Label	Element	Value
SIIT Screened World Equity Ex-US Fund
Risk/Return:	rr_RiskReturnAbstract
Supplement to Prospectus [Text Block]	rr_SupplementToProspectusTextBlock	SEI INSTITUTIONAL INVESTMENTS TRUST Screened World Equity Ex-US Fund (the "Fund") Supplement Dated February 18, 2022 to the Prospectus dated September 30, 2021, as amended on November 2, 2021, December 17, 2021 and February 4, 2022 This Supplement provides new and additional information beyond that contained in the Prospectus and should be read in conjunction with such Prospectus. The Prospectus is hereby amended and supplemented to reflect the following changes to the Fund.
Risk/Return [Heading]	rr_RiskReturnHeading	Screened World Equity Ex-US Fund
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Change in Investment Strategy for the Fund In the Fund Summary for the Fund, under the heading titled "Principal Investment Strategies," the first paragraph thereunder is hereby deleted and replaced with the following: Under normal circumstances, the Screened World Equity Ex-US Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of foreign companies of various capitalization ranges. These securities may include common stocks, preferred stocks, depositary receipts, warrants, exchange-traded funds (ETFs) based on an international equity index, derivative instruments (principally futures and forward contracts) whose value is based on an international equity index or an underlying equity security or basket of equity securities and investment companies whose portfolios are designed to correlate with a portfolio of international equity securities. The Fund will invest in securities of foreign issuers located in developed and emerging market countries, but will seek to avoid investing in companies whose activities directly or indirectly benefit the governments of countries that support terrorism, genocide or human rights abuses. The Fund will also maintain an Anti-BDS approach. BDS refers to the Palestinian-led movement promoting boycotts, divestments and economic sanctions against Israel. The Fund will seek to avoid investing in companies identified as having adopted or implemented a BDS stance. This policy has been adopted to enable investment in the Fund by institutional investors that seek to support Israel or oppose the BDS movement in their investment implementation. This Fund policy is for the benefit of such noted investors and not meant as a formal representation of SEI's official corporate policy or position on the issue of BDS. The Fund will not invest more than 35% of its assets in the common stocks or other equity securities of issuers located in emerging market countries. The Fund may also, to a lesser extent, invest in swaps on securities for risk management purposes or as part of its investment strategies. The Fund's benchmark is the MSCI All Country World Ex-U.S. Net Index (net of dividends). The Fund is expected to have an absolute return and risk profile similar to the international equity market. The Fund is diversified as to issuers, market capitalization, industry and country. There are no other changes to the Investment Strategy of the Fund.
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Change in Principal Risks for the Fund In the Fund Summary for the Fund, under the heading titled "Principal Risks", the first sentence of "Social Investment Criteria Risk" is hereby deleted and replaced with the following: The Fund's portfolio is subject to certain social investment criteria, including its anti-BDS approach. There are no other changes to the Principal Risks of the Fund.
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