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]

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Annual Fund Operating Expenses(expenses that you pay each year as a percentage of the value of your investment)*

^[1]

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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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 48% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

48.00%

Strategy [Heading]

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INVESTMENTS, RISKS AND PERFORMANCEPrincipal Investment Strategies

Strategy Narrative [Text Block]

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Under normal market conditions, the Fund will invest substantially all of its assets, and may invest up to 100% of its assets, in high income securities (“High-Income Securities”). High-Income Securities are fixed-income securities that Loomis Sayles believes have the potential to generate relatively high levels of current income. High-Income Securities are often rated below investment-grade (below investment-grade securities are sometimes referred to as “high-yield securities” or “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’s Global Ratings) have rated the securities in one of their respective top four rating 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 approximately 20% of its assets in investment-grade fixed-income securities. The Fund may invest a portion of its assets in senior floating-rate loans made to U.S. and foreign borrowers. A significant portion of the securities purchased by the Fund may be issued by smaller-capitalization companies. There is no minimum rating for debt in which the Fund may invest.

Under normal market conditions, the Fund may invest up to 40% of its assets in foreign securities, including emerging market securities. The Fund may invest without limit in obligations of supranational entities (e.g., the World Bank). Although certain securities purchased by the Fund may be issued by domestic companies incorporated outside of the United States, the Adviser does not consider these securities to be foreign if the issuer is included in the U.S. fixed-income indices published by Bloomberg. The Fund may also invest in derivatives, including 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), purchasing or selling options or futures contracts to manage interest rate and credit risk.

The Fund’s investments may include, among other things, corporate debt securities, U.S. government obligations, U.S. dollar denominated foreign securities, zero-coupon and pay-in-kind securities, loan assignments and participations, delayed funding loans and revolving credit facilities, commercial paper, mortgage-backed securities, collateralized mortgage obligations, mortgage dollar rolls, collateralized debt and loan obligations and other asset-backed securities, securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A securities”), other privately placed investments such as private credit investments, when-issued securities, municipal bonds, repurchase agreements, debt-linked and equity-linked securities, convertible securities, preferred shares and illiquid securities.

In deciding which High-Income Securities to buy and sell, Loomis Sayles will consider, among other things, the financial strength of the issuer, yield, coupon rate, current interest rates, current valuations and comparisons of the level of risk associated with particular investments with Loomis Sayles’ expectations concerning the potential return of those types of investments. As part of its investment approach, Loomis Sayles generally seeks fixed-income securities of issuers whose credit profiles Loomis Sayles believes have the potential to stabilize or improve. With respect to investments in foreign securities, Loomis Sayles will consider the global economic environment, and the economic environment of the relevant country, taking into account factors such as GDP growth, inflation and other economic conditions, monetary policy, fiscal policy, leadership and social stability.

Loomis Sayles may invest significantly in securities whose price Loomis Sayles believes is more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates.

Risk [Heading]

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Principal Risks

Bar Chart and Performance Table [Heading]

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Risk/Return Bar Chart and Table

Performance Narrative [Text Block]

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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 and ten-year periods compare to those of a broad-based securities market index that reflects the performance of the overall market applicable to the Fund and an additional index that represents the market sectors in which the Fund primarily invests. Updated performance information is available online at www.loomissayles.com and/or by calling the Fund toll-free at 800-633-3330.

The bar chart and the table do not reflect any “wrap fees” that a participant in a “wrap” program may be required to pay to a program’s sponsor. See the section “Management” in the Statutory Prospectus. A “wrap fee” will reduce your return.

Performance Information Illustrates Variability of Returns [Text]

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Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-633-3330

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.loomissayles.com

Bar Chart [Heading]

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Total Returns for Institutional Class 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

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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.

Bar Chart Closing [Text Block]

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Highest Quarterly Return:

Second Quarter 2020, 9.87%

Lowest Quarterly Return:

First Quarter 2020, -12.05%

Performance Table Heading

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Average Annual Total Returns(for the periods ended December 31, 2023)

Performance Table Closing [Text Block]

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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. Index performance reflects no deduction for fees, expenses or taxes.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Risk Lose Money [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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You may lose money by investing in the Fund.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Risk Not Insured Depository Institution [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Credit/Counterparty Risk [Member]

Prospectus:

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Risk [Text Block]

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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. Senior loans and other floating rate securities that are rated below investment-grade are considered predominantly speculative with respect to the ability of the issuer to make timely principal and interest payments.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Below Investment-Grade Fixed-Income Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Liquidity Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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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. 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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Market/Issuer Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Interest Rate Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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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 securities, pay-in-kind bonds and 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 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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Currency Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Cybersecurity and Technology Risk [Member]

Prospectus:

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Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Derivatives Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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Derivatives Risk is the risk that the value of the Fund’s derivative investments such as options, futures transactions and 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 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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Emerging Markets Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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Emerging Markets Risk is the risk that the Fund’s investments in emerging markets may face greater foreign securities risk. 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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Equity Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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Equity Securities Risk is the risk that 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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Foreign Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Inflation/Deflation Risk [Member]

Prospectus:

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Risk [Text Block]

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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. 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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Large Investor Risk [Member]

Prospectus:

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Risk [Text Block]

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Large Investor Risk is the risk associated with ownership of shares of the Fund that may be concentrated in one or a few large investors. Such investors may redeem shares in large quantities or on a frequent basis. Redemptions by a large investor can affect the performance of the Fund, may increase realized capital gains, including short-term capital gains taxable as ordinary income, may accelerate the realization of taxable income to shareholders and may increase transaction costs. These transactions potentially limit the use of any capital loss carryforwards and certain other losses to offset future realized capital gains (if any). Such transactions may also increase the Fund’s expenses.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Leverage Risk [Member]

Prospectus:

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Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Management Risk [Member]

Prospectus:

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Risk [Text Block]

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Management Risk is the risk that Loomis Sayles’ investment techniques will be unsuccessful and cause the Fund to incur losses.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Mortgage-Related and Asset-Backed Securities Risk [Member]

Prospectus:

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Risk [Text Block]

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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, inflation and valuation risks).

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Small-Capitalization Companies Risk [Member]

Prospectus:

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Risk [Text Block]

rr_RiskTextBlock

Small-Capitalization Companies Risk is the risk that the Fund’s investments may be subject to more abrupt price movements, limited markets, increased volatility and less liquidity than investments in larger, more established companies, which could adversely affect the value of the portfolio.

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Bloomberg U.S. Aggregate Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

5.53%

^[2]

Past 5 Years

rr_AverageAnnualReturnYear05

1.10%

^[2]

Past 10 Years

rr_AverageAnnualReturnYear10

1.81%

^[2]

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Bloomberg U.S. Corporate High Yield Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

13.44%

Past 5 Years

rr_AverageAnnualReturnYear05

5.37%

Past 10 Years

rr_AverageAnnualReturnYear10

4.60%

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Institutional Class

Prospectus:

rr_ProspectusTable

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

none

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

none

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

none

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

none

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

none

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

none

Annual Return 2014

rr_AnnualReturn2014

4.59%

Annual Return 2015

rr_AnnualReturn2015

(3.13%)

Annual Return 2016

rr_AnnualReturn2016

15.85%

Annual Return 2017

rr_AnnualReturn2017

8.39%

Annual Return 2018

rr_AnnualReturn2018

(2.08%)

Annual Return 2019

rr_AnnualReturn2019

13.01%

Annual Return 2020

rr_AnnualReturn2020

9.24%

Annual Return 2021

rr_AnnualReturn2021

4.32%

Annual Return 2022

rr_AnnualReturn2022

(12.86%)

Annual Return 2023

rr_AnnualReturn2023

10.81%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

9.87%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2020

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(12.05%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2020

Past 1 Year

rr_AverageAnnualReturnYear01

10.81%

Past 5 Years

rr_AverageAnnualReturnYear05

4.46%

Past 10 Years

rr_AverageAnnualReturnYear10

4.48%

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Institutional Class | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

7.50%

Past 5 Years

rr_AverageAnnualReturnYear05

1.57%

Past 10 Years

rr_AverageAnnualReturnYear10

1.74%

(Loomis Sayles Funds I) | (Loomis Sayles High Income Opportunities Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

6.30%

Past 5 Years

rr_AverageAnnualReturnYear05

2.20%

Past 10 Years

rr_AverageAnnualReturnYear10

2.23%

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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The Fund’s investment objective is to seek a high level of current income consistent with capital preservation.

Expense [Heading]

rr_ExpenseHeading

FUND FEES & EXPENSES

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The Fund does not impose a sales charge, a redemption fee or an exchange fee.

Operating Expenses Caption [Text]

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Annual Fund Operating Expenses(expenses that you pay each year as a percentage of the value of your investment)*

^[3]

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

106.00%

Strategy [Heading]

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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 a diversified portfolio of securitized assets, such as mortgage-backed and other asset-backed securities. The Fund may invest in asset-backed securities of any type, including residential and commercial asset-backed securities, asset-backed securities related to automobiles, credit cards, home equity loans, manufactured housing, utilities, and other miscellaneous asset-backed securities. The Fund may only buy securities that are rated investment-grade at the time of purchase by at least one of the three major rating agencies (Moody’s Investors Service, Inc., Fitch Investor Services, Inc. or S&P Global Ratings) or, if unrated, are determined by Loomis Sayles to be of comparable quality. It is expected that a majority of the Fund’s securities will be rated AAA or Aaa by at least one of the rating agencies at the time of

purchase. The Fund may continue to hold securities that are downgraded in credit rating subsequent to their purchase if Loomis Sayles believes it would be advantageous to do so.

The Fund may, without limitation, seek to obtain market exposure to the securities in which it primarily invests by entering into a series of purchase and sale contracts (including on a “to be announced” basis) or by using investment techniques such as buybacks and dollar rolls.

Loomis Sayles uses a bottom-up, fundamental research process to select individual securities for the Fund. The decision to buy or sell a particular security is largely driven by Loomis Sayles’ view of the fundamentals of the issue compared to the prevailing market valuation, which may be higher (suggesting a potential sell decision) or lower (suggesting a potential buy decision). Loomis Sayles also may seek to construct a portfolio with risk characteristics similar, but not identical to, certain of the securities in the Bloomberg U.S. Securitized Bond Index (the “Index”). Examples of typical risk characteristics that Loomis Sayles might consider include average life, credit quality, effective duration, yield curve exposure and sector exposure. The portfolio will not necessarily exhibit similarities with the Index for some or all risk characteristics. It is currently anticipated that the Fund’s effective duration will be within +/- 1 year of the effective duration of the Index.

In deciding which securities to buy and sell, Loomis Sayles will consider, among other things, the financial strength of the issuer, current interest rates, current valuations, Loomis Sayles’ expectations regarding future changes in interest rates and comparisons of the level of risk associated with particular investments with Loomis Sayles’ expectations concerning the potential return of those investments.

The Fund’s investments may also include, among other things, the following: fixed and floating-rate instruments, mortgage pass-through securities issued or guaranteed by agencies or instrumentalities of the U.S. government, collateralized mortgage obligations, commercial mortgage-backed securities, mortgage-related asset-backed securities, other collateralized asset-backed securities, securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A Securities”), other privately placed investments such as private credit instruments, U.S. government securities, corporate debt securities, zero-coupon securities, step coupon securities, commercial paper, structured notes, other mortgage-related securities (including adjustable rate mortgage securities, stripped mortgage-backed securities and mortgage dollar rolls), when-issued securities and repurchase agreements. The Fund may also invest in options, futures and 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).

The Fund may also engage in active and frequent trading of securities. Frequent trading may produce a high level of taxable gains, including short-term capital gains taxable as ordinary income, as well as increased trading costs, which may lower the Fund’s return.

Risk [Heading]

rr_RiskHeading

Principal Risks

Bar Chart and Performance Table [Heading]

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Risk/Return Bar Chart and Table

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-633-3330

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.loomissayles.com

Bar Chart [Heading]

rr_BarChartHeading

Total Returns for Institutional Class 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

Bar Chart Closing [Text Block]

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Highest Quarterly Return:

Fourth Quarter 2023, 7.10%

Lowest Quarterly Return:

First Quarter 2022, -4.89%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns(for the periods ended December 31, 2023)

Performance Table Closing [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Risk Lose Money [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

You may lose money by investing in the Fund.

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Risk Not Insured Depository Institution [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Credit/Counterparty Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Liquidity Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

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. 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. 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.

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Market/Issuer Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Interest Rate Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

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 securities and 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.

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Cybersecurity and Technology Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Derivatives Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

Derivatives Risk is the risk that the value of the Fund’s derivative investments such as structured notes, options, futures transactions and 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 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.

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Inflation/Deflation Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Large Investor Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Leverage Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Management Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

Management Risk is the risk that Loomis Sayles’ investment techniques will be unsuccessful and cause the Fund to incur losses.

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Mortgage-Related and Asset-Backed Securities Risk [Member]

Prospectus:

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Risk [Text Block]

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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, inflation and valuation risks).

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Bloomberg U.S. Aggregate Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

5.53%

^[4]

Past 5 Years

rr_AverageAnnualReturnYear05

1.10%

^[4]

Past 10 Years

rr_AverageAnnualReturnYear10

1.81%

^[4]

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Bloomberg U.S. Securitized Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

5.08%

Past 5 Years

rr_AverageAnnualReturnYear05

0.37%

Past 10 Years

rr_AverageAnnualReturnYear10

1.43%

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Institutional Class

Prospectus:

rr_ProspectusTable

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

none

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

none

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

none

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

none

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

none

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

none

Annual Return 2014

rr_AnnualReturn2014

6.45%

Annual Return 2015

rr_AnnualReturn2015

1.98%

Annual Return 2016

rr_AnnualReturn2016

3.10%

Annual Return 2017

rr_AnnualReturn2017

3.40%

Annual Return 2018

rr_AnnualReturn2018

2.48%

Annual Return 2019

rr_AnnualReturn2019

6.80%

Annual Return 2020

rr_AnnualReturn2020

4.67%

Annual Return 2021

rr_AnnualReturn2021

0.64%

Annual Return 2022

rr_AnnualReturn2022

(11.83%)

Annual Return 2023

rr_AnnualReturn2023

7.01%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

7.10%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2023

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(4.89%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2022

Past 1 Year

rr_AverageAnnualReturnYear01

7.01%

Past 5 Years

rr_AverageAnnualReturnYear05

1.20%

Past 10 Years

rr_AverageAnnualReturnYear10

2.33%

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Institutional Class | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

4.54%

Past 5 Years

rr_AverageAnnualReturnYear05

(1.18%)

Past 10 Years

rr_AverageAnnualReturnYear10

none

(Loomis Sayles Funds I) | (Loomis Sayles Securitized Asset Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

4.09%

Past 5 Years

rr_AverageAnnualReturnYear05

(0.05%)

Past 10 Years

rr_AverageAnnualReturnYear10

0.78%

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

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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 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, 2025

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

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Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

35.00%

Strategy [Heading]

rr_StrategyHeading

INVESTMENTS, RISKS AND PERFORMANCEPrincipal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in fixed-income securities. The Fund may invest up to 35% of its assets in below investment-grade fixed-income securities (commonly known as “junk bonds”) and up to 20% of its assets in equity securities, such as common stocks and preferred stocks. 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., 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.

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, including, 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).

Three themes typically drive the Fund’s investment approach. First, Loomis Sayles generally seeks fixed-income securities that are attractively valued relative to the Loomis Sayles’ credit research team’s assessment of credit risk. The broad coverage combined with the objective of identifying attractive investment opportunities makes this an important component of the investment approach. Second, the Fund may invest significantly in securities the prices of which Loomis Sayles believes are more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates. These securities may not have a direct correlation with changes in interest rates, thus helping to manage interest rate risk and to offer diversified sources for return. Third, Loomis Sayles analyzes different sectors of the economy and differences in the yields (“spreads”) of various fixed-income securities (U.S. government securities, investment-grade corporate securities, securitized assets, high-yield corporate securities, emerging market securities, non-U.S. sovereigns and credits, convertibles, bank loans and municipals) in an effort to find securities that it believes may produce attractive returns for the Fund in comparison to their risk.

In deciding which equity securities to buy and sell, Loomis Sayles intends to emphasize dividend-paying stocks issued by companies with strong fundamentals and relatively limited anticipated volatility to supplement its fixed-income holdings. These securities will be selected with the same bottom-up investment process that is the foundation of the Fund’s overall strategy.

The Fund may invest up to 20% of its assets in foreign securities, including emerging market securities. The Fund may invest without limit in obligations of supranational entities (e.g., the World Bank). Although certain securities purchased by the Fund may be issued by domestic companies incorporated outside of the United States, the Adviser does not consider these securities to be foreign if the issuer is included in the U.S. fixed-income indices published by Bloomberg.

The fixed-income securities in which the Fund may invest include, among other instruments, corporate bonds and other debt securities (including junior and senior bonds), U.S. government securities, commercial paper, collateralized loan obligations, zero-coupon securities, mortgage-backed securities, stripped mortgage-backed securities, collateralized mortgage obligations and other asset-backed securities, including mortgage dollar rolls, when-issued securities, real estate investment trusts (“REITs”), securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A securities”), other privately placed investments such as private credit investments, repurchase agreements and convertible securities. The Fund may also engage in options and futures transactions, foreign currency transactions (such as forward currency contracts) and swap transactions (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).

Risk [Heading]

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Principal Risks

Bar Chart and Performance Table [Heading]

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Risk/Return Bar Chart and Table

Performance Narrative [Text Block]

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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 and ten-year periods compare to those of a broad-based securities market index that reflects the performance of the overall market applicable to the Fund. 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.

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

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

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

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

The after-tax returns are shown for the Institutional Class of the Fund.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Highest Quarterly Return:

Second Quarter 2020, 9.15%

Lowest Quarterly Return:

First Quarter 2020, -12.99%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns(for the periods ended December 31, 2023)

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

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. Index performance reflects no deduction for fees, expenses or taxes.

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Risk Lose Money [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

You may lose money by investing in the Fund.

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Risk Not Insured Depository Institution [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Credit/Counterparty Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Below Investment-Grade Fixed-Income Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Liquidity Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Market/Issuer Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Interest Rate Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

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 securities and 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 and/or central bank monetary policy and action may also affect the level of interest rates.

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Currency Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Cybersecurity and Technology Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Derivatives Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

Derivatives Risk is the risk that the value of the Fund’s derivative investments such as forward currency contracts, options, futures transactions and 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.

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Emerging Markets Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Equity Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Foreign Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Inflation/Deflation Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

issuer default more likely, which may result in a decline in the value of the Fund’s portfolio.

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Large Investor Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Leverage Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Management Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

Management Risk is the risk that Loomis Sayles’ investment techniques will be unsuccessful and cause the Fund to incur losses.

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Mortgage-Related and Asset-Backed Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | REITs Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

REITs Risk is the risk that the value of the Fund’s investments in REITs will fall as a result of changes in underlying real estate values, rising interest rates, limited diversification of holdings, higher costs and prepayment risk associated with related mortgages, as well as other risks particular to investments in real estate. Many REITs are highly leveraged, increasing their risk. The Fund will indirectly bear its proportionate share of expenses, including management fees, paid by each REIT in which it invests in addition to the expenses of the Fund.

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Bloomberg U.S. Aggregate Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

5.53%

^[5]

Past 5 Years

rr_AverageAnnualReturnYear05

1.10%

^[5]

Past 10 Years

rr_AverageAnnualReturnYear10

1.81%

^[5]

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Bloomberg U.S. Government/Credit Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

5.72%

Past 5 Years

rr_AverageAnnualReturnYear05

1.41%

Past 10 Years

rr_AverageAnnualReturnYear10

1.97%

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Institutional Class

Prospectus:

rr_ProspectusTable

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.50%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.11%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.61%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[6]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

0.61%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 62

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

195

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

340

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 762

Annual Return 2014

rr_AnnualReturn2014

4.62%

Annual Return 2015

rr_AnnualReturn2015

(6.03%)

Annual Return 2016

rr_AnnualReturn2016

9.94%

Annual Return 2017

rr_AnnualReturn2017

8.40%

Annual Return 2018

rr_AnnualReturn2018

(3.06%)

Annual Return 2019

rr_AnnualReturn2019

13.55%

Annual Return 2020

rr_AnnualReturn2020

5.38%

Annual Return 2021

rr_AnnualReturn2021

2.88%

Annual Return 2022

rr_AnnualReturn2022

(11.75%)

Annual Return 2023

rr_AnnualReturn2023

8.20%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

9.15%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2020

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(12.99%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2020

Past 1 Year

rr_AverageAnnualReturnYear01

8.20%

Past 5 Years

rr_AverageAnnualReturnYear05

3.29%

Past 10 Years

rr_AverageAnnualReturnYear10

2.93%

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Institutional Class | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

6.34%

Past 5 Years

rr_AverageAnnualReturnYear05

1.69%

Past 10 Years

rr_AverageAnnualReturnYear10

1.04%

(Loomis Sayles Funds I) | (Loomis Sayles Fixed Income Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

4.86%

Past 5 Years

rr_AverageAnnualReturnYear05

2.01%

Past 10 Years

rr_AverageAnnualReturnYear10

1.55%

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund)

Prospectus:

rr_ProspectusTable

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 high current income and capital appreciation.

Expense [Heading]

rr_ExpenseHeading

FUND FEES & EXPENSES

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

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, 2025

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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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 examples 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 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:

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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Portfolio Turnover, Rate

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49.00%

Strategy [Heading]

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INVESTMENTS, RISKS AND PERFORMANCEPrincipal Investment Strategies

Strategy Narrative [Text Block]

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The Fund will normally invest at least 80% of its net assets (plus any borrowings made for investment purposes) in fixed-income securities (for example, bonds and other investments that Loomis Sayles believes have similar economic characteristics, such as notes, debentures and loans). The Fund invests primarily in investment-grade fixed-income securities worldwide, although it may invest up to 20% 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 rating 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. Securities held by the Fund may be denominated in any currency and may be issued by issuers located in countries with emerging securities markets. The Fund may invest in fixed-income securities of any maturity. The Fund may also invest in foreign currencies and may engage in other foreign currency transactions (such as forward currency contracts) for investment or hedging purposes.

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, including 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).

In assessing both risks and opportunities related to the Fund’s investments, Loomis Sayles seeks to take into account the factors that may influence an investment’s performance over time. This includes material environmental, social, and governance (“ESG”) risks and opportunities (those which could cause a material impact on the value of an investment).

In integrating risks and opportunities into its investment process, Loomis Sayles takes into account ESG factors that it deems may be material to an investment, such as carbon intensity, renewable energy usage from low carbon sources, workplace diversity, and board composition, at all stages of the investment management process, including strategy development, investment analysis and due diligence, and portfolio construction (including at the point where the investment team considers investment opportunities), and as part of its ongoing monitoring and risk analysis.

To the extent that Loomis Sayles concludes that there is an ESG risk associated with an investment, Loomis Sayles assesses the probability and potential impact of that ESG risk against the potential pecuniary advantage to the Fund of making the investment. If Loomis Sayles believes the potential pecuniary advantage outweighs the actual or potential impact of the ESG risk, then Loomis Sayles may still make the investment.

The fixed-income securities in which the Fund may invest include, among other instruments, corporate bonds and other debt securities, U.S. government securities, commercial paper, zero-coupon securities, securitized and mortgage-related securities (including senior and junior loans, mortgage dollar rolls and collateralized mortgage obligations) and other asset-backed securities, when-issued securities, securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A securities”), other privately placed investments such as private credit investments, bank loans, structured notes, collateralized loan obligations, repurchase agreements and convertible securities. The Fund may also engage in options and futures transactions and swap transactions (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).

Risk [Heading]

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Principal Risks

Bar Chart and Performance Table [Heading]

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Risk/Return Bar Chart and Table

Performance Narrative [Text Block]

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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 and ten-year periods 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]

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Performance Availability Phone [Text]

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800-633-3330

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.loomissayles.com

Performance Past Does Not Indicate Future [Text]

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The Fund’s past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.

Bar Chart [Heading]

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Total Returns for Institutional Class Shares

Index No Deduction for Fees, Expenses, Taxes [Text]

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Index performance reflects no deduction for fees, expenses or taxes.

Performance Table Uses Highest Federal Rate

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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

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Performance Table One Class of after Tax Shown [Text]

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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.

Bar Chart Closing [Text Block]

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Highest Quarterly Return:

Fourth Quarter 2023, 8.69%

Lowest Quarterly Return:

Second Quarter 2022, -9.58%

Performance Table Heading

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Average Annual Total Returns(for the periods ended December 31, 2023)

Performance Table Closing [Text Block]

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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 Funds I) | (Loomis Sayles Global Bond Fund) | Risk Lose Money [Member]

Prospectus:

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Risk [Text Block]

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You may lose money by investing in the Fund.

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Risk Not Insured Depository Institution [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Credit/Counterparty Risk [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Below Investment-Grade Fixed-Income Securities Risk [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Liquidity Risk [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Market/Issuer Risk [Member]

Prospectus:

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Risk [Text Block]

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Fund’s investments, such as management performance, financial condition and demand for the issuers’ goods and services.

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Interest Rate Risk [Member]

Prospectus:

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Risk [Text Block]

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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 securities and 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 and/or central bank monetary policy and action may also affect the level of interest rates.

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Currency Risk [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Cybersecurity and Technology Risk [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Derivatives Risk [Member]

Prospectus:

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Risk [Text Block]

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Derivatives Risk is the risk that the value of the Fund’s derivative investments such as forward currency contracts, structured notes, options, futures transactions and 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.

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Emerging Markets Risk [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Foreign Securities Risk [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Inflation/Deflation Risk [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Leverage Risk [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Management Risk [Member]

Prospectus:

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Risk [Text Block]

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Management Risk is the risk that Loomis Sayles’ investment techniques will be unsuccessful and cause the Fund to incur losses.

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Mortgage-Related and Asset-Backed Securities Risk [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Bank Loans Risk [Member]

Prospectus:

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Risk [Text Block]

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Bank Loans Risk is the risk that the Fund’s investments in bank loans are subject to credit risk and may not be adequately collateralized. Indebtedness of borrowers whose creditworthiness is poor involves substantially greater risks and may be highly speculative. The interest rates on many bank loans reset frequently, and thus bank loans are subject to interest rate risk. Most bank loans, like most investment-grade bonds, are not traded on any national securities exchange. There may also be less public information available about bank loans as compared to other debt securities.

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Collateralized Loan Obligation (CLO) Risk [Member]

Prospectus:

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Risk [Text Block]

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Collateralized Loan Obligation (“CLO”) Risk is the risk that the Fund’s investments in CLOs involve risks in addition to the risks associated with investments in debt obligations and other fixed-income securities such as credit risk, interest rate risk, liquidity risk and market/issuer risk. The degree of such risk will generally correspond to the type of underlying assets and the specific tranche in which the Fund is invested. A CLO’s performance is linked to the expertise of the CLO manager and its ability to manage the CLO’s portfolio. Changes in the regulation of CLOs may adversely affect the value of the CLO investments held by the Fund. The tranche of the CLO held by the Fund may be subordinate to other classes of the CLO’s debt. CLO debt is payable solely from the proceeds of the CLO’s underlying assets and, therefore, if the income from the underlying loans is insufficient to make payments on one or more tranches of the CLO’s debt, no other assets will be available for payment. CLO debt securities may be subject to redemption and the timing of redemptions may adversely affect the returns on CLO debt. The CLO manager may not find suitable assets in which to invest and the CLO manager’s

opportunities to invest may be limited.

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | ESG Risk [Member]

Prospectus:

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Risk [Text Block]

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ESG Risk is the risk related to ESG factors that may impact the performance of securities in which the Fund invests. Such ESG factors include, for example, climate change; resource depletion; renewal energy usage; governance, diversity and labor practices; workplace health and safety; supply chain standards; and product health and safety. The companies or issuers in which the Fund invests may not have favorable ESG characteristics.

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Bloomberg Global Aggregate Bond Index

Prospectus:

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Past 1 Year

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5.72%

Past 5 Years

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(0.32%)

Past 10 Years

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0.38%

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Institutional Class

Prospectus:

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Management Fees (as a percentage of Assets)

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0.55%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.23%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.78%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.09%

^[7]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

0.69%

Expense Example, with Redemption, 1 Year

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$ 70

Expense Example, with Redemption, 3 Years

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240

Expense Example, with Redemption, 5 Years

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424

Expense Example, with Redemption, 10 Years

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$ 958

Annual Return 2014

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0.34%

Annual Return 2015

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(5.05%)

Annual Return 2016

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3.61%

Annual Return 2017

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8.87%

Annual Return 2018

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(2.49%)

Annual Return 2019

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6.82%

Annual Return 2020

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13.49%

Annual Return 2021

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(4.93%)

Annual Return 2022

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(17.18%)

Annual Return 2023

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5.48%

Highest Quarterly Return, Label

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Highest Quarterly Return:

Highest Quarterly Return

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8.69%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2023

Lowest Quarterly Return, Label

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Lowest Quarterly Return:

Lowest Quarterly Return

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(9.58%)

Lowest Quarterly Return, Date

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Jun. 30, 2022

Past 1 Year

rr_AverageAnnualReturnYear01

5.48%

Past 5 Years

rr_AverageAnnualReturnYear05

0.13%

Past 10 Years

rr_AverageAnnualReturnYear10

0.54%

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Institutional Class | Return After Taxes on Distributions

Prospectus:

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Past 1 Year

rr_AverageAnnualReturnYear01

5.48%

Past 5 Years

rr_AverageAnnualReturnYear05

(0.58%)

Past 10 Years

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(0.01%)

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

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Past 1 Year

rr_AverageAnnualReturnYear01

3.24%

Past 5 Years

rr_AverageAnnualReturnYear05

(0.09%)

Past 10 Years

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0.24%

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Retail Class

Prospectus:

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Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.55%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.23%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.03%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.09%

^[7]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

0.94%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 96

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

319

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

560

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,251

Past 1 Year

rr_AverageAnnualReturnYear01

5.15%

Past 5 Years

rr_AverageAnnualReturnYear05

(0.13%)

Past 10 Years

rr_AverageAnnualReturnYear10

0.28%

(Loomis Sayles Funds I) | (Loomis Sayles Global Bond Fund) | Class N

Prospectus:

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Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.55%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.13%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.68%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[7]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

0.64%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 65

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

214

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

375

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 843

Past 1 Year

rr_AverageAnnualReturnYear01

5.46%

Past 5 Years

rr_AverageAnnualReturnYear05

0.16%

Past 10 Years

rr_AverageAnnualReturnYear10

0.60%

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund)

Prospectus:

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Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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The Fund’s investment objective is high total investment return through a combination of current income and capital appreciation.

Expense [Heading]

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FUND FEES & EXPENSES

Expense Narrative [Text Block]

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The Fund does not impose a sales charge, a redemption fee or an exchange fee.

Operating Expenses Caption [Text]

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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

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January 31, 2025

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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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:

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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Portfolio Turnover, Rate

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36.00%

Strategy [Heading]

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INVESTMENTS, RISKS AND PERFORMANCEPrincipal Investment Strategies

Strategy Narrative [Text Block]

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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”), other privately placed investments such as private credit investments, 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]

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Principal Risks

Bar Chart and Performance Table [Heading]

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Risk/Return Bar Chart and Table

Performance Narrative [Text Block]

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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-based securities market index that reflects the performance of the overall market applicable to the Fund and an additional index that represents the market sectors in which the Fund primarily invests. 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]

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Performance Availability Phone [Text]

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800-633-3330

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.loomissayles.com

Performance Past Does Not Indicate Future [Text]

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The Fund’s past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.

Bar Chart [Heading]

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Total Returns for Institutional Class Shares

Index No Deduction for Fees, Expenses, Taxes [Text]

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Index performance reflects no deduction for fees, expenses or taxes.

Performance Table Uses Highest Federal Rate

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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

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Performance Table One Class of after Tax Shown [Text]

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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.

Bar Chart Closing [Text Block]

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Highest Quarterly Return:

Second Quarter 2020, 5.24%

Lowest Quarterly Return:

Second Quarter 2022, -6.73%

Performance Table Heading

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Average Annual Total Returns(for the periods ended December 31, 2023)

Performance Table Closing [Text Block]

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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 Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Risk Lose Money [Member]

Prospectus:

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Risk [Text Block]

rr_RiskTextBlock

You may lose money by investing in the Fund.

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Risk Not Insured Depository Institution [Member]

Prospectus:

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Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Credit/Counterparty Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Below Investment-Grade Fixed-Income Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Liquidity Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Market/Issuer Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Interest Rate Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

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 and/or central bank monetary policy and action may also affect the level of interest rates.

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Currency Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Cybersecurity and Technology Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Derivatives Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

Derivatives Risk is the risk that the value of the Fund’s derivative investments such as forward currency contracts, structured notes, futures transactions, and 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.

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Foreign Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Inflation/Deflation Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Large Investor Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Leverage Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Management Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

Management Risk is the risk that Loomis Sayles’ investment techniques will be unsuccessful and cause the Fund to incur losses.

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Mortgage-Related and Asset-Backed Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | TIPS Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

TIPS Risk is the risk that the securities will not work as intended. The principal of TIPS increases with inflation and decreases with deflation. The interest rate on TIPS is fixed at issuance, but over the life of the bond this interest may be paid on an increasing or decreasing principal value that has been adjusted for inflation based upon an index intended to measure the rate of inflation. However, there can be no assurance that the relevant index will accurately measure the rate of inflation. Although repayment of the original bond principal upon maturity is guaranteed, the market value of TIPS is not guaranteed, and will fluctuate.

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Bloomberg U.S. Aggregate Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

5.53%

^[8]

Past 5 Years

rr_AverageAnnualReturnYear05

1.10%

^[8]

Past 10 Years

rr_AverageAnnualReturnYear10

1.81%

^[8]

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Bloomberg U.S. TIPS Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

3.90%

Past 5 Years

rr_AverageAnnualReturnYear05

3.15%

Past 10 Years

rr_AverageAnnualReturnYear10

2.42%

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Institutional Class

Prospectus:

rr_ProspectusTable

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.25%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.31%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.56%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.16%

^[9],[10]

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

163

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

297

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 686

Annual Return 2014

rr_AnnualReturn2014

1.75%

Annual Return 2015

rr_AnnualReturn2015

(1.50%)

Annual Return 2016

rr_AnnualReturn2016

4.38%

Annual Return 2017

rr_AnnualReturn2017

3.61%

Annual Return 2018

rr_AnnualReturn2018

(2.23%)

Annual Return 2019

rr_AnnualReturn2019

8.64%

Annual Return 2020

rr_AnnualReturn2020

13.97%

Annual Return 2021

rr_AnnualReturn2021

5.02%

Annual Return 2022

rr_AnnualReturn2022

(12.46%)

Annual Return 2023

rr_AnnualReturn2023

3.63%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

5.24%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2020

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(6.73%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Jun. 30, 2022

Past 1 Year

rr_AverageAnnualReturnYear01

3.63%

Past 5 Years

rr_AverageAnnualReturnYear05

3.36%

Past 10 Years

rr_AverageAnnualReturnYear10

2.26%

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Institutional Class | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

2.01%

Past 5 Years

rr_AverageAnnualReturnYear05

1.71%

Past 10 Years

rr_AverageAnnualReturnYear10

1.04%

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

2.13%

Past 5 Years

rr_AverageAnnualReturnYear05

1.92%

Past 10 Years

rr_AverageAnnualReturnYear10

1.22%

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Retail Class

Prospectus:

rr_ProspectusTable

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.25%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.31%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.81%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.16%

^[9],[10]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

0.65%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 66

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

243

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

434

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 987

Past 1 Year

rr_AverageAnnualReturnYear01

3.48%

Past 5 Years

rr_AverageAnnualReturnYear05

3.13%

Past 10 Years

rr_AverageAnnualReturnYear10

2.00%

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Class N

Prospectus:

rr_ProspectusTable

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.25%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.22%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.47%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.12%

^[9],[10]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

0.35%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 36

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

139

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

251

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 580

Past 1 Year

rr_AverageAnnualReturnYear01

3.69%

Past 5 Years

rr_AverageAnnualReturnYear05

3.43%

Since Inception

rr_AverageAnnualReturnSinceInception

2.57%

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Class N | Bloomberg U.S. Aggregate Bond Index

Prospectus:

rr_ProspectusTable

Since Inception

rr_AverageAnnualReturnSinceInception

1.27%

^[8]

(Loomis Sayles Funds I) | (Loomis Sayles Inflation Protected Securities Fund) | Class N | Bloomberg U.S. TIPS Index

Prospectus:

rr_ProspectusTable

Since Inception

rr_AverageAnnualReturnSinceInception

2.40%

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund)

Prospectus:

rr_ProspectusTable

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 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, 2025

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

64.00%

Strategy [Heading]

rr_StrategyHeading

INVESTMENTS, RISKS AND PERFORMANCEPrincipal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund will invest primarily in below investment-grade fixed-income securities (commonly known as “junk bonds”) and other securities that are expected to produce a relatively high level of income (including income-producing preferred stocks and common stocks). 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., 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.

Three themes typically drive the Fund’s investment approach. First, Loomis Sayles generally seeks fixed-income securities that are attractively valued relative to the Loomis Sayles’ credit research team’s assessment of credit risk. The broad coverage combined with the objective of identifying attractive investment opportunities makes this an important component of the investment approach. Second, the Fund may invest significantly in securities the prices of which Loomis Sayles believes are more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates. These securities may not have a direct correlation with changes in interest rates, thus helping to manage interest rate risk and to offer diversified sources for return. Third, Loomis Sayles analyzes different sectors of the economy and differences in the yields (“spreads”) of various fixed-income securities (U.S. governments, investment-grade corporates, securitized assets, high-yield corporates, emerging markets, non-U.S. sovereigns and credits, convertibles, bank loans and municipals) in an effort to find securities that it believes may produce attractive returns for the Fund in comparison to their risk.

The Fund may invest up to 50% of its assets in foreign securities, including emerging market securities. The Fund may invest without limit in obligations of supranational entities (e.g., the World Bank). Although certain securities purchased by the Fund may be issued by domestic companies incorporated outside of the United States, the Adviser does not consider these securities to be foreign if the issuer is included in the U.S. fixed-income indices published by Bloomberg.

The fixed-income securities in which the Fund may invest include, among other instruments, corporate bonds and other debt securities (including junior and senior loans), U.S. government securities, commercial paper, collateralized loan obligations, zero-coupon securities, mortgage-backed securities, including mortgage dollar rolls, stripped mortgage-backed securities, and collateralized mortgage obligations, other asset-backed securities, when-issued securities, real estate investment trusts (“REITs”), securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A securities”), other privately placed investments such as private credit investments, repurchase agreements and convertible securities. The Fund may also engage in options and futures transactions, foreign currency transactions (such as forward currency contracts) and swap transactions (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).

Risk [Heading]

rr_RiskHeading

Principal Risks

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 and ten-year periods compare to those of a broad-based securities market index that reflects the performance of the overall market applicable to the Fund and an additional index that represents the market sectors in which the Fund primarily invests. 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

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

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

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

The after-tax returns are shown for the Institutional Class of the Fund.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Highest Quarterly Return:

Second Quarter 2020, 11.00%

Lowest Quarterly Return:

First Quarter 2020, -18.43%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns(for the periods ended December 31, 2023)

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

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. Index performance reflects no deduction for fees, expenses or taxes.

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Risk Lose Money [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

You may lose money by investing in the Fund.

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Risk Not Insured Depository Institution [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Credit/Counterparty Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Below Investment-Grade Fixed-Income Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Liquidity Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Market/Issuer Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Interest Rate Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

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 securities and 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 and/or central bank monetary policy and action may also affect the level of interest rates.

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Currency Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Cybersecurity and Technology Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Derivatives Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Emerging Markets Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Equity Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Foreign Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Large Investor Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Leverage Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

the Fund’s returns, and may lead to significant losses if investments are not successful.

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Management Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

Management Risk is the risk that Loomis Sayles’ investment techniques will be unsuccessful and cause the Fund to incur losses.

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Mortgage-Related and Asset-Backed Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | REITs Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Bloomberg U.S. Aggregate Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

5.53%

^[11]

Past 5 Years

rr_AverageAnnualReturnYear05

1.10%

^[11]

Past 10 Years

rr_AverageAnnualReturnYear10

1.81%

^[11]

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Bloomberg U.S. Corporate High Yield Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

13.44%

Past 5 Years

rr_AverageAnnualReturnYear05

5.37%

Past 10 Years

rr_AverageAnnualReturnYear10

4.60%

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Institutional Class

Prospectus:

rr_ProspectusTable

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.58%

^[12]

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.12%

^[13]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.70%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[14]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

0.70%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 72

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

224

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

390

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 871

Annual Return 2014

rr_AnnualReturn2014

5.17%

Annual Return 2015

rr_AnnualReturn2015

(10.27%)

Annual Return 2016

rr_AnnualReturn2016

18.95%

Annual Return 2017

rr_AnnualReturn2017

8.40%

Annual Return 2018

rr_AnnualReturn2018

(3.52%)

Annual Return 2019

rr_AnnualReturn2019

10.53%

Annual Return 2020

rr_AnnualReturn2020

3.47%

Annual Return 2021

rr_AnnualReturn2021

8.25%

Annual Return 2022

rr_AnnualReturn2022

(11.67%)

Annual Return 2023

rr_AnnualReturn2023

9.98%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

11.00%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2020

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(18.43%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2020

Past 1 Year

rr_AverageAnnualReturnYear01

9.98%

Past 5 Years

rr_AverageAnnualReturnYear05

3.76%

Past 10 Years

rr_AverageAnnualReturnYear10

3.51%

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Institutional Class | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

7.33%

Past 5 Years

rr_AverageAnnualReturnYear05

1.50%

Past 10 Years

rr_AverageAnnualReturnYear10

0.90%

(Loomis Sayles Funds I) | (Loomis Sayles Institutional High Income Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

5.92%

Past 5 Years

rr_AverageAnnualReturnYear05

1.98%

Past 10 Years

rr_AverageAnnualReturnYear10

1.61%

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund’s investment objective is long-term capital growth from investments in common stocks or other equity securities.

Expense [Heading]

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FUND FEES & EXPENSES

Expense Narrative [Text Block]

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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, 2025

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

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Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

26.00%

Strategy [Heading]

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INVESTMENTS, RISKS AND PERFORMANCEPrincipal Investment Strategies

Strategy Narrative [Text Block]

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The Fund normally will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in the equity securities of “small-cap companies,” including preferred stocks, warrants, securities convertible into common or preferred stocks and other equity-like interests in an entity. Currently, the Fund defines a small-cap company to be one whose market capitalization falls within the capitalization range of the Russell 2000^® Index, an index that tracks stocks of 2,000 of the smallest U.S. companies. The Fund may invest the rest of its assets in companies of any size, including large-capitalization companies.

In deciding which securities to buy and sell, Loomis Sayles seeks to identify securities of smaller companies that it believes are undervalued by the market using a disciplined bottom-up approach to investing. Utilizing fundamental research, Loomis Sayles seeks to identify those stocks selling at a discount to its assessment of intrinsic value. The Fund’s investments focus on market inefficiencies and may include companies that are misunderstood by other investors; are undergoing a change in the business model or financial structure; or those companies that are not yet well-known to the investment community but are considered to have favorable fundamental prospects and attractive valuation. The portfolio managers analyze fundamental trends across the various industries in the sectors and use this information along with security valuation procedures to determine which stocks they believe are best positioned to outperform the industry or sector. Sell decisions are made when there is a deterioration in fundamentals, a stock reaches a target price or a more attractive opportunity is found.

The Fund may invest up to 20% of its assets in foreign securities, including emerging markets securities. Although certain equity securities purchased by the Fund may be issued by domestic companies incorporated outside of the United States, the Adviser does not consider these securities to be foreign if they are included in the U.S. equity indices published by S&P Global Ratings or Russell Investments. The Fund may also invest in real estate investment trusts (“REITs”), securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A securities”) and other privately placed investments such as private equity investments and, to the extent permitted by the Investment Company Act of 1940, and the rules thereunder (the “1940 Act”), investment companies. The Fund may engage, for hedging and investment purposes, in foreign currency transactions (such as forward currency contracts), options and futures transactions.

Risk [Heading]

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Principal Risks

Bar Chart and Performance Table [Heading]

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Risk/Return Bar Chart and Table

Performance Narrative [Text Block]

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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 and ten-year periods compare to those of a broad-based securities market index that reflects the performance of the overall market applicable to the Fund and additional indices that represent the market sectors in which the Fund primarily invests. 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

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]

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Total Returns for Institutional Class 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

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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.

Bar Chart Closing [Text Block]

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Highest Quarterly Return:

Fourth Quarter 2020, 27.47%

Lowest Quarterly Return:

First Quarter 2020, -33.76%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns(for the periods ended December 31, 2023)

Performance Table Closing [Text Block]

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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 Funds I) | (Loomis Sayles Small Cap Value Fund) | Risk Lose Money [Member]

Prospectus:

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Risk [Text Block]

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You may lose money by investing in the Fund.

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Risk Not Insured Depository Institution [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Credit/Counterparty Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Liquidity Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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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. 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 equity 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. 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.

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Market/Issuer Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Currency Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Cybersecurity and Technology Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Derivatives Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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Derivatives Risk is the risk that the value of the Fund’s derivative investments such as forward currency contracts, options and futures 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 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.

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Emerging Markets Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Equity Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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Equity Securities Risk is the risk that the value of a stock may decline for a number of reasons that relate directly to the issuer, such as management performance, financial leverage and reduced demand for the issuer’s goods and services, or the equity markets generally. Value stocks can perform differently from the market as a whole and from other types of stocks. Value stocks also present the risk that their lower valuations fairly reflect their business prospects and that investors will not agree that the stocks represent favorable investment opportunities, and they may fall out of favor with investors and underperform growth stocks during any given period. 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.

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Foreign Securities Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Leverage Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Management Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

Management Risk is the risk that Loomis Sayles’ investment techniques will be unsuccessful and cause the Fund to incur losses.

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Small-Capitalization Companies Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | REITs Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

rr_RiskTextBlock

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Investments in Other Investment Companies Risk [Member]

Prospectus:

rr_ProspectusTable

Risk [Text Block]

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Investments in Other Investment Companies Risk is the risk that the Fund will indirectly bear the management service and other fees of the other investment company in addition to its own expenses.

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Russell 3000® Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

25.96%

^[15]

Past 5 Years

rr_AverageAnnualReturnYear05

15.16%

^[15]

Past 10 Years

rr_AverageAnnualReturnYear10

11.48%

^[15]

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Russell 2000® Value Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

14.65%

Past 5 Years

rr_AverageAnnualReturnYear05

10.00%

Past 10 Years

rr_AverageAnnualReturnYear10

6.76%

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Russell 2000® Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

16.93%

Past 5 Years

rr_AverageAnnualReturnYear05

9.97%

Past 10 Years

rr_AverageAnnualReturnYear10

7.16%

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Institutional Class

Prospectus:

rr_ProspectusTable

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.75%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.21%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.96%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.06%

^[16]

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.90%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 92

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

300

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

525

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,173

Annual Return 2014

rr_AnnualReturn2014

5.33%

Annual Return 2015

rr_AnnualReturn2015

(3.36%)

Annual Return 2016

rr_AnnualReturn2016

26.47%

Annual Return 2017

rr_AnnualReturn2017

10.02%

Annual Return 2018

rr_AnnualReturn2018

(16.52%)

Annual Return 2019

rr_AnnualReturn2019

25.08%

Annual Return 2020

rr_AnnualReturn2020

2.18%

Annual Return 2021

rr_AnnualReturn2021

29.01%

Annual Return 2022

rr_AnnualReturn2022

(11.54%)

Annual Return 2023

rr_AnnualReturn2023

19.45%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

27.47%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2020

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(33.76%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2020

Past 1 Year

rr_AverageAnnualReturnYear01

19.45%

Past 5 Years

rr_AverageAnnualReturnYear05

11.75%

Past 10 Years

rr_AverageAnnualReturnYear10

7.50%

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Institutional Class | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

14.68%

Past 5 Years

rr_AverageAnnualReturnYear05

8.56%

Past 10 Years

rr_AverageAnnualReturnYear10

4.51%

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

14.96%

Past 5 Years

rr_AverageAnnualReturnYear05

9.08%

Past 10 Years

rr_AverageAnnualReturnYear10

5.45%

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Retail Class

Prospectus:

rr_ProspectusTable

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.75%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.21%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

1.21%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.06%

^[16]

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

1.15%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 117

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

378

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

659

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,461

Past 1 Year

rr_AverageAnnualReturnYear01

19.10%

Past 5 Years

rr_AverageAnnualReturnYear05

11.47%

Past 10 Years

rr_AverageAnnualReturnYear10

7.23%

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Admin Class

Prospectus:

rr_ProspectusTable

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.75%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.46%

^[17]

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

1.46%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.06%

^[16]

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

1.40%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 143

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

456

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

792

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,741

Past 1 Year

rr_AverageAnnualReturnYear01

18.81%

Past 5 Years

rr_AverageAnnualReturnYear05

11.18%

Past 10 Years

rr_AverageAnnualReturnYear10

6.96%

(Loomis Sayles Funds I) | (Loomis Sayles Small Cap Value Fund) | Class N

Prospectus:

rr_ProspectusTable

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.75%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.12%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.87%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.02%

^[16]

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.85%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 87

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

276

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

480

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,071

Past 1 Year

rr_AverageAnnualReturnYear01

19.46%

Past 5 Years

rr_AverageAnnualReturnYear05

11.80%

Past 10 Years

rr_AverageAnnualReturnYear10

7.56%

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

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Investment Goal

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund’s investment objective is above-average total 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 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 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

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

138.00%

Strategy [Heading]

rr_StrategyHeading

Investments, Risks and PerformancePrincipal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in fixed-income securities (for example, bonds and other investments that Loomis Sayles believes have similar economic characteristics, such as notes, debentures and loans). It is anticipated that the Fund’s weighted average duration will generally be between two and five years. 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.

The Fund will purchase only investment-grade fixed-income securities, which are those securities that are rated in one of the top four rating categories at the time of purchase by at least one of the three major ratings agencies (Moody’s Investors Service, Inc., Fitch Investor Services, Inc. or S&P Global Ratings) or, if unrated, are determined by Loomis Sayles to be of comparable quality. The Fund may continue to hold up to 10% of its net assets in securities that are downgraded to a rating below investment-grade subsequent to their purchase if Loomis Sayles believes it is appropriate to do so.

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 including, 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).

Three themes typically drive the Fund’s investment approach. First, Loomis Sayles generally seeks fixed-income securities that are attractively valued relative to the Loomis Sayles’ credit research team’s assessment of credit risk. The broad coverage combined with the objective of identifying attractive investment opportunities makes this an important component of the investment approach. Second, the Fund may invest significantly in securities the prices of which Loomis Sayles believes are more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates. These securities may not have a direct correlation with changes in interest rates, thus helping to manage interest rate risk and to offer diversified sources for return. Third, Loomis Sayles analyzes different sectors of the economy and differences in the yields (“spreads”) of various fixed-income securities in an effort to find securities that it believes may produce attractive returns for the Fund in comparison to their risk.

The Fund may invest up to 20% of its assets in U.S. dollar-denominated foreign securities, including emerging market securities. The Fund may invest without limit in obligations of supranational entities (e.g., the World Bank). Although certain securities purchased by the Fund may be issued by domestic companies incorporated outside of the United States, the Adviser does not consider these securities to be foreign if the issuer is included in the U.S. fixed-income indices published by Bloomberg. The Fund may also invest in mortgage-related securities, including mortgage dollar rolls. The Fund may also engage in futures transactions for hedging and investment purposes.

The fixed-income securities in which the Fund may invest include, among other things, corporate bond and other debt securities (including junior and senior bonds), U.S. government securities, zero-coupon securities, collateralized loan obligations, mortgage-backed securities and other asset-backed securities, real estate investment trusts (“REITs”), securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A securities”) and other privately placed investments such as private credit investments.

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, ten-year and life-of-class periods (as applicable) compare to those of a broad-based securities market index that reflects the performance of the overall market applicable to the Fund and an additional index that represents the market sectors in which the Fund primarily invests. 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

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]

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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.

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

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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]

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Highest Quarterly Return:

Second Quarter 2020, 5.03%

Lowest Quarterly Return:

First Quarter 2022, -4.85%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns(for the periods ended December 31, 2023)

Performance Table Closing [Text Block]

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Effective August 31, 2016, the Fund’s Retail Class shares and Institutional Class shares were redesignated as Class A shares and Class Y shares, respectively. Accordingly, the returns shown in the table for Class A shares prior to August 31, 2016 are those of Retail Class shares, restated to reflect the sales loads of Class A shares, and the returns in the table for Class Y shares prior to August 31, 2016 are those of Institutional Class shares. Prior to the inception of Class C shares (August 31, 2016), performance is that of Retail Class shares, restated to reflect the higher net expenses and sales loads of Class C shares.

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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Risk Lose Money [Member]

Prospectus:

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Risk [Text Block]

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You may lose money by investing in the Fund.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Risk Not Insured Depository Institution [Member]

Prospectus:

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Risk [Text Block]

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(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Credit/Counterparty Risk [Member]

Prospectus:

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Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Liquidity Risk [Member]

Prospectus:

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Risk [Text Block]

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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 equity 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. Derivatives, and particularly OTC derivatives, are generally subject to liquidity risk as well. 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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Market/Issuer Risk [Member]

Prospectus:

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Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Interest Rate Risk [Member]

Prospectus:

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Risk [Text Block]

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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. Monetary policy measures have in the past, and may in the future, exacerbate risks associated with rising interest rates.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Currency Risk [Member]

Prospectus:

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Risk [Text Block]

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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 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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Cybersecurity and Technology Risk [Member]

Prospectus:

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Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Derivatives Risk [Member]

Prospectus:

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Risk [Text Block]

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Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including futures transactions) 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 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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Emerging Markets Risk [Member]

Prospectus:

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Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Foreign Securities Risk [Member]

Prospectus:

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Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Large Investor Risk [Member]

Prospectus:

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Risk [Text Block]

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Large Investor Risk: Ownership of shares of the Fund may be concentrated in one or a few large investors. Such investors may redeem shares in large quantities or on a frequent basis. Redemptions by a large investor can affect the performance of the Fund, may increase realized capital gains, including short-term capital gains taxable as ordinary income, may accelerate the realization of taxable income to shareholders and may increase transaction costs. These transactions potentially limit the use of any capital loss carryforwards and certain other losses to offset future realized capital gains (if any). Such transactions may also increase the Fund’s expenses.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Leverage Risk [Member]

Prospectus:

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Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Management Risk [Member]

Prospectus:

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Risk [Text Block]

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Management Risk: A strategy used by the Fund’s portfolio managers may fail to produce the intended result.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Mortgage-Related and Asset-Backed Securities Risk [Member]

Prospectus:

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Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Below Investment Grade Fixed-Income Securities Risk [Member]

Prospectus:

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Risk [Text Block]

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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.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | REITs Risk [Member]

Prospectus:

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Risk [Text Block]

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REITs Risk: Investments in the real estate industry, including REITs, are particularly sensitive to economic downturns and are sensitive to factors such as changes in real estate values, property taxes and tax laws, interest rates, cash flow of underlying real estate assets, occupancy rates, government regulations affecting zoning, land use and rents and the management skill and creditworthiness of the issuer. Companies in the real estate industry also may be subject to liabilities under environmental and hazardous waste laws. In addition, the value of a REIT is affected by changes in the value of the properties owned by the REIT or mortgage loans held by the REIT. REITs are also subject to default and prepayment risk. Many REITs are highly leveraged, increasing their risk. The Fund will indirectly bear its proportionate share of expenses, including management fees, paid by each REIT in which it invests in addition to the expenses of the Fund.

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Bloomberg U.S. Aggregate Bond Index

Prospectus:

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Past 1 Year

rr_AverageAnnualReturnYear01

5.53%

^[18]

Past 5 Years

rr_AverageAnnualReturnYear05

1.10%

^[18]

Past 10 Years

rr_AverageAnnualReturnYear10

1.81%

^[18]

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Bloomberg U.S. Intermediate Government/Credit Bond Index

Prospectus:

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Past 1 Year

rr_AverageAnnualReturnYear01

5.24%

Past 5 Years

rr_AverageAnnualReturnYear05

1.59%

Past 10 Years

rr_AverageAnnualReturnYear10

1.72%

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration 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

^[19]

Redemption Fee (as a percentage of Amount Redeemed)

rr_RedemptionFeeOverRedemption

none

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.25%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.21%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.71%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.06%

^[20],[21]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

0.65%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 489

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

637

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

798

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,265

Past 1 Year

rr_AverageAnnualReturnYear01

0.90%

Past 5 Years

rr_AverageAnnualReturnYear05

0.90%

Past 10 Years

rr_AverageAnnualReturnYear10

1.35%

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Class C

Prospectus:

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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

0.25%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.21%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.46%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.06%

^[20],[21]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

1.40%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 243

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

456

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

792

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,537

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

143

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

456

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

792

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,537

Past 1 Year

rr_AverageAnnualReturnYear01

3.66%

Past 5 Years

rr_AverageAnnualReturnYear05

1.03%

Past 10 Years

rr_AverageAnnualReturnYear10

1.18%

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration 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

0.25%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.14%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.39%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[20],[21]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

0.35%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 36

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

121

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

215

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 489

Past 1 Year

rr_AverageAnnualReturnYear01

5.81%

Since Inception

rr_AverageAnnualReturnSinceInception

1.95%

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Class N | Bloomberg U.S. Aggregate Bond Index

Prospectus:

rr_ProspectusTable

Since Inception

rr_AverageAnnualReturnSinceInception

0.90%

^[18]

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Class N | Bloomberg U.S. Intermediate Government/Credit Bond Index

Prospectus:

rr_ProspectusTable

Since Inception

rr_AverageAnnualReturnSinceInception

1.48%

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration 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

0.25%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.21%

^[22]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.71%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.06%

^[20],[21]

Total Annual Fund Operating Expenses After Expense Reimbursement

rr_NetExpensesOverAssets

0.65%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 315

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

465

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

629

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,105

Past 1 Year

rr_AverageAnnualReturnYear01

2.70%

Past 5 Years

rr_AverageAnnualReturnYear05

1.25%

Past 10 Years

rr_AverageAnnualReturnYear10

1.54%

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration 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

0.25%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.21%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.46%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.06%

^[20],[21]

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

142

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

252

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 573

Annual Return 2014

rr_AnnualReturn2014

3.87%

Annual Return 2015

rr_AnnualReturn2015

0.76%

Annual Return 2016

rr_AnnualReturn2016

2.74%

Annual Return 2017

rr_AnnualReturn2017

2.66%

Annual Return 2018

rr_AnnualReturn2018

0.52%

Annual Return 2019

rr_AnnualReturn2019

7.64%

Annual Return 2020

rr_AnnualReturn2020

7.74%

Annual Return 2021

rr_AnnualReturn2021

(1.38%)

Annual Return 2022

rr_AnnualReturn2022

(8.55%)

Annual Return 2023

rr_AnnualReturn2023

5.75%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return:

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

5.03%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2020

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return:

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(4.85%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2022

Past 1 Year

rr_AverageAnnualReturnYear01

5.75%

Past 5 Years

rr_AverageAnnualReturnYear05

2.04%

Past 10 Years

rr_AverageAnnualReturnYear10

2.07%

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Class Y | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

4.13%

Past 5 Years

rr_AverageAnnualReturnYear05

0.78%

Past 10 Years

rr_AverageAnnualReturnYear10

0.87%

(Loomis Sayles Funds I) | (Loomis Sayles Intermediate Duration Bond Fund) | Class Y | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

3.37%

Past 5 Years

rr_AverageAnnualReturnYear05

1.05%

Past 10 Years

rr_AverageAnnualReturnYear10

1.07%

[1]

The amounts shown in the table are 0.00% to reflect the fact that the Fund does not pay any advisory, administration or distribution and service fees, and that Loomis, Sayles & Company, L.P. (“Loomis Sayles” or the “Adviser”) has agreed to pay certain expenses of the Fund. You should be aware, however, that shares of the Fund are available only to institutional investment advisory clients of Loomis Sayles and Natixis Advisors, LLC (“Natixis Advisors”) and to participants in certain approved “wrap fee” programs sponsored by broker-dealers and investment advisers that may be affiliated or unaffiliated with the Fund, Loomis Sayles or Natixis Advisors. The institutional investment advisory clients of Loomis Sayles and Natixis Advisors pay Loomis Sayles or Natixis Advisors a fee for their investment advisory services, while participants in “wrap fee” programs pay a “wrap” fee to the program’s sponsor. The “wrap fee” program sponsors in turn pay fees to Natixis Advisors. Participants in “wrap fee” programs should carefully read the wrap fee brochure provided to them by their program’s sponsor. The brochure is required to include information about the fees charged by the “wrap fee” program sponsor and the fees paid by such sponsor to Natixis Advisors. Investors pay no additional fees or expenses to purchase shares of the Fund. Investors will, however, indirectly pay a proportionate share of those costs, such as brokerage commissions, taxes and extraordinary expenses that are borne by the Fund through a reduction in their net asset value. See the section “Management” in the Statutory Prospectus.

[2]

Effective February 1, 2024, the Fund’s primary broad-based performance index changed to the Bloomberg U.S. Aggregate Bond Index. The Bloomberg U.S. Aggregate Bond Index is a broad-based securities market index that represents the overall market applicable to the Fund. The Fund will retain the Bloomberg U.S. Corporate High Yield Bond Index as its additional benchmark for performance comparison.

[3]

[4]

Effective February 1, 2024, the Fund’s primary broad-based performance index changed to the Bloomberg U.S. Aggregate Bond Index. The Bloomberg U.S. Aggregate Bond Index is a broad-based securities market index that represents the overall market applicable to the Fund. The Fund will retain the Bloomberg U.S. Securitized Bond Index as its additional benchmark for performance comparison.

[5]

Effective February 1, 2024, the Fund’s primary broad-based performance index changed to the Bloomberg U.S. Aggregate Bond Index. The Bloomberg U.S. Aggregate Bond Index is a broad-based securities market index that represents the overall market applicable to the Fund. The Bloomberg U.S. Aggregate Bond Index replaced the Bloomberg U.S. Government/Credit Bond Index as the Fund’s primary benchmark because the Fund believes it provides a more appropriate comparison to the Fund’s investable universe.

[6]

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 0.65% of the Fund’s average daily net assets, 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, 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 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.

[7]

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 0.69%, 0.94% and 0.64% 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, 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.

[8]

Effective February 1, 2024, the Fund’s primary broad-based performance index changed to the Bloomberg U.S. Aggregate Bond Index. The Bloomberg U.S. Aggregate Bond Index is a broad-based securities market index that represents the overall market applicable to the Fund. The Fund will retain the Bloomberg U.S. TlPS Index as its additional benchmark for performance comparison.

[9]

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, 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.

[10]

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, 2025 and may be terminated before then only with the consent of the Fund’s Board of Trustees.

[11]

Effective February 1, 2024, the Fund’s primary broad-based performance index changed to the Bloomberg U.S. Aggregate Bond Index. The Bloomberg U.S. Aggregate Bond Index is a broad-based securities market index that represents the overall market applicable to the Fund. The Fund will retain the Bloomberg U.S. Corporate High-Yield Bond Index as its additional benchmark for performance comparison.

[12]

1	The Fund’s operating expenses have been restated to reflect a reduction in management fees, effective as of July 1, 2023, as if such reduction had been in effect during the fiscal year ended September 30, 2023. The information has been restated to better reflect anticipated expenses of the Fund.

[13]

2	Other expenses include acquired fund fees and expenses of less than 0.01%.

[14]

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 0.73% of the Fund’s average daily net assets, 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, 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 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.

[15]

Effective February 1, 2024, the Fund’s primary broad-based performance index changed to the Russell 3000® Index. The Russell 3000® Index is a broad-based securities market index that represents the overall market applicable to the Fund. The Fund will retain the Russell 2000® VaIue Index and the Russell 2000® Index as its additional benchmarks for performance comparison.

[16]

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 0.90%, 1.15%, 1.40% and 0.85% of the Fund’s average daily net assets for Institutional Class shares, Retail Class shares, Admin 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, 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.

[17]

1	Other expenses include an administrative services fee of 0.25% for Admin Class shares.

[18]

Effective February 1, 2024, the Fund’s primary broad-based performance index changed to the Bloomberg U.S. Aggregate Bond Index. The Bloomberg U.S. Aggregate Bond Index is a broad-based securities market index that represents the overall market applicable to the Fund. The Fund will retain the Bloomberg U.S. Intermediate Government/Credit Bond Index as its additional benchmark for performance comparison.

[19]

*	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.

[20]

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 0.65%, 1.40%, 0.35%, 0.65% and 0.40% of the Fund’s average daily net assets for Class A, C, N, T and Y 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, 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.

[21]

[22]

1	Other expenses for Class T shares are estimated for the current fiscal year.