Label	Element	Value
Frontier Markets Portfolio
Risk/Return:	rr_RiskReturnAbstract
Supplement to Prospectus [Text Block]	rr_SupplementToProspectusTextBlock	Prospectus Supplement June 24, 2021 Morgan Stanley Institutional Fund, Inc. Supplement dated June 24, 2021 to the Morgan Stanley Institutional Fund, Inc. Prospectus dated April 30, 2021 Frontier Markets Portfolio (the "Fund")
Risk/Return [Heading]	rr_RiskReturnHeading	Frontier Markets Portfolio
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	On June 23, 2021, Fund shareholders approved changing the Fund's fundamental investment policy regarding industry concentration, eliminating the requirement that the Fund invest more than 25% of its total assets in the banking industry (i.e., "concentrate" in the banking industry). Effective June 30, 2021, the Fund's principal investment strategies and process are revised accordingly to reflect the elimination of the Fund's fundamental investment policy to concentrate in the banking industry.
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Effective June 30, 2021, the section of the Prospectus entitled "Fund Summary—Frontier Markets Portfolio—Principal Risks—Banking Industry" is deleted in its entirety and replaced with the following: Banking Industry. Investment opportunities in many frontier emerging markets may be in the banking industry. The banking industry can be affected by global and local economic conditions, such as the levels and liquidity of the global and local financial and asset markets, the absolute and relative level and volatility of interest rates and equity prices, investor sentiment, inflation, and the availability and cost of credit. Adverse developments in these conditions can have a greater adverse effect on the banking industry of a frontier emerging market economy than on other industries of its economy. The enactment of new legislation or regulations, as well as changes in interpretation and enforcement of current laws, may affect the manner of operations and profitability of the banking industry. To the extent the Fund invests a substantial portion of its assets in the banking industry, factors that have an adverse impact on this industry may have a disproportionate impact on the Fund's performance.
Risk Closing [Text Block]	rr_RiskClosingTextBlock	Please retain this supplement for future reference.

- Definition

(ii) (A) If the Fund is a Money Market Fund that is not a government Money Market Fund, as defined in §270.2a– 7(a)(16) or a retail Money Market Fund, as defined in § 270.2a–7(a)(25), include the following statement: You could lose money by investing in the Fund. Because the share price of the Fund will fluctuate, when you sell your shares they may be worth more or less than what you originally paid for them. The Fund may impose a fee upon sale of your shares or may temporarily suspend your ability to sell shares if the Fund's liquidity falls below required minimums because of market conditions or other factors. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund's sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time. (B) If the Fund is a Money Market Fund that is a government Money Market Fund, as defined in § 270.2a–7(a)(16), or a retail Money Market Fund, as defined in § 270.2a–7(a)(25), and that is subject to the requirements of §§ 270.2a–7(c)(2)(i) and/or (ii) of this chapter (or is not subject to the requirements of §§ 270.2a–7(c)(2)(i) and/or (ii) of this chapter pursuant to § 270.2a–7(c)(2)(iii) of this chapter, but has chosen to rely on the ability to impose liquidity fees and suspend redemptions consistent with the requirements of §§ 270.2a–7(c)(2)(i) and/or (ii)), include the following statement: You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. The Fund may impose a fee upon sale of your shares or may temporarily suspend your ability to sell shares if the Fund's liquidity falls below required minimums because of market conditions or other factors. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund's sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time. (C) If the Fund is a Money Market Fund that is a government Money Market Fund, as defined in § 270.2a–7(a)(16), that is not subject to the requirements of §§ 270.2a–7(c)(2)(i) and/or (ii) of this chapter pursuant to § 270.2a–7(c)(2)(iii) of this chapter, and that has not chosen to rely on the ability to impose liquidity fees and suspend redemptions consistent with the requirements of §§ 270.2a–7(c)(2)(i) and/or (ii), include the following statement: You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund's sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time. Instruction. If an affiliated person, promoter, or principal underwriter of the Fund, or an affiliated person of such a person, has contractually committed to provide financial support to the Fund, and the term of the agreement will extend for at least one year following the effective date of the Fund's registration statement, the statement specified in Item 4(b)(1)(ii)(A), Item 4(b)(1)(ii)(B), or Item 4(b)(1)(ii)(C) may omit the last sentence ("The Fund's sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time."). For purposes of this Instruction, the term "financial support" includes any capital contribution, purchase of a security from the Fund in reliance on § 270.17a–9, purchase of any defaulted or devalued security at par, execution of letter of credit or letter of indemnity, capital support agreement (whether or not the Fund ultimately received support), performance guarantee, or any other similar action reasonably intended to increase or stabilize the value or liquidity of the fund's portfolio; however, the term "financial support" excludes any routine waiver of fees or reimbursement of fund expenses, routine inter-fund lending, routine inter-fund purchases of fund shares, or any action that would qualify as financial support as defined above, that the board of directors has otherwise determined not to be reasonably intended to increase or stabilize the value or liquidity of the fund's portfolio. (iii) If the Fund is advised by or sold through an insured depository institution, state that: An investment in the Fund is not a deposit of the bank and is not insured or guaranteed by the Federal Deposit Insurance corporation or any other government agency. Instruction. A Money Market Fund that is advised by or sold through an insured depository institution should combine the disclosure required by Items 4(b)(1)(ii) and (iii) in a single statement.

+ References + Details