Label	Element	Value
Multi-Asset Portfolio
Risk/Return:	rr_RiskReturnAbstract
Supplement [Text Block]	ck0000836487_SupplementTextBlock	Prospectus Supplement August 16, 2013 Morgan Stanley Institutional Fund, Inc. Supplement dated August 16, 2013 to the Morgan Stanley Institutional Fund, Inc. (the "Fund") Prospectus dated April 30, 2013 of: Multi-Asset Portfolio (the "Portfolio")
Risk/Return [Heading]	rr_RiskReturnHeading	Multi-Asset Portfolio
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The section of the Prospectus entitled "Portfolio Summary—Objective" is hereby deleted and replaced with the following: The Multi-Asset Portfolio seeks total return. The Portfolio's "Adviser," Morgan Stanley Investment Management Inc., seeks to achieve this objective with an emphasis on positive absolute return and controlling downside portfolio risk.
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The section of the Prospectus entitled "Portfolio Summary—Principal Investment Strategies" are hereby deleted and replaced with the following: The Adviser seeks to achieve the Portfolio's investment objective by emphasizing positive absolute return while actively controlling downside portfolio risk. To implement this approach, the Adviser will take long and short positions in a range of equity and equity related securities of any market capitalization, bonds, currencies and commodities. The Adviser may implement these positions either directly by purchasing securities or (specifically in the case of short positions) through the use of derivatives. The Adviser's top-down investment approach focuses on asset class, sector, region, country and currency selection as opposed to individual security selection. The Portfolio's allocations are the result of directional views of the markets or individual asset classes taken by the Adviser based on the results of its fundamental and quantitative research. The Portfolio's investments may be U.S. and non-U.S. dollar denominated. The Portfolio may invest in real estate investment trusts ("REITs") and similar entities established outside the United States ("foreign real estate companies"). In addition, the Portfolio may invest in fixed income securities issued or guaranteed by foreign governments or supranational organizations or any of their instrumentalities, including debt obligations of governmental issuers located in emerging market or developing countries and sovereign debt, as well as fixed income securities that are rated below "investment grade" or are not rated, but are of equivalent quality. These fixed income securities are often referred to as "high yield securities" or "junk bonds." High yield securities are fixed income securities rated below Baa by Moody's Investors Service, Inc. ("Moody's") or below BBB by Standard & Poor's Rating Group, a division of The McGraw-Hill Companies, Inc. ("S&P"), or if unrated considered by the Adviser to be an appropriate investment for the Portfolio. The Portfolio may invest in asset-backed securities. The Portfolio may also invest in privately placed and restricted securities. The mortgage-backed securities in which the Portfolio may invest include mortgage pass-through securities which represent a participation interest in a pool of mortgage loans originated by U.S. governmental or private lenders such as banks. The Portfolio may also invest in other investment companies, including exchange-traded funds ("ETFs"). The Portfolio will use derivative instruments for a variety of purposes, including as part of its investment strategies, hedging, risk management, portfolio management or to earn income. The Portfolio's use of derivatives may involve the purchase and sale of derivative instruments such as futures, options, swaps, structured investments (including commodity-linked notes) and other related instruments and techniques. The Portfolio may also invest in currency derivatives, including, but not limited to, foreign currency forward exchange contracts, and currency and currency index futures and options contracts for hedging and non-hedging purposes. The use of these currency derivatives may allow the Portfolio to obtain net long or net negative (short) exposure to selected currencies. At times, the Portfolio may enter into "cross-currency" transactions involving currencies other than those in which securities held or proposed to be purchased are denominated. Derivative instruments used by the Portfolio will be counted toward the Portfolio's exposure in the types of securities listed above to the extent they have economic characteristics similar to such securities.
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	The following replaces the section of the Prospectus entitled "Portfolio Summary—Principal Risks—Derivatives:" • *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 they relate 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 Portfolio's exposure to currency exchange rates and could result in losses to the Portfolio 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 Portfolio's securities are not denominated.
Risk Closing [Text Block]	rr_RiskClosingTextBlock	Please retain this supplement for future reference.

Label

Element

Value

Multi-Asset Portfolio

Risk/Return:

rr_RiskReturnAbstract

Supplement [Text Block]

ck0000836487_SupplementTextBlock

Prospectus Supplement

August 16, 2013

Morgan Stanley Institutional Fund, Inc.

Supplement dated August 16, 2013 to the Morgan Stanley Institutional Fund, Inc. (the "Fund") Prospectus dated April 30, 2013 of:

Multi-Asset Portfolio
(the "Portfolio")

Risk/Return [Heading]

rr_RiskReturnHeading

Multi-Asset Portfolio

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The section of the Prospectus entitled "Portfolio Summary—Objective" is hereby deleted and replaced with the following:

The Multi-Asset Portfolio seeks total return. The Portfolio's "Adviser," Morgan Stanley Investment Management Inc., seeks to achieve this objective with an emphasis on positive absolute return and controlling downside portfolio risk.

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The section of the Prospectus entitled "Portfolio Summary—Principal Investment Strategies" are hereby deleted and replaced with the following:

The Adviser seeks to achieve the Portfolio's investment objective by emphasizing positive absolute return while actively controlling downside portfolio risk. To implement this approach, the Adviser will take long and short positions in a range of equity and equity related securities of any market capitalization, bonds, currencies and commodities. The Adviser may implement these positions either directly by purchasing securities or (specifically in the case of short positions) through the use of derivatives.

The Adviser's top-down investment approach focuses on asset class, sector, region, country and currency selection as opposed to individual security selection. The Portfolio's allocations are the result of directional views of the markets or individual asset classes taken by the Adviser based on the results of its fundamental and quantitative research. The Portfolio's investments may be U.S. and non-U.S. dollar denominated.

The Portfolio may invest in real estate investment trusts ("REITs") and similar entities established outside the United States ("foreign real estate companies"). In addition, the Portfolio may invest in fixed income securities issued or guaranteed by foreign governments or supranational organizations or any of their instrumentalities, including debt obligations of governmental issuers located in emerging market or developing countries and sovereign debt, as well as fixed income securities that are rated below "investment grade" or are not rated, but are of equivalent quality. These fixed income securities are often referred to as "high yield securities" or "junk bonds." High yield securities are fixed income securities rated below Baa by Moody's Investors Service, Inc. ("Moody's") or below BBB by Standard & Poor's Rating Group, a division of The McGraw-Hill Companies, Inc. ("S&P"), or if unrated considered by the Adviser to be an appropriate investment for the Portfolio.

The Portfolio may invest in asset-backed securities. The Portfolio may also invest in privately placed and restricted securities. The mortgage-backed securities in which the Portfolio may invest include mortgage pass-through securities which represent a participation interest in a pool of mortgage loans originated by U.S. governmental or private lenders such as banks. The Portfolio may also invest in other investment companies, including exchange-traded funds ("ETFs").

The Portfolio will use derivative instruments for a variety of purposes, including as part of its investment strategies, hedging, risk management, portfolio management or to earn income. The Portfolio's use of derivatives may involve the purchase and sale of derivative instruments such as futures, options, swaps, structured investments (including commodity-linked notes) and other related instruments and techniques. The Portfolio may also invest in currency derivatives, including, but not limited to, foreign currency forward exchange contracts, and currency and currency index futures and options contracts for hedging and non-hedging purposes. The use of these currency derivatives may allow the Portfolio to obtain net long or net negative (short) exposure to selected currencies. At times, the Portfolio may enter into "cross-currency" transactions involving currencies other than those in which securities held or proposed to be purchased are denominated. Derivative instruments used by the Portfolio will be counted toward the Portfolio's exposure in the types of securities listed above to the extent they have economic characteristics similar to such securities.

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The following replaces the section of the Prospectus entitled "Portfolio Summary—Principal Risks—Derivatives:"

• 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 they relate 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 Portfolio's exposure to currency exchange rates and could result in losses to the Portfolio 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 Portfolio's securities are not denominated.

Risk Closing [Text Block]

rr_RiskClosingTextBlock

Please retain this supplement for future reference.