Label	Element	Value
Multi-Class Prospectus \| Permanence Portfolio
Risk/Return:	rr_RiskReturnAbstract
Supplement to Prospectus [Text Block]	rr_SupplementToProspectusTextBlock	Prospectus Supplement March 30, 2020 Morgan Stanley Institutional Fund, Inc. Supplement dated March 30, 2020 to the Morgan Stanley Institutional Fund, Inc. Prospectus dated March 6, 2019 Permanence Portfolio
Risk/Return [Heading]	rr_RiskReturnHeading	Permanence Portfolio
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	The following is hereby added at the end of the section of the Prospectus entitled "Fund Summary—Principal Risks": Market and Geopolitical Risk. The value of your investment in the Fund is based on the market prices and values of the Fund's investments, which change daily due to economic and other events that affect markets generally, as well as those that affect particular regions, countries, industries, companies or governments. These events may be sudden and unexpected, and could adversely affect the value and liquidity of the Fund's investments, which may in turn impact a Fund's ability to sell securities and/or its ability to meet redemptions. The risks associated with these developments may be magnified if certain social, political, economic and other conditions and events (such as natural disasters, epidemics and pandemics, terrorism, conflicts and social unrest) adversely interrupt the global economy and financial markets. It is difficult to predict when events affecting the U.S. or global financial markets may occur, the effects that such events may have and the duration of those effects (which may last for extended periods).
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