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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Prospectus Date rr_ProspectusDate Apr. 29, 2011
ACTIVE INTERNATIONAL ALLOCATION PORTFOLIO (Prospectus Summary): | ACTIVE INTERNATIONAL ALLOCATION PORTFOLIO
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return, Heading rr_RiskReturnHeading Active International Allocation Portfolio
Supplement Text ck0000836487_SupplementTextBlock

Prospectus Supplement

June 30, 2011

Morgan Stanley Institutional Fund, Inc.

Supplement dated June 30, 2011 to the Morgan Stanley Institutional Fund, Inc. Prospectus dated April 29, 2011 of:

Active International Allocation Portfolio

The Board of Directors of Morgan Stanley Institutional Fund, Inc. (the "Fund") has approved an increase in the expense cap with respect to the Class I and Class P shares of the Active International Allocation Portfolio (the "Portfolio"), effective July 1, 2011. Accordingly, the following changes to the Prospectus will become effective on July 1, 2011.

The Portfolio's Annual Portfolio Operating Expenses table under the section of the Prospectus entitled "Portfolio Summary—Active International Allocation Portfolio—Fees and Expenses—Annual Portfolio Operating Expenses" is hereby deleted in its entirety and replaced with the following: Please retain this supplement for future reference.

  MSIGLINSPT1

 
Operating Expenses, Caption rr_OperatingExpensesCaption Annual Portfolio Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Expense Example Supplement Heading ck0000836487_ExpenseExampleSupplementHeading

The Portfolio's Example information under the section of the Prospectus entitled "Portfolio Summary—Active International Allocation Portfolio—Fees and Expenses—Example" is hereby deleted in its entirety and replaced with the following:
Expense Example, Heading rr_ExpenseExampleHeading Example
Expense Example, Narrative rr_ExpenseExampleNarrativeTextBlock

This example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds.

The example assumes that you invest $10,000 in the Portfolio, your investment has a 5% return each year and that the Portfolio's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
ACTIVE INTERNATIONAL ALLOCATION PORTFOLIO | CLASS I
  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MSACX
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.65% [1]
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.27% [1]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.92% [1]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.02%) [1]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.90% [1]
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 92
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 287
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 498
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,108
ACTIVE INTERNATIONAL ALLOCATION PORTFOLIO | CLASS P
  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MSIBX
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.65% [1]
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.27% [1]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.17% [1]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.02%) [1]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.15% [1]
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 117
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 365
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 633
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,398
[1] The Adviser has agreed to reduce its advisory fee and/or reimburse the Portfolio so that Total Annual Portfolio Operating Expenses, excluding certain investment related expenses, will not exceed 0.90% for Class I and 1.15% for Class P. The fee waivers and/or expense reimbursements are expected to continue for one year or until such time that the Fund's Board of Directors acts to discontinue all or a portion of such waivers and/or reimbursements when it deems that such action is appropriate.