position no longer satisfies their investment criteria.
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, contracts for difference ("CFDs") 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 exposure in the types of securities listed above to the extent they have economic characteristics similar to such securities.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
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:
  • 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.
  • 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, 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, entities and/or individuals, changes in international trading patterns, trade barriers and other protectionist or retaliatory measures. Economic sanctions could, among other things, effectively restrict or eliminate the Fund's ability to purchase or sell securities or groups of securities for a substantial period of time, and may make the Fund's investments in such securities harder to value. The risks of investing in emerging market countries are greater than the risks associated with investments in foreign developed 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 could reduce or preclude the opportunity for gain if the value of the currency moves 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.
  • 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. 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.
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] rr_RiskLoseMoney 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] rr_RiskNotInsuredDepositoryInstitution 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] rr_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
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 I shares' performance from year-to-year and by showing how the Fund's average annual returns for the past one, five and 10 year periods 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 (800) 548-7786.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns—Calendar Years
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

High Quarter

06/30/09

24.16%

Low Quarter

09/30/11

-20.43%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the calendar periods ended December 31, 2018)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
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 I 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.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses or taxes)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate 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.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred 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 Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher 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.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund's past performance, before and after taxes, is not necessarily an indication of how the Fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns 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 I shares' performance from year-to-year and by showing how the Fund's average annual returns for the past one, five and 10 year periods 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.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns for the Fund's Class IR shares will vary from Class I shares' returns.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.morganstanley.com/im
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone (800) 548-7786
(MSIF Active International Allocation Portfolio - Class IR) | (Active International Allocation Portfolio) | MSCI All Country World ex USA Index (reflects no deduction for fees, expenses or taxes)  
Prospectus: rr_ProspectusTable  
Past One Year rr_AverageAnnualReturnYear01 (14.20%) [1]
Past Five Years rr_AverageAnnualReturnYear05 0.68% [1]
Past Ten Years rr_AverageAnnualReturnYear10 6.57% [1]
(MSIF Active International Allocation Portfolio - Class IR) | (Active International Allocation Portfolio) | Active International Allocation Blend Index (reflects no deduction for fees, expenses or taxes)  
Prospectus: rr_ProspectusTable  
Past One Year rr_AverageAnnualReturnYear01 (14.20%) [2]
Past Five Years rr_AverageAnnualReturnYear05 0.78% [2]
Past Ten Years rr_AverageAnnualReturnYear10 6.45% [2]
(MSIF Active International Allocation Portfolio - Class IR) | (Active International Allocation Portfolio) | Lipper International Multi-Cap Growth Funds Index (reflects no deduction for taxes)  
Prospectus: rr_ProspectusTable  
Past One Year rr_AverageAnnualReturnYear01 (14.74%) [3]
Past Five Years rr_AverageAnnualReturnYear05 0.60% [3]
Past Ten Years rr_AverageAnnualReturnYear10 7.62% [3]
(MSIF Active International Allocation Portfolio - Class IR) | (Active International Allocation Portfolio) | Class I  
Prospectus: rr_ProspectusTable  
Annual Return 2009 rr_AnnualReturn2009 27.26%
Annual Return 2010 rr_AnnualReturn2010 8.95%
Annual Return 2011 rr_AnnualReturn2011 (14.56%)
Annual Return 2012 rr_AnnualReturn2012 17.30%
Annual Return 2013 rr_AnnualReturn2013 21.38%
Annual Return 2014 rr_AnnualReturn2014 (6.37%)
Annual Return 2015 rr_AnnualReturn2015 (1.63%)
Annual Return 2016 rr_AnnualReturn2016 (0.67%)
Annual Return 2017 rr_AnnualReturn2017 24.76%
Annual Return 2018 rr_AnnualReturn2018 (15.14%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel High Quarter
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 24.16%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Low Quarter
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (20.43%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Past One Year rr_AverageAnnualReturnYear01 (15.14%) [8]
Past Five Years rr_AverageAnnualReturnYear05 (0.64%) [8]
Past Ten Years rr_AverageAnnualReturnYear10 5.03% [8]
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 17, 1992 [8]
(MSIF Active International Allocation Portfolio - Class IR) | (Active International Allocation Portfolio) | Class I | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past One Year rr_AverageAnnualReturnYear01 (15.47%) [8],[9]
Past Five Years rr_AverageAnnualReturnYear05 (1.00%) [8],[9]
Past Ten Years rr_AverageAnnualReturnYear10 4.65% [8],[9]
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 17, 1992 [8],[9]
(MSIF Active International Allocation Portfolio - Class IR) | (Active International Allocation Portfolio) | Class I | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past One Year rr_AverageAnnualReturnYear01 (8.72%) [8]
Past Five Years rr_AverageAnnualReturnYear05 (0.39%) [8]
Past Ten Years rr_AverageAnnualReturnYear10 4.12% [8]
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 17, 1992 [8]
(MSIF Active International Allocation Portfolio - Class IR) | (Active International Allocation Portfolio) | Class IR  
Prospectus: rr_ProspectusTable  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage based on the lesser of the offering price or net asset value per share ("NAV") at redemption) rr_MaximumDeferredSalesChargeOverOther none
Redemption Fee (as a percentage of the amount redeemed on redemptions made within 30 days of purchase) rr_RedemptionFeeOverRedemption 2.00%
Advisory Fee rr_ManagementFeesOverAssets 0.65%
Distribution and/or Shareholder Service (12b-1) Fee rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 14.10% [10]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 14.75% [11]
Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets 13.90% [11]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 0.85% [11]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 87
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 2,867
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 87
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 $ 2,867
Past One Year rr_AverageAnnualReturnYear01 [8]
Past Five Years rr_AverageAnnualReturnYear05 [8]
Past Ten Years rr_AverageAnnualReturnYear10 [8]
[1] The MSCI All Country World ex USA Index is a free float-adjusted market capitalization weighted index designed to measure the equity market performance of developed and emerging markets, excluding the United States. The term "free float" represents the portion of shares outstanding that are deemed to be available for purchase in the public equity markets by investors. The performance of the index is listed in U.S. dollars and assumes reinvestment of net dividends. Net total return indices reinvest dividends after the deduction of withholding taxes, using (for international indices) a tax rate applicable to non-resident institutional investors who do not benefit from double taxation treaties. It is not possible to invest directly in an index.
[2] The Active International Allocation Blend Index is a performance linked benchmark of the old and new benchmark of the Fund, the old benchmark represented by MSCI EAFE Index (index that is designed to measure the international equity market performance of developed markets, excluding the United States and Canada) from the Fund's inception to December 31, 2016 and the new benchmark represented by MSCI All Country World ex USA Index for periods thereafter. It is not possible to invest directly in an index.
[3] The Lipper International Multi-Cap Growth Funds Index is an equally-weighted performance index of the largest qualifying funds (based on net assets) in the Lipper International Multi-Cap Growth Funds classification. There are currently 30 funds represented in this index.
[4] Class I shares are not offered in the Prospectus. Ordinarily, Class IS shares would have similar annual returns because the shares are invested in the same portfolio of securities and the annual returns may likely differ to the extent that the classes do not have the same expenses. Class IS shares of the Fund had not completed a full calendar year of operations as of December 31, 2018 and therefore Class IS shares do not have annualized return information to report. Return information for the Fund's Class IS shares will be shown in future prospectuses offering the Fund's Class IS shares after the Fund's Class IS shares have a full calendar year of return information to report.
[5] These returns do not reflect any tax consequences from a sale of your shares at the end of each period.
[6] Other Expenses have been estimated for the current fiscal year.
[7] The Fund's "Adviser," Morgan Stanley Investment Management Inc., has agreed to reduce its advisory fee and/or reimburse the Fund so that Total Annual Fund Operating Expenses, excluding certain investment related expenses, taxes, interest and other extraordinary expenses (including litigation), will not exceed 0.85% for Class IS. The fee waivers and/or expense reimbursements will continue for at least one year or until such time as the Board of Directors of Morgan Stanley Institutional Fund, Inc. (the "Company") acts to discontinue all or a portion of such waivers and/or reimbursements when it deems such action is appropriate.
[8] Class I shares are not offered in the Prospectus. Ordinarily, Class IR shares would have similar annual returns because the shares are invested in the same portfolio of securities and the annual returns may likely differ to the extent that the classes do not have the same expenses. Class IR shares of the Fund had not completed a full calendar year of operations as of December 31, 2018 and therefore Class IR shares do not have annualized return information to report. Return information for the Fund's Class IR shares will be shown in future prospectuses offering the Fund's Class IR shares after the Fund's Class IR shares have a full calendar year of return information to report.
[9] These returns do not reflect any tax consequences from a sale of your shares at the end of each period.
[10] Other Expenses have been estimated for the current fiscal year.
[11] The Fund's "Adviser," Morgan Stanley Investment Management Inc., has agreed to reduce its advisory fee and/or reimburse the Fund so that Total Annual Fund Operating Expenses, excluding certain investment related expenses, taxes, interest and other extraordinary expenses (including litigation), will not exceed 0.85% for Class IR. The fee waivers and/or expense reimbursements will continue for at least one year or until such time as the Board of Directors of Morgan Stanley Institutional Fund, Inc. (the "Company") acts to discontinue all or a portion of such waivers and/or reimbursements when it deems such action is appropriate.