485BPOS

Registration Nos. 033-39133

811-06241

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933	☐
Pre-Effective Amendment No.	☐
Post-Effective Amendment No. 87	☒

and/or

REGISTRATION STATEMENT

UNDER

THE INVESTMENT COMPANY ACT OF 1940	☐
Amendment No. 90	☒

(Check appropriate box or boxes.)

LOOMIS SAYLES FUNDS II

(Exact Name of Registrant as Specified in Charter)

888 Boylston Street, Boston, Massachusetts 02199-8197

(Address of principal executive offices) (Zip Code)

Registrant’s Telephone Number, including Area Code (617) 449-2822

Copy to:

Russell Kane, Esq. Natixis Distribution, L.P. 888 Boylston Street Boston, Massachusetts 02199-8197	John M. Loder, Esq. Ropes & Gray 800 Boylston Street Boston, Massachusetts 02199
(Name and Address of Agent for Service)

Approximate Date of Proposed Public Offering

It is proposed that this filing will become effective (check appropriate box):

☒ immediately upon filing pursuant to paragraph (b)

☐ on (date) pursuant to paragraph (b)

☐ 60 days after filing pursuant to paragraph (a)(1)

☐ on (date) pursuant to paragraph (a)(1)

☐ 75 days after filing pursuant to paragraph (a)(2)

☐ on (date) pursuant to paragraph (a)(2) of Rule 485.

If appropriate, check the following box:

☐ This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

LOOMIS SAYLES FUNDS II

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, and the Investment Company Act of 1940, as amended, the Registrant has duly caused Post-Effective Amendment No. 87 to its Registration Statement to be signed on its behalf by the undersigned, duly authorized, in the City of Boston, and the Commonwealth of Massachusetts on the 21^st day of February, 2019.

LOOMIS SAYLES FUNDS II
By:	/s/ David L. Giunta
	David L. Giunta
	President and Chief Executive Officer

Pursuant to the requirements of the Securities Act of 1933, as amended, this amendment to the Registration Statement has been signed below by the following persons in the capacities and on the date indicated.

Signature	Title	Date
/s/ David L. Giunta	President, Chief
David L. Giunta	Executive Officer and Trustee	February 21, 2019
/s/ Michael C. Kardok
Michael C. Kardok	Treasurer	February 21, 2019
Kevin P. Charleston*
Kevin P. Charleston	Trustee	February 21, 2019
Kenneth A. Drucker*
Kenneth A. Drucker	Trustee, Chairperson of the Board	February 21, 2019
Edmond J. English*
Edmond J. English	Trustee	February 21, 2019
Richard A. Goglia*
Richard A. Goglia	Trustee	February 21, 2019
Wendell J. Knox*
Wendell J. Knox	Trustee	February 21, 2019
Martin T. Meehan*
Martin T. Meehan	Trustee	February 21, 2019
Maureen Mitchell*
Maureen Mitchell	Trustee	February 21, 2019
James P. Palermo*
James P. Palermo	Trustee	February 21, 2019

Erik Sirri*
Erik Sirri	Trustee	February 21, 2019
Peter Smail*
Peter Smail	Trustee	February 21, 2019
Cynthia L. Walker*	Trustee	February 21, 2019
Cynthia L. Walker

*By:	/s/ Russell Kane
	Russell Kane
	Attorney-In-Fact 1
	February 21, 2019

¹ Powers of Attorney for Kevin P. Charleston, Kenneth A. Drucker, Edmond J. English, David L. Giunta, Richard A. Goglia, Wendell J. Knox, Martin T. Meehan, Maureen B. Mitchell, James P. Palermo, Erik R. Sirri, Peter J. Smail and Cynthia L. Walker dated December 5, 2018, effective December 10, 2018, designating John M. Loder, Russell Kane, Kirk Johnson and Michael Kardok as attorneys to sign for each Trustee is incorporated by reference to exhibit (q)(1) to PEA No. 86 filed on January 28, 2019.

Loomis Sayles Funds II

Exhibit Index

Exhibit	Exhibit Description
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase

XML

Label	Element	Value
Prospectus:	rr_ProspectusTable
Document Type	dei_DocumentType	485BPOS
Document Period End Date	dei_DocumentPeriodEndDate	Sep. 30, 2018
Registrant Name	dei_EntityRegistrantName	LOOMIS SAYLES FUNDS II
Central Index Key	dei_EntityCentralIndexKey	0000872649
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Jan. 28, 2019
Document Effective Date	dei_DocumentEffectiveDate	Feb. 01, 2019
Prospectus Date	rr_ProspectusDate	Feb. 01, 2019

XML

(Loomis Sayles Global Allocation Fund)

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

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

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Natixis Fund 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 49 of the Prospectus, in Appendix A to the Prospectus and on page 108 in the section "Reduced Sales Charges" of the Statement of Additional Information ("SAI").

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Shareholder Fees - (Loomis Sayles Global Allocation Fund) - USD ($)	Class A		Class C	Class N	Class T	Class Y
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	5.75%		none	none	2.50%	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	none	[1]	1.00%	none	none	none
Redemption fees	none		none	none	none	none

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Annual Fund Operating Expenses - (Loomis Sayles Global Allocation Fund)		Class A	Class C	Class N	Class T		Class Y
Management fees		0.75%	0.75%	0.75%	0.75%		0.75%
Distribution and/or service (12b-1) fees		0.25%	1.00%	none	0.25%		none
Other expenses		0.16%	0.16%	0.08%	0.16%	[1]	0.16%
Total annual fund operating expenses		1.16%	1.91%	0.83%	1.16%		0.91%
Fee waiver and/or expense reimbursement	[2],[3]	none	none	none	none		none
Total annual fund operating expenses after fee waiver and/or expense reimbursement		1.16%	1.91%	0.83%	1.16%		0.91%

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example - (Loomis Sayles Global Allocation Fund) - USD ($)	1 Year	3 Years	5 Years	10 Years
Class A	686	922	1,177	1,903
Class C	294	600	1,032	2,233
Class N	85	265	460	1,025
Class T	365	609	872	1,624
Class Y	93	290	504	1,120

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Expense Example, No Redemption - (Loomis Sayles Global Allocation Fund)	1 Year	3 Years	5 Years	10 Years
Class C | USD ($)	194	600	1,032	2,233

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 22% of the average value of its portfolio.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

Under normal market conditions, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in equity and fixed-income securities of U.S. and foreign issuers. Equity securities purchased by the Fund may include common stocks, preferred stocks, depositary receipts, warrants, securities convertible into common or preferred stocks, interests in real estate investment trusts ("REITs") and/or real estate-related securities and other equity-like interests in an issuer. Fixed-income securities purchased by the Fund may include bonds and other debt obligation of U.S. and foreign issuers, including but not limited to corporations, governments and supranational entities. The Fund will invest a significant portion of its assets outside the U.S., including securities of issuers located in emerging market countries.

The portfolio managers reallocate the Fund's assets between equity and fixed income securities based on their assessment of current market conditions and the relative opportunities within each asset class, among other factors. In deciding which equity securities to buy and sell, the Adviser generally looks to purchase quality companies at attractive valuations with the potential to grow intrinsic value over time. The Adviser uses discounted cash flow analysis, among other methods of analysis, to determine a company's intrinsic value. In deciding which fixed-income securities to buy and sell, the Adviser generally looks for securities that it believes are undervalued and have the potential for credit upgrades, which may include securities that are below investment grade (also known as "junk bonds").

The Fund may also invest in foreign currencies, collateralized mortgage obligations, collateralized loan obligations, zero-coupon securities, when-issued securities, REITs, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), mortgage-related securities, convertible securities and structured notes. The Fund may also engage in active and frequent trading of securities and engage in options or foreign currency transactions (such as forward currency contracts) for hedging and investment purposes and futures transactions and swap transactions (including credit default swaps). Frequent trading may produce high transaction costs and a high level of taxable capital gains, including short-term capital gains taxable as ordinary income, which may lower the Fund's return. The Adviser may hedge currency risk for the Fund (including "cross hedging" between two or more foreign currencies) if it believes the outlook for a particular foreign currency is unfavorable. Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

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.

Allocation Risk: The Fund's allocations between asset classes and market exposures may not be optimal in every market condition and may adversely affect the Fund's performance.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. The Fund will be subject to credit risks with respect to the counterparties of its derivatives transactions. Many of the protections afforded to participants on organized exchanges, such as the performance guarantee of an exchange clearing house, are not available in connection with over-the-counter ("OTC") derivatives transactions, such as foreign currency transactions. As a result, in instances when the Fund enters into OTC derivatives transactions, the Fund will be subject to the risk that its counterparties will not perform their obligations under the transactions and that the Fund will sustain losses or be unable to realize gains.

Currency Risk: Fluctuations in the exchange rates between different currencies may negatively affect an investment. The Fund may be subject to currency risk because it may invest in currency-related instruments and may invest in securities or other instruments denominated in, or that generate income denominated in, foreign currencies. The Fund may elect not to hedge currency risk, or may hedge such risk imperfectly, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged.

Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including options, forward currency contracts, futures transactions, structured notes and swap transactions (including credit default swaps)) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund's exposure to securities 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, such as options, forward currency contracts, futures transactions, structured notes and swap transactions (including credit default swaps) 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 required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives 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 the U.S. government 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.

Equity Securities Risk: The value of the Fund's investments in equity securities could be subject to unpredictable declines in the value of individual securities and periods of below-average performance in individual securities or in the equity market as a whole. 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.

Foreign Securities Risk: Investments in foreign securities may be subject to greater political, economic, environmental, credit/counterparty and information risks. The Fund's investments in foreign securities also are subject to foreign currency fluctuations and other foreign currency-related risks. Foreign securities may be subject to higher volatility than U.S. securities, varying degrees of regulation and limited liquidity.

Interest Rate Risk: Interest rate risk is the risk that the value of the Fund's investments will fall if interest rates rise. Generally, the value of fixed-income securities rises when prevailing interest rates fall and falls when interest rates rise. Interest rate risk generally is greater for funds that invest in fixed-income securities with relatively longer durations than for funds that invest in fixed-income securities with shorter durations. The value 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

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.

Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices 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 a fund's returns, and may lead to significant losses if investments are not successful.

Liquidity Risk: Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Decreases in the number of financial institutions willing to make markets in the Fund's investments or in their capacity or willingness to transact may increase the Fund's exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund's investments when it needs to dispose of them. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. 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. Non-exchange traded derivatives are generally subject to greater liquidity risk as well. Liquidity issues may also make it difficult to value the Fund's investments.

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

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 Securities Risk: In addition to the risks associated with investments in fixed-income securities generally (for example, credit, liquidity and valuation risk), mortgage-related securities are subject to the risks of the mortgages 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 security beyond the expected prepayment time, typically reducing the security's value. 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.

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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods (as applicable) compare to those of two broad measures of market performance. The Blended Index is an unmanaged, blended index composed of the following weights: 60% MSCI All Country World Index (Net) and 40% Bloomberg Barclays Global Aggregate Bond Index. The two indices composing the Blended Index measure, respectively, the performance of global equity securities and global investment grade fixed income securities. 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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Class Y Shares </b></div>

Highest Quarterly Return: Second Quarter 2009, 19.91%

Lowest Quarterly Return: Third Quarter 2011, -14.72%

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Average Annual Total Returns - (Loomis Sayles Global Allocation Fund)	Past 1 Year	Past 5 Years	Past 10 Years	Life of Class N	Inception Date
Class Y	(5.04%)	5.03%	11.44%
Class Y | Return After Taxes on Distributions	(6.11%)	3.95%	10.54%
Class Y | Return After Taxes on Distributions and Sale of Fund Shares	(2.27%)	3.75%	9.31%
Class A	(10.69%)	3.53%	10.51%
Class C	(6.83%)	3.99%	10.33%
Class N	(4.92%)			6.38%	Feb. 01, 2017
Class T	(7.62%)	4.24%	10.88%
MSCI All Country World Index (Net)	(9.42%)	4.26%	9.46%	4.71%
Blended Index	(6.00%)	3.12%	6.84%	4.07%

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 Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. 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 Growth Fund)

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

The Fund's investment goal is long-term growth of capital.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Natixis Fund 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 49 of the Prospectus, in Appendix A to the Prospectus and on page 108 in the section "Reduced Sales Charges" of the Statement of Additional Information ("SAI").

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Shareholder Fees - (Loomis Sayles Growth Fund) - USD ($)	Class A		Class C	Class N	Class T	Class Y
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	5.75%		none	none	2.50%	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	none	[1]	1.00%	none	none	none
Redemption fees	none		none	none	none	none

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Annual Fund Operating Expenses - (Loomis Sayles Growth Fund)		Class A	Class C	Class N	Class T		Class Y
Management fees		0.50%	0.50%	0.50%	0.50%		0.50%
Distribution and/or service (12b-1) fees		0.25%	1.00%	none	0.25%		none
Other expenses		0.15%	0.15%	0.08%	0.15%	[1]	0.15%
Total annual fund operating expenses		0.90%	1.65%	0.58%	0.90%		0.65%
Fee waiver and/or expense reimbursement	[2],[3]	none	none	none	none		none
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.90%	1.65%	0.58%	0.90%		0.65%

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example - (Loomis Sayles Growth Fund) - USD ($)	1 Year	3 Years	5 Years	10 Years
Class A	662	845	1,045	1,619
Class C	268	520	897	1,955
Class N	59	186	324	726
Class T	340	530	736	1,330
Class Y	66	208	362	810

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Expense Example, No Redemption - (Loomis Sayles Growth Fund)	1 Year	3 Years	5 Years	10 Years
Class C | USD ($)	168	520	897	1,955

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 11% of the average value of its portfolio.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

Under normal market conditions, the Fund will invest primarily in equity securities, including common stocks, convertible securities and warrants. The Fund focuses on stocks of large capitalization companies, but the Fund may invest in companies of any size.

The Fund normally invests across a wide range of sectors and industries. The Fund's portfolio manager employs a growth style of equity management, which means that the Fund seeks to invest in companies with sustainable competitive advantages, long-term structural growth drivers, attractive cash flow returns on invested capital, and management teams focused on creating long-term value for shareholders. The Fund's portfolio manager also aims to invest in companies when they trade at a significant discount to the estimate of intrinsic value.

The Fund will consider selling a portfolio investment when the portfolio manager believes an unfavorable structural change occurs within a given business or the markets in which it operates, a critical underlying investment assumption is flawed, when a more attractive reward-to-risk opportunity becomes available, when the current price fully reflects intrinsic value, or for other investment reasons which the portfolio manager deems appropriate.

The Fund may also invest up to 20% of its assets in foreign securities, including depositary receipts and emerging market 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 or if the security's country of risk defined by Bloomberg is the United States. The Fund may also engage in foreign currency transactions (including foreign currency forwards and foreign currency futures) for hedging purposes, invest in options for hedging and investment purposes and invest in securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"). Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

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.

Credit/Counterparty Risk: Credit/counterparty risk is the risk that the issuer or guarantor of a fixed-income security, or the counterparty to a derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. The Fund will be subject to credit risks with respect to the counterparties of its derivatives transactions. Many of the protections afforded to participants on organized exchanges, such as the performance guarantee of an exchange clearing house, are not available in connection with over-the-counter ("OTC") derivatives transactions, such as foreign currency transactions. As a result, in instances when the Fund enters into OTC derivatives transactions, the Fund will be subject to the risk that its counterparties will not perform their obligations under the transactions and that the Fund will sustain losses or be unable to realize gains.

Currency Risk: Fluctuations in the exchange rates between different currencies may negatively affect an investment. The Fund may be subject to currency risk because it may invest in currency related instruments and may invest in securities or other instruments denominated in, or that generate income denominated in, foreign currencies. The Fund may elect not to hedge currency risk, or may hedge such risk imperfectly, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged.

Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including foreign currency forwards, foreign currency futures and options) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund's exposure to securities market values, interest rates or currency exchange rates. It is possible that the Fund's liquid assets may be insufficient to support its obligations under its derivatives positions. The use of derivatives for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. The use of derivatives may cause the Fund to incur losses greater than those that would have occurred had derivatives not been used. The Fund's use of derivatives such as foreign currency forwards, foreign currency futures and options, involves other risks, such as the credit risk relating to the other party to a derivative contract (which is greater for forward currency contracts 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 required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives 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 the U.S. government 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.

Equity Securities Risk: The value of the Fund's investments in equity securities could be subject to unpredictable declines in the value of individual securities and periods of below-average performance in individual securities or in the equity market as a whole. Growth stocks are generally more sensitive to market movements than other types of stocks primarily because their stock prices are based heavily on future expectations. If the Adviser's assessment of the prospects for a company's growth is wrong, or if the Adviser's judgment of how other investors will value the company's growth is wrong, then the price of the company's stock may fall or not approach the value that the Adviser has placed on it. 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.

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.

Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices 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 a fund's returns, and may lead to significant losses if investments are not successful.

Liquidity Risk: Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Decreases in the number of financial institutions willing to make markets in the Fund's investments or in their capacity or willingness to transact may increase the Fund's exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund's investments when it needs to dispose of them. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. 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. Non-exchange traded derivatives are generally subject to greater liquidity risk as well. Liquidity issues may also make it difficult to value the Fund's investments.

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

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.

Small- and Mid-Capitalization Companies Risk: Compared to large-capitalization companies, small- and mid-capitalization companies are more likely to have limited product lines, markets or financial resources. Stocks of these companies often trade less frequently and in limited volume and their prices may fluctuate more than stocks of large-capitalization companies. As a result, it may be relatively more difficult for the Fund to buy and sell securities of small- and mid-capitalization companies.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

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 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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Class Y Shares </b></div>

Highest Quarterly Returns: Third Quarter 2010, 15.01%

Lowest Quarterly Return: Second Quarter 2010, -12.73%

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Average Annual Total Returns - (Loomis Sayles Growth Fund)	Past 1 Year	Past 5 Years	Past 10 Years	Life of Class N	Inception Date
Class Y	(2.48%)	10.89%	15.34%
Class Y | Return After Taxes on Distributions	(3.78%)	10.33%	15.01%
Class Y | Return After Taxes on Distributions and Sale of Fund Shares	(0.57%)	8.64%	13.03%
Class A	(8.32%)	9.31%	14.34%
Class C	(4.36%)	9.77%	14.19%
Class N	(2.39%)	10.93%		13.44%	Feb. 01, 2013
Class T	(5.13%)	10.06%	14.75%
Russell 1000® Growth Index	(1.51%)	10.40%	15.29%	13.18%

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 Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. 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 Limited Term Government and Agency Fund)

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

The Fund seeks high current return consistent with preservation of capital.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. 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 Fund 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 49 of the Prospectus, in Appendix A to the Prospectus and on page 108 in the section "Reduced Sales Charges" of the Statement of Additional Information ("SAI").

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Shareholder Fees - (Loomis Sayles Limited Term Government and Agency Fund) - USD ($)	Class A		Class C	Class N	Class T	Class Y
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	2.25%		none	none	2.50%	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	none	[1]	1.00%	none	none	none
Redemption fees	none		none	none	none	none

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Annual Fund Operating Expenses - (Loomis Sayles Limited Term Government and Agency Fund)		Class A	Class C	Class N	Class T		Class Y
Management fees		0.37%	0.37%	0.37%	0.37%		0.37%
Distribution and/or service (12b-1) fees		0.25%	1.00%	none	0.25%		none
Other expenses		0.18%	0.18%	0.11%	0.18%	[1]	0.18%
Total annual fund operating expenses		0.80%	1.55%	0.48%	0.80%		0.55%
Fee waiver and/or expense reimbursement	[2],[3]	none	none	0.02%	none		none
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.80%	1.55%	0.46%	0.80%		0.55%

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

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 for Class N 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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example - (Loomis Sayles Limited Term Government and Agency Fund) - USD ($)	1 Year	3 Years	5 Years	10 Years
Class A	305	475	659	1,193
Class C	258	490	845	1,845
Class N	47	152	267	602
Class T	330	499	683	1,215
Class Y	56	176	307	689

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Expense Example, No Redemption - (Loomis Sayles Limited Term Government and Agency Fund)	1 Year	3 Years	5 Years	10 Years
Class C | USD ($)	158	490	845	1,845

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 157% of the average value of its portfolio.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

Under normal market conditions, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in investments issued or guaranteed by the U.S. government, its agencies or instrumentalities.

The Adviser follows a total return-oriented investment approach in selecting securities for the Fund. It seeks securities that will provide the Fund with an average credit quality equal to the credit rating of the U.S. Government's long-term debt and an effective portfolio duration range of two to four years (although not all securities selected will have these characteristics and the Adviser may look for other characteristics if market conditions change). The Fund may invest in securities with credit quality above or below the credit rating of the U.S. Government's long-term debt. In determining credit quality, the Adviser will look to the highest credit rating assigned by S&P Global Ratings ("S&P"), Fitch Investor Services, Inc. ("Fitch") or Moody's Investors Service, Inc. ("Moody's").

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

In selecting investments for the Fund, the Adviser's research analysts work closely with the Fund's portfolio managers to develop an outlook on the economy from research produced by various financial firms and specific forecasting services or from economic data released by the U.S. and foreign governments as well as the Federal Reserve Bank. The analysts also conduct a thorough review of individual securities to identify what they consider attractive values in the U.S. government security marketplace through the use of quantitative tools such as internal and external computer systems and software. The Adviser continuously monitors an issuer's creditworthiness to assess whether the obligation remains an appropriate investment for the Fund. The Adviser seeks to balance opportunities for yield and price performance by combining macroeconomic analysis with individual security selection. It emphasizes securities that tend to perform particularly well in response to interest rate changes, such as U.S. Treasury securities in a declining interest rate environment and mortgage-backed or U.S. government agency securities in a steady or rising interest rate environment. The Adviser seeks to increase the opportunity for higher yields while maintaining the greater price stability that intermediate-term bonds have compared to bonds with longer maturities.

In connection with its principal investment strategies, the Fund may also invest in investment grade corporate notes and bonds, collateralized loan obligations, zero-coupon bonds, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), asset-backed securities and mortgage-related securities including mortgage dollar rolls. Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

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.

Agency Securities Risk: Certain debt securities issued or guaranteed by agencies of the U.S. government are guaranteed as to the payment of principal and interest by the relevant entity but have not been backed by the full faith and credit of the U.S. government. Instead, they have been supported only by the discretionary authority of the U.S. government to purchase the agency's obligations. An event affecting the guaranteeing entity could adversely affect the payment of principal or interest or both on the security and, therefore, these types of securities should be considered to be riskier than U.S. government securities.

Credit Risk: Credit risk is the risk that the issuer or the guarantor of a fixed-income security will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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 value 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

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. Liquidity issues may also make it difficult to value the Fund's investments.

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

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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

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 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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Class Y Shares </b> </div>

Highest Quarterly Return: Third Quarter 2009, 3.07%

Lowest Quarterly Return: Second Quarter 2013, -1.07%

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Average Annual Total Returns - (Loomis Sayles Limited Term Government and Agency Fund)	Past 1 Year	Past 5 Years	Past 10 Years	Life of Class N	Inception Date
Class Y	1.39%	1.15%	2.46%
Class Y | Return After Taxes on Distributions	0.49%	0.30%	1.51%
Class Y | Return After Taxes on Distributions and Sale of Fund Shares	0.81%	0.50%	1.52%
Class A	(1.15%)	0.44%	1.97%
Class C	(0.70%)	0.13%	1.43%
Class N	1.48%			1.35%	Feb. 01, 2017
Class T	(1.41%)	0.39%	1.94%
Bloomberg Barclays U.S. 1-5 Year Government Bond Index	1.53%	1.07%	1.39%	1.08%

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 Strategic Income Fund)

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

The Fund seeks high current income with a secondary objective of capital growth.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. 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 Fund 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 49 of the Prospectus, in Appendix A to the Prospectus and on page 108 in the section "Reduced Sales Charges" of the Statement of Additional Information ("SAI").

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Shareholder Fees - (Loomis Sayles Strategic Income Fund) - USD ($)	Class A		Class C	Class N	Class T	Class Y	Admin Class
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	4.25%		none	none	2.50%	none	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	none	[1]	1.00%	none	none	none	none
Redemption fees	none		none	none	none	none	none

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Annual Fund Operating Expenses - (Loomis Sayles Strategic Income Fund)		Class A	Class C	Class N	Class T		Class Y	Admin Class
Management fees		0.56%	0.56%	0.56%	0.56%		0.56%	0.56%
Distribution and/or service (12b-1) fees		0.25%	1.00%	none	0.25%		none	0.25%
Other expenses	[1]	0.15%	0.15%	0.07%	0.15%	[2]	0.15%	0.39%	[3]
Total annual fund operating expenses		0.96%	1.71%	0.63%	0.96%		0.71%	1.20%
Fee waiver and/or expense reimbursement	[4]	none	none	none	none		none	none
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.96%	1.71%	0.63%	0.96%		0.71%	1.20%

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example - (Loomis Sayles Strategic Income Fund) - USD ($)	1 Year	3 Years	5 Years	10 Years
Class A	519	718	933	1,553
Class C	274	539	928	2,019
Class N	64	202	351	786
Class T	345	548	768	1,399
Class Y	73	227	395	883
Admin Class	122	381	660	1,455

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Expense Example, No Redemption - (Loomis Sayles Strategic Income Fund)	1 Year	3 Years	5 Years	10 Years
Class C | USD ($)	174	539	928	2,019

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 6% of the average value of its portfolio.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

Under normal market conditions, the Fund will invest substantially all of its assets in income producing securities (including below investment grade securities, or "junk bonds") with a focus on U.S. corporate bonds, convertible securities, foreign debt instruments, including those in emerging markets and related foreign currency transactions, and U.S. government securities. Below investment grade fixed-income securities are rated below investment grade quality (i.e., none of the three major ratings agencies (Moody's Investors Service, Inc. ("Moody's"), Fitch Investors Services, Inc. ("Fitch") or S&P Global Ratings ("S&P")), have rated the securities in one of its top four rating categories) or, if the security is unrated, are determined by the Adviser to be of comparable quality. The Fund may invest up to 35% of its assets in preferred stocks and dividend-paying common stocks. The portfolio managers may shift the Fund's assets among various types of income-producing securities based upon changing market conditions. The Adviser performs its own extensive credit analyses to determine the creditworthiness and potential for capital appreciation of a security.

The Fund's portfolio managers use a flexible approach to identify securities in the global marketplace with characteristics including discounted price compared to economic value, undervalued credit ratings with strong or improving credit profiles and yield premium relative to its benchmark (although not all of the securities selected will have these attributes).

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

In selecting investments for the Fund, the Adviser utilizes the skills of its in-house team of more than 30 research analysts to cover a broad universe of industries, companies and markets. The Fund's portfolio managers take advantage of these extensive resources to identify securities that meet the Fund's investment criteria. The Adviser seeks to buy bonds that offer a positive yield advantage over the market and, in its view, have room to increase in price. It may also invest to take advantage of what the portfolio managers believe are temporary disparities in the yield of different segments of the market for U.S. government securities. The Adviser provides the portfolio managers with maximum flexibility to find investment opportunities in a wide range of markets, both domestic and foreign. This flexible approach provides the Fund with access to a wide array of investment opportunities. The three key sectors that the portfolio managers focus upon are U.S. corporate issues (including convertible securities), foreign debt securities and U.S. government securities. The Fund's portfolio managers maintain a core of the Fund's investments in corporate bond issues and shift its assets among other income-producing securities as opportunities develop. The Fund generally seeks to maintain a high level of diversification as a form of risk management.

In connection with its principal investment strategies, the Fund may also invest in securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), structured notes, collateralized loan obligations, zero-coupon bonds, pay-in-kind bonds, mortgage-related securities, stripped securities and futures, swaps (including credit default swaps) and foreign currency transactions (such as forward currency contracts) for hedging and investment purposes. Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. The Fund will be subject to credit risks with respect to the counterparties of its derivatives transactions. Many of the protections afforded to participants on organized exchanges, such as the performance guarantee of an exchange clearing house, are not available in connection with over-the-counter ("OTC") derivatives transactions, such as foreign currency transactions. As a result, in instances when the Fund enters into OTC derivatives transactions, the Fund will be subject to the risk that its counterparties will not perform their obligations under the transactions and that the Fund will sustain losses or be unable to realize gains.

Currency Risk: Fluctuations in the exchange rates between different currencies may negatively affect an investment. The Fund may be subject to currency risk because it may invest in currency-related instruments and may invest in securities or other instruments denominated in, or that generate income denominated in, foreign currencies. The Fund may elect not to hedge currency risk, or may hedge such risk imperfectly, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged.

Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including futures, structured notes, swaps (including credit default swaps) and forward currency contracts) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund's exposure to securities 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, such as futures, structured notes, swaps (including credit default swaps) and forward currency contracts 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 required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives 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 the U.S. government 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.

Equity Securities Risk: The value of the Fund's investments in equity securities could be subject to unpredictable declines in the value of individual securities and periods of below-average performance in individual securities or in the equity market as a whole. In the event an issuer is liquidated or declares bankruptcy, the claims of owners of the issuer's bonds generally take precedence over the claims of those who own preferred stock or common stock.

Foreign Securities Risk: Investments in foreign securities may be subject to greater political, economic, environmental, credit/counterparty and information risks. The Fund's investments in foreign securities also are subject to foreign currency fluctuations and other foreign currency-related risks. Foreign securities may be subject to higher volatility than U.S. securities, varying degrees of regulation and limited liquidity.

Interest Rate Risk: Interest rate risk is the risk that the value of the Fund's investments will fall if interest rates rise. Generally, the value of fixed-income securities rises when prevailing interest rates fall and falls when interest rates rise. Interest rate risk generally is greater for funds that invest in fixed-income securities with relatively longer durations than for funds that invest in fixed-income securities with shorter durations. The 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

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.

Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices 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 a fund's returns, and may lead to significant losses if investments are not successful.

Liquidity Risk: Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Decreases in the number of financial institutions willing to make markets in the Fund's investments or in their capacity or willingness to transact may increase the Fund's exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund's investments when it needs to dispose of them. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. 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. Non-exchange traded derivatives are generally subject to greater liquidity risk as well. Liquidity issues may also make it difficult to value the Fund's investments.

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

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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods (as applicable) compare to those of two broad measures of market performance. The Bloomberg Barclays U.S. Universal Bond Index represents the union of the U.S. Aggregate Index, the U.S. High-Yield Corporate Index, the 144A Index, the Eurodollar Index, the Emerging Markets Index, and the non-ERISA portion of the CMBS Index. Municipal debt, private placements, and non-dollar-denominated issues are excluded from the Universal Bond Index. The only constituent of the index that includes floating-rate debt is the Emerging Markets Index. 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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"> <b> Total Returns for Class Y Shares </b> </div>

Highest Quarterly Return: Second Quarter 2009, 18.22%

Lowest Quarterly Return: Third Quarter 2011, -6.33%

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Average Annual Total Returns - (Loomis Sayles Strategic Income Fund)	Past 1 Year	Past 5 Years	Past 10 Years	Life of Class N	Inception Date
Class Y	(2.69%)	2.16%	8.77%
Class Y | Return After Taxes on Distributions	(4.27%)	0.15%	6.59%
Class Y | Return After Taxes on Distributions and Sale of Fund Shares	(1.44%)	1.02%	6.27%
Class A	(7.15%)	1.01%	8.03%
Class C	(4.60%)	1.14%	7.69%
Class N	(2.61%)	2.24%		3.32%	Feb. 01, 2013
Class T	(5.41%)	1.39%	8.23%
Admin Class	(3.12%)	1.66%	8.23%
Bloomberg Barclays U.S. Aggregate Bond Index	0.01%	2.52%	3.48%	1.91%
Bloomberg Barclays U.S. Universal Bond Index	(0.25%)	2.72%	4.06%	2.17%

Prior to the inception of Admin Class shares (February 1, 2010), performance is that of Class A shares, restated to reflect the higher net expenses of Admin Class 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 Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. 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.

[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.

[1] Other expenses are estimated for the current fiscal year.

[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 1.25%, 2.00%, 0.95%, 1.25% and 1.00% 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, 2020 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 and 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. 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, 2020 and may be terminated before then only with the consent of the Fund's Board of Trustees.

[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.

[1] Other expenses are estimated for the current fiscal year.

[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 1.25%, 2.00%, 0.95%, 1.25% and 1.00% 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, 2020 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 and 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. has given a binding contractual undertaking to the Fund to reimburse any and all transfer agency expenses attributable to accounts admitted to Class N shares via a prospectus provision that allows Natixis Distribution, L.P., at its sole discretion, to waive the investment minimum for accounts as to which the relevant financial intermediary has provided assurances, in writing, that the accounts will be held in omnibus fashion beginning no more than two years following the establishment date of such accounts in Class N shares. This undertaking is in effect through June 30, 2019 and may be terminated before then only with the consent of the Fund's Board of Trustees.

[1] A 0.75% contingent deferred sales charge ("CDSC") may apply to certain purchases of Class A shares of $500,000 or more that are redeemed within eighteen months of the date of purchase.

[1] Other expenses are estimated for the current fiscal year.

[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 0.80%, 1.55%, 0.50%, 0.80% and 0.55% 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, 2020 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 and 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. 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, 2020 and may be terminated before then only with the consent of the Fund's Board of Trustees.

[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.

[1] Other expenses include acquired fund fees and expenses of less than 0.01%.

[2] Other expenses are estimated for the current fiscal year.

[3] Other expenses include an administrative services fee of 0.24% for Admin Class shares.

[4] 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 1.25%, 2.00%, 0.95%, 1.25%, 1.00% and 1.50% of the Fund's average daily net assets for Class A, C, N, T, Y and Admin Class shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2020 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, Y and Admin Class shares. 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.

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(Loomis Sayles High Income Fund)

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

The Fund seeks high current income plus the opportunity for capital appreciation to produce a high total return.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. 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 Fund 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 20 of the Prospectus, in Appendix A to the Prospectus and on page 88 in the section "Reduced Sales Charges" of the Statement of Additional Information ("SAI").

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Shareholder Fees - (Loomis Sayles High Income Fund) - USD ($)	Class A		Class C	Class N	Class T	Class Y
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	4.25%		none	none	2.50%	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	none	[1]	1.00%	none	none	none
Redemption fees	none		none	none	none	none

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Annual Fund Operating Expenses - (Loomis Sayles High Income Fund)		Class A	Class C	Class N	Class T		Class Y
Management fees		0.60%	0.60%	0.60%	0.60%		0.60%
Distribution and/or service (12b-1) fees		0.25%	1.00%	none	0.25%		none
Other expenses		0.31%	0.31%	0.19%	0.31%	[1]	0.31%
Total annual fund operating expenses		1.16%	1.91%	0.79%	1.16%		0.91%
Fee waiver and/or expense reimbursement	[2],[3]	0.11%	0.11%	0.04%	0.11%		0.11%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		1.05%	1.80%	0.75%	1.05%		0.80%

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example - (Loomis Sayles High Income Fund) - USD ($)	1 Year	3 Years	5 Years	10 Years
Class A	528	765	1,023	1,762
Class C	283	587	1,019	2,221
Class N	77	247	434	973
Class T	354	596	859	1,612
Class Y	82	276	490	1,107

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Expense Example, No Redemption - (Loomis Sayles High Income Fund)	1 Year	3 Years	5 Years	10 Years
Class C | USD ($)	183	587	1,019	2,221

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 55% of the average value of its portfolio.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

Under normal market conditions, the Fund will invest at least 80% 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 ratings agencies (Moody's Investors Service, Inc. ("Moody's"), Fitch Investors Services, Inc. ("Fitch") or S&P Global Ratings ("S&P")), have rated the securities in one of its top four rating categories) or, if the security is unrated, are determined by the Adviser to be of comparable quality. There is no minimum rating for the securities in which the Fund may invest. The Fund may invest up to 30% of its assets in U.S. dollar-denominated foreign fixed-income securities, including those in emerging markets. 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.

The Adviser performs its own extensive credit analysis to determine the creditworthiness and potential for capital appreciation of a security. The Fund's management minimizes both market timing and interest rate forecasting. Instead, it uses a strategy based on gaining a thorough understanding of industry and company dynamics as well as individual security characteristics such as issuer debt and debt maturity schedules, earnings prospects, responsiveness to changes in interest rates, experience and perceived strength of management, borrowing requirements and liquidation value, market price in relation to cash flow, interest and dividends.

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

In selecting investments for the Fund, the Adviser utilizes the skills of its in-house team of more than 30 research analysts to cover a broad universe of industries, companies and markets. The Fund's portfolio managers take advantage of these extensive resources to identify securities that meet the Fund's investment criteria. The Adviser employs a selection strategy that focuses on a value-driven, bottom-up approach to identify securities that provide an opportunity for both generous yields and capital appreciation. The Adviser analyzes an individual company's potential for positive financial news to determine if it has growth potential. Examples of positive financial news include an upward turn in the business cycle, improvement in cash flows, rising profits or the awarding of new contracts. The Adviser emphasizes in-depth credit analysis, appreciation potential and diversification in its bond selection. Each bond is evaluated to assess the ability of its issuer to pay interest and, ultimately, principal (which helps the Fund generate an ongoing flow of income). The Adviser also assesses a bond's relation to market conditions within its industry and favors bonds whose prices may benefit from positive business developments. The Adviser seeks to diversify the Fund's holdings to reduce the inherent risk in below investment grade fixed-income securities.

In connection with its principal investment strategies, the Fund may also invest in structured notes, collateralized loan obligations, zero-coupon securities, pay-in-kind securities, convertible securities, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), and futures, forward contracts and swaps (including credit default swaps) for hedging and investment purposes. Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

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.

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 the guarantor of a fixed-income security, or the counterparty to a derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. The Fund will be subject to credit risks with respect to the counterparties of its derivatives transactions. Many of the protections afforded to participants on organized exchanges, such as the performance guarantee of an exchange clearing house, are not available in connection with over-the-counter ("OTC") derivatives transactions, such as foreign currency transactions. As a result, in instances when the Fund enters into OTC derivatives transactions, the Fund will be subject to the risk that its counterparties will not perform their obligations under the transactions and that the Fund will sustain losses or be unable to realize gains.

Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including futures, forward contracts, structured notes and swaps (including credit default swaps)) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund's exposure to securities 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, such as futures, forward contracts, structured notes and swaps (including credit default swaps) 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 required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives 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 the U.S. government 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. 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices 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 a fund's returns, and may lead to significant losses if investments are not successful.

Liquidity Risk: Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Decreases in the number of financial institutions willing to make markets in the Fund's investments or in their capacity or willingness to transact may increase the Fund's exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund's investments when it needs to dispose of them. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. 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. Non-exchange traded derivatives are generally subject to greater liquidity risk as well. Liquidity issues may also make it difficult to value the Fund's investments.

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

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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

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 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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Class Y Shares </b></div>

Highest Quarterly Return: Second Quarter 2009, 16.46%

Lowest Quarterly Return: Third Quarter 2011, -10.92%

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Average Annual Total Returns - (Loomis Sayles High Income Fund)	Past 1 Year	Past 5 Years	Past 10 Years	Life of Class N	Inception Date
Class Y	(3.21%)	3.31%	9.70%
Class Y | Return After Taxes on Distributions	(5.07%)	1.16%	6.87%
Class Y | Return After Taxes on Distributions and Sale of Fund Shares	(1.80%)	1.63%	6.72%
Class A	(7.51%)	2.12%	8.96%
Class C	(5.33%)	2.25%	8.59%
Class N	(3.15%)			2.91%	Nov. 30, 2016
Class T	(5.84%)	2.53%	9.15%
Bloomberg Barclays U.S. Corporate High-Yield Bond Index	(2.08%)	3.83%	11.12%	3.40%

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. Prior to February 1, 2019, Total Returns in the bar chart and Return After Taxes on Distributions and Return After Taxes on Distributions and Sale of Fund Shares in the table were presented for Class A shares; such returns are now presented for Class Y shares, the largest share class in the Natixis Fund Complex.

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 Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. 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 Investment Grade Bond Fund)

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

The Fund seeks high total investment return through a combination of current income and capital appreciation.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. 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 Fund 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 20 of the Prospectus, in Appendix A to the Prospectus and on page 88 in the section "Reduced Sales Charges" of the Statement of Additional Information ("SAI").

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Shareholder Fees - (Loomis Sayles Investment Grade Bond Fund) - USD ($)	Class A		Class C	Class N	Class T	Class Y	Admin Class
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	4.25%		none	none	2.50%	none	none
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	none	[1]	1.00%	none	none	none	none
Redemption fees	none		none	none	none	none	none

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Annual Fund Operating Expenses - (Loomis Sayles Investment Grade Bond Fund)		Class A	Class C	Class N	Class T		Class Y	Admin Class
Management fees		0.40%	0.40%	0.40%	0.40%		0.40%	0.40%
Distribution and/or service (12b-1) fees		0.25%	1.00%	none	0.25%		none	0.25%
Other expenses		0.17%	0.17%	0.08%	0.17%	[1]	0.17%	0.40%	[2]
Total annual fund operating expenses		0.82%	1.57%	0.47%	0.82%		0.57%	1.05%
Fee waiver and/or expense reimbursement	[3]	0.04%	0.04%	none	0.04%		0.04%	0.02%
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.78%	1.53%	0.47%	0.78%		0.53%	1.03%

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same, except that the examples for Class A, Class C, Class T, Class Y and Admin Class 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 dates noted above and on the Total Annual Fund Operating Expenses for the remaining periods. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example - (Loomis Sayles Investment Grade Bond Fund) - USD ($)	1 Year	3 Years	5 Years	10 Years
Class A	501	671	856	1,391
Class C	256	491	850	1,863
Class N	48	151	263	591
Class T	328	500	689	1,234
Class Y	54	178	313	709
Admin Class	105	332	577	1,280

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Expense Example, No Redemption - (Loomis Sayles Investment Grade Bond Fund)	1 Year	3 Years	5 Years	10 Years
Class C | USD ($)	156	491	850	1,863

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 3% of the average value of its portfolio.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

Under normal market conditions, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in investment grade fixed-income securities (for example, bonds and other investments that the Adviser believes have similar economic characteristics, such as notes, debentures and loans). "Investment grade" securities are those securities that are rated in one of the top four categories at the time of purchase by at least one of the three major rating agencies — Moody's Investors Service, Inc. ("Moody's"), Fitch Investor Services, Inc. ("Fitch") or S&P Global Ratings ("S&P") or, if unrated, are determined by the Adviser to be of comparable quality. Although the Fund invests primarily in investment grade fixed-income securities, it may invest up to 15% of its assets in below investment grade fixed-income securities (also known as "junk bonds"). There is no minimum rating for the securities in which the Fund may invest. The Fund may invest in fixed-income securities of any maturity.

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

Three themes typically drive the Fund's investment approach. First, the Adviser generally seeks fixed-income securities of issuers whose credit profiles it believes are improving. Second, the Fund may invest significantly in securities the prices of which the Adviser believes are more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates. The Adviser believes that the Fund may generate positive returns by having a portion of the Fund's assets invested in non-market-related securities, rather than by relying primarily on changes in interest rates to produce returns for the Fund. Third, the Adviser 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 Adviser generally prefers securities that are protected against calls (early redemption by the issuer).

In connection with its principal investment strategies, the Fund may invest up to 30% of its assets in U.S. dollar-denominated foreign securities, including emerging markets securities. The Fund may also invest in U.S. dollar-denominated obligations of supranational entities without limit (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 Barclays. The Fund may also invest in corporate securities, U.S. government securities, commercial paper, zero-coupon securities, collateralized loan obligations, mortgage-backed securities, including mortgage dollar rolls, stripped mortgage-backed securities and collateralized mortgage obligations and other asset-backed securities, when-issued securities, convertible securities, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities") and structured notes. The Fund may also invest in futures, forward contracts and swaps (including credit default swaps) for hedging and investment purposes. Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. The Fund will be subject to credit risks with respect to the counterparties of its derivatives transactions. Many of the protections afforded to participants on organized exchanges, such as the performance guarantee of an exchange clearing house, are not available in connection with over-the-counter ("OTC") derivatives transactions, such as foreign currency transactions. As a result, in instances when the Fund enters into OTC derivatives transactions, the Fund will be subject to the risk that its counterparties will not perform their obligations under the transactions and that the Fund will sustain losses or be unable to realize gains.

Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including forward currency contracts, structured notes and swap transactions (including credit default swaps)) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund's exposure to securities 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, such as forward currency contracts, structured notes and swap transactions (including credit default swaps), 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 required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives 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 the U.S. government 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. The value 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices 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 a fund's returns, and may lead to significant losses if investments are not successful.

Liquidity Risk: Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Decreases in the number of financial institutions willing to make markets in the Fund's investments or in their capacity or willingness to transact may increase the Fund's exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund's investments when it needs to dispose of them. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. 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. Non-exchange traded derivatives are generally subject to greater liquidity risk as well. Liquidity issues may also make it difficult to value the Fund's investments.

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

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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

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 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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Class Y Shares </b></div>

Highest Quarterly Return: Second Quarter 2009, 12.65%

Lowest Quarterly Return: Second Quarter 2013, -3.16%

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Average Annual Total Returns - (Loomis Sayles Investment Grade Bond Fund)	Past 1 Year	Past 5 Years	Past 10 Years	Life of Class N	Inception Date
Class Y	(0.32%)	2.41%	6.69%
Class Y | Return After Taxes on Distributions	(1.09%)	0.84%	4.72%
Class Y | Return After Taxes on Distributions and Sale of Fund Shares	(0.09%)	1.29%	4.61%
Class A	(4.86%)	1.27%	5.96%
Class C	(2.34%)	1.39%	5.63%
Class N	(0.35%)	2.52%		2.23%	Feb. 01, 2013
Class T	(3.10%)	1.65%	6.15%
Admin Class	(0.72%)	1.94%	6.15%
Bloomberg Barclays U.S. Government/Credit Bond Index	(0.42%)	2.53%	3.46%	1.89%

Prior to the inception of Admin Class shares (February 1, 2010), performance is that of Class A shares, restated to reflect the higher net expenses of Admin Class 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 Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. 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.

[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.

[1] Other expenses are estimated for the current fiscal year.

[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 April 30, 2020 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 and 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. 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 April 30, 2020 and may be terminated before then only with the consent of the Fund's Board of Trustees.

[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.

[1] Other expenses are estimated for the current fiscal year.

[2] Other expenses include an administrative services fee of 0.23% for Admin Class shares.

[3] Loomis, Sayles & Company, L.P. ("Loomis Sayles" or the "Adviser") has given a binding contractual undertaking to the Fund to limit the amount of the Fund's total annual fund operating expenses to 0.78%, 1.53%, 0.48%, 0.78%, 0.53% and 1.03% of the Fund's average daily net assets for Class A, C, N, T, Y and Admin Class shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through April 30, 2020 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, Y and Admin Class shares. 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.

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(Loomis Sayles Small Cap Growth Fund)

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> INVESTMENT OBJECTIVE </b></div>

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

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> FUND FEES & EXPENSES </b></div>

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

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

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Annual Fund Operating Expenses - (Loomis Sayles Small Cap Growth Fund)		Institutional Class	Retail Class	Class N
Management fees		0.75%	0.75%	0.75%
Distribution and/or service (12b-1) fees		none	0.25%	none
Other expenses		0.19%	0.19%	0.07%
Total annual fund operating expenses		0.94%	1.19%	0.82%
Fee waiver and/or expense reimbursement	[1]	none	none	none
Total annual fund operating expenses after fee waiver and/or expense reimbursement		0.94%	1.19%	0.82%

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

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 the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example - (Loomis Sayles Small Cap Growth Fund) - USD ($)	1 Year	3 Years	5 Years	10 Years
Institutional Class	96	300	520	1,155
Retail Class	121	378	654	1,443
Class N	84	262	455	1,014

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 41% of the average value of its portfolio.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> INVESTMENTS, RISKS AND PERFORMANCE </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

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 either falls within the capitalization range of the Russell 2000® Index, an index that tracks stocks of 2,000 of the smallest U.S. companies, or is $3 billion or less at the time of investment. 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 typically seeks to identify companies that it believes have distinctive products, technologies, or services; dynamic earnings growth; prospects for high levels of profitability; and solid management. Loomis Sayles typically does not consider current income when making buy and sell decisions.

The Fund may invest any portion of its assets in securities of Canadian issuers and up to 20% of its assets in other 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 securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities").

The Fund may engage, for hedging and investment purposes, in foreign currency transactions (such as forward currency contracts), options and futures transactions.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Risks </b></div>

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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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.

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 derivatives 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 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.

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, nationalization or confiscatory taxation, currency exchange restrictions 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.

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. Growth stocks are generally more sensitive to market movements than other types of stocks, primarily because their stock prices are based heavily on future expectations. If Loomis Sayles' assessment of the prospects for a company's growth is wrong, or if Loomis Sayles' judgment of how other investors will value the company's growth is wrong, then the price of the company's stock may fall or not approach the value that Loomis Sayles has placed on it. 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.

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.

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, 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.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures and forward currency contracts are derivatives and may be subject to this type of 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. 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. Liquidity issues may also make it difficult to value the Fund's investments.

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

Market/Issuer Risk is the risk that the market value of the Fund's investments will move up and down, sometimes rapidly and unpredictably, based upon overall market and economic conditions, as well as a number of reasons that directly relate to the issuers of the Fund's investments, such as management performance, financial condition and demand for the issuers' goods and services.

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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

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 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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Institutional Class Shares </b></div>

Highest Quarterly Return: Fourth Quarter 2010, 18.10%

Lowest Quarterly Return: Third Quarter 2011, -20.61%

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Average Annual Total Returns - (Loomis Sayles Small Cap Growth Fund)	Past 1 Year	Past 5 Years	Past 10 Years	Life of Fund / Life of Class N	Inception Date
Institutional Class	0.45%	6.60%	14.90%
Institutional Class | Return After Taxes on Distributions	(2.06%)	4.44%	13.55%
Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares	1.94%	4.94%	12.47%
Retail Class	0.23%	6.34%	14.60%
Class N	0.60%	6.72%		11.55%	Feb. 01, 2013
Russell 2000® Growth Index	(9.31%)	5.13%	13.52%	9.51%

The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.

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 Small/Mid Cap Growth Fund)

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> INVESTMENT OBJECTIVE </b></div>

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

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> FUND FEES & EXPENSES </b></div>

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

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

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Annual Fund Operating Expenses - (Loomis Sayles Small/Mid Cap Growth Fund)	Institutional Class
Management fees	0.75%
Distribution and/or service (12b-1) fees	none
Other expenses	0.67%	[1]
Total annual fund operating expenses	1.42%
Fee waiver and/or expense reimbursement	0.57%	[2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement	0.85%

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

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 the Fund's operating expenses remain the same, except that the example is based on 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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example - (Loomis Sayles Small/Mid Cap Growth Fund)	1 Year	3 Years	5 Years	10 Years
Institutional Class | USD ($)	87	393	722	1,653

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 102% of the average value of its portfolio.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> INVESTMENTS, RISKS AND PERFORMANCE </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

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/mid-cap companies," including preferred stocks, warrants and securities convertible into common or preferred stocks. Currently, the Fund defines a small/mid-cap company to be one whose market capitalization either falls within the capitalization range of the Russell 2500® Index, an index that tracks some or all of the stocks of the 2,500 of the smallest U.S. companies, or is $7 billion or less at the time of investment. 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 typically seeks to identify companies that it believes have distinctive products, technologies, or services; dynamic earnings growth; prospects for high levels of profitability; and solid management. Loomis Sayles typically does not consider current income when making buy and sell decisions.

The Fund may invest any portion of its assets in securities of Canadian issuers and up to 20% of its assets in other 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 securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities").

The Fund may engage, for hedging and investment purposes, in foreign currency transactions (such as forward currency contracts), options and futures transactions.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Risks </b></div>

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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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.

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 derivatives 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 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.

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, nationalization or confiscatory taxation, currency exchange restrictions 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.

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. Growth stocks are generally more sensitive to market movements than other types of stocks, primarily because their stock prices are based heavily on future expectations. If Loomis Sayles' assessment of the prospects for a company's growth is wrong, or if Loomis Sayles' judgment of how other investors will value the company's growth is wrong, then the price of the company's stock may fall or not approach the value that Loomis Sayles has placed on it. 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.

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.

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, 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.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures and forward currency contracts are derivatives and may be subject to this type of 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. 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. Liquidity issues may also make it difficult to value the Fund's investments.

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

Market/Issuer Risk is the risk that the market value of the Fund's investments will move up and down, sometimes rapidly and unpredictably, based upon overall market and economic conditions, as well as a number of reasons that directly relate to the issuers of the Fund's investments, such as management performance, financial condition and demand for the issuers' goods and services.

Small/Mid-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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

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 and life-of-fund 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.

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Institutional Class Shares </b></div>

Highest Quarterly Return: Third Quarter 2017, 7.51%

Lowest Quarterly Return: Fourth Quarter 2018, -20.24%

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Average Annual Total Returns - (Loomis Sayles Small/Mid Cap Growth Fund)	Past 1 Year	Life of Fund / Life of Class N	Inception Date
Institutional Class	(6.26%)	6.27%	Jun. 30, 2015
Institutional Class | Return After Taxes on Distributions	(13.64%)	3.80%	Jun. 30, 2015
Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares	1.06%	4.77%	Jun. 30, 2015
Russell 2500™ Growth Index	(7.47%)	4.50%	Jun. 30, 2015

The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.

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.

[1] Loomis, Sayles & Company, L.P. ("Loomis Sayles" or the "Adviser") has given a binding contractual undertaking to the Fund to limit the amount of the Fund's total annual fund operating expenses to 1.00%, 1.25% and 0.95% 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, 2020 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 Institutional Class shares, Retail Class shares and Class N shares. 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.

[1] Other expenses have been restated to reflect current custodian fees for the Fund effective October 1, 2018.

[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 0.85% of the Fund's average daily net assets for Institutional Class shares, 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, 2020 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 limitation for Institutional Class shares. 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.

XML

Label

Element

Value

(Loomis Sayles Global Allocation Fund)

Prospectus:

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Objective [Heading]

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<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

Objective, Primary [Text Block]

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

Expense [Heading]

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<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

Expense Narrative [Text Block]

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The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Natixis Fund 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 49 of the Prospectus, in Appendix A to the Prospectus and on page 108 in the section "Reduced Sales Charges" of the Statement of Additional Information ("SAI").

Expense Breakpoint Discounts [Text]

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You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Natixis Fund Complex.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

$ 50,000

Shareholder Fees Caption [Text]

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<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Operating Expenses Caption [Text]

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<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

January 31, 2020

Expense Example [Heading]

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<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

Expense Example Narrative [Text Block]

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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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example by, Year, Caption [Text]

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<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example, No Redemption, By Year, Caption [Text]

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<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Portfolio Turnover [Heading]

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<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 22% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

22.00%

Strategy [Heading]

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<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

Strategy Narrative [Text Block]

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Under normal market conditions, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in equity and fixed-income securities of U.S. and foreign issuers. Equity securities purchased by the Fund may include common stocks, preferred stocks, depositary receipts, warrants, securities convertible into common or preferred stocks, interests in real estate investment trusts ("REITs") and/or real estate-related securities and other equity-like interests in an issuer. Fixed-income securities purchased by the Fund may include bonds and other debt obligation of U.S. and foreign issuers, including but not limited to corporations, governments and supranational entities. The Fund will invest a significant portion of its assets outside the U.S., including securities of issuers located in emerging market countries.

The portfolio managers reallocate the Fund's assets between equity and fixed income securities based on their assessment of current market conditions and the relative opportunities within each asset class, among other factors. In deciding which equity securities to buy and sell, the Adviser generally looks to purchase quality companies at attractive valuations with the potential to grow intrinsic value over time. The Adviser uses discounted cash flow analysis, among other methods of analysis, to determine a company's intrinsic value. In deciding which fixed-income securities to buy and sell, the Adviser generally looks for securities that it believes are undervalued and have the potential for credit upgrades, which may include securities that are below investment grade (also known as "junk bonds").

The Fund may also invest in foreign currencies, collateralized mortgage obligations, collateralized loan obligations, zero-coupon securities, when-issued securities, REITs, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), mortgage-related securities, convertible securities and structured notes. The Fund may also engage in active and frequent trading of securities and engage in options or foreign currency transactions (such as forward currency contracts) for hedging and investment purposes and futures transactions and swap transactions (including credit default swaps). Frequent trading may produce high transaction costs and a high level of taxable capital gains, including short-term capital gains taxable as ordinary income, which may lower the Fund's return. The Adviser may hedge currency risk for the Fund (including "cross hedging" between two or more foreign currencies) if it believes the outlook for a particular foreign currency is unfavorable. Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

Risk [Heading]

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<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

Risk Narrative [Text Block]

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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.

Allocation Risk: The Fund's allocations between asset classes and market exposures may not be optimal in every market condition and may adversely affect the Fund's performance.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. The Fund will be subject to credit risks with respect to the counterparties of its derivatives transactions. Many of the protections afforded to participants on organized exchanges, such as the performance guarantee of an exchange clearing house, are not available in connection with over-the-counter ("OTC") derivatives transactions, such as foreign currency transactions. As a result, in instances when the Fund enters into OTC derivatives transactions, the Fund will be subject to the risk that its counterparties will not perform their obligations under the transactions and that the Fund will sustain losses or be unable to realize gains.

Currency Risk: Fluctuations in the exchange rates between different currencies may negatively affect an investment. The Fund may be subject to currency risk because it may invest in currency-related instruments and may invest in securities or other instruments denominated in, or that generate income denominated in, foreign currencies. The Fund may elect not to hedge currency risk, or may hedge such risk imperfectly, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged.

Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including options, forward currency contracts, futures transactions, structured notes and swap transactions (including credit default swaps)) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund's exposure to securities 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, such as options, forward currency contracts, futures transactions, structured notes and swap transactions (including credit default swaps) 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 required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives 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 the U.S. government 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.

Equity Securities Risk: The value of the Fund's investments in equity securities could be subject to unpredictable declines in the value of individual securities and periods of below-average performance in individual securities or in the equity market as a whole. 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.

Foreign Securities Risk: Investments in foreign securities may be subject to greater political, economic, environmental, credit/counterparty and information risks. The Fund's investments in foreign securities also are subject to foreign currency fluctuations and other foreign currency-related risks. Foreign securities may be subject to higher volatility than U.S. securities, varying degrees of regulation and limited liquidity.

Interest Rate Risk: Interest rate risk is the risk that the value of the Fund's investments will fall if interest rates rise. Generally, the value of fixed-income securities rises when prevailing interest rates fall and falls when interest rates rise. Interest rate risk generally is greater for funds that invest in fixed-income securities with relatively longer durations than for funds that invest in fixed-income securities with shorter durations. The value 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

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.

Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices 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 a fund's returns, and may lead to significant losses if investments are not successful.

Liquidity Risk: Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Decreases in the number of financial institutions willing to make markets in the Fund's investments or in their capacity or willingness to transact may increase the Fund's exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund's investments when it needs to dispose of them. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. 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. Non-exchange traded derivatives are generally subject to greater liquidity risk as well. Liquidity issues may also make it difficult to value the Fund's investments.

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

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 Securities Risk: In addition to the risks associated with investments in fixed-income securities generally (for example, credit, liquidity and valuation risk), mortgage-related securities are subject to the risks of the mortgages 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 security beyond the expected prepayment time, typically reducing the security's value. 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.

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.

Risk Lose Money [Text]

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You may lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

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<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

Performance Narrative [Text Block]

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The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods (as applicable) compare to those of two broad measures of market performance. The Blended Index is an unmanaged, blended index composed of the following weights: 60% MSCI All Country World Index (Net) and 40% Bloomberg Barclays Global Aggregate Bond Index. The two indices composing the Blended Index measure, respectively, the performance of global equity securities and global investment grade fixed income securities. 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.

Bar Chart [Heading]

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<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Class Y Shares </b></div>

Bar Chart Does Not Reflect Sales Loads [Text]

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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]

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Highest Quarterly Return: Second Quarter 2009, 19.91%

Lowest Quarterly Return: Third Quarter 2011, -14.72%

Performance Table Heading

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<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Performance Table Closing [Text Block]

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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 Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. 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.

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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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 Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.

Performance 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.

Performance Information Illustrates Variability of Returns [Text]

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The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods (as applicable) compare to those of two broad measures of market performance.

Performance Table One Class of after Tax Shown [Text]

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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 Availability Website Address [Text]

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im.natixis.com

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-225-5478

(Loomis Sayles Global Allocation Fund) | MSCI All Country World Index (Net)

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(9.42%)

Past 5 Years

rr_AverageAnnualReturnYear05

4.26%

Past 10 Years

rr_AverageAnnualReturnYear10

9.46%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

4.71%

(Loomis Sayles Global Allocation Fund) | Blended Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(6.00%)

Past 5 Years

rr_AverageAnnualReturnYear05

3.12%

Past 10 Years

rr_AverageAnnualReturnYear10

6.84%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

4.07%

(Loomis Sayles Global Allocation Fund) | Class A

Prospectus:

rr_ProspectusTable

Maximum sales charge (load) imposed on purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)

rr_MaximumDeferredSalesChargeOverOther

none

^[1]

Redemption fees

rr_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.75%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.16%

Total annual fund operating expenses

rr_ExpensesOverAssets

1.16%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[2],[3]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.16%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 686

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

922

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,177

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,903

Past 1 Year

rr_AverageAnnualReturnYear01

(10.69%)

Past 5 Years

rr_AverageAnnualReturnYear05

3.53%

Past 10 Years

rr_AverageAnnualReturnYear10

10.51%

(Loomis Sayles Global Allocation Fund) | Class C

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.75%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.16%

Total annual fund operating expenses

rr_ExpensesOverAssets

1.91%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[2],[3]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.91%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 294

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

600

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,032

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,233

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

194

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

600

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,032

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 2,233

Past 1 Year

rr_AverageAnnualReturnYear01

(6.83%)

Past 5 Years

rr_AverageAnnualReturnYear05

3.99%

Past 10 Years

rr_AverageAnnualReturnYear10

10.33%

(Loomis Sayles Global Allocation Fund) | Class N

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.75%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.08%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.83%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[2],[3]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.83%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 85

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

265

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

460

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,025

Past 1 Year

rr_AverageAnnualReturnYear01

(4.92%)

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

6.38%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 01, 2017

(Loomis Sayles Global Allocation Fund) | Class T

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.75%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.16%

^[4]

Total annual fund operating expenses

rr_ExpensesOverAssets

1.16%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[2],[3]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.16%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 365

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

609

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

872

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,624

Past 1 Year

rr_AverageAnnualReturnYear01

(7.62%)

Past 5 Years

rr_AverageAnnualReturnYear05

4.24%

Past 10 Years

rr_AverageAnnualReturnYear10

10.88%

(Loomis Sayles Global Allocation Fund) | Class Y

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.75%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.16%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.91%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[2],[3]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.91%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 93

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

290

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

504

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,120

Annual Return 2009

rr_AnnualReturn2009

42.52%

Annual Return 2010

rr_AnnualReturn2010

21.69%

Annual Return 2011

rr_AnnualReturn2011

(0.73%)

Annual Return 2012

rr_AnnualReturn2012

15.49%

Annual Return 2013

rr_AnnualReturn2013

16.25%

Annual Return 2014

rr_AnnualReturn2014

3.53%

Annual Return 2015

rr_AnnualReturn2015

1.69%

Annual Return 2016

rr_AnnualReturn2016

4.67%

Annual Return 2017

rr_AnnualReturn2017

22.11%

Annual Return 2018

rr_AnnualReturn2018

(5.04%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return: Second Quarter 2009, 19.91%

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

19.91%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return: Third Quarter 2011, -14.72%

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(14.72%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Past 1 Year

rr_AverageAnnualReturnYear01

(5.04%)

Past 5 Years

rr_AverageAnnualReturnYear05

5.03%

Past 10 Years

rr_AverageAnnualReturnYear10

11.44%

(Loomis Sayles Global Allocation Fund) | Class Y | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(6.11%)

Past 5 Years

rr_AverageAnnualReturnYear05

3.95%

Past 10 Years

rr_AverageAnnualReturnYear10

10.54%

(Loomis Sayles Global Allocation Fund) | Class Y | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(2.27%)

Past 5 Years

rr_AverageAnnualReturnYear05

3.75%

Past 10 Years

rr_AverageAnnualReturnYear10

9.31%

(Loomis Sayles Growth Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

rr_ObjectiveHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund's investment goal is long-term growth of capital.

Expense [Heading]

rr_ExpenseHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the Natixis Fund 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 49 of the Prospectus, in Appendix A to the Prospectus and on page 108 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 $50,000 in the Natixis Fund Complex.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

$ 50,000

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

January 31, 2020

Expense Example [Heading]

rr_ExpenseExampleHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

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. 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

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 11% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

11.00%

Strategy [Heading]

rr_StrategyHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal market conditions, the Fund will invest primarily in equity securities, including common stocks, convertible securities and warrants. The Fund focuses on stocks of large capitalization companies, but the Fund may invest in companies of any size.

The Fund normally invests across a wide range of sectors and industries. The Fund's portfolio manager employs a growth style of equity management, which means that the Fund seeks to invest in companies with sustainable competitive advantages, long-term structural growth drivers, attractive cash flow returns on invested capital, and management teams focused on creating long-term value for shareholders. The Fund's portfolio manager also aims to invest in companies when they trade at a significant discount to the estimate of intrinsic value.

The Fund will consider selling a portfolio investment when the portfolio manager believes an unfavorable structural change occurs within a given business or the markets in which it operates, a critical underlying investment assumption is flawed, when a more attractive reward-to-risk opportunity becomes available, when the current price fully reflects intrinsic value, or for other investment reasons which the portfolio manager deems appropriate.

The Fund may also invest up to 20% of its assets in foreign securities, including depositary receipts and emerging market 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 or if the security's country of risk defined by Bloomberg is the United States. The Fund may also engage in foreign currency transactions (including foreign currency forwards and foreign currency futures) for hedging purposes, invest in options for hedging and investment purposes and invest in securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"). Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

Risk [Heading]

rr_RiskHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

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.

Credit/Counterparty Risk: Credit/counterparty risk is the risk that the issuer or guarantor of a fixed-income security, or the counterparty to a derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. The Fund will be subject to credit risks with respect to the counterparties of its derivatives transactions. Many of the protections afforded to participants on organized exchanges, such as the performance guarantee of an exchange clearing house, are not available in connection with over-the-counter ("OTC") derivatives transactions, such as foreign currency transactions. As a result, in instances when the Fund enters into OTC derivatives transactions, the Fund will be subject to the risk that its counterparties will not perform their obligations under the transactions and that the Fund will sustain losses or be unable to realize gains.

Currency Risk: Fluctuations in the exchange rates between different currencies may negatively affect an investment. The Fund may be subject to currency risk because it may invest in currency related instruments and may invest in securities or other instruments denominated in, or that generate income denominated in, foreign currencies. The Fund may elect not to hedge currency risk, or may hedge such risk imperfectly, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged.

Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including foreign currency forwards, foreign currency futures and options) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund's exposure to securities market values, interest rates or currency exchange rates. It is possible that the Fund's liquid assets may be insufficient to support its obligations under its derivatives positions. The use of derivatives for other than hedging purposes may be considered a speculative activity, and involves greater risks than are involved in hedging. The use of derivatives may cause the Fund to incur losses greater than those that would have occurred had derivatives not been used. The Fund's use of derivatives such as foreign currency forwards, foreign currency futures and options, involves other risks, such as the credit risk relating to the other party to a derivative contract (which is greater for forward currency contracts 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 required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives 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 the U.S. government 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.

Equity Securities Risk: The value of the Fund's investments in equity securities could be subject to unpredictable declines in the value of individual securities and periods of below-average performance in individual securities or in the equity market as a whole. Growth stocks are generally more sensitive to market movements than other types of stocks primarily because their stock prices are based heavily on future expectations. If the Adviser's assessment of the prospects for a company's growth is wrong, or if the Adviser's judgment of how other investors will value the company's growth is wrong, then the price of the company's stock may fall or not approach the value that the Adviser has placed on it. 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.

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.

Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices 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 a fund's returns, and may lead to significant losses if investments are not successful.

Liquidity Risk: Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Decreases in the number of financial institutions willing to make markets in the Fund's investments or in their capacity or willingness to transact may increase the Fund's exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund's investments when it needs to dispose of them. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. 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. Non-exchange traded derivatives are generally subject to greater liquidity risk as well. Liquidity issues may also make it difficult to value the Fund's investments.

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

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.

Small- and Mid-Capitalization Companies Risk: Compared to large-capitalization companies, small- and mid-capitalization companies are more likely to have limited product lines, markets or financial resources. Stocks of these companies often trade less frequently and in limited volume and their prices may fluctuate more than stocks of large-capitalization companies. As a result, it may be relatively more difficult for the Fund to buy and sell securities of small- and mid-capitalization companies.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

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 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.

Bar Chart [Heading]

rr_BarChartHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Class Y Shares </b></div>

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 Returns: Third Quarter 2010, 15.01%

Lowest Quarterly Return: Second Quarter 2010, -12.73%

Performance Table Heading

rr_PerformanceTableHeading

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

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 Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. 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.

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

rr_IndexNoDeductionForFeesExpensesTaxes

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

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.

Performance 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.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods (as applicable) compare to those of a broad measure of market performance.

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 Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

im.natixis.com

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-225-5478

(Loomis Sayles Growth Fund) | Russell 1000® Growth Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(1.51%)

Past 5 Years

rr_AverageAnnualReturnYear05

10.40%

Past 10 Years

rr_AverageAnnualReturnYear10

15.29%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

13.18%

(Loomis Sayles Growth Fund) | Class A

Prospectus:

rr_ProspectusTable

Maximum sales charge (load) imposed on purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)

rr_MaximumDeferredSalesChargeOverOther

none

^[5]

Redemption fees

rr_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.50%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.15%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.90%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[6],[7]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.90%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 662

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

845

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,045

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,619

Past 1 Year

rr_AverageAnnualReturnYear01

(8.32%)

Past 5 Years

rr_AverageAnnualReturnYear05

9.31%

Past 10 Years

rr_AverageAnnualReturnYear10

14.34%

(Loomis Sayles Growth Fund) | Class C

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.50%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.15%

Total annual fund operating expenses

rr_ExpensesOverAssets

1.65%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[6],[7]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.65%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 268

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

520

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

897

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,955

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

168

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

520

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

897

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,955

Past 1 Year

rr_AverageAnnualReturnYear01

(4.36%)

Past 5 Years

rr_AverageAnnualReturnYear05

9.77%

Past 10 Years

rr_AverageAnnualReturnYear10

14.19%

(Loomis Sayles Growth Fund) | Class N

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.50%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.08%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.58%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[6],[7]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.58%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 59

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

186

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

324

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 726

Past 1 Year

rr_AverageAnnualReturnYear01

(2.39%)

Past 5 Years

rr_AverageAnnualReturnYear05

10.93%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

13.44%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 01, 2013

(Loomis Sayles Growth Fund) | Class T

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.50%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.15%

^[4]

Total annual fund operating expenses

rr_ExpensesOverAssets

0.90%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[6],[7]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.90%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 340

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

530

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

736

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,330

Past 1 Year

rr_AverageAnnualReturnYear01

(5.13%)

Past 5 Years

rr_AverageAnnualReturnYear05

10.06%

Past 10 Years

rr_AverageAnnualReturnYear10

14.75%

(Loomis Sayles Growth Fund) | Class Y

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.50%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.15%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.65%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[6],[7]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.65%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 66

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

208

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

362

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 810

Annual Return 2009

rr_AnnualReturn2009

32.65%

Annual Return 2010

rr_AnnualReturn2010

15.70%

Annual Return 2011

rr_AnnualReturn2011

0.72%

Annual Return 2012

rr_AnnualReturn2012

18.75%

Annual Return 2013

rr_AnnualReturn2013

35.36%

Annual Return 2014

rr_AnnualReturn2014

11.27%

Annual Return 2015

rr_AnnualReturn2015

10.02%

Annual Return 2016

rr_AnnualReturn2016

5.87%

Annual Return 2017

rr_AnnualReturn2017

32.64%

Annual Return 2018

rr_AnnualReturn2018

(2.48%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Returns: Third Quarter 2010, 15.01%

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.01%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2010

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return: Second Quarter 2010, -12.73%

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(12.73%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Jun. 30, 2010

Past 1 Year

rr_AverageAnnualReturnYear01

(2.48%)

Past 5 Years

rr_AverageAnnualReturnYear05

10.89%

Past 10 Years

rr_AverageAnnualReturnYear10

15.34%

(Loomis Sayles Growth Fund) | Class Y | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(3.78%)

Past 5 Years

rr_AverageAnnualReturnYear05

10.33%

Past 10 Years

rr_AverageAnnualReturnYear10

15.01%

(Loomis Sayles Growth Fund) | Class Y | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(0.57%)

Past 5 Years

rr_AverageAnnualReturnYear05

8.64%

Past 10 Years

rr_AverageAnnualReturnYear10

13.03%

(Loomis Sayles Limited Term Government and Agency Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

rr_ObjectiveHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks high current return consistent with preservation of capital.

Expense [Heading]

rr_ExpenseHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. 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 Fund 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 49 of the Prospectus, in Appendix A to the Prospectus and on page 108 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 Fund Complex.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

$ 100,000

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

January 31, 2020

Expense Example [Heading]

rr_ExpenseExampleHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

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 for Class N 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. 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

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 157% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

157.00%

Strategy [Heading]

rr_StrategyHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

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 investments issued or guaranteed by the U.S. government, its agencies or instrumentalities.

The Adviser follows a total return-oriented investment approach in selecting securities for the Fund. It seeks securities that will provide the Fund with an average credit quality equal to the credit rating of the U.S. Government's long-term debt and an effective portfolio duration range of two to four years (although not all securities selected will have these characteristics and the Adviser may look for other characteristics if market conditions change). The Fund may invest in securities with credit quality above or below the credit rating of the U.S. Government's long-term debt. In determining credit quality, the Adviser will look to the highest credit rating assigned by S&P Global Ratings ("S&P"), Fitch Investor Services, Inc. ("Fitch") or Moody's Investors Service, Inc. ("Moody's").

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

In selecting investments for the Fund, the Adviser's research analysts work closely with the Fund's portfolio managers to develop an outlook on the economy from research produced by various financial firms and specific forecasting services or from economic data released by the U.S. and foreign governments as well as the Federal Reserve Bank. The analysts also conduct a thorough review of individual securities to identify what they consider attractive values in the U.S. government security marketplace through the use of quantitative tools such as internal and external computer systems and software. The Adviser continuously monitors an issuer's creditworthiness to assess whether the obligation remains an appropriate investment for the Fund. The Adviser seeks to balance opportunities for yield and price performance by combining macroeconomic analysis with individual security selection. It emphasizes securities that tend to perform particularly well in response to interest rate changes, such as U.S. Treasury securities in a declining interest rate environment and mortgage-backed or U.S. government agency securities in a steady or rising interest rate environment. The Adviser seeks to increase the opportunity for higher yields while maintaining the greater price stability that intermediate-term bonds have compared to bonds with longer maturities.

In connection with its principal investment strategies, the Fund may also invest in investment grade corporate notes and bonds, collateralized loan obligations, zero-coupon bonds, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), asset-backed securities and mortgage-related securities including mortgage dollar rolls. Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

Risk [Heading]

rr_RiskHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

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.

Agency Securities Risk: Certain debt securities issued or guaranteed by agencies of the U.S. government are guaranteed as to the payment of principal and interest by the relevant entity but have not been backed by the full faith and credit of the U.S. government. Instead, they have been supported only by the discretionary authority of the U.S. government to purchase the agency's obligations. An event affecting the guaranteeing entity could adversely affect the payment of principal or interest or both on the security and, therefore, these types of securities should be considered to be riskier than U.S. government securities.

Credit Risk: Credit risk is the risk that the issuer or the guarantor of a fixed-income security will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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 value 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

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. Liquidity issues may also make it difficult to value the Fund's investments.

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

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.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

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 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.

Bar Chart [Heading]

rr_BarChartHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Class Y Shares </b> </div>

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: Third Quarter 2009, 3.07%

Lowest Quarterly Return: Second Quarter 2013, -1.07%

Performance Table Heading

rr_PerformanceTableHeading

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

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.

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

rr_IndexNoDeductionForFeesExpensesTaxes

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

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.

Performance 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.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods (as applicable) compare to those of a broad measure of market performance.

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 Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

im.natixis.com

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-225-5478

(Loomis Sayles Limited Term Government and Agency Fund) | Bloomberg Barclays U.S. 1-5 Year Government Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

1.53%

Past 5 Years

rr_AverageAnnualReturnYear05

1.07%

Past 10 Years

rr_AverageAnnualReturnYear10

1.39%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

1.08%

(Loomis Sayles Limited Term Government and Agency Fund) | Class A

Prospectus:

rr_ProspectusTable

Maximum sales charge (load) imposed on purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

2.25%

Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)

rr_MaximumDeferredSalesChargeOverOther

none

^[8]

Redemption fees

rr_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.37%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.18%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.80%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[3],[9]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.80%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 305

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

475

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

659

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,193

Past 1 Year

rr_AverageAnnualReturnYear01

(1.15%)

Past 5 Years

rr_AverageAnnualReturnYear05

0.44%

Past 10 Years

rr_AverageAnnualReturnYear10

1.97%

(Loomis Sayles Limited Term Government and Agency Fund) | Class C

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.37%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.18%

Total annual fund operating expenses

rr_ExpensesOverAssets

1.55%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[3],[9]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.55%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 258

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

490

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

845

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,845

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

158

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

490

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

845

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,845

Past 1 Year

rr_AverageAnnualReturnYear01

(0.70%)

Past 5 Years

rr_AverageAnnualReturnYear05

0.13%

Past 10 Years

rr_AverageAnnualReturnYear10

1.43%

(Loomis Sayles Limited Term Government and Agency Fund) | Class N

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.37%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.11%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.48%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.02%

^[3],[9]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.46%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 47

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

152

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

267

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 602

Past 1 Year

rr_AverageAnnualReturnYear01

1.48%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

1.35%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 01, 2017

(Loomis Sayles Limited Term Government and Agency Fund) | Class T

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.37%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.18%

^[4]

Total annual fund operating expenses

rr_ExpensesOverAssets

0.80%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[3],[9]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.80%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 330

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

499

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

683

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,215

Past 1 Year

rr_AverageAnnualReturnYear01

(1.41%)

Past 5 Years

rr_AverageAnnualReturnYear05

0.39%

Past 10 Years

rr_AverageAnnualReturnYear10

1.94%

(Loomis Sayles Limited Term Government and Agency Fund) | Class Y

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.37%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.18%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.55%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[3],[9]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.55%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 56

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

176

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

307

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 689

Annual Return 2009

rr_AnnualReturn2009

8.08%

Annual Return 2010

rr_AnnualReturn2010

5.38%

Annual Return 2011

rr_AnnualReturn2011

2.85%

Annual Return 2012

rr_AnnualReturn2012

3.41%

Annual Return 2013

rr_AnnualReturn2013

(0.60%)

Annual Return 2014

rr_AnnualReturn2014

1.87%

Annual Return 2015

rr_AnnualReturn2015

0.47%

Annual Return 2016

rr_AnnualReturn2016

0.95%

Annual Return 2017

rr_AnnualReturn2017

1.09%

Annual Return 2018

rr_AnnualReturn2018

1.39%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return: Third Quarter 2009, 3.07%

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

3.07%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return: Second Quarter 2013, -1.07%

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(1.07%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Jun. 30, 2013

Past 1 Year

rr_AverageAnnualReturnYear01

1.39%

Past 5 Years

rr_AverageAnnualReturnYear05

1.15%

Past 10 Years

rr_AverageAnnualReturnYear10

2.46%

(Loomis Sayles Limited Term Government and Agency Fund) | Class Y | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

0.49%

Past 5 Years

rr_AverageAnnualReturnYear05

0.30%

Past 10 Years

rr_AverageAnnualReturnYear10

1.51%

(Loomis Sayles Limited Term Government and Agency Fund) | Class Y | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

0.81%

Past 5 Years

rr_AverageAnnualReturnYear05

0.50%

Past 10 Years

rr_AverageAnnualReturnYear10

1.52%

(Loomis Sayles Strategic Income Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

rr_ObjectiveHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks high current income with a secondary objective of capital growth.

Expense [Heading]

rr_ExpenseHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. 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 Fund 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 49 of the Prospectus, in Appendix A to the Prospectus and on page 108 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 Fund Complex.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

$ 100,000

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

January 31, 2020

Expense Example [Heading]

rr_ExpenseExampleHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

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. 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

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 6% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

6.00%

Strategy [Heading]

rr_StrategyHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal market conditions, the Fund will invest substantially all of its assets in income producing securities (including below investment grade securities, or "junk bonds") with a focus on U.S. corporate bonds, convertible securities, foreign debt instruments, including those in emerging markets and related foreign currency transactions, and U.S. government securities. Below investment grade fixed-income securities are rated below investment grade quality (i.e., none of the three major ratings agencies (Moody's Investors Service, Inc. ("Moody's"), Fitch Investors Services, Inc. ("Fitch") or S&P Global Ratings ("S&P")), have rated the securities in one of its top four rating categories) or, if the security is unrated, are determined by the Adviser to be of comparable quality. The Fund may invest up to 35% of its assets in preferred stocks and dividend-paying common stocks. The portfolio managers may shift the Fund's assets among various types of income-producing securities based upon changing market conditions. The Adviser performs its own extensive credit analyses to determine the creditworthiness and potential for capital appreciation of a security.

The Fund's portfolio managers use a flexible approach to identify securities in the global marketplace with characteristics including discounted price compared to economic value, undervalued credit ratings with strong or improving credit profiles and yield premium relative to its benchmark (although not all of the securities selected will have these attributes).

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

In selecting investments for the Fund, the Adviser utilizes the skills of its in-house team of more than 30 research analysts to cover a broad universe of industries, companies and markets. The Fund's portfolio managers take advantage of these extensive resources to identify securities that meet the Fund's investment criteria. The Adviser seeks to buy bonds that offer a positive yield advantage over the market and, in its view, have room to increase in price. It may also invest to take advantage of what the portfolio managers believe are temporary disparities in the yield of different segments of the market for U.S. government securities. The Adviser provides the portfolio managers with maximum flexibility to find investment opportunities in a wide range of markets, both domestic and foreign. This flexible approach provides the Fund with access to a wide array of investment opportunities. The three key sectors that the portfolio managers focus upon are U.S. corporate issues (including convertible securities), foreign debt securities and U.S. government securities. The Fund's portfolio managers maintain a core of the Fund's investments in corporate bond issues and shift its assets among other income-producing securities as opportunities develop. The Fund generally seeks to maintain a high level of diversification as a form of risk management.

In connection with its principal investment strategies, the Fund may also invest in securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), structured notes, collateralized loan obligations, zero-coupon bonds, pay-in-kind bonds, mortgage-related securities, stripped securities and futures, swaps (including credit default swaps) and foreign currency transactions (such as forward currency contracts) for hedging and investment purposes. Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

Risk [Heading]

rr_RiskHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. The Fund will be subject to credit risks with respect to the counterparties of its derivatives transactions. Many of the protections afforded to participants on organized exchanges, such as the performance guarantee of an exchange clearing house, are not available in connection with over-the-counter ("OTC") derivatives transactions, such as foreign currency transactions. As a result, in instances when the Fund enters into OTC derivatives transactions, the Fund will be subject to the risk that its counterparties will not perform their obligations under the transactions and that the Fund will sustain losses or be unable to realize gains.

Currency Risk: Fluctuations in the exchange rates between different currencies may negatively affect an investment. The Fund may be subject to currency risk because it may invest in currency-related instruments and may invest in securities or other instruments denominated in, or that generate income denominated in, foreign currencies. The Fund may elect not to hedge currency risk, or may hedge such risk imperfectly, which may cause the Fund to incur losses that would not have been incurred had the risk been hedged.

Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including futures, structured notes, swaps (including credit default swaps) and forward currency contracts) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund's exposure to securities 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, such as futures, structured notes, swaps (including credit default swaps) and forward currency contracts 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 required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives 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 the U.S. government 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.

Equity Securities Risk: The value of the Fund's investments in equity securities could be subject to unpredictable declines in the value of individual securities and periods of below-average performance in individual securities or in the equity market as a whole. In the event an issuer is liquidated or declares bankruptcy, the claims of owners of the issuer's bonds generally take precedence over the claims of those who own preferred stock or common stock.

Foreign Securities Risk: Investments in foreign securities may be subject to greater political, economic, environmental, credit/counterparty and information risks. The Fund's investments in foreign securities also are subject to foreign currency fluctuations and other foreign currency-related risks. Foreign securities may be subject to higher volatility than U.S. securities, varying degrees of regulation and limited liquidity.

Interest Rate Risk: Interest rate risk is the risk that the value of the Fund's investments will fall if interest rates rise. Generally, the value of fixed-income securities rises when prevailing interest rates fall and falls when interest rates rise. Interest rate risk generally is greater for funds that invest in fixed-income securities with relatively longer durations than for funds that invest in fixed-income securities with shorter durations. The 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

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.

Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices 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 a fund's returns, and may lead to significant losses if investments are not successful.

Liquidity Risk: Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Decreases in the number of financial institutions willing to make markets in the Fund's investments or in their capacity or willingness to transact may increase the Fund's exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund's investments when it needs to dispose of them. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. 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. Non-exchange traded derivatives are generally subject to greater liquidity risk as well. Liquidity issues may also make it difficult to value the Fund's investments.

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

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.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods (as applicable) compare to those of two broad measures of market performance. The Bloomberg Barclays U.S. Universal Bond Index represents the union of the U.S. Aggregate Index, the U.S. High-Yield Corporate Index, the 144A Index, the Eurodollar Index, the Emerging Markets Index, and the non-ERISA portion of the CMBS Index. Municipal debt, private placements, and non-dollar-denominated issues are excluded from the Universal Bond Index. The only constituent of the index that includes floating-rate debt is the Emerging Markets Index. 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.

Bar Chart [Heading]

rr_BarChartHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"> <b> Total Returns for Class Y Shares </b> </div>

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 2009, 18.22%

Lowest Quarterly Return: Third Quarter 2011, -6.33%

Performance Table Heading

rr_PerformanceTableHeading

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Prior to the inception of Admin Class shares (February 1, 2010), performance is that of Class A shares, restated to reflect the higher net expenses of Admin Class 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 Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. 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.

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

rr_IndexNoDeductionForFeesExpensesTaxes

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

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.

Performance 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.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods (as applicable) compare to those of two broad measures of market performance.

Performance 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 Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

im.natixis.com

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-225-5478

(Loomis Sayles Strategic Income Fund) | Bloomberg Barclays U.S. Aggregate Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

0.01%

Past 5 Years

rr_AverageAnnualReturnYear05

2.52%

Past 10 Years

rr_AverageAnnualReturnYear10

3.48%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

1.91%

(Loomis Sayles Strategic Income Fund) | Bloomberg Barclays U.S. Universal Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(0.25%)

Past 5 Years

rr_AverageAnnualReturnYear05

2.72%

Past 10 Years

rr_AverageAnnualReturnYear10

4.06%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

2.17%

(Loomis Sayles Strategic Income Fund) | Class A

Prospectus:

rr_ProspectusTable

Maximum sales charge (load) imposed on purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

4.25%

Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)

rr_MaximumDeferredSalesChargeOverOther

none

^[1]

Redemption fees

rr_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.56%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.15%

^[10]

Total annual fund operating expenses

rr_ExpensesOverAssets

0.96%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[11]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.96%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 519

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

718

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

933

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,553

Past 1 Year

rr_AverageAnnualReturnYear01

(7.15%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.01%

Past 10 Years

rr_AverageAnnualReturnYear10

8.03%

(Loomis Sayles Strategic Income Fund) | Class C

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.56%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.15%

^[10]

Total annual fund operating expenses

rr_ExpensesOverAssets

1.71%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[11]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.71%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 274

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

539

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

928

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,019

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

174

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

539

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

928

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 2,019

Past 1 Year

rr_AverageAnnualReturnYear01

(4.60%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.14%

Past 10 Years

rr_AverageAnnualReturnYear10

7.69%

(Loomis Sayles Strategic Income Fund) | Class N

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.56%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.07%

^[10]

Total annual fund operating expenses

rr_ExpensesOverAssets

0.63%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[11]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.63%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 64

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

202

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

351

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 786

Past 1 Year

rr_AverageAnnualReturnYear01

(2.61%)

Past 5 Years

rr_AverageAnnualReturnYear05

2.24%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

3.32%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 01, 2013

(Loomis Sayles Strategic Income Fund) | Class T

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.56%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.15%

^[10],[12]

Total annual fund operating expenses

rr_ExpensesOverAssets

0.96%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[11]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.96%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 345

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

548

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

768

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,399

Past 1 Year

rr_AverageAnnualReturnYear01

(5.41%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.39%

Past 10 Years

rr_AverageAnnualReturnYear10

8.23%

(Loomis Sayles Strategic Income Fund) | Class Y

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.56%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.15%

^[10]

Total annual fund operating expenses

rr_ExpensesOverAssets

0.71%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[11]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.71%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 73

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

227

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

395

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 883

Annual Return 2009

rr_AnnualReturn2009

39.59%

Annual Return 2010

rr_AnnualReturn2010

13.82%

Annual Return 2011

rr_AnnualReturn2011

3.54%

Annual Return 2012

rr_AnnualReturn2012

13.93%

Annual Return 2013

rr_AnnualReturn2013

11.16%

Annual Return 2014

rr_AnnualReturn2014

5.86%

Annual Return 2015

rr_AnnualReturn2015

(7.42%)

Annual Return 2016

rr_AnnualReturn2016

8.56%

Annual Return 2017

rr_AnnualReturn2017

7.50%

Annual Return 2018

rr_AnnualReturn2018

(2.69%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return: Second Quarter 2009, 18.22%

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

18.22%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return: Third Quarter 2011, -6.33%

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(6.33%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Past 1 Year

rr_AverageAnnualReturnYear01

(2.69%)

Past 5 Years

rr_AverageAnnualReturnYear05

2.16%

Past 10 Years

rr_AverageAnnualReturnYear10

8.77%

(Loomis Sayles Strategic Income Fund) | Class Y | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(4.27%)

Past 5 Years

rr_AverageAnnualReturnYear05

0.15%

Past 10 Years

rr_AverageAnnualReturnYear10

6.59%

(Loomis Sayles Strategic Income Fund) | Class Y | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(1.44%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.02%

Past 10 Years

rr_AverageAnnualReturnYear10

6.27%

(Loomis Sayles Strategic Income Fund) | Admin Class

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.56%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.39%

^[10],[13]

Total annual fund operating expenses

rr_ExpensesOverAssets

1.20%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[11]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.20%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 122

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

381

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

660

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,455

Past 1 Year

rr_AverageAnnualReturnYear01

(3.12%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.66%

Past 10 Years

rr_AverageAnnualReturnYear10

8.23%

(Loomis Sayles High Income Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

rr_ObjectiveHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks high current income plus the opportunity for capital appreciation to produce a high total return.

Expense [Heading]

rr_ExpenseHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. 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 Fund 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 20 of the Prospectus, in Appendix A to the Prospectus and on page 88 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 Fund Complex.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

$ 100,000

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

April 30, 2020

Expense Example [Heading]

rr_ExpenseExampleHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

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. 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

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 55% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

55.00%

Strategy [Heading]

rr_StrategyHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal market conditions, the Fund will invest at least 80% 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 ratings agencies (Moody's Investors Service, Inc. ("Moody's"), Fitch Investors Services, Inc. ("Fitch") or S&P Global Ratings ("S&P")), have rated the securities in one of its top four rating categories) or, if the security is unrated, are determined by the Adviser to be of comparable quality. There is no minimum rating for the securities in which the Fund may invest. The Fund may invest up to 30% of its assets in U.S. dollar-denominated foreign fixed-income securities, including those in emerging markets. 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.

The Adviser performs its own extensive credit analysis to determine the creditworthiness and potential for capital appreciation of a security. The Fund's management minimizes both market timing and interest rate forecasting. Instead, it uses a strategy based on gaining a thorough understanding of industry and company dynamics as well as individual security characteristics such as issuer debt and debt maturity schedules, earnings prospects, responsiveness to changes in interest rates, experience and perceived strength of management, borrowing requirements and liquidation value, market price in relation to cash flow, interest and dividends.

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

In selecting investments for the Fund, the Adviser utilizes the skills of its in-house team of more than 30 research analysts to cover a broad universe of industries, companies and markets. The Fund's portfolio managers take advantage of these extensive resources to identify securities that meet the Fund's investment criteria. The Adviser employs a selection strategy that focuses on a value-driven, bottom-up approach to identify securities that provide an opportunity for both generous yields and capital appreciation. The Adviser analyzes an individual company's potential for positive financial news to determine if it has growth potential. Examples of positive financial news include an upward turn in the business cycle, improvement in cash flows, rising profits or the awarding of new contracts. The Adviser emphasizes in-depth credit analysis, appreciation potential and diversification in its bond selection. Each bond is evaluated to assess the ability of its issuer to pay interest and, ultimately, principal (which helps the Fund generate an ongoing flow of income). The Adviser also assesses a bond's relation to market conditions within its industry and favors bonds whose prices may benefit from positive business developments. The Adviser seeks to diversify the Fund's holdings to reduce the inherent risk in below investment grade fixed-income securities.

In connection with its principal investment strategies, the Fund may also invest in structured notes, collateralized loan obligations, zero-coupon securities, pay-in-kind securities, convertible securities, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities"), and futures, forward contracts and swaps (including credit default swaps) for hedging and investment purposes. Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

Risk [Heading]

rr_RiskHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

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.

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 the guarantor of a fixed-income security, or the counterparty to a derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. The Fund will be subject to credit risks with respect to the counterparties of its derivatives transactions. Many of the protections afforded to participants on organized exchanges, such as the performance guarantee of an exchange clearing house, are not available in connection with over-the-counter ("OTC") derivatives transactions, such as foreign currency transactions. As a result, in instances when the Fund enters into OTC derivatives transactions, the Fund will be subject to the risk that its counterparties will not perform their obligations under the transactions and that the Fund will sustain losses or be unable to realize gains.

Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including futures, forward contracts, structured notes and swaps (including credit default swaps)) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund's exposure to securities 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, such as futures, forward contracts, structured notes and swaps (including credit default swaps) 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 required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives 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 the U.S. government 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. 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices 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 a fund's returns, and may lead to significant losses if investments are not successful.

Liquidity Risk: Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Decreases in the number of financial institutions willing to make markets in the Fund's investments or in their capacity or willingness to transact may increase the Fund's exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund's investments when it needs to dispose of them. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. 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. Non-exchange traded derivatives are generally subject to greater liquidity risk as well. Liquidity issues may also make it difficult to value the Fund's investments.

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

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.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

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 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.

Bar Chart [Heading]

rr_BarChartHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Class Y Shares </b></div>

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 2009, 16.46%

Lowest Quarterly Return: Third Quarter 2011, -10.92%

Performance Table Heading

rr_PerformanceTableHeading

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

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. Prior to February 1, 2019, Total Returns in the bar chart and Return After Taxes on Distributions and Return After Taxes on Distributions and Sale of Fund Shares in the table were presented for Class A shares; such returns are now presented for Class Y shares, the largest share class in the Natixis Fund Complex.

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 Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. 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.

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

rr_IndexNoDeductionForFeesExpensesTaxes

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

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.

Performance 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.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods (as applicable) compare to those of a broad measure of market performance.

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 Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

im.natixis.com

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-225-5478

(Loomis Sayles High Income Fund) | Bloomberg Barclays U.S. Corporate High-Yield Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(2.08%)

Past 5 Years

rr_AverageAnnualReturnYear05

3.83%

Past 10 Years

rr_AverageAnnualReturnYear10

11.12%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

3.40%

(Loomis Sayles High Income Fund) | Class A

Prospectus:

rr_ProspectusTable

Maximum sales charge (load) imposed on purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

4.25%

Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)

rr_MaximumDeferredSalesChargeOverOther

none

^[1]

Redemption fees

rr_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.60%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.31%

Total annual fund operating expenses

rr_ExpensesOverAssets

1.16%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.11%

^[14],[15]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.05%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 528

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

765

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,023

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,762

Past 1 Year

rr_AverageAnnualReturnYear01

(7.51%)

Past 5 Years

rr_AverageAnnualReturnYear05

2.12%

Past 10 Years

rr_AverageAnnualReturnYear10

8.96%

(Loomis Sayles High Income Fund) | Class C

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.60%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.31%

Total annual fund operating expenses

rr_ExpensesOverAssets

1.91%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.11%

^[14],[15]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.80%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 283

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

587

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,019

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,221

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

183

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

587

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,019

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 2,221

Past 1 Year

rr_AverageAnnualReturnYear01

(5.33%)

Past 5 Years

rr_AverageAnnualReturnYear05

2.25%

Past 10 Years

rr_AverageAnnualReturnYear10

8.59%

(Loomis Sayles High Income Fund) | Class N

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.60%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.19%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.79%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[14],[15]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.75%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 77

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

247

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

434

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 973

Past 1 Year

rr_AverageAnnualReturnYear01

(3.15%)

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

2.91%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 30, 2016

(Loomis Sayles High Income Fund) | Class T

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.60%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.31%

^[16]

Total annual fund operating expenses

rr_ExpensesOverAssets

1.16%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.11%

^[14],[15]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.05%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 354

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

596

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

859

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,612

Past 1 Year

rr_AverageAnnualReturnYear01

(5.84%)

Past 5 Years

rr_AverageAnnualReturnYear05

2.53%

Past 10 Years

rr_AverageAnnualReturnYear10

9.15%

(Loomis Sayles High Income Fund) | Class Y

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.60%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.31%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.91%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.11%

^[14],[15]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.80%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 82

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

276

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

490

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,107

Annual Return 2009

rr_AnnualReturn2009

50.44%

Annual Return 2010

rr_AnnualReturn2010

13.99%

Annual Return 2011

rr_AnnualReturn2011

(2.53%)

Annual Return 2012

rr_AnnualReturn2012

21.70%

Annual Return 2013

rr_AnnualReturn2013

5.42%

Annual Return 2014

rr_AnnualReturn2014

4.55%

Annual Return 2015

rr_AnnualReturn2015

(6.22%)

Annual Return 2016

rr_AnnualReturn2016

15.04%

Annual Return 2017

rr_AnnualReturn2017

7.80%

Annual Return 2018

rr_AnnualReturn2018

(3.21%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return: Second Quarter 2009, 16.46%

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

16.46%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return: Third Quarter 2011, -10.92%

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(10.92%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Past 1 Year

rr_AverageAnnualReturnYear01

(3.21%)

Past 5 Years

rr_AverageAnnualReturnYear05

3.31%

Past 10 Years

rr_AverageAnnualReturnYear10

9.70%

(Loomis Sayles High Income Fund) | Class Y | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(5.07%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.16%

Past 10 Years

rr_AverageAnnualReturnYear10

6.87%

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

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(1.80%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.63%

Past 10 Years

rr_AverageAnnualReturnYear10

6.72%

(Loomis Sayles Investment Grade Bond Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

rr_ObjectiveHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investment Goal </b></div>

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks high total investment return through a combination of current income and capital appreciation.

Expense [Heading]

rr_ExpenseHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Fund Fees & Expenses </b></div>

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. 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 Fund 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 20 of the Prospectus, in Appendix A to the Prospectus and on page 88 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 Fund Complex.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

$ 100,000

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Shareholder Fees </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(fees paid directly from your investment)</b></div>

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

April 30, 2020

Expense Example [Heading]

rr_ExpenseExampleHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same, except that the examples for Class A, Class C, Class T, Class Y and Admin Class 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 dates noted above and on the Total Annual Fund Operating Expenses for the remaining periods. 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

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are redeemed: </b></div>

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> If shares are not redeemed: </b></div>

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 3% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

3.00%

Strategy [Heading]

rr_StrategyHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Investments, Risks and Performance </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

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 investment grade fixed-income securities (for example, bonds and other investments that the Adviser believes have similar economic characteristics, such as notes, debentures and loans). "Investment grade" securities are those securities that are rated in one of the top four categories at the time of purchase by at least one of the three major rating agencies — Moody's Investors Service, Inc. ("Moody's"), Fitch Investor Services, Inc. ("Fitch") or S&P Global Ratings ("S&P") or, if unrated, are determined by the Adviser to be of comparable quality. Although the Fund invests primarily in investment grade fixed-income securities, it may invest up to 15% of its assets in below investment grade fixed-income securities (also known as "junk bonds"). There is no minimum rating for the securities in which the Fund may invest. The Fund may invest in fixed-income securities of any maturity.

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

Three themes typically drive the Fund's investment approach. First, the Adviser generally seeks fixed-income securities of issuers whose credit profiles it believes are improving. Second, the Fund may invest significantly in securities the prices of which the Adviser believes are more sensitive to events related to the underlying issuer than to changes in general interest rates or overall market default rates. The Adviser believes that the Fund may generate positive returns by having a portion of the Fund's assets invested in non-market-related securities, rather than by relying primarily on changes in interest rates to produce returns for the Fund. Third, the Adviser 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 Adviser generally prefers securities that are protected against calls (early redemption by the issuer).

In connection with its principal investment strategies, the Fund may invest up to 30% of its assets in U.S. dollar-denominated foreign securities, including emerging markets securities. The Fund may also invest in U.S. dollar-denominated obligations of supranational entities without limit (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 Barclays. The Fund may also invest in corporate securities, U.S. government securities, commercial paper, zero-coupon securities, collateralized loan obligations, mortgage-backed securities, including mortgage dollar rolls, stripped mortgage-backed securities and collateralized mortgage obligations and other asset-backed securities, when-issued securities, convertible securities, securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities") and structured notes. The Fund may also invest in futures, forward contracts and swaps (including credit default swaps) for hedging and investment purposes. Except as provided above or as required by applicable law, the Fund is not limited in the percentage of its assets that it may invest in these instruments.

Risk [Heading]

rr_RiskHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Risks </b></div>

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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations. The Fund will be subject to credit risks with respect to the counterparties of its derivatives transactions. Many of the protections afforded to participants on organized exchanges, such as the performance guarantee of an exchange clearing house, are not available in connection with over-the-counter ("OTC") derivatives transactions, such as foreign currency transactions. As a result, in instances when the Fund enters into OTC derivatives transactions, the Fund will be subject to the risk that its counterparties will not perform their obligations under the transactions and that the Fund will sustain losses or be unable to realize gains.

Derivatives Risk: Derivative instruments (such as those in which the Fund may invest, including forward currency contracts, structured notes and swap transactions (including credit default swaps)) are subject to changes in the value of the underlying assets or indices on which such instruments are based. There is no guarantee that the use of derivatives will be effective or that suitable transactions will be available. Even a small investment in derivatives may give rise to leverage risk and can have a significant impact on the Fund's exposure to securities 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, such as forward currency contracts, structured notes and swap transactions (including credit default swaps), 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 required to initiate derivatives positions. There is also the risk that the Fund may be unable to terminate or sell a derivatives 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 the U.S. government 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. The value 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, and the current historically low interest rate environment increases the likelihood of interest rates rising in the future.

Leverage Risk: Use of derivative instruments may involve leverage. Leverage is the risk associated with securities or practices 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 a fund's returns, and may lead to significant losses if investments are not successful.

Liquidity Risk: Liquidity risk is the risk that the Fund may be unable to find a buyer for its investments when it seeks to sell them or to receive the price it expects. Decreases in the number of financial institutions willing to make markets in the Fund's investments or in their capacity or willingness to transact may increase the Fund's exposure to this risk. Events that may lead to increased redemptions, such as market disruptions or increases in interest rates, may also negatively impact the liquidity of the Fund's investments when it needs to dispose of them. If the Fund is forced to sell its investments at an unfavorable time and/or under adverse conditions in order to meet redemption requests, such sales could negatively affect the Fund. 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. Non-exchange traded derivatives are generally subject to greater liquidity risk as well. Liquidity issues may also make it difficult to value the Fund's investments.

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

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.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

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 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.

Bar Chart [Heading]

rr_BarChartHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Class Y Shares </b></div>

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 2009, 12.65%

Lowest Quarterly Return: Second Quarter 2013, -3.16%

Performance Table Heading

rr_PerformanceTableHeading

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Prior to the inception of Admin Class shares (February 1, 2010), performance is that of Class A shares, restated to reflect the higher net expenses of Admin Class 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 Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period. 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.

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

rr_IndexNoDeductionForFeesExpensesTaxes

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

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.

Performance 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.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year-to-year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods (as applicable) compare to those of a broad measure of market performance.

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 Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

im.natixis.com

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-225-5478

(Loomis Sayles Investment Grade Bond Fund) | Bloomberg Barclays U.S. Government/Credit Bond Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(0.42%)

Past 5 Years

rr_AverageAnnualReturnYear05

2.53%

Past 10 Years

rr_AverageAnnualReturnYear10

3.46%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

1.89%

(Loomis Sayles Investment Grade Bond Fund) | Class A

Prospectus:

rr_ProspectusTable

Maximum sales charge (load) imposed on purchases (as a percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

4.25%

Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)

rr_MaximumDeferredSalesChargeOverOther

none

^[1]

Redemption fees

rr_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.40%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.17%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.82%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[17]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.78%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 501

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

671

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

856

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,391

Past 1 Year

rr_AverageAnnualReturnYear01

(4.86%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.27%

Past 10 Years

rr_AverageAnnualReturnYear10

5.96%

(Loomis Sayles Investment Grade Bond Fund) | Class C

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.40%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.17%

Total annual fund operating expenses

rr_ExpensesOverAssets

1.57%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[17]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.53%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 256

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

491

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

850

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,863

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

156

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

491

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

850

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,863

Past 1 Year

rr_AverageAnnualReturnYear01

(2.34%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.39%

Past 10 Years

rr_AverageAnnualReturnYear10

5.63%

(Loomis Sayles Investment Grade Bond Fund) | Class N

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.40%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.08%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.47%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[17]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.47%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 48

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

151

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

263

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 591

Past 1 Year

rr_AverageAnnualReturnYear01

(0.35%)

Past 5 Years

rr_AverageAnnualReturnYear05

2.52%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

2.23%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 01, 2013

(Loomis Sayles Investment Grade Bond Fund) | Class T

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.40%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.17%

^[16]

Total annual fund operating expenses

rr_ExpensesOverAssets

0.82%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[17]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.78%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 328

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

500

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

689

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,234

Past 1 Year

rr_AverageAnnualReturnYear01

(3.10%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.65%

Past 10 Years

rr_AverageAnnualReturnYear10

6.15%

(Loomis Sayles Investment Grade Bond Fund) | Class Y

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.40%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.17%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.57%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.04%

^[17]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.53%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 54

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

178

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

313

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 709

Annual Return 2009

rr_AnnualReturn2009

27.27%

Annual Return 2010

rr_AnnualReturn2010

11.52%

Annual Return 2011

rr_AnnualReturn2011

5.08%

Annual Return 2012

rr_AnnualReturn2012

12.25%

Annual Return 2013

rr_AnnualReturn2013

1.36%

Annual Return 2014

rr_AnnualReturn2014

5.14%

Annual Return 2015

rr_AnnualReturn2015

(5.08%)

Annual Return 2016

rr_AnnualReturn2016

6.16%

Annual Return 2017

rr_AnnualReturn2017

6.66%

Annual Return 2018

rr_AnnualReturn2018

(0.32%)

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return: Second Quarter 2009, 12.65%

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

12.65%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return: Second Quarter 2013, -3.16%

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(3.16%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Jun. 30, 2013

Past 1 Year

rr_AverageAnnualReturnYear01

(0.32%)

Past 5 Years

rr_AverageAnnualReturnYear05

2.41%

Past 10 Years

rr_AverageAnnualReturnYear10

6.69%

(Loomis Sayles Investment Grade Bond Fund) | Class Y | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(1.09%)

Past 5 Years

rr_AverageAnnualReturnYear05

0.84%

Past 10 Years

rr_AverageAnnualReturnYear10

4.72%

(Loomis Sayles Investment Grade Bond Fund) | Class Y | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(0.09%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.29%

Past 10 Years

rr_AverageAnnualReturnYear10

4.61%

(Loomis Sayles Investment Grade Bond Fund) | Admin Class

Prospectus:

rr_ProspectusTable

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_RedemptionFee

none

Management fees

rr_ManagementFeesOverAssets

0.40%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.40%

^[18]

Total annual fund operating expenses

rr_ExpensesOverAssets

1.05%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.02%

^[17]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.03%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 105

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

332

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

577

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,280

Past 1 Year

rr_AverageAnnualReturnYear01

(0.72%)

Past 5 Years

rr_AverageAnnualReturnYear05

1.94%

Past 10 Years

rr_AverageAnnualReturnYear10

6.15%

(Loomis Sayles Small Cap Growth Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

rr_ObjectiveHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> INVESTMENT OBJECTIVE </b></div>

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]

rr_ExpenseHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> FUND FEES & EXPENSES </b></div>

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

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

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

January 31, 2020

Expense Example [Heading]

rr_ExpenseExampleHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 41% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

41.00%

Strategy [Heading]

rr_StrategyHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> INVESTMENTS, RISKS AND PERFORMANCE </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

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 either falls within the capitalization range of the Russell 2000® Index, an index that tracks stocks of 2,000 of the smallest U.S. companies, or is $3 billion or less at the time of investment. 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 typically seeks to identify companies that it believes have distinctive products, technologies, or services; dynamic earnings growth; prospects for high levels of profitability; and solid management. Loomis Sayles typically does not consider current income when making buy and sell decisions.

The Fund may invest any portion of its assets in securities of Canadian issuers and up to 20% of its assets in other 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 securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities").

The Fund may engage, for hedging and investment purposes, in foreign currency transactions (such as forward currency contracts), options and futures transactions.

Risk [Heading]

rr_RiskHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Risks </b></div>

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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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.

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 derivatives 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 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.

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, nationalization or confiscatory taxation, currency exchange restrictions 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.

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. Growth stocks are generally more sensitive to market movements than other types of stocks, primarily because their stock prices are based heavily on future expectations. If Loomis Sayles' assessment of the prospects for a company's growth is wrong, or if Loomis Sayles' judgment of how other investors will value the company's growth is wrong, then the price of the company's stock may fall or not approach the value that Loomis Sayles has placed on it. 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.

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.

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, 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.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures and forward currency contracts are derivatives and may be subject to this type of 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. 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. Liquidity issues may also make it difficult to value the Fund's investments.

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

Market/Issuer Risk is the risk that the market value of the Fund's investments will move up and down, sometimes rapidly and unpredictably, based upon overall market and economic conditions, as well as a number of reasons that directly relate to the issuers of the Fund's investments, such as management performance, financial condition and demand for the issuers' goods and services.

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.

Risk Lose Money [Text]

rr_RiskLoseMoney

You may lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods 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.

Bar Chart [Heading]

rr_BarChartHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Institutional Class Shares </b></div>

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Highest Quarterly Return: Fourth Quarter 2010, 18.10%

Lowest Quarterly Return: Third Quarter 2011, -20.61%

Performance Table Heading

rr_PerformanceTableHeading

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.

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.

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

rr_IndexNoDeductionForFeesExpensesTaxes

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

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on an investor's tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans, qualified plans, education savings accounts, such as 529 plans, or individual retirement accounts.

Performance Table Explanation after Tax Higher

rr_PerformanceTableExplanationAfterTaxHigher

The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.

Performance 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.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following bar chart and table give an indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for the one-year, five-year, ten-year and life-of-class periods compare to those of a broad measure of market performance.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

The after-tax returns are shown for the Institutional Class of the Fund. After-tax returns for the other classes of the Fund will vary.

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.loomissayles.com

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-633-3330

(Loomis Sayles Small Cap Growth Fund) | Russell 2000® Growth Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(9.31%)

Past 5 Years

rr_AverageAnnualReturnYear05

5.13%

Past 10 Years

rr_AverageAnnualReturnYear10

13.52%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

9.51%

(Loomis Sayles Small Cap Growth Fund) | Institutional Class

Prospectus:

rr_ProspectusTable

Management fees

rr_ManagementFeesOverAssets

0.75%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.19%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.94%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[19]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.94%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 96

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

300

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

520

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,155

Annual Return 2009

rr_AnnualReturn2009

31.90%

Annual Return 2010

rr_AnnualReturn2010

31.40%

Annual Return 2011

rr_AnnualReturn2011

3.20%

Annual Return 2012

rr_AnnualReturn2012

10.29%

Annual Return 2013

rr_AnnualReturn2013

47.71%

Annual Return 2014

rr_AnnualReturn2014

1.06%

Annual Return 2015

rr_AnnualReturn2015

1.11%

Annual Return 2016

rr_AnnualReturn2016

5.72%

Annual Return 2017

rr_AnnualReturn2017

26.86%

Annual Return 2018

rr_AnnualReturn2018

0.45%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return: Fourth Quarter 2010, 18.10%

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

18.10%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2010

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return: Third Quarter 2011, -20.61%

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(20.61%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Past 1 Year

rr_AverageAnnualReturnYear01

0.45%

Past 5 Years

rr_AverageAnnualReturnYear05

6.60%

Past 10 Years

rr_AverageAnnualReturnYear10

14.90%

(Loomis Sayles Small Cap Growth Fund) | Institutional Class | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

(2.06%)

Past 5 Years

rr_AverageAnnualReturnYear05

4.44%

Past 10 Years

rr_AverageAnnualReturnYear10

13.55%

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

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

1.94%

Past 5 Years

rr_AverageAnnualReturnYear05

4.94%

Past 10 Years

rr_AverageAnnualReturnYear10

12.47%

(Loomis Sayles Small Cap Growth Fund) | Retail Class

Prospectus:

rr_ProspectusTable

Management fees

rr_ManagementFeesOverAssets

0.75%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.19%

Total annual fund operating expenses

rr_ExpensesOverAssets

1.19%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[19]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

1.19%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 121

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

378

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

654

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,443

Past 1 Year

rr_AverageAnnualReturnYear01

0.23%

Past 5 Years

rr_AverageAnnualReturnYear05

6.34%

Past 10 Years

rr_AverageAnnualReturnYear10

14.60%

(Loomis Sayles Small Cap Growth Fund) | Class N

Prospectus:

rr_ProspectusTable

Management fees

rr_ManagementFeesOverAssets

0.75%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.07%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.82%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[19]

Total annual fund operating expenses after fee waiver and/or expense reimbursement

rr_NetExpensesOverAssets

0.82%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 84

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

262

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

455

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,014

Past 1 Year

rr_AverageAnnualReturnYear01

0.60%

Past 5 Years

rr_AverageAnnualReturnYear05

6.72%

Life of Fund / Life of Class N

rr_AverageAnnualReturnSinceInception

11.55%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 01, 2013

(Loomis Sayles Small/Mid Cap Growth Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

rr_ObjectiveHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> INVESTMENT OBJECTIVE </b></div>

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]

rr_ExpenseHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> FUND FEES & EXPENSES </b></div>

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

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

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Annual Fund Operating Expenses </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(expenses that you pay each year as a percentage of the value of your investment)</b></div>

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

January 31, 2020

Expenses Restated to Reflect Current [Text]

rr_ExpensesRestatedToReflectCurrent

Other expenses have been restated to reflect current custodian fees for the Fund effective October 1, 2018.

Expense Example [Heading]

rr_ExpenseExampleHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Example </b></div>

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

The example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund's operating expenses remain the same, except that the example is based on 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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Portfolio Turnover </b></div>

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 102% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

102.00%

Strategy [Heading]

rr_StrategyHeading

<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> INVESTMENTS, RISKS AND PERFORMANCE </b></div> <div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Investment Strategies </b></div>

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/mid-cap companies," including preferred stocks, warrants and securities convertible into common or preferred stocks. Currently, the Fund defines a small/mid-cap company to be one whose market capitalization either falls within the capitalization range of the Russell 2500® Index, an index that tracks some or all of the stocks of the 2,500 of the smallest U.S. companies, or is $7 billion or less at the time of investment. 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 typically seeks to identify companies that it believes have distinctive products, technologies, or services; dynamic earnings growth; prospects for high levels of profitability; and solid management. Loomis Sayles typically does not consider current income when making buy and sell decisions.

The Fund may invest any portion of its assets in securities of Canadian issuers and up to 20% of its assets in other 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 securities issued pursuant to Rule 144A under the Securities Act of 1933 ("Rule 144A securities").

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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<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Principal Risks </b></div>

Risk Narrative [Text Block]

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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.

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 derivatives or other transaction, will be unable or unwilling to make timely payments of interest or principal or to otherwise honor its obligations.

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.

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 derivatives 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 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.

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, nationalization or confiscatory taxation, currency exchange restrictions 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.

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. Growth stocks are generally more sensitive to market movements than other types of stocks, primarily because their stock prices are based heavily on future expectations. If Loomis Sayles' assessment of the prospects for a company's growth is wrong, or if Loomis Sayles' judgment of how other investors will value the company's growth is wrong, then the price of the company's stock may fall or not approach the value that Loomis Sayles has placed on it. 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.

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.

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, 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.

Leverage Risk is the risk associated with securities or practices (e.g., borrowing and the use of certain derivatives) and investment in certain types of derivatives that multiply small index, market or asset price movements into larger changes in value. Use of derivative instruments 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. Futures and forward currency contracts are derivatives and may be subject to this type of 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. 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. Liquidity issues may also make it difficult to value the Fund's investments.

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

Market/Issuer Risk is the risk that the market value of the Fund's investments will move up and down, sometimes rapidly and unpredictably, based upon overall market and economic conditions, as well as a number of reasons that directly relate to the issuers of the Fund's investments, such as management performance, financial condition and demand for the issuers' goods and services.

Small/Mid-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.

Risk Lose Money [Text]

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You may lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

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<div style="font-size:10pt;padding-top:5pt;padding-bottom:0;padding-left:0;"><b> Risk/Return Bar Chart and Table </b></div>

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 and life-of-fund 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.

Bar Chart [Heading]

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<div style="font-size:10pt;padding-top:5pt;padding-bottom:8;padding-left:0;"><b> Total Returns for Institutional Class Shares </b></div>

Bar Chart Closing [Text Block]

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Highest Quarterly Return: Third Quarter 2017, 7.51%

Lowest Quarterly Return: Fourth Quarter 2018, -20.24%

Performance Table Heading

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<div style="font-size:10pt;padding-top:2;padding-bottom:8;padding-left:0;"><b> Average Annual Total Returns </b></div> <div style="font-size:10pt;padding-top:2;padding-bottom:0;padding-left:0;"><b>(for the periods ended December 31, 2018)</b></div>

Performance Table Closing [Text Block]

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The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.

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.

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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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 Explanation after Tax Higher

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The Return After Taxes on Distributions and Sale of Fund Shares for the 1-year period exceeds the Return Before Taxes due to an assumed tax benefit from losses on a sale of Fund shares at the end of the measurement period.

Performance 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.

Performance Information Illustrates Variability of Returns [Text]

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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 and life-of-fund periods compare to those of a broad measure of market performance.

Performance Availability Website Address [Text]

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www.loomissayles.com

Performance Availability Phone [Text]

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800-633-3330

(Loomis Sayles Small/Mid Cap Growth Fund) | Russell 2500™ Growth Index

Prospectus:

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Past 1 Year

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(7.47%)

Life of Fund / Life of Class N

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4.50%

Inception Date

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Jun. 30, 2015

(Loomis Sayles Small/Mid Cap Growth Fund) | Institutional Class

Prospectus:

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Management fees

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0.75%

Distribution and/or service (12b-1) fees

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none

Other expenses

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0.67%

^[20]

Total annual fund operating expenses

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1.42%

Fee waiver and/or expense reimbursement

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0.57%

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Total annual fund operating expenses after fee waiver and/or expense reimbursement

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0.85%

Expense Example, with Redemption, 1 Year

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$ 87

Expense Example, with Redemption, 3 Years

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393

Expense Example, with Redemption, 5 Years

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722

Expense Example, with Redemption, 10 Years

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$ 1,653

Annual Return 2016

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7.26%

Annual Return 2017

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31.80%

Annual Return 2018

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(6.26%)

Highest Quarterly Return, Label

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Highest Quarterly Return: Third Quarter 2017, 7.51%

Highest Quarterly Return

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7.51%

Highest Quarterly Return, Date

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Sep. 30, 2017

Lowest Quarterly Return, Label

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Lowest Quarterly Return: Fourth Quarter 2018, -20.24%

Lowest Quarterly Return

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(20.24%)

Lowest Quarterly Return, Date

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Dec. 31, 2018

Past 1 Year

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(6.26%)

Life of Fund / Life of Class N

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6.27%

Inception Date

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Jun. 30, 2015

(Loomis Sayles Small/Mid Cap Growth Fund) | Institutional Class | Return After Taxes on Distributions

Prospectus:

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Past 1 Year

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(13.64%)

Life of Fund / Life of Class N

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3.80%

Inception Date

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Jun. 30, 2015

(Loomis Sayles Small/Mid Cap Growth Fund) | Institutional Class | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

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Past 1 Year

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1.06%

Life of Fund / Life of Class N

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4.77%

Inception Date

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Jun. 30, 2015

[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 1.25%, 2.00%, 0.95%, 1.25% and 1.00% 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, 2020 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 and 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. 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, 2020 and may be terminated before then only with the consent of the Fund's Board of Trustees.

[4] Other expenses are estimated for the current fiscal year.

[5] 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.

[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 1.25%, 2.00%, 0.95%, 1.25% and 1.00% 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, 2020 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 and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

[7] Natixis Advisors, L.P. has given a binding contractual undertaking to the Fund to reimburse any and all transfer agency expenses attributable to accounts admitted to Class N shares via a prospectus provision that allows Natixis Distribution, L.P., at its sole discretion, to waive the investment minimum for accounts as to which the relevant financial intermediary has provided assurances, in writing, that the accounts will be held in omnibus fashion beginning no more than two years following the establishment date of such accounts in Class N shares. This undertaking is in effect through June 30, 2019 and may be terminated before then only with the consent of the Fund's Board of Trustees.

[8] A 0.75% contingent deferred sales charge ("CDSC") may apply to certain purchases of Class A shares of $500,000 or more that are redeemed within eighteen months of the date of purchase.

[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 0.80%, 1.55%, 0.50%, 0.80% and 0.55% 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, 2020 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 and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

[10] Other expenses include acquired fund fees and expenses of less than 0.01%.

[11] 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 1.25%, 2.00%, 0.95%, 1.25%, 1.00% and 1.50% of the Fund's average daily net assets for Class A, C, N, T, Y and Admin Class shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through January 31, 2020 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, Y and Admin Class shares. 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.

[12] Other expenses are estimated for the current fiscal year.

[13] Other expenses include an administrative services fee of 0.24% for Admin Class shares.

[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 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 April 30, 2020 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 and expenses more than one year after the end of the fiscal year in which the fees or expenses were waived/reimbursed.

[15] Natixis Advisors, L.P. 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 April 30, 2020 and may be terminated before then only with the consent of the Fund's Board of Trustees.

[16] Other expenses are estimated for the current fiscal year.

[17] 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 0.78%, 1.53%, 0.48%, 0.78%, 0.53% and 1.03% of the Fund's average daily net assets for Class A, C, N, T, Y and Admin Class shares, respectively, exclusive of brokerage expenses, interest expense, taxes, acquired fund fees and expenses, organizational and extraordinary expenses, such as litigation and indemnification expenses. This undertaking is in effect through April 30, 2020 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, Y and Admin Class shares. 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.

[18] Other expenses include an administrative services fee of 0.23% for Admin Class shares.

[19] 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 1.00%, 1.25% and 0.95% 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, 2020 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 Institutional Class shares, Retail Class shares and Class N shares. 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.

[20] Other expenses have been restated to reflect current custodian fees for the Fund effective October 1, 2018.

[21] 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 0.85% of the Fund's average daily net assets for Institutional Class shares, 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, 2020 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 limitation for Institutional Class shares. 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.