Label	Element	Value
Dreyfus Institutional Preferred Government Money Market Fund
Risk/Return:	rr_RiskReturnAbstract
Supplement to Prospectus [Text Block]	rr_SupplementToProspectusTextBlock	September 21, 2020 DREYFUS INSTITUTIONAL Reserves FUNDS Dreyfus Institutional Preferred Government Money Market Fund Supplement to Current Summary Prospectus and Prospectus
Risk/Return [Heading]	rr_RiskReturnHeading	Dreyfus Institutional Preferred Government Money Market Fund
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The following information supplements the information contained in "Principal Investment Strategy" in the summary prospectus and "Fund Summary—Principal Investment Strategy" and "Fund Details—Goal and Approach" in the prospectus: Shares of the fund are intended to qualify as eligible investments for federally chartered credit unions. The fund intends to review changes in the applicable laws, rules and regulations governing eligible investments for federally chartered credit unions, and to take such action as may be necessary so that shares of the fund qualify as eligible investments under the Federal Credit Union Act and the regulations thereunder. Shares of the fund, however, may or may not qualify as eligible investments for particular state-chartered credit unions. A state-chartered credit union should consult its legal counsel to determine whether the fund is a permissible investment under the laws applicable to it.

No definition available.

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- Definition

Risk/Return Summary Investment Objectives/Goals Include the following information, in plain English under rule 421(d) under the Securities Act, in the order and subject matter indicated

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 2

+ Details

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- Definition

Principal investment strategies of the Fund. Summarize how the Fund intends to achieve its investment objectives by identifying the Fund's principal investment strategies (including the type or types of securities in which the Fund invests or will invest principally) and any policy to concentrate in securities of issuers in a particular industry or group of industries.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 4
-Subsection a

+ Details

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- Definition

This element contains the text of a prospectus supplement (submission type 497) not already contained in an element containing amended text or other data from a previous submission.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A

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