S000001267 [Member] Investment Risks - U.S. GOVERNMENT SELECT MONEY MARKET FUND |
Mar. 31, 2026 |
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| MANAGEMENT RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | MANAGEMENT RISK is the risk that a strategy used by the Fund’s investment adviser may fail to produce the intended results or that imperfections, errors or limitations in the tools and data used by the investment adviser may cause unintended results.
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| CREDIT OR DEFAULT RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | CREDIT (OR DEFAULT) RISK is the risk that the inability or unwillingness of an issuer or guarantor of a fixed-income security, or a counterparty to a repurchase or other transaction, to meet its principal or interest payments or other financial obligations in a timely manner will adversely affect the value of the Fund’s investments and its returns. Changes in an issuer’s financial strength, the market’s perception of an issuer’s creditworthiness, or in the credit rating of the issuer or the security may also affect the value of the Fund’s investment in that issuer.
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| DEBT EXTENSION RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | DEBT EXTENSION RISK is the risk that when interest rates rise an issuer will exercise its right to pay principal on certain debt securities held by the Fund later than expected. This will cause the value of the security to decrease and the Fund may lose opportunities to invest in higher yielding securities.
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| INTEREST RATE RISKS [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | INTEREST RATE RISK is the risk that during periods of rising interest rates, the market value of the Fund’s securities will tend to be lower than prevailing market rates and in periods of falling interest rates, the market value of the Fund’s securities will tend to be higher. The Fund’s yield will vary as short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. In general, securities with longer maturities or durations are more sensitive to interest rate changes. A general rise in interest rates may cause investors to move out of fixed income securities on a large scale, which could adversely affect the price and liquidity of fixed income securities and could also result in increased redemptions for the Fund. During periods when inflation rates are high or rising, or during periods of low interest rates, the Fund may be subject to a greater risk of rising interest rates. Interest rate changes can be sudden and unpredictable and may have unpredictable effects on the markets and the Fund’s investments, may result in heightened market volatility, may impact the liquidity of fixed-income securities and of the Fund, and may detract from Fund performance.
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| PREPAYMENT OR CALL RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | PREPAYMENT (OR CALL) RISK is the risk that an issuer could exercise its right to pay principal on callable debt securities held by the Fund earlier than expected. Issuers may be more likely to prepay their securities if interest rates fall. If this happens, the Fund will not benefit from the rise in the market price of the securities that normally accompanies a decline in interest rates, and will be forced to reinvest prepayment proceeds in lower yielding securities, which may reduce the Fund’s returns. The Fund may also lose any premium it paid to purchase the securities.
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| US GOVERNMENT SECURITIES RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | U.S. GOVERNMENT SECURITIES RISK is the risk that the U.S. government will not provide financial support to its agencies, instrumentalities or sponsored enterprises if it is not obligated to do so by law. Certain U.S. government securities purchased by the Fund are neither issued nor guaranteed by the U.S. Treasury and, therefore, may not be backed by the full faith and credit of the United States. The maximum potential liability of the issuers of some U.S. government securities may greatly exceed their current resources, including any legal right to support from the U.S. Treasury. U.S. Treasury obligations that are held to maturity have historically involved minimal risk of loss of principal. Securities issued or guaranteed by the U.S. Treasury are backed by the full faith and credit of the United States, but are guaranteed only as to the timely payment of interest and principal when held to maturity, and the market prices for such securities will fluctuate. Changes to the financial condition or credit rating of the U.S. government may cause the value of the U.S. Treasury obligations held by the Fund to decline. It is possible that the issuers of U.S. government securities, including U.S. Treasury obligations, will not have the funds to meet their payment obligations in the future, which could result in losses to and redemptions from the Fund. U.S. government securities include zero coupon securities, which tend to be subject to greater market risk than interest-paying securities of similar maturities.
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| STABLE NAV RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | STABLE NAV RISK is the risk that the Fund will not be able to maintain a NAV per share of $1.00 at all times. A significant enough market disruption or drop in market prices of securities held by the Fund, especially at a time when the Fund needs to sell securities to meet shareholder redemption requests, could cause the value of the Fund’s shares to decrease to a price less than $1.00 per share. If the Fund fails to maintain a stable NAV (or if there is a perceived threat of such a failure) the Fund could be subject to increased redemption activity, which could adversely affect its NAV.
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| VARIABLE OR FLOATING RATE INSTRUMENTS RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | VARIABLE OR FLOATING RATE INSTRUMENTS RISK is the risk that securities with variable or floating rates can be less sensitive to interest rate changes than securities with fixed interest rates, but may decline in value and negatively impact the Fund, particularly if changes in prevailing interest rates are more frequent or sudden than the rate changes for the variable or floating rate securities, which only occur periodically. Although variable and floating rate securities are less sensitive to interest rate risk than fixed-rate securities, they are subject to greater liquidity risk, which could impede their value.
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| INCOME RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | INCOME RISK is the risk that the Fund’s ability to distribute income to shareholders depends on the yield available from the Fund’s investments. Falling interest rates will cause the Fund’s income to decline. Income risk is generally higher for short-term debt securities.
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| REPURCHASE AGREEMENTS RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | REPURCHASE AGREEMENTS RISK is the risk that the counterparty may default on its obligation to repurchase the underlying instruments collateralizing the repurchase agreement, which may cause the Fund to lose money.
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| INVESTMENT COMPANY RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | INVESTMENT COMPANY RISK is the risk that the Fund will be subject to the risks associated with investments in registered investment companies (“Underlying Funds”), such as the possibility that the value of the securities or instruments held by the Underlying Funds could decrease. Investments in Underlying Funds may involve duplication of management fees and certain other expenses, as the Fund indirectly hears its proportionate share of any expenses paid by the Underlying Funds in which it invests. NTI may be subject to potential conflicts of interest with respect to investments in affiliated Underlying Funds, which are Underlying Funds managed by NTI or its affiliates, because the fees paid to NTI by some affiliated Underlying Funds may be higher than the fees paid by other Underlying Funds.
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| CASH POSITIONS RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | CASH POSITIONS RISK is the risk that maintaining cash positions may negatively affect the Fund’s performance and potentially limit investment opportunities as a result of the Fund’s uninvested assets. Maintaining cash positions may also subject the Fund to increased credit risk exposure to the custodian bank.
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| LARGE SHAREHOLDER RISK [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | LARGE SHAREHOLDER RISK is the risk that a large proportion of the interests of the Fund may be held by a small number of investors (or a single investor) and the Fund may experience adverse effects when certain large shareholders, including funds or accounts over which the Fund’s investment adviser or an affiliate of the investment adviser has investment discretion, purchase or redeem large amounts of shares of the Fund. Such large shareholder redemptions, which may occur rapidly and unexpectedly, may cause the Fund to sell its securities at times it would not otherwise do so, which may negatively impact its liquidity and/or NAV. Such sales may also accelerate the realization of taxable income to shareholders if these sales result in gains, and may also increase transaction costs. In addition, large redemptions could lead to an increase in the Fund’s expense ratio due to expenses being allocated over a smaller asset base. Large purchases of the Fund’s shares or having a more concentrated shareholder base may also adversely affect the Fund’s performance to the extent that the Fund is delayed in investing new cash or otherwise maintains a larger cash position than it ordinarily would.
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| 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 market conditions, the Fund’s exposure to risks described elsewhere in this summary will likely increase.
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| Risk Lose Money [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | You could lose money by investing in the Fund. |
| Risk Not Insured Depository Institution [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | An investment in the Fund is not a bank account and is notinsured 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 Money Market Fund May Not Preserve Dollar [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Although the Fund seeks to preserve the value of your investment at $1.00 per share, the Fund cannot guarantee it will do so. |
| Risk Money Market Fund Sponsor May Not Provide Support [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | The Fund’s sponsor is not required to reimburse to the Fund for losses, and you should not expect that the sponsor will provide financial support to the Fund at any time, including during periods of market stress. |