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Loomis Sayles Inflation Protected Securities Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Loomis Sayles Inflation Protected Securities Fund
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Fund’s investment objective is 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.
The Fund does not impose a sales charge, a redemption fee or an exchange fee.
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, 2023
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 57% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 57.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
The 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. 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 date noted above and on the Total Annual Fund Operating Expenses for the remaining periods. 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:
Strategy [Heading] rr_StrategyHeading INVESTMENTS, RISKS AND PERFORMANCE Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
The Fund will normally invest at least 80% of its net assets (plus any borrowings made for investment purposes) in inflation-protected securities. The emphasis will be on debt securities issued by the U.S. Treasury (Treasury Inflation-Protected Securities, or “TIPS”). The principal value of these securities is periodically adjusted according to the rate of inflation, and repayment of the original bond principal upon maturity is guaranteed by the U.S. government.
In deciding which securities to buy and sell, Loomis Sayles may consider a number of factors related to the bond issue and the current bond market, for example, the stability and volatility of a country’s bond markets, the financial strength of the issuer, current interest rates, current valuations, Loomis Sayles’ expectations regarding general trends in interest rates and currency considerations. Loomis Sayles will also consider how purchasing or selling a bond would impact the overall portfolio’s risk profile (for example, its sensitivity to currency risk, interest rate risk and sector-specific risk) and potential return (income and capital gains).
The Fund may invest in other securities, including but not limited to inflation-protected debt securities issued by U.S. government agencies and instrumentalities other than the U.S. Treasury, by other entities such as corporations and foreign governments and by foreign issuers. The Fund may also invest in nominal (i.e., non-inflation-protected) treasury securities, corporate bonds, securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A securities”), structured notes, collateralized loan obligations, asset-backed securities and mortgage-related securities, including mortgage dollar rolls, and may invest up to 10% of its assets in below investment-grade fixed-income securities (commonly known as “junk bonds”). Below investment-grade fixed-income securities are rated below investment-grade quality (i.e., none of the three major rating agencies (Moody’s Investors Service, Inc., Fitch Investor Services, Inc. or S&P Global Ratings) have rated the securities in one of their respective top four ratings categories). The Fund’s fixed-income securities investments may include unrated securities (securities that are not rated by a rating agency) if Loomis Sayles determines that the securities are of comparable quality to rated securities that the Fund may purchase. The Fund may invest in fixed-income securities of any maturity. The Fund may also invest in swaps (including credit default swaps, in which one party agrees to make periodic payments to a counterparty in exchange for the right to receive a payment in the event of a default of the underlying reference security) and other derivatives. The Fund may also engage in futures transactions and foreign currency transactions (such as forward currency contracts).
Risk [Heading] rr_RiskHeading Principal 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. 
Inflation/Deflation 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. 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. 
TIPS Risk is the risk that the rate of inflation will be lower than expected. Inflation-protected securities are intended to protect against inflation by adjusting the interest or principal payable on the security by an amount based upon an index intended to measure the rate of inflation. There can be no assurance that the relevant index will accurately measure the rate of inflation, in which case the securities may not work as intended. 
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 securities with longer maturities are generally 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 monetary policy may affect the level of interest rates. 
Below Investment-Grade Fixed-Income Securities Risk is the risk that the Fund’s investments in below investment-grade fixed-income  
securities may be subject to greater risks than other fixed-income securities, including being subject to greater levels of interest rate risk, credit 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. 
Derivatives Risk is the risk that the value of the Fund’s derivative investments such as forward currency contracts, structured notes, futures transactions, swap transactions will fall, for example, because of changes in the value of the underlying reference instruments, pricing difficulties or lack of correlation with the underlying investments. The use of derivatives for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. 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. This risk is greater for forward currency contracts, uncleared swaps and other over-the-counter (“OTC”) traded derivatives. Investing in derivatives gives rise to other risks, such as leverage risk, liquidity risk, credit/counterparty risk, interest rate risk and market/issuer risk. The use of derivatives may cause the Fund to incur losses greater than those which would have occurred had derivatives not been used. 
Credit/Counterparty Risk is the risk that the issuer or guarantor of a fixed-income security in which the Fund invests, 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. 
Currency Risk is the risk that the value of the Fund’s investments will fall as a result of changes in exchange rates. Loomis Sayles may elect not to hedge currency risk or may hedge imperfectly, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged. 
Cybersecurity and Technology Risk is the risk associated with the increasing dependence of the Fund, its service providers, and other market participants on complex information technology and communications systems. Such systems 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. 
Foreign Securities Risk is the risk that the value of the Fund’s foreign investments will fall as a result of foreign political, social, economic, environmental, credit, informational or currency changes or other issues relating to foreign investing generally. Foreign securities may be subject to higher volatility than U.S. securities, varying degrees of regulation and limited liquidity. The Fund’s investments in foreign securities may be subject to foreign withholding or other taxes, which would decrease the yield on those securities. 
Leverage Risk 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. Use of derivative instruments (such as futures and forward currency contracts) may involve leverage. When a derivative is used as a hedge against an offsetting position that the Fund also holds, any gains generated by the derivative should be substantially offset by losses on the hedged instrument, and vice versa. To the extent that the Fund uses a derivative for purposes other than as a hedge, or if the Fund hedges imperfectly, the Fund is directly exposed to the risks of that derivative and any loss generated by the derivative will not be offset by a gain. 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 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. 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. Liquidity issues may also make it difficult to value the Fund’s investments. 
Management Risk is the risk that Loomis Sayles’ investment techniques will be unsuccessful and cause the Fund to incur losses. 
Market/Issuer Risk is the risk that 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. 
Mortgage-Related and Asset-Backed Securities Risk is the risk associated with the mortgages and assets underlying the securities, as well as 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 may also incur a loss  
when there is a prepayment of securities that were purchased at a premium. It also includes risks associated with investing in the mortgages underlying the mortgage-backed securities. 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. The Fund’s investments in mortgage-related and other asset-backed securities are also subject to the risks associated with investments in fixed-income securities generally (e.g., credit/counterparty, liquidity and valuation risks). 
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 following bar chart and table give an 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 a broad measure of market performance. 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 www.loomissayles.com and/or by calling the Fund toll-free at 800-633-3330.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table give an 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 a broad measure of market performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-633-3330
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.loomissayles.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 Institutional Class Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Highest Quarterly Return: Second Quarter 2020, 5.24% Lowest Quarterly Return: Second Quarter 2013, -6.88%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2021)
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 the Institutional Class of the Fund. After-tax returns for the other classes of the Fund will vary.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock
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 the Institutional 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.
Loomis Sayles Inflation Protected Securities Fund | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 0.52%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.12% [1],[2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.40%
1 year rr_ExpenseExampleYear01 $ 41
3 years rr_ExpenseExampleYear03 155
5 years rr_ExpenseExampleYear05 279
10 years rr_ExpenseExampleYear10 $ 641
2012 rr_AnnualReturn2012 6.98%
2013 rr_AnnualReturn2013 (8.20%)
2014 rr_AnnualReturn2014 1.75%
2015 rr_AnnualReturn2015 (1.50%)
2016 rr_AnnualReturn2016 4.38%
2017 rr_AnnualReturn2017 3.61%
2018 rr_AnnualReturn2018 (2.23%)
2019 rr_AnnualReturn2019 8.64%
2020 rr_AnnualReturn2020 13.97%
2021 rr_AnnualReturn2021 5.02%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 5.24%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2013
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (6.88%)
Past 1 Year rr_AverageAnnualReturnYear01 5.02%
Past 5 Years rr_AverageAnnualReturnYear05 5.66%
Past 10 Years rr_AverageAnnualReturnYear10 3.07%
Life of Class N rr_AverageAnnualReturnSinceInception
Loomis Sayles Inflation Protected Securities Fund | Retail Class  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.27%
Total annual fund operating expenses rr_ExpensesOverAssets 0.77%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.12% [1],[2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.65%
1 year rr_ExpenseExampleYear01 $ 66
3 years rr_ExpenseExampleYear03 234
5 years rr_ExpenseExampleYear05 416
10 years rr_ExpenseExampleYear10 $ 943
Past 1 Year rr_AverageAnnualReturnYear01 4.71%
Past 5 Years rr_AverageAnnualReturnYear05 5.41%
Past 10 Years rr_AverageAnnualReturnYear10 2.80%
Life of Class N rr_AverageAnnualReturnSinceInception
Loomis Sayles Inflation Protected Securities Fund | Class N  
Risk/Return: rr_RiskReturnAbstract  
Management fees rr_ManagementFeesOverAssets 0.25%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.21%
Total annual fund operating expenses rr_ExpensesOverAssets 0.46%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.11% [1],[2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.35%
1 year rr_ExpenseExampleYear01 $ 36
3 years rr_ExpenseExampleYear03 137
5 years rr_ExpenseExampleYear05 247
10 years rr_ExpenseExampleYear10 $ 568
Past 1 Year rr_AverageAnnualReturnYear01 5.06%
Past 5 Years rr_AverageAnnualReturnYear05
Past 10 Years rr_AverageAnnualReturnYear10
Life of Class N rr_AverageAnnualReturnSinceInception 5.69%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2017
Loomis Sayles Inflation Protected Securities Fund | Return After Taxes on Distributions | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 2.78%
Past 5 Years rr_AverageAnnualReturnYear05 4.50%
Past 10 Years rr_AverageAnnualReturnYear10 2.02%
Life of Class N rr_AverageAnnualReturnSinceInception
Loomis Sayles Inflation Protected Securities Fund | Return After Taxes on Distributions and Sale of Fund Shares | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 3.05%
Past 5 Years rr_AverageAnnualReturnYear05 3.87%
Past 10 Years rr_AverageAnnualReturnYear10 1.95%
Life of Class N rr_AverageAnnualReturnSinceInception
Loomis Sayles Inflation Protected Securities Fund | Bloomberg U.S. Treasury Inflation Protected Securities Index (Series-L)  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 5.96%
Past 5 Years rr_AverageAnnualReturnYear05 5.34%
Past 10 Years rr_AverageAnnualReturnYear10 3.09%
Life of Class N rr_AverageAnnualReturnSinceInception 5.26%
[1] 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 0.40%, 0.65% and 0.35% of the Fund’s average daily net assets for Institutional Class shares, Retail Class shares and Class N 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 January 31, 2023 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.
[2] Natixis Advisors, LLC (“Natixis Advisors”) has given a binding contractual undertaking to the Fund to reimburse any and all transfer agency expenses for Class N shares. This undertaking is in effect through January 31, 2023 and may be terminated before then only with the consent of the Fund’s Board of Trustees.