Label	Element	Value
Fundamental Multi-Cap Core Portfolio
Risk/Return:	rr_RiskReturnAbstract
Supplement [Text Block]	ck0000836487_SupplementTextBlock	Prospectus Supplement September 30, 2016 Morgan Stanley Institutional Fund, Inc. Supplement dated September 30, 2016 to the Morgan Stanley Institutional Fund, Inc. Prospectus dated May 11, 2016 Fundamental Multi-Cap Core Portfolio (each, a "Portfolio")
Risk/Return [Heading]	rr_RiskReturnHeading	Fundamental Multi-Cap Core Portfolio
Expense [Heading]	rr_ExpenseHeading	The second sentence of the section of each Portfolio's Prospectus entitled "Portfolio Summary—Fees and Expenses" is hereby deleted and replaced with the following:
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	For purchases of Class A shares, you may qualify for a sales charge discount if the cumulative net asset value ("NAV") of Class A shares of the Portfolio being purchased in a single transaction, together with the NAV of any Class A, Class C and Class L shares of the Portfolio of Morgan Stanley Institutional Fund, Inc. (the "Fund") already held in Related Accounts as of the date of the transaction as well as Class A, Class C and Class L shares of any other Morgan Stanley Multi-Class Fund (as defined in the section of this Prospectus entitled "Shareholder Information—Exchange Privilege" and including shares of Morgan Stanley Money Market Funds (as defined in the section of this Prospectus entitled "Shareholder Information—Exchange Privilege") which you acquired in an exchange from Class A shares of the Portfolio or Class A shares of another Morgan Stanley Multi-Class Fund) held in Related Accounts (as defined in the section of this Prospectus entitled "Shareholder Information—Sales Charges Applicable to Purchases of Class A Shares") which you acquired in an exchange from Class A shares of the Portfolio or Class A shares of another Morgan Stanley Multi-Class Fund already held in Related Accounts as of the date of the transaction, amounts to $25,000 or more. Please retain this supplement for future reference.
Fundamental Multi-Cap Core Portfolio \| Class A
Risk/Return:	rr_RiskReturnAbstract
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	For purchases of Class A shares, you may qualify for a sales charge discount if the cumulative net asset value ("NAV") of Class A shares of the Portfolio being purchased in a single transaction, together with the NAV of any Class A, Class C and Class L shares of the Portfolio of Morgan Stanley Institutional Fund, Inc. (the "Fund") already held in Related Accounts as of the date of the transaction as well as Class A, Class C and Class L shares of any other Morgan Stanley Multi-Class Fund (as defined in the section of this Prospectus entitled "Shareholder Information—Exchange Privilege" and including shares of Morgan Stanley Money Market Funds (as defined in the section of this Prospectus entitled "Shareholder Information—Exchange Privilege") which you acquired in an exchange from Class A shares of the Portfolio or Class A shares of another Morgan Stanley Multi-Class Fund) held in Related Accounts (as defined in the section of this Prospectus entitled "Shareholder Information—Sales Charges Applicable to Purchases of Class A Shares") which you acquired in an exchange from Class A shares of the Portfolio or Class A shares of another Morgan Stanley Multi-Class Fund already held in Related Accounts as of the date of the transaction, amounts to $25,000 or more.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 25,000

- Definition

Risk/Return Summary Fee Table Includes the following information, in plain English under rule 421(d) under the Securities Act, after Item 2 Fees and expenses of the Fund This table describes the fees and expenses that you may pay if you buy and hold shared of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $[_____] in [name of fund family] funds. Shareholder Fees (fees paid directly from your investment) Example This Example 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 for the time periods indicated and then you redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return per year and that the Fund's operating expenses remained the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be You would pay the following expenses if you did not redeem your shares The Example does not reflect sales charges (loads) on reinvested dividends [and other distributions]. If these sales charges (loads) were included, your costs would be higher. Portfolio Turnover The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover may indicate higher transaction costs. These costs, which are not reflected in 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 __% of the average value of its whole portfolio. Instructions. A.3.instructions.6 New Funds. For purposes of this Item, a "New Fund" is a Fund that does not include in Form N-1A financial statements reporting operating results or that includes financial statements for the Fund's initial fiscal year reporting operating results for a period of 6 months or less. The following Instructions apply to New Funds.

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