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(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund)  
Prospectus: rr_ProspectusTable  
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Fund seeks high total investment return through a combination of current income and capital appreciation.
Expense [Heading] rr_ExpenseHeading Fund Fees & Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses that you may pay if you buy, hold, and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in this table. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $100,000 in the Natixis Funds Complex. More information about these and other discounts is available from your financial professional and in the section “How Sales Charges Are Calculated” on page 48 of the Prospectus, in Appendix A to the Prospectus and on page 111 in the section “Reduced Sales Charges” of the Statement of Additional Information (“SAI”).
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $100,000 in the Natixis Funds Complex.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 100,000
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees(fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses(expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination January 31, 2025
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock A 1.00% contingent deferred sales charge (“CDSC”) may apply to certain purchases of Class A shares of $1,000,000 or more that are redeemed within eighteen months of the date of purchase.
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates Other expenses for Class T shares are estimated for the current fiscal year.
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same, except that the examples for the Class A, Class C, Class T and Class Y shares are based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement assuming that such waiver and/or reimbursement will only be in place through the date noted above and on the Total Annual Fund Operating Expenses for the remaining periods. The example for Class C shares for the ten-year period reflects the conversion to Class A shares after eight years. The example does not take into account brokerage commissions and other fees to financial intermediaries that you may pay on your purchases and sales of shares of the Fund. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption If shares are redeemed:
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If shares are not redeemed:
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes for you if your Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During its most recently ended fiscal year, the Fund’s portfolio turnover rate was 168% of the average value of its portfolio. 
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 168.00%
Strategy [Heading] rr_StrategyHeading Investments, Risks and PerformancePrincipal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
Under normal market conditions, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in bonds, which include debt securities of any maturity. In addition, the Fund will invest at least 65% of its net assets in investment grade securities. “Investment grade” securities are those securities that are rated in one of the top four ratings categories at the time of purchase by at least one of the three major ratings agencies (Moody’s Investors Service, Inc. (“Moody’s”), Fitch Investors Services, Inc. (“Fitch”) or S&P Global Ratings (“S&P”)), or, if unrated, are determined by the Adviser to be of comparable quality. For purposes of this restriction, investment grade securities also include cash and cash equivalent securities. The Fund will generally seek to maintain an effective duration of +/- 2 years relative to the Bloomberg U.S. Aggregate Bond Index. Duration is a measure of the expected life of a fixed-income security that is used to determine the sensitivity of a security’s price to changes in interest rates. A fund with a longer average portfolio duration will be more sensitive to changes in interest rates than a fund with a shorter average portfolio duration. By way of example, the price of a bond fund with an average duration of five years would be expected to fall approximately 5% if interest rates rose by one percentage point. While the effective duration for the Bloomberg U.S. Aggregate Bond Index fluctuates, as of December 31, 2023, the effective duration was approximately 6.89 years. The Fund may also invest up to 20% of its assets, at the time of purchase, in bonds rated below investment grade (i.e., none of the three major ratings agencies (Moody’s, Fitch or S&P) have rated the securities in one of their top four ratings categories) (commonly known as “junk bonds”), or, if unrated, securities determined by the Adviser to be of comparable quality, and up to 10% of its assets in non-U.S. dollar-denominated securities. There is no minimum rating for the securities in which the Fund may invest.
The Fund’s investments may include securities issued by U.S. and non-U.S. corporations and governments, securities issued by supranational entities, U.S. government-sponsored agency debenture and pass-through securities, commercial mortgage-backed and other asset-backed securities and inflation-linked securities.
The portfolio management team seeks to build and manage a portfolio that will perform well on a benchmark-relative and, secondarily, on an absolute basis in the market environment it anticipates over the short to intermediate term. The primary factors for broad sector positioning are the Adviser’s expected performance of sectors in the benchmark and the incremental performance or diversification benefits the Fund’s portfolio managers anticipate from opportunistic allocations to securities that are not included in the Fund’s benchmark. In addition, the Fund’s portfolio managers will look at individual security selection, position size and overall duration contribution to the portfolio.
Purchase and sale considerations also include overall portfolio yield, interest rate sensitivity across different maturities held, fixed-income sector fundamentals and outlook, technical supply/demand factors, credit risk, cash flow variability, security optionality and structure, as well as potential currency and liquidity risk. The Adviser also considers economic factors. Individual securities are assessed on a risk/return basis, both on a benchmark-relative and on an absolute return basis, and on their fit within the overall portfolio strategy.
Specifically, the Adviser follows a total return-oriented investment approach and considers broad sector allocation, quality and liquidity bias, yield curve positioning and duration in selecting securities for the Fund. The Fund’s portfolio managers consider economic and market conditions as well as issuer-specific data, such as fixed-charge coverage, the relationship between cash flows and debt service obligations, the experience and perceived strength of management or security structure, price responsiveness of the security to interest rate changes, earnings prospects, debt as a percentage of assets, borrowing requirements, debt maturity schedules and liquidation value.
In selecting investments for the Fund, the Adviser’s research analysts and sector teams work closely with the Fund’s portfolio managers to develop an outlook for the economy from research produced by various financial firms and specific forecasting services or from economic data released by U.S. and foreign governments, as well as the Federal Reserve Bank. The analysts conduct a thorough review of individual securities to identify what they consider attractive values in the high quality bond market through the use of quantitative tools such as internal and external computer systems and software. The Adviser continuously monitors an issuer’s creditworthiness or cash flow stability to assess whether the obligation remains an appropriate investment for the Fund. It
may relax its emphasis on quality with respect to a given security if it believes that the issuer’s financial outlook is promising. This may create an opportunity for higher returns. The Adviser seeks to balance opportunities for yield and price performance by combining macro economic analysis with individual security selection. Fund holdings are generally diversified across sectors and industry groups such as utilities or telecommunications, which tend to move independently of the ebbs and flows in economic growth.
In connection with its principal investment strategies, the Fund may also invest in securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A securities”), other privately placed investments such as private credit investments, structured notes, collateralized loan obligations, foreign securities, including those in emerging markets, mortgage-related securities, including mortgage dollar rolls, futures and swaps (including credit default swaps). The Fund may use such derivatives for hedging or investment purposes. Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.
The Fund may engage in active and frequent trading of securities and other instruments. Effects of frequent trading may include high transaction costs, which may lower the Fund’s returns, and realization of short-term capital gains, distributions of which are taxable to shareholders who are individuals as ordinary income. Trading costs and tax effects associated with frequent trading may adversely affect the Fund’s performance.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Risk/Return Bar Chart and Table
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual returns for the one-year, five-year and ten-year periods compare to those of a broad measure of market performance. Performance for Class C shares includes the automatic conversion to Class A shares after eight years. The Fund’s past performance
(before and after taxes) does not necessarily indicate how the Fund will perform in the future. Updated performance information is available online at im.natixis.com and/or by calling the Fund toll-free at 800-225-5478.
The chart does not reflect any sales charge that you may be required to pay when you buy or redeem the Fund’s shares. A sales charge will reduce your return. To the extent that a class of shares was subject to the waiver or reimbursement of certain expenses during a period, had such expenses not been waived or reimbursed during the period, total returns would have been lower.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual returns for the one-year, five-year and ten-year periods compare to those of a broad measure of market performance.
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess The Fund did not have Class T shares outstanding during the periods shown above.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-225-5478
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress im.natixis.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund’s past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Total Returns for Class Y Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The chart does not reflect any sales charge that you may be required to pay when you buy or redeem the Fund’s shares. A sales charge will reduce your return.
Performance Table Does Reflect Sales Loads rr_PerformanceTableDoesReflectSalesLoads Performance of Class T shares shown above is that of Class A shares, which have the same expenses as Class T shares, restated to reflect the different sales load applicable to Class T shares.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Index performance reflects no deduction for fees, expenses or taxes.
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown for only one class of the Fund. After-tax returns for the other classes of the Fund will vary.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Highest Quarterly Return:
Fourth Quarter 2023, 7.28%

Lowest Quarterly Return:
Second Quarter 2022, -5.97%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns(for the periods ended December 31, 2023)
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
The Fund did not have Class T shares outstanding during the periods shown above. The returns of Class T shares would have been substantially similar to the returns of the Fund’s other share classes because they would have been invested in the same portfolio of securities and would only differ to the extent the other share classes did not have the same expenses. Performance of Class T shares shown above is that of Class A shares, which have the same expenses as Class T shares, restated to reflect the different sales load applicable to Class T shares.
After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts. The after-tax returns are shown for only one class of the Fund. After-tax returns for the other classes of the Fund will vary. Index performance reflects no deduction for fees, expenses or taxes. 
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Risk Lose Money [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock You may lose money by investing in the Fund.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Risk Not Insured Depository Institution [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock Fund shares are not bank deposits and are not guaranteed, endorsed or insured by the Federal Deposit Insurance Corporation or any other government agency, and are subject to investment risks, including possible loss of the principal invested.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Interest Rate Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Interest Rate Risk: Interest rate risk is the risk that the value of the Fund’s investments will fall if interest rates rise. Generally, the value of fixed-income securities rises when prevailing interest rates fall and falls when interest rates rise. Interest rate risk generally is greater for funds that invest in fixed-income securities with relatively longer durations than for funds that invest in fixed-income securities with shorter durations. In addition, an economic downturn or period of rising interest rates could adversely affect the market for these securities and reduce the Fund’s ability to sell them, negatively impacting the performance of the Fund. Potential future changes in government and/or central bank monetary policy and action may also affect the level of interest rates. Recently, there have been inflationary price movements, which have caused the fixed income securities markets to experience heightened levels of interest volatility and liquidity risk. Monetary policy measures have in the past, and may in the future, exacerbate risks associated with rising interest rates.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Currency Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Currency Risk: Fluctuations in the exchange rates between different currencies may negatively affect an investment. The Fund may be subject to currency risk because it may invest in currency-related instruments and may invest in securities or other instruments denominated in, or that generate income denominated in, foreign currencies. The Fund may elect not to hedge currency risk, or may hedge such risk imperfectly, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged.  
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Below Investment Grade Fixed-Income Securities Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Below Investment Grade Fixed-Income Securities Risk: The Fund’s investments in below investment grade fixed-income securities, also known as “junk bonds,” may be subject to greater risks than other fixed-income securities, including being subject to greater levels of interest rate risk, credit/counterparty risk (including a greater risk of default) and liquidity risk. The ability of the issuer to make principal and interest payments is predominantly speculative for below investment grade fixed-income securities.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Emerging Markets Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Emerging Markets Risk: In addition to the risks of investing in foreign investments generally, emerging markets investments are subject to greater risks arising from political or economic instability, war, nationalization or confiscatory taxation, currency exchange or repatriation restrictions, sanctions by other countries (such as the United States or the European Union), new or inconsistent government treatment of or restrictions on issuers and instruments, and an issuer’s unwillingness or inability to make dividend, principal or interest payments on its securities. Emerging markets companies may be smaller and have shorter operating histories than companies in developed markets.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Credit/Counterparty Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Credit/Counterparty Risk: Credit/counterparty risk is the risk that the issuer or guarantor of a fixed-income security, or the counterparty to a derivative or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. As a result, the Fund may sustain losses or be unable or delayed in its ability to realize gains. The Fund will be subject to credit/counterparty risk with respect to the counterparties to its derivatives transactions. This risk will be heightened to the extent the Fund enters into derivative transactions with a single counterparty (or affiliated counterparties that are part of the same organization), causing the Fund to have significant exposure to such counterparty. Many of the protections afforded to participants on organized exchanges and clearing houses, such as the performance guarantee given by a central clearing house, are not available in connection with over-the-counter (“OTC”) derivatives transactions, such as foreign currency transactions. For centrally cleared derivatives, such as cleared swaps, futures and many options, the primary credit/counterparty risk is the creditworthiness of the Fund’s clearing broker and the central clearing house itself. 
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Foreign Securities Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Foreign Securities Risk: Investments in foreign securities may be subject to greater political, economic, environmental, credit/counterparty and information risks. The Fund’s investments in foreign securities also are subject to foreign currency fluctuations and other foreign currency-related risks. Foreign securities may be subject to higher volatility than U.S. securities, varying degrees of regulation and limited liquidity.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Mortgage-Related and Asset-Backed Securities Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Mortgage-Related and Asset-Backed Securities Risk: In addition to the risks associated with investments in fixed-income securities generally (for example, credit, liquidity, inflation and valuation risk), mortgage-related and asset-backed securities are subject to the risks of the mortgages and assets underlying the securities as well as prepayment risk, the risk that the securities may be prepaid and result in the reinvestment of the prepaid amounts in securities with lower yields than the prepaid obligations. Conversely, there is a risk that a rise in interest rates will extend the life of a mortgage-related or asset-backed security beyond the expected prepayment time, typically reducing the security’s value, which is called extension risk. The Fund also may incur a loss when there is a prepayment of securities that were purchased at a premium. The Fund’s investments in other asset-backed securities are subject to risks similar to those associated with mortgage-related securities, as well as additional risks associated with the nature of the assets and the servicing of those assets.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Cybersecurity and Technology Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Cybersecurity and Technology Risk: The Fund, its service providers, and other market participants increasingly depend on complex information technology and communications systems, which are subject to a number of different threats and risks that could adversely affect the Fund and its shareholders. Cybersecurity and other operational and technology issues may result in financial losses to the Fund and its shareholders.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Derivatives Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including forward currency contracts, structured notes, futures and swaps (including credit default swaps)) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund’s exposure to securities market values, interest rates or currency exchange rates. It is possible that the Fund’s liquid assets may be insufficient to support its obligations under its derivatives positions. The use of derivatives for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. The use of derivatives may cause the Fund to incur losses greater than those that would have occurred had derivatives not been used. The Fund’s use of derivatives involves other risks, such as credit/counterparty risk relating to the other party to a derivative contract (which is greater for forward currency contracts, uncleared swaps and other OTC derivatives), the risk of difficulties in pricing and valuation, the risk that changes in the value of a derivative may not correlate as expected with changes in the value of relevant assets, rates or indices, liquidity risk, allocation risk and the risk of losing more than any amounts paid or margin transferred to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivative position at an advantageous time or price. The Fund’s derivative counterparties may experience financial difficulties or otherwise be unwilling or unable to honor their obligations, possibly resulting in losses to the Fund.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Inflation/Deflation Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Inflation/Deflation Risk: Inflation risk is the risk that the value of assets or income from investments will be worth less in the future as inflation decreases the present value of future payments. As inflation increases, the real value of the Fund’s portfolio could decline. Inflation rates may change frequently and drastically. The Fund’s investments may not keep pace with inflation, which may result in losses to the Fund’s investors.  Recently, inflation rates in the United States and elsewhere have been increasing. There can be no assurance that this trend will not continue or that efforts to slow or reverse inflation will not harm the economy and asset values. Deflation risk is the risk that prices throughout the economy decline over time - the opposite of inflation. Deflation may have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s portfolio. 
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Leverage Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Leverage Risk: Leverage is the risk associated with securities or investment practices (e.g., borrowing and the use of certain derivatives) that multiply small index, market or asset-price movements into larger changes in value. The use of leverage increases the impact of gains and losses on the Fund’s returns, and may lead to significant losses if investments are not successful.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Liquidity Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Liquidity Risk: Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Decreases in the number of financial institutions willing to make markets in the Fund’s investments or in their capacity or willingness to transact may increase the Fund’s exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund’s investments when it needs to dispose of them. Markets may become illiquid quickly. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. During times of market turmoil, there may be no buyers or sellers for securities in certain asset classes. Securities acquired in a private placement, such as Rule 144A securities and privately negotiated credit and other investments, are generally subject to significant liquidity risk because they are subject to strict restrictions on resale and there may be no liquid secondary market or ready purchaser for such securities. In other circumstances, liquid investments may become illiquid.  Derivatives, and particularly OTC derivatives, are generally subject to liquidity risk as well. Liquidity issues may also make it difficult to value the Fund’s investments. The Fund may invest in liquid investments that become illiquid due to financial distress, or geopolitical events such as sanctions, trading halts or wars.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Management Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Management Risk: A strategy used by the Fund’s portfolio managers may fail to produce the intended result. 
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Market/Issuer Risk [Member]  
Prospectus: rr_ProspectusTable  
Risk [Text Block] rr_RiskTextBlock
Market/Issuer Risk: The market value of the Fund’s investments will move up and down, sometimes rapidly and unpredictably, based upon overall market and economic conditions, as well as a number of reasons that directly relate to the issuers of the Fund’s investments, such as management performance, financial condition and demand for the issuers’ goods and services.
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Bloomberg U.S. Aggregate Bond Index  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 5.53%
Past 5 Years rr_AverageAnnualReturnYear05 1.10%
Past 10 Years rr_AverageAnnualReturnYear10 1.81%
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Class A  
Prospectus: rr_ProspectusTable  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.25%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [1]
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.32%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.18%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.75%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.01% [2]
Total Annual Fund Operating Expenses After Expense Reimbursement rr_NetExpensesOverAssets 0.74%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 497
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 654
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 823
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,315
Past 1 Year rr_AverageAnnualReturnYear01 1.44%
Past 5 Years rr_AverageAnnualReturnYear05 0.81%
Past 10 Years rr_AverageAnnualReturnYear10 1.67%
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Class C  
Prospectus: rr_ProspectusTable  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00%
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.32%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.18%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.50%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.01% [2]
Total Annual Fund Operating Expenses After Expense Reimbursement rr_NetExpensesOverAssets 1.49%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 252
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 473
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 818
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,587
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 152
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 473
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 818
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,587
Past 1 Year rr_AverageAnnualReturnYear01 4.09%
Past 5 Years rr_AverageAnnualReturnYear05 0.92%
Past 10 Years rr_AverageAnnualReturnYear10 1.50%
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Class N  
Prospectus: rr_ProspectusTable  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.32%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.08%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.40%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Total Annual Fund Operating Expenses After Expense Reimbursement rr_NetExpensesOverAssets 0.40%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 41
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 128
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 224
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 505
Past 1 Year rr_AverageAnnualReturnYear01 6.21%
Past 5 Years rr_AverageAnnualReturnYear05 2.02%
Past 10 Years rr_AverageAnnualReturnYear10 2.45%
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Class T  
Prospectus: rr_ProspectusTable  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.32%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.18% [3]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.75%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.01% [2]
Total Annual Fund Operating Expenses After Expense Reimbursement rr_NetExpensesOverAssets 0.74%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 324
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 483
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 656
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,156
Past 1 Year rr_AverageAnnualReturnYear01 3.27%
Past 5 Years rr_AverageAnnualReturnYear05 1.17%
Past 10 Years rr_AverageAnnualReturnYear10 1.86%
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Class Y  
Prospectus: rr_ProspectusTable  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.32%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.18%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.50%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.01% [2]
Total Annual Fund Operating Expenses After Expense Reimbursement rr_NetExpensesOverAssets 0.49%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 50
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 159
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 279
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 627
Annual Return 2014 rr_AnnualReturn2014 6.40%
Annual Return 2015 rr_AnnualReturn2015 (3.93%)
Annual Return 2016 rr_AnnualReturn2016 7.49%
Annual Return 2017 rr_AnnualReturn2017 5.22%
Annual Return 2018 rr_AnnualReturn2018 (0.69%)
Annual Return 2019 rr_AnnualReturn2019 8.96%
Annual Return 2020 rr_AnnualReturn2020 10.63%
Annual Return 2021 rr_AnnualReturn2021 (1.42%)
Annual Return 2022 rr_AnnualReturn2022 (12.75%)
Annual Return 2023 rr_AnnualReturn2023 6.12%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return:
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 7.28%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2023
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return:
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (5.97%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2022
Past 1 Year rr_AverageAnnualReturnYear01 6.12%
Past 5 Years rr_AverageAnnualReturnYear05 1.93%
Past 10 Years rr_AverageAnnualReturnYear10 2.36%
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Class Y | Return After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 4.46%
Past 5 Years rr_AverageAnnualReturnYear05 0.57%
Past 10 Years rr_AverageAnnualReturnYear10 0.99%
(Natixis Funds Trust I) | (Loomis Sayles Core Plus Bond Fund) | Class Y | Return After Taxes on Distributions and Sale of Fund Shares  
Prospectus: rr_ProspectusTable  
Past 1 Year rr_AverageAnnualReturnYear01 3.58%
Past 5 Years rr_AverageAnnualReturnYear05 0.93%
Past 10 Years rr_AverageAnnualReturnYear10 1.22%
[1]
* A 1.00% contingent deferred sales charge (“CDSC”) may apply to certain purchases of Class A shares of $1,000,000 or more that are redeemed within eighteen months of the date of purchase.
[2]
2 Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) and Natixis Advisors, LLC (“Natixis Advisors”), the Fund’s advisory administrator, have given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.74%, 1.49%, 0.44%, 0.74% and 0.49% of the Fund’s average daily net assets for Class A, C, N, T and Y shares, respectively, exclusive of acquired fund fees and expenses, brokerage expenses, interest expense, taxes, and organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2025 and may be terminated before then only with the consent of the Fund’s Board of Trustees. The Adviser will be permitted to recover, on a class-by-class basis, management fees waived and/or expenses reimbursed to the extent that expenses in later periods fall below both (1) the class’ applicable expense limitation at the time such amounts were waived/reimbursed and (2) the class’ current applicable expense limitation. The Fund will not be obligated to repay any such waived/reimbursed fees and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.
[3]
1 Other expenses for Class T shares are estimated for the current fiscal year.