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S000019579 [Member] Investment Risks - World Selection Index Fund
Mar. 31, 2026
ESG INVESTING RISK [Member]  
Prospectus [Line Items]  
Risk [Text Block]
ESG INVESTING RISK is the risk that the ESG investment methodology of the Index may restrict the investments available to the Fund. This may affect the Fund’s exposure to certain companies or industries and cause the Fund to forego certain investment opportunities. This could cause the Fund to underperform or perform differently than the broader equity market or other funds that do or do not track an ESG index or use ESG factors, scores, or screens in their securities selection process, or use a different ESG methodology. The construction of the Index depends in large part on the ESG criteria considered and research methodologies employed by MSCI Solutions. Information used by MSCI to evaluate ESG factors may not be readily available, complete or accurate, which could negatively impact MSCI’s ability to apply its ESG standards when compiling the Index, which could negatively impact the Fund’s performance. Although the Index is designed to measure a portfolio of companies with certain ESG characteristics, there is no assurance that every security in the Index or Fund will have ESG characteristics or that companies that have historically exhibited such characteristics will continue to exhibit such characteristics. Currently, there is a lack of common industry standards relating to the development and application of ESG criteria, and MSCI’s assessment of a company, based on the company’s level of involvement in a particular industry or the company’s ESG Rating and Controversies Score, may differ from that of other funds, other index providers, the investment adviser or an investor. As a result, the companies deemed eligible for inclusion in the Index may not reflect the beliefs and values of any particular investor and may not be deemed to exhibit positive or favorable ESG characteristics if different metrics were used to evaluate them. ESG standards differ by region and industry, and a company’s ESG practices or MSCI’s or data providers’ assessment of a company’s ESG practices may change over time.
FOREIGN SECURITIES RISK [Member]  
Prospectus [Line Items]  
Risk [Text Block]
FOREIGN SECURITIES RISK is the risk that investing in foreign (non‑U.S.) securities may result in the Fund experiencing more rapid and extreme changes in value than a fund that invests exclusively in securities of U.S. companies, due to less liquid markets and adverse economic, political, diplomatic, financial, and regulatory factors. Foreign governments may impose limitations on foreigners’ ownership of interests in local issuers, restrictions on the ability to repatriate assets, and may also impose taxes. Any of these events could cause the value of the Fund’s investments to decline. Foreign banks, agents and securities depositories that hold the Fund’s foreign assets may be subject to little or no regulatory oversight over, or independent evaluation, of their operations. Additional costs associated with investments in foreign securities may include higher custodial fees than those applicable to domestic custodial arrangements and transaction costs of foreign currency conversions. Unless the Fund has hedged its foreign currency exposure, foreign securities risk also involves the risk of negative foreign currency rate fluctuations, which may cause the value of securities denominated in such foreign currency (or other instruments through which the Fund has exposure to foreign currencies) to decline in value. Currency exchange rates may fluctuate significantly over short periods of time. Currency hedging strategies, if used, are not always successful. For instance, forward foreign currency exchange contracts, if used by the Fund, could reduce performance if there are unanticipated changes in currency exchange rates.
DEPOSITARY RECEIPTS RISK [Member]  
Prospectus [Line Items]  
Risk [Text Block]
DEPOSITARY RECEIPTS RISK Foreign securities may trade in the form of depositary receipts. In addition to investment risks associated with the underlying issuer, depositary receipts may expose the Fund to additional risks associated with non‑uniform terms that apply to depositary receipt programs, including credit exposure to the depository bank and to the sponsors and other parties with whom the depository bank establishes the programs, currency, political, economic, market risks and the risks of an illiquid market for depositary receipts. Depositary receipts are generally subject to the same risks as the foreign securities that they evidence or into which they may be converted. Depositary receipts may not track the price of the underlying foreign securities on which they are based, may have limited voting rights, and may have a distribution subject to a fee charged by the depository. As a result, equity shares of the underlying issuer may trade at a discount or premium to the market price of the depositary receipts.
TRACKING RISK [Member]  
Prospectus [Line Items]  
Risk [Text Block]
TRACKING RISK is the risk that the Fund’s performance may vary from the performance of the index it tracks as a result of share purchases and redemptions, transaction costs, expenses and other factors. Market disruptions, regulatory restrictions or other abnormal market conditions could have an adverse effect on the Fund’s ability to adjust its exposure to required levels in order to track its Index or cause delays in the Index’s rebalancing schedule. During any such delay, it is possible that
the Index, and, in turn, the Fund will deviate from the Index’s stated methodology and therefore experience returns different than those that would have been achieved under a normal rebalancing or reconstitution schedule.
SECTOR RISK [Member]  
Prospectus [Line Items]  
Risk [Text Block]
SECTOR RISK is the risk that companies in similar businesses may be similarly affected by particular economic or market events, which may, in certain circumstances, cause the value of
securities of all companies in a particular sector of the market to decrease.
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INFORMATION TECHNOLOGY SECTOR RISK is the risk that securities of technology companies may be subject to greater price volatility than securities of companies in other sectors. These securities may fall in and out of favor with investors rapidly, which may cause sudden selling and dramatically lower market prices. Technology companies also may be affected adversely by changes in technology, consumer and business purchasing patterns, government scrutiny or regulation, legal action and/or obsolete products or services.
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FINANCIALS SECTOR RISK is the risk that companies in the financials sector can be significantly affected by changes in interest rates, government regulation, the rate of corporate and consumer debt defaulted, price competition, and the availability and cost of capital, among other factors.
MID CAP STOCK RISK [Member]  
Prospectus [Line Items]  
Risk [Text Block]
MID CAP STOCK RISK is the risk that stocks of mid‑sized companies may be more volatile than stocks of larger, more established companies, and may lack sufficient market liquidity. Mid‑sized companies may have limited product lines or financial resources, may be dependent upon a particular niche of the market, or may be dependent upon a small or inexperienced management group. Securities of mid‑sized companies may trade less frequently and in lower volume than the securities of larger companies, which could lead to higher transaction costs. Generally, the smaller the company size, the greater the risk.
INDEX RISK [Member]  
Prospectus [Line Items]  
Risk [Text Block]
INDEX RISK is the risk that that the Fund would not necessarily buy or sell a security unless that security is added or removed, respectively, from the Index, even if that security generally is underperforming, because unlike many investment companies, the Fund does not utilize an investing strategy that seeks returns in excess of the Index. Additionally, the Fund rebalances its portfolio in accordance with the Index, and, therefore, any changes to the Index’s rebalance schedule will result in corresponding changes to the Fund’s rebalance schedule.
SECURITIES LENDING RISK [Member]  
Prospectus [Line Items]  
Risk [Text Block]
SECURITIES LENDING RISK is the risk that the Fund may lose money because the borrower of the loaned securities fails to return the securities in a timely manner or at all. The Fund could also lose money in the event of a decline in the value of collateral provided for loaned securities or a decline in the value of any investments made with cash collateral.
MARKET RISKS [Member]  
Prospectus [Line Items]  
Risk [Text Block]
MARKET RISK is the risk that the value of the Fund’s investments may increase or decrease in response to expected, real or perceived economic, political or financial events in the
U.S. or global markets. The frequency and magnitude of such changes in value cannot be predicted. Certain securities and other investments held by the Fund may experience increased volatility, illiquidity, or other potentially adverse effects in response to changing market conditions, inflation, elevated levels of government debt, changes in interest rates, lack of liquidity in the bond or equity markets or volatility in the equity markets. Market disruptions caused by local or regional events such as financial institution failures, changes in trade regulation or economic sanctions, internal unrest and discord, war, acts of terrorism, the spread of infectious illness (including epidemics and pandemics) or other public health issues, recessions, the threat or occurrence of a government shutdown, or other events or adverse investor sentiment could have a significant impact on the Fund and its investments. During periods of market disruption or other abnormal market conditions, the Fund’s exposure to risks described elsewhere in this summary will likely increase.
Risk Lose Money [Member]  
Prospectus [Line Items]  
Risk [Text Block] As with any mutual fund, it is possible to lose money on an investment in the Fund.
Risk Not Insured Depository Institution [Member]  
Prospectus [Line Items]  
Risk [Text Block] An investment in the Fund is not a deposit of any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation, any other government agency, or The Northern Trust Company, its affiliates, subsidiaries or any other bank.
Risk Nondiversified Status [Member]  
Prospectus [Line Items]  
Risk [Text Block]
NON‑DIVERSIFICATION RISK Under the 1940 Act, a fund designated as “diversified” must limit its holdings such that the securities of issuers which individually represent more than 5% of its total assets must in the aggregate represent less than 25% of its total assets. The Fund is “diversified” for purposes of the 1940 Act. However, in seeking to track its Index, the Fund may become “non‑diversified,” as defined in the 1940 Act, solely as a result of a change in relative market capitalization or index weighting of one or more constituents of the Index. A non‑diversified fund can invest a greater portion of its assets in the obligations or securities of a small portion of its assets in the obligations or securities of a small number of issuers or any single issuer than a diversified fund can. In such circumstances, a change in the value of one or a few issuers’ securities will therefore affect the value of the Fund more than if it was a diversified fund.