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Loomis Sayles Senior Floating Rate and Fixed Income Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading Loomis Sayles Senior Floating Rate and Fixed Income Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Fund seeks to provide a high level of current income.
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
32 of the Prospectus
, in Appendix A to the
Prospectus and on page 
104 in the section “Reduced Sales Charges” of the Statement of Additional Information (“SAI”).
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination March 31, 2022
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may
indicate higher transaction costs and may result in higher taxes for you if your Fund shares are held in a taxable account. These costs, which are not reflected
in annual fund operating expenses or in the example, affect the Fund’s performance. During its most recently ended fiscal year, the Fund’s portfolio turnover rate was
65
% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 65.00%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock
A 1.00% contingent deferred sales charge (“CDSC”) may apply to certain purchases of Class A shares of $1,000,000 or more that are redeemed within eighteen months of the
date of purchase.
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may 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.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 100,000
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates Other expenses for Class T shares are estimated for the current fiscal year.
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that
you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The
example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same, except that the example is
based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement assuming that such waiver and/or reimbursement will
only be in place through the dates noted above and on the Total Annual Fund Operating Expenses for the remaining periods. This example does not take into
account brokerage commissions and other fees to financial intermediaries that you may pay on your purchases and sales of shares of the Fund. Although your
actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption If shares are redeemed:
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If shares are not redeemed:
Strategy [Heading] rr_StrategyHeading Investments, Risks and Performance Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
Under normal market conditions, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in a combination of
adjustable floating rate loans and other floating rate debt instruments issued by U.S. and non-U.S. corporations or other business entities and fixed-income
securities, including derivatives that reference the returns of these instruments.
Under normal market conditions, the Fund will invest at least 65% of its net assets (plus any borrowings made for investment purposes) in floating rate loans
that either hold a senior position in the capital structure of the borrower, hold an equal ranking with other senior debt, or have characteristics (such as a
senior position secured by liens with other senior debt) that the Adviser believes justify treatment as senior debt (“Senior Loans”). The Fund may invest in
Senior Loans directly as an original lender or by assignment from a lender, or it may invest indirectly through participation agreements, interests in
collateralized loan obligations (“CLOs”) and derivatives that reference such instruments. Derivatives that reference the returns of Senior Loans may pay
returns at fixed rather than variable rates. The Fund’s investments may also include, but are not limited to, subordinated loans, below investment grade
corporate bonds and investment grade fixed-income debt securities. The fixed-income securities in which the Fund may invest include preferred stocks. The
Fund may invest in pay-in-kind (“PIK”) securities and zero-coupon securities. The Fund may receive debt, equity or other securities or instruments as a result of
the general restructuring of the debt of an issuer, the restructuring of a floating rate loan or as part of a package of securities acquired with a loan.
The Fund may invest any portion of its assets in securities of Canadian issuers and up to 20% of its net assets (plus any borrowings made for investment
purposes) in other foreign securities, including up to 10% of its net assets (plus any borrowings made for investment purposes) in emerging market securities.
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 Barclays.
Floating rate loans are debt obligations that have interest rates that adjust or “float” periodically (normally on a monthly or quarterly basis) based on a
generally recognized base rate, such as the London Inter-Bank Offered Rate (“LIBOR”) or the prime rate offered by one or more major U.S. banks. Floating rate
loans are generally unrated or rated less than investment grade and may be subject to restrictions on resale. The Fund may invest without limit in securities of
any rating, including those that are in default. The Fund has no requirements as to the range of maturities of the debt instruments in which it can invest or as
to the market capitalization of the issuers of those instruments.
The Fund can borrow up to one-third of the Fund’s assets (including the amount borrowed) and use other techniques to purchase investments, to manage its
cash flow or to redeem shares, a technique referred to as “leverage.” The Fund may also use derivative instruments, including, but not limited to, futures
contracts, forward contracts, swaps (including, among others, credit default swaps, credit default swap indices, loan-only credit default swaps and loan-only
credit default swap indices) and structured notes to try to increase the Fund’s leverage, to enhance income, to hedge against fluctuations in interest rates or
currency exchange rates, and/or as a substitute for the purchase or sale of securities.
The Fund may also invest in securities issued pursuant to Rule 144A under the Securities Act of 1933 (“Rule 144A securities”), convertible securities,
exchange-traded funds (“ETFs”), and mortgage-related securities, including adjustable rate mortgage securities and collateralized mortgage obligations,
asset-backed securities, and U.S. government securities (including its agencies, instrumentalities and sponsored entities). The Fund may also engage in
currency-related transactions. Except as provided above, the Fund is not limited in the percentage of its assets that it may invest in these instruments.
When deciding which securities to buy and sell, the Adviser will consider credit quality and whether credit quality is improving or declining, as well as return
potential, in the context of market and economic risks. In addition to security selection, the Adviser expects to use cycle evaluation in conjunction with sector
rotation in an effort to enhance or offset cyclical influences.
The Fund is “non-diversified.” As a non-diversified fund, the Fund may invest a greater percentage of its assets in a particular issuer and may invest in fewer
issuers, as compared with other mutual funds that are diversified.
The Fund expects to engage in active and frequent trading of securities and other instruments. Effects of frequent trading may include high transaction costs,
which may lower the Fund’s return, and realization of short-term capital gains, distributions of which are taxable to shareholders who are individuals as
ordinary income. Trading costs and tax effects associated with frequent trading may adversely affect the Fund’s performance.
With the exception of the 80% test described above, the percentage limitations set forth herein are not investment restrictions and the Fund may exceed
these limits from time to time. In addition, when calculating these exposures, the Fund may use the notional value or an adjusted notional value of a
derivative to reflect what the Adviser believes to be the most accurate assessment of the Fund’s real economic exposure.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
The principal risks of investing in the Fund are summarized below. The Fund does not represent a complete investment program.
You may lose money
by investing in the Fund.
 
The significance of any specific risk to an investment in the Fund will vary over time, depending on the composition of the Fund’s portfolio, market conditions,
and other factors. You should read all of the risk information presented below carefully, because any one or more of these risks may result in losses to the
Fund.
Senior Loans Risk:
 The risks associated with Senior Loans are similar to the risks of investing in below investment-grade securities. The Senior Loans in
which the Fund invests will generally not be rated investment grade by the rating agencies. Economic downturns generally lead to higher non-payment rates
and a Senior Loan could lose a substantial part of its value prior to default. Senior Loans are subject to credit risk, and secured Senior Loans may not be
adequately collateralized. The interest rates of Senior Loans reset frequently, and thus Senior Loans are subject to interest rate risk. Senior Loans are
generally less liquid than many other debt securities and there may also be less public information available about Senior Loans as compared to other debt
securities. Senior Loans may be difficult to value and may be subject to restrictions on resale, irregular trading activity, wide bid/ask spreads and extended
trade settlement periods. Transactions in Senior Loans may take significantly longer than seven days to settle and, as a result, proceeds related to the sale of
Senior Loans may not be readily available to make additional investments or to meet the Fund’s redemption obligations. In order to satisfy redemption
requests pending settlement of Senior Loans, the Fund may take a variety of measures, including, without limitation drawing on its cash and other short term
positions and borrowing from banks (including under the Fund’s line of credit), all of which may adversely affect the Fund’s performance. With limited
exceptions, the Adviser will take steps intended to ensure that it does not receive material non-public information about the issuers of Senior Loans who also
issue publicly traded securities, and therefore the Adviser may have less information than other investors about certain of the Senior Loans in which it seeks
to invest. Investing in Senior Loan participations exposes the Fund to the credit of the counterparty issuing the participation in addition to the credit of the
ultimate borrower.
Liquidity Risk:
  Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it
expects. Decreases in the number of financial institutions willing to make markets in the Fund’s investments or in their capacity or willingness to transact may
increase the Fund’s exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also
negatively impact the liquidity of the Fund’s investments when it needs to dispose of them. If the Fund is forced to sell its investments at an unfavorable time
and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. Securities acquired in a private
placement, such as Rule 144A securities, are generally subject to significant liquidity risk because they are subject to strict restrictions on resale and there
may be no liquid secondary market or ready purchaser for such securities. Derivatives, and particularly over-the-counter (“OTC’”) derivatives, are generally
subject to liquidity risk as well. Liquidity issues may also make it difficult to value the Fund’s investments.
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.
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. In the event of bankruptcy
of a borrower, the Fund could experience delays or limitations with respect to its ability to realize the benefits of the collateral securing a Senior Loan. 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. The value of loans made to such borrowers is likely to be more sensitive to adverse news about the
borrower, markets or economy. 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 risks 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.
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.
Management Risk:
A strategy used by the Fund’s 
portfolio managers may fail to produce the intended result.
 
Borrowing and Leverage Risk:
Borrowing and other investment techniques that utilize leverage, including use of derivatives, will increase the Fund’s
exposure to fluctuations in the prices of its assets and, therefore, the volatility of its share price. This magnifies the potential for gain and the risk of loss.
Leverage may also cause the Fund to liquidate positions at unfavorable times or prices. The costs of leverage, such as interest on borrowed funds, will
increase the Fund’s expenses.
Derivatives Risk:
Derivative instruments (such as those in which the Fund may invest, including futures contracts, forward contracts, swaps and structured
notes) 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 markets 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 the credit risk relating to the other party to
a derivative contract (which is greater for forward currency contracts, swaps and other OTC derivatives), the risk of difficulties in pricing and valuation, the
risk that changes in the value of a derivative may not correlate as expected with changes in the value of relevant assets, rates or indices; liquidity risk;
allocation risk and the risk of losing more than the initial margin (if any) required to initiate derivatives positions. There is also the risk that the Fund may be
unable to terminate or sell a derivative position at an advantageous time or price. The Fund’s derivative counterparties may experience financial difficulties or
otherwise be unwilling or unable to honor their obligations, possibly resulting in losses to the Fund.
Emerging Markets Risk:
In addition to the risks of investing in foreign investments generally, emerging markets investments are subject to greater risks
arising from political or economic instability, nationalization or confiscatory taxation, currency exchange restrictions, sanctions by other countries (such as the
United States) and an issuer’s unwillingness or inability to make principal or interest payments on its obligations. Emerging markets companies may be
smaller and have shorter operating histories than companies in developed markets.
Foreign Securities Risk:
Investments in foreign securities may be subject to greater political, economic, environmental, credit
/counterparty and information
risks.
Foreign securities may be subject to higher volatility than U.S. securities, varying degrees of regulation and limited liquidity.
Interest Rate Risk:
Interest rate risk is the risk that the value of the Fund’s investments will fall if interest rates rise.
 Generally, the value of fixed-income
securities rises when prevailing interest rates fall and falls when interest rates rise.  Interest rate risk generally is greater for funds that invest in fixed-income
securities with relatively longer durations than for funds that invest in fixed-income securities with shorter durations. 
Senior Loans typically have adjustable
interest rates. As a result, it is expected that the values of Senior Loans held by the Fund will fluctuate less in response to interest rate changes than will
fixed-rate debt securities; however, the interest rates paid by these loans will generally decrease if interest rates fall. Senior Loans and other fixed-income
securities are subject to the risk that borrowers pay off the debts sooner than expected, possibly requiring the Fund to re-invest in lower-yielding securities.
The value 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 monetary policy may affect the level of interest rates. 
Investments in Other Investment Companies Risk:
The Fund will indirectly bear the management, service and other fees of any other investment
companies, including ETFs, in which it invests in addition to its own expenses.
LIBOR Risk:
LIBOR risk is the risk that the transition away from the London Interbank Offered Rate (“LIBOR”) may lead to increased volatility and illiquidity in
markets that are tied to LIBOR. LIBOR is a benchmark interest rate that is used extensively as a “reference rate” for financial instruments, including many
corporate and municipal bonds, bank loans, asset-backed and mortgage-related securities, interest rate swaps and other derivatives. Additionally, the Fund
may borrow money at rates that are based on LIBOR. In July 2017, the head of the United Kingdom Financial Conduct Authority, the agency that oversees
LIBOR, announced that after 2021 it will cease its active encouragement of banks to provide the quotations needed to sustain LIBOR. That announcement
suggests that LIBOR may cease to be published after that time. The transition away from LIBOR poses a number of other risks, including changed values of
LIBOR-related investments and reduced effectiveness of hedging strategies, each of which may adversely affect the Fund’s performance.
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.
Mortgage-Related and Asset-Backed Securities Risk:
In addition to the risks associated with investments in fixed-income securities generally (for
example, credit, liquidity 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
.
Non-Diversification Risk:
Compared with other mutual funds, the Fund may invest a greater percentage of its assets in a particular issuer and may invest
in fewer issuers. Therefore, the Fund may have more risk because changes in the value of a single security or the impact of a single economic, political or
regulatory occurrence may have a greater adverse impact on the Fund’s net asset value.
Risk Lose Money [Text] rr_RiskLoseMoney You may lose money by investing in the Fund.
Risk Nondiversified Status [Text] rr_RiskNondiversifiedStatus Non-Diversification Risk: Compared with other mutual funds, the Fund may invest a greater percentage of its assets in a particular issuer and may invest in fewer issuers. Therefore, the Fund may have more risk because changes in the value of a single security or the impact of a single economic, political or regulatory occurrence may have a greater adverse impact on the Fund’s net asset value.
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, life-of-class
and life-of-fund periods (as applicable) compare to
those of a broad measure of market performance.
The Fund’s past performance (before and after taxes) does not necessarily indicate how the Fund will
perform in the future.
Updated performance information is available online at 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.
Effective May 1, 2021, Class C shares will automatically convert to Class A shares after eight years. Class C total returns in the table below do not reflect the
automatic conversion of Class C shares to Class A shares after eight years.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual returns for the one-year, five-year, life-of-class and life-of-fund periods (as applicable) compare to those of a broad measure of market performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 800-225-5478
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress im.natixis.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund’s past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Total Returns for Class Y Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The chart does not reflect any sales charge that you may be required to pay when you buy or redeem the Fund’s shares. A sales charge will reduce your return.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Highest Quarterly Return:

Second Quarter 2020,
10.92%

Lowest Quarterly Return:

First Quarter 2020,
-16.32%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2020)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown for only one class of the Fund. After-tax returns for the other classes of the Fund will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
The Fund did not have Class T shares outstanding during the periods shown above. The returns of Class T shares would have been substantially similar to the
returns of the Fund’s other share classes because they would have been invested in the same portfolio of securities and would only differ to the extent the
other share classes did not have the same expenses. Performance of Class T shares shown above is that of Class A shares, which have the same expenses as
Class T shares, restated to reflect the different sales load applicable to Class T shares.
After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who
hold their shares through tax-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.
The after-tax returns are shown for only one class of the Fund. After-tax returns for the other classes of the Fund will vary. Index
performance reflects no deduction for fees, expenses or taxes.
Loomis Sayles Senior Floating Rate and Fixed Income Fund | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 3.50%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther none [1]
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.35%
Total annual fund operating expenses rr_ExpensesOverAssets 1.20%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.13% [2],[3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.07%
1 year rr_ExpenseExampleYear01 $ 455
3 years rr_ExpenseExampleYear03 705
5 years rr_ExpenseExampleYear05 975
10 years rr_ExpenseExampleYear10 $ 1,743
Past 1 Year rr_AverageAnnualReturnYear01 (2.42%)
Past 5 Years rr_AverageAnnualReturnYear05 3.68%
Life of Class N / Life of Fund rr_AverageAnnualReturnSinceInception 4.40%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2011
Loomis Sayles Senior Floating Rate and Fixed Income Fund | Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther 1.00%
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other expenses rr_OtherExpensesOverAssets 0.35%
Total annual fund operating expenses rr_ExpensesOverAssets 1.95%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.13% [2],[3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.82%
1 year rr_ExpenseExampleYear01 $ 285
3 years rr_ExpenseExampleYear03 600
5 years rr_ExpenseExampleYear05 1,040
10 years rr_ExpenseExampleYear10 2,264
1 year rr_ExpenseExampleNoRedemptionYear01 185
3 years rr_ExpenseExampleNoRedemptionYear03 600
5 years rr_ExpenseExampleNoRedemptionYear05 1,040
10 years rr_ExpenseExampleNoRedemptionYear10 $ 2,264
Past 1 Year rr_AverageAnnualReturnYear01 (0.57%)
Past 5 Years rr_AverageAnnualReturnYear05 3.64%
Life of Class N / Life of Fund rr_AverageAnnualReturnSinceInception 4.02%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2011
Loomis Sayles Senior Floating Rate and Fixed Income Fund | Class N  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.64%
Total annual fund operating expenses rr_ExpensesOverAssets 1.24%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.47% [2],[3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.77%
1 year rr_ExpenseExampleYear01 $ 79
3 years rr_ExpenseExampleYear03 347
5 years rr_ExpenseExampleYear05 636
10 years rr_ExpenseExampleYear10 $ 1,458
Past 1 Year rr_AverageAnnualReturnYear01 1.34%
Past 5 Years rr_AverageAnnualReturnYear05
Life of Class N / Life of Fund rr_AverageAnnualReturnSinceInception 2.91%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 31, 2017
Loomis Sayles Senior Floating Rate and Fixed Income Fund | Class T  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.50%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other expenses rr_OtherExpensesOverAssets 0.35% [4]
Total annual fund operating expenses rr_ExpensesOverAssets 1.20%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.13% [2],[3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 1.07%
1 year rr_ExpenseExampleYear01 $ 356
3 years rr_ExpenseExampleYear03 609
5 years rr_ExpenseExampleYear05 881
10 years rr_ExpenseExampleYear10 $ 1,657
Past 1 Year rr_AverageAnnualReturnYear01 (1.39%)
Past 5 Years rr_AverageAnnualReturnYear05 3.89%
Life of Class N / Life of Fund rr_AverageAnnualReturnSinceInception 4.52%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2011
Loomis Sayles Senior Floating Rate and Fixed Income Fund | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Maximum sales charge (load) imposed on purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable) rr_MaximumDeferredSalesChargeOverOther none
Redemption fees rr_RedemptionFeeOverRedemption none
Management fees rr_ManagementFeesOverAssets 0.60%
Distribution and/or service (12b-1) fees rr_DistributionAndService12b1FeesOverAssets none
Other expenses rr_OtherExpensesOverAssets 0.35%
Total annual fund operating expenses rr_ExpensesOverAssets 0.95%
Fee waiver and/or expense reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.13% [2],[3]
Total annual fund operating expenses after fee waiver and/or expense reimbursement rr_NetExpensesOverAssets 0.82%
1 year rr_ExpenseExampleYear01 $ 84
3 years rr_ExpenseExampleYear03 290
5 years rr_ExpenseExampleYear05 513
10 years rr_ExpenseExampleYear10 $ 1,154
2012 rr_AnnualReturn2012 12.04%
2013 rr_AnnualReturn2013 6.39%
2014 rr_AnnualReturn2014 2.41%
2015 rr_AnnualReturn2015 (1.14%)
2016 rr_AnnualReturn2016 11.51%
2017 rr_AnnualReturn2017 5.06%
2018 rr_AnnualReturn2018 0.39%
2019 rr_AnnualReturn2019 5.41%
2020 rr_AnnualReturn2020 1.42%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Return:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 10.92%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Return:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (16.32%)
Past 1 Year rr_AverageAnnualReturnYear01 1.42%
Past 5 Years rr_AverageAnnualReturnYear05 4.69%
Life of Class N / Life of Fund rr_AverageAnnualReturnSinceInception 5.07%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2011
Loomis Sayles Senior Floating Rate and Fixed Income Fund | Return After Taxes on Distributions | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 (0.78%)
Past 5 Years rr_AverageAnnualReturnYear05 2.17%
Life of Class N / Life of Fund rr_AverageAnnualReturnSinceInception 2.50%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2011
Loomis Sayles Senior Floating Rate and Fixed Income Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 0.76%
Past 5 Years rr_AverageAnnualReturnYear05 2.48%
Life of Class N / Life of Fund rr_AverageAnnualReturnSinceInception 2.77%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2011
Loomis Sayles Senior Floating Rate and Fixed Income Fund | S&P / LSTA Leveraged Loan Index  
Risk/Return: rr_RiskReturnAbstract  
Past 1 Year rr_AverageAnnualReturnYear01 3.10%
Past 5 Years rr_AverageAnnualReturnYear05 5.21%
Life of Class N / Life of Fund rr_AverageAnnualReturnSinceInception 4.78%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 30, 2011
Loomis Sayles Senior Floating Rate and Fixed Income Fund | S&P / LSTA Leveraged Loan Index (3/31/17)  
Risk/Return: rr_RiskReturnAbstract  
Life of Class N / Life of Fund rr_AverageAnnualReturnSinceInception 4.00%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 31, 2017
[1] A 1.00% contingent deferred sales charge (“CDSC”) may apply to certain purchases of Class A shares of $1,000,000 or more that are redeemed within eighteen months of the date of purchase.
[2] 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 1.05%, 1.80%, 0.75%, 1.05% and 0.80% 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 March 31, 2022 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 the applicable expense limitations for Class A, C, N, T and Y shares. The Fund will not be obligated to repay any such waived/reimbursed fees or expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.
[3] Natixis Advisors, L.P. (“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 March 31, 2022 and may be terminated before then only with the consent of the Fund’s Board of Trustees.
[4] Other expenses for Class T shares are estimated for the current fiscal year.