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Loomis Sayles Strategic Income Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Loomis Sayles Strategic Income Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The Fund seeks high current income
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock with a secondary objective of capital growth.
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 71 of the Prospectus, in Appendix A to the Prospectus and on page 131 in the section “Reduced Sales Charges” of the Statement of Additional Information (“SAI”).
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 April 30, 2024
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 23% of the average value of its portfolio. 
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 23.00%
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.
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
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 example is 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 dates 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:
Strategy [Heading] rr_StrategyHeading Investments, Risks and Performance Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
Under normal market conditions, the Fund will invest substantially all of its assets in income producing securities (including below investment grade securities, or “junk bonds”) with a focus on U.S. corporate bonds, convertible securities, foreign debt instruments, including those in emerging markets and related foreign currency transactions, and U.S. government securities. Below investment grade fixed-income securities are rated below investment grade quality (i.e., none 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”)), have rated the securities in one of its top four rating categories) or, if the security is unrated, are determined by the Adviser to be of comparable quality. The Fund may invest up to 35% of its assets in preferred stocks and dividend-paying common stocks. The portfolio managers may shift the Fund’s assets among various types of income-producing securities based upon changing market conditions. The Adviser performs its own extensive credit analyses to determine the creditworthiness and potential for capital appreciation of a security.
The Fund’s portfolio managers use a flexible approach to identify securities in the global marketplace with characteristics including discounted price compared to economic value, undervalued credit ratings with strong or improving credit profiles and yield premium relative to its benchmark (although not all of the securities selected will have these attributes).
In deciding which securities to buy and sell, the Adviser will consider, among other things, the financial strength of the issuer, current interest rates, current valuations, the Adviser’s expectations regarding future changes in interest rates and comparisons of the level of risk associated with particular investments with the Adviser’s expectations concerning the potential return of those investments.
In selecting investments for the Fund, the Adviser utilizes the skills of its in-house team of more than 30 research analysts to cover a broad universe of industries, companies and markets. The Fund’s portfolio managers take advantage of these extensive resources to identify securities that meet the Fund’s investment criteria. The Adviser seeks to buy bonds that offer a positive yield advantage over the market and, in its view, have room to increase in price. It may also invest to take advantage of what the portfolio managers believe are temporary disparities in the yield of different segments of the market for U.S. government securities. The Adviser provides the portfolio managers with maximum flexibility to find investment opportunities in a wide range of markets, both domestic and foreign. This flexible approach provides the Fund with access to a wide array of investment opportunities. The three key sectors that the portfolio managers focus upon are U.S. corporate issues (including convertible securities), foreign debt securities and U.S. government securities. The Fund’s portfolio managers maintain a core of the Fund’s investments in corporate bond issues and shift its assets among other income-producing securities as opportunities develop. The Fund generally seeks to maintain a high level of diversification as a form of risk management.
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”), structured notes, collateralized loan obligations, zero-coupon bonds, pay-in-kind bonds, mortgage-related securities, stripped securities and futures, swaps (including credit default swaps) and foreign currency transactions (such as forward currency contracts) for hedging and 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.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
The principal risks of investing in the Fund are summarized below. The Fund does not represent a complete investment program. You may lose money by investing in the Fund.  
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. 
The significance of any specific risk to an investment in the Fund will vary over time, depending on the composition of the Fund’s portfolio, market conditions, and other factors. You should read all of the risk information presented below carefully, because any one or more of these risks may result in losses to the Fund. 
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 clearinghouses, such as the performance guarantee given by a central clearinghouse, 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 clearinghouse itself. 
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. 
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.  
Equity Securities Risk: The value of the Fund’s investments in equity securities could be subject to unpredictable declines in the value of individual securities and periods of below-average performance in individual securities or in the equity market as a whole. In the event an issuer is liquidated or declares bankruptcy, the claims of owners of the issuer’s bonds generally take precedence over the claims of those who own preferred stock or common stock. 
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.  
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. 
Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including futures, structured notes, swaps (including credit default swaps) and forward currency contracts) 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, such as futures, structured notes, swaps (including credit default swaps) and forward currency contracts 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 the initial margin (if any) required 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.  
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. 
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. 
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. The values of zero-coupon bonds may be more sensitive to fluctuations in interest rates than other fixed-income securities. 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. The risks associated with rising interest rates may be particularly acute because of recent monetary policy measures. 
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. 
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. 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, 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. 
Management Risk: A strategy used by the Fund’s portfolio managers may fail to produce the intended result.  
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. 
Risk Lose Money [Text] rr_RiskLoseMoney You may lose money by investing in the Fund. 
RIsk Not Insured [Text] rr_RiskNotInsured 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. 
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, ten-year and life-of-class periods (as applicable) compare to those of two broad measures of market performance. The Bloomberg U.S. Universal Bond Index represents the union of the U.S. Aggregate Index, the U.S. High-Yield Corporate Index, the 144A Index, the Eurodollar Index, the Emerging Markets Index, and the non-ERISA portion of the CMBS Index. Municipal debt, private placements, and non-dollar-denominated issues are excluded from the Universal Bond Index. The only constituent of the index that includes floating-rate debt is the Emerging Markets Index. 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. 
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, ten-year and life-of-class periods (as applicable) compare to those of two broad measures of market performance.
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.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Highest Quarterly Return: Second Quarter 2020, 6.42% Lowest Quarterly Return: First Quarter 2020, -12.29%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2022)
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.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock
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. The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.
Loomis Sayles Strategic Income Fund | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.25%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther none [1]
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.58%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.15% [2]
Total annual fund operating expenses rr_ExpensesOverAssets 0.98%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.04% [3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.94%
1 year rr_ExpenseExampleYear01 $ 517
3 years rr_ExpenseExampleYear03 720
5 years rr_ExpenseExampleYear05 940
10 years rr_ExpenseExampleYear10 $ 1,572
Past 1 Year rr_AverageAnnualReturnYear01 (16.51%)
Past 5 Years rr_AverageAnnualReturnYear05 (1.18%)
Past 10 Years rr_AverageAnnualReturnYear10 1.70%
Life of Class N rr_AverageAnnualReturnSinceInception
Loomis Sayles Strategic Income Fund | Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther 1.00%
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.58%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.15% [2]
Total annual fund operating expenses rr_ExpensesOverAssets 1.73%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.04% [3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.69%
1 year rr_ExpenseExampleYear01 $ 272
3 years rr_ExpenseExampleYear03 541
5 years rr_ExpenseExampleYear05 935
10 years rr_ExpenseExampleYear10 1,839
1 year rr_ExpenseExampleNoRedemptionYear01 172
3 years rr_ExpenseExampleNoRedemptionYear03 541
5 years rr_ExpenseExampleNoRedemptionYear05 935
10 years rr_ExpenseExampleNoRedemptionYear10 $ 1,839
Past 1 Year rr_AverageAnnualReturnYear01 (14.30%)
Past 5 Years rr_AverageAnnualReturnYear05 (1.05%)
Past 10 Years rr_AverageAnnualReturnYear10 1.53%
Life of Class N rr_AverageAnnualReturnSinceInception
Loomis Sayles Strategic Income Fund | Class N  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.58%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.06% [2]
Total annual fund operating expenses rr_ExpensesOverAssets 0.64%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets none [3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.64%
1 year rr_ExpenseExampleYear01 $ 65
3 years rr_ExpenseExampleYear03 205
5 years rr_ExpenseExampleYear05 357
10 years rr_ExpenseExampleYear10 $ 798
Past 1 Year rr_AverageAnnualReturnYear01 (12.55%)
Past 5 Years rr_AverageAnnualReturnYear05 0.02%
Past 10 Years rr_AverageAnnualReturnYear10
Life of Class N rr_AverageAnnualReturnSinceInception 2.25%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
Loomis Sayles Strategic Income Fund | Class T  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.50%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.58%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.15% [2],[4]
Total annual fund operating expenses rr_ExpensesOverAssets 0.98%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.04% [3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.94%
1 year rr_ExpenseExampleYear01 $ 344
3 years rr_ExpenseExampleYear03 550
5 years rr_ExpenseExampleYear05 774
10 years rr_ExpenseExampleYear10 $ 1,418
Past 1 Year rr_AverageAnnualReturnYear01 (14.96%)
Past 5 Years rr_AverageAnnualReturnYear05 (0.81%)
Past 10 Years rr_AverageAnnualReturnYear10 1.89%
Life of Class N rr_AverageAnnualReturnSinceInception
Loomis Sayles Strategic Income Fund | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.58%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.15% [2]
Total annual fund operating expenses rr_ExpensesOverAssets 0.73%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.04% [3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.69%
1 year rr_ExpenseExampleYear01 $ 70
3 years rr_ExpenseExampleYear03 229
5 years rr_ExpenseExampleYear05 402
10 years rr_ExpenseExampleYear10 $ 903
2013 rr_AnnualReturn2013 11.16%
2014 rr_AnnualReturn2014 5.86%
2015 rr_AnnualReturn2015 (7.42%)
2016 rr_AnnualReturn2016 8.56%
2017 rr_AnnualReturn2017 7.50%
2018 rr_AnnualReturn2018 (2.69%)
2019 rr_AnnualReturn2019 11.05%
2020 rr_AnnualReturn2020 1.40%
2021 rr_AnnualReturn2021 4.12%
2022 rr_AnnualReturn2022 (12.60%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return: 
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 6.42%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return: 
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (12.29%)
Past 1 Year rr_AverageAnnualReturnYear01 (12.60%)
Past 5 Years rr_AverageAnnualReturnYear05 (0.06%)
Past 10 Years rr_AverageAnnualReturnYear10 2.40%
Life of Class N rr_AverageAnnualReturnSinceInception
Loomis Sayles Strategic Income Fund | Admin Class  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.58%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.40% [2],[5]
Total annual fund operating expenses rr_ExpensesOverAssets 1.23%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.04% [3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.19%
1 year rr_ExpenseExampleYear01 $ 121
3 years rr_ExpenseExampleYear03 386
5 years rr_ExpenseExampleYear05 672
10 years rr_ExpenseExampleYear10 $ 1,485
Past 1 Year rr_AverageAnnualReturnYear01 (13.07%)
Past 5 Years rr_AverageAnnualReturnYear05 (0.55%)
Past 10 Years rr_AverageAnnualReturnYear10 1.90%
Life of Class N rr_AverageAnnualReturnSinceInception
Loomis Sayles Strategic Income Fund | Return After Taxes on Distributions | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (14.77%)
Past 5 Years rr_AverageAnnualReturnYear05 (1.71%)
Past 10 Years rr_AverageAnnualReturnYear10 0.51%
Life of Class N rr_AverageAnnualReturnSinceInception
Loomis Sayles Strategic Income Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (7.40%)
Past 5 Years rr_AverageAnnualReturnYear05 (0.62%)
Past 10 Years rr_AverageAnnualReturnYear10 1.20%
Life of Class N rr_AverageAnnualReturnSinceInception
Loomis Sayles Strategic Income Fund | Bloomberg U.S. Aggregate Bond Index  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (13.01%)
Past 5 Years rr_AverageAnnualReturnYear05 0.02%
Past 10 Years rr_AverageAnnualReturnYear10 1.06%
Loomis Sayles Strategic Income Fund | Bloomberg U.S. Aggregate Bond Index | Class N  
Risk/Return: rr_RiskReturnAbstract  
Life of Class N rr_AverageAnnualReturnSinceInception 1.14%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
Loomis Sayles Strategic Income Fund | Bloomberg U.S. Universal Bond Index  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (12.99%)
Past 5 Years rr_AverageAnnualReturnYear05 0.18%
Past 10 Years rr_AverageAnnualReturnYear10 1.33%
Loomis Sayles Strategic Income Fund | Bloomberg U.S. Universal Bond Index | Class N  
Risk/Return: rr_RiskReturnAbstract  
Life of Class N rr_AverageAnnualReturnSinceInception 1.40%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
[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] Other expenses include acquired fund fees and expenses of less than 0.01%.
[3] Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has given a binding contractual undertaking to the Fund to limit the amount of the Fund’s total annual fund operating expenses to 0.94%, 1.69%, 0.64%, 0.94%, 0.69% and 1.19% of the Fund’s average daily net assets for Class A, C, N, T, Y and Admin Class shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through April 30, 2024 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.
[4] Other expenses for Class T shares are estimated for the current fiscal year.
[5] Other expenses include an administrative services fee of 0.25% for Admin Class shares.