485BPOS

Registration Nos. 333-144744

811-22099

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933	☐
Pre-Effective Amendment No.	☐
Post-Effective Amendment No. 40	☒
and/or
REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940	☐
Amendment No. 44	☒
(Check appropriate box or boxes.)

GATEWAY TRUST

(Exact Name of Registrant as Specified in Charter)

399 Boylston Street, Boston, Massachusetts	02116
(Address of principal executive offices)	(Zip Code)

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

Russell Kane, Esq.

NGAM Distribution, L.P.

399 Boylston Street

Boston, Massachusetts 02116

(Name and Address of Agent for Service)

Copy to:

John M. Loder, Esq.

Ropes & Gray

800 Boylston Street

Boston, Massachusetts 02199

Approximate Date of 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.

GATEWAY TRUST

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, and the Investment Company Act of 1940, as amended, the Registrant certifies that it meets all of the requirements for effectiveness of this Post-Effective Amendment to its Registration Statement under Rule 485(b) under the Securities Act of 1933, as amended, and has duly caused this Post-Effective Amendment 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 April, 2017.

GATEWAY TRUST
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.

/s/ David L. Giunta
David L. Giunta	Trustee, President and Chief Executive Officer	April 21, 2017
/s/ Michael C. Kardok
Michael C. Kardok	Treasurer	April 21, 2017
Kevin P. Charleston*
Kevin P. Charleston	Trustee	April 21, 2017
Kenneth A. Drucker *
Kenneth A. Drucker	Trustee, Chairperson of the Board	April 21, 2017
Edmond J. English *
Edmond J. English	Trustee	April 21, 2017
Richard A. Goglia *
Richard A. Goglia	Trustee	April 21, 2017
Wendell J. Knox *
Wendell J. Knox	Trustee	April 21, 2017
Martin T. Meehan *
Martin T. Meehan	Trustee	April 21, 2017
Sandra O. Moose *
Sandra O. Moose	Trustee	April 21, 2017
James P. Palermo*
James P. Palermo	Trustee	April 21, 2017
Erik R. Sirri *
Erik R. Sirri	Trustee	April 21, 2017

Peter J. Smail *
Peter J. Smail	Trustee	April 21, 2017
Cynthia L. Walker *
Cynthia L. Walker	Trustee	April 21, 2017

*By:	/s/ Russell Kane
	Russell Kane
	Attorney-In-Fact 1
	April 21, 2017

¹  Powers of Attorney for Kevin P. Charleston, Kenneth A. Drucker, Edmond J. English, Richard A. Goglia, Wendell J. Knox, Martin T. Meehan, Sandra O. Moose, James P. Palermo, Erik R. Sirri, Peter J. Smail and Cynthia L. Walker is incorporated by reference to exhibit (q)(1) to PEA No. 39 to the Registration Statement filed on March 30, 2017.

Gateway Trust

Exhibit Index

Exhibits for Item 28 of Form N-1A

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	Dec. 31, 2016
Registrant Name	dei_EntityRegistrantName	Gateway Trust
Central Index Key	dei_EntityCentralIndexKey	0001406305
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Mar. 30, 2017
Document Effective Date	dei_DocumentEffectiveDate	Mar. 31, 2017
Prospectus Date	rr_ProspectusDate	Mar. 31, 2017

XML

(Gateway Equity Call Premium Fund)

Investment Goal

The Fund seeks total return with less risk than U.S. equity markets.

Fund Fees & Expenses

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 a sales charge discount if you invest at least $250,000 in the Fund. More information about this and other discounts is available from your financial professional and in the section "How Sales Charges Are Calculated" on page 77 of the Prospectus.

Shareholder Fees

(fees paid directly from your investment)

Shareholder Fees - (Gateway Equity Call Premium Fund)	Class T USD ($)
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	2.50%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	none
Redemption fees	none

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses - (Gateway Equity Call Premium Fund)	Class T
Management fees	0.65%
Distribution and/or service (12b-1) fees	0.25%
Other expenses	0.41%	[1]
Total annual fund operating expenses	1.31%
Fee waiver and/or expense reimbursement	0.11%	[2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement	1.20%

Example

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same, except that the example is based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement assuming that such waiver and/or reimbursement will only be in place through the date noted above and on the Total Annual Fund Operating Expenses for the remaining periods. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example - (Gateway Equity Call Premium Fund)	1 Year	3 Years	5 Years	10 Years
Class T | USD ($)	369	643	939	1,779

Portfolio Turnover

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 24% of the average value of its portfolio.

Investments, Risks and Performance

Principal Investment Strategies

Under normal market conditions, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in equity securities. Equity securities purchased by the Fund may include the following U.S. exchange-listed securities: common stocks; American Depositary Receipts ("ADRs"), which are securities issued by a U.S. bank that represent interests in foreign equity securities; and interests in real estate investment trusts ("REITs"). The Fund ordinarily invests in a broadly diversified equity portfolio, while also writing (selling) index call options with an aggregate notional value approximately equal to the market value of the equity portfolio. Writing index call options is intended to reduce the Fund's volatility and provide steady cash flow. Cash flow from call option writing is intended to be an important source of the Fund's return, although the Fund's option writing activity reduces the Fund's ability to profit from increases in the value of its equity portfolio. The combination of a diversified stock portfolio and the steady cash flow from the sale of index call options is intended to moderate the volatility of returns relative to an all-equity portfolio. The Fund may invest in companies with small, medium or large market capitalizations.

The Fund's combination of a broadly diversified portfolio of common stocks and written index call options is similar to the components of the CBOE S&P 500 BuyWrite Index (the "BXM℠"). The BXM℠ is a passive total return index based on (1) buying an S&P 500® stock index portfolio, and (2) writing (selling) the near-term S&P 500® Index "covered" call option. The Fund's more flexible, active option management approach creates the potential for it to achieve higher long-term returns than the BXM℠ while exhibiting a similar level of volatility, as defined by standard deviation of returns. The similarities between the BXM℠ and the Fund's equity investment strategy are expected to result in the Fund exhibiting a positive correlation to the broad U.S. equity markets similar to that exhibited by the BXM℠.

With its core investment in equities, the Fund is intended to be significantly less vulnerable to fluctuations in value caused by interest rate volatility, a risk factor present in both fixed-income investments and "hybrid investments" (blends of equity and fixed-income securities). Through the use of index options, the Fund intends that its risk management strategy will reduce the volatility inherent in equity investments while also allowing for more participation in equity returns than hybrid investments. Thus, the Fund seeks to provide an efficient trade-off between risk and reward, where risk is characterized by volatility or fluctuations in value over time.

Purchasing Stocks

The Fund invests in a diversified stock portfolio, generally consisting of approximately 200 to 400 stocks (including ADRs and REITs), designed to support the Fund's index option-based risk management strategy as efficiently as possible while seeking to enhance the Fund's after-tax total return. The Adviser uses a multifactor quantitative model to construct the stock portfolio. The model evaluates approximately 9,000 equity securities to construct a portfolio of U.S.-exchange-traded equities that meets the criteria and constraints established by the Adviser. Generally, the Adviser tries to minimize the difference between the performance of the Fund's stock portfolio and the performance of the index or indices underlying the Fund's option strategies while also considering other factors, such as predicted dividend yield. The Adviser monitors this difference and other factors, and rebalances and adjusts the stock portfolio from time to time, by purchasing and selling stocks. To the extent consistent with the Fund's investment goal, the Adviser may also sell stocks to realize capital losses in an effort to minimize any required capital gain distributions. The Adviser expects the portfolio to generally represent the broad U.S. equity market.

Writing Index Call Options

The Fund continuously writes index call options, typically on broad-based securities market indices, with an aggregate notional value approximately equal to the market value of its broadly diversified stock portfolio. As the seller of the index call option, the Fund receives cash (the "premium") from the purchaser. The purchaser of an index call option has the right to any appreciation in the value of the index over a fixed price (the "exercise price") on a certain date in the future (the "expiration date"). If the purchaser does not exercise the option, the Fund retains the premium. If the purchaser exercises the option, the Fund pays the purchaser the difference between the value of the index and the exercise price of the option. The premium, the exercise price and the value of the index determine the gain or loss realized by the Fund as the seller of the index call option. The Fund can also repurchase the call option prior to the expiration date, ending its obligation. In such a case, the difference between the cost of repurchasing the option and the premium received will determine the gain or loss realized by the Fund.

Other Investments

The Fund may invest in foreign securities traded in U.S. markets (through ADRs or stocks traded in U.S. dollars). The Fund may enter into repurchase agreements and/or hold cash and cash equivalents.

Principal Investment Risks

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.

Call Options Risk: The value of the Fund's positions in index options will fluctuate in response to changes in the value of the underlying index. Writing index call options limits the opportunity to profit from an increase in the market value of stocks in exchange for up-front cash at the time of selling the call option. Unusual market conditions or the lack of a ready market for any particular option at a specific time may reduce the effectiveness of the Fund's option-based risk management strategy, and for these and other reasons the Fund's option strategy may not reduce the Fund's volatility to the extent desired.

Correlation Risk: The Fund's ability to manage the volatility of its equity portfolio by writing index call options depends on the correlation between the returns of the equity portfolio and those of the index on which the call options are written. Accordingly, the effectiveness of the Fund's index option-based risk management strategy may be reduced to the extent the performance of the Fund's equity portfolio does not correlate to that of the indices underlying its option positions.

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. Small- and mid-capitalization and emerging growth companies may be subject to more abrupt price movements, limited markets and less liquidity than larger, more established companies, which could adversely affect the value of the Fund's equity portfolio.

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.

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.

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.

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/Return Bar Chart and Table

The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing the Fund's performance in the first full year and by showing how the Fund's average annual returns for the one-year and Life-of-Fund periods compare to those of two broad measures 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 ngam.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.

Total Returns for Class T Shares

Highest Quarterly Return:
Fourth Quarter 2015, 4.00%

Lowest Quarterly Return:
Third Quarter 2015, -3.59%

Average Annual Total Returns

(for the periods ended December 31, 2016)

Average Annual Total Returns - (Gateway Equity Call Premium Fund)	Past 1 Year	Life of Fund (9/30/14)	Inception Date
Class T	4.91%	3.88%	Sep. 30, 2014
Class T | Return After Taxes on Distributions	4.67%	3.59%	Sep. 30, 2014
Class T | Return After Taxes on Distributions and Sale of Fund Shares	2.96%	2.95%	Sep. 30, 2014
CBOE S&P 500 BuyWrite Index (BXM℠)	7.07%	5.05%	Sep. 30, 2014
S&P 500® Index	11.96%	8.07%	Sep. 30, 2014

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 are offered in a separate prospectus and have the same expenses as Class T shares, restated in the table 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.

(Gateway Fund)

Investment Goal

The Fund seeks to capture the majority of the returns associated with equity market investments, while exposing investors to less risk than other equity investments.

Fund Fees & Expenses

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 a sales charge discount if you invest at least $250,000 in the Fund. More information about this and other discounts is available from your financial professional and in the section "How Sales Charges Are Calculated" on page 77 of the Prospectus.

Shareholder Fees

(fees paid directly from your investment)

Shareholder Fees - (Gateway Fund)	Class T USD ($)
Maximum sales charge (load) imposed on purchases (as a percentage of offering price)	2.50%
Maximum deferred sales charge (load) (as a percentage of original purchase price or redemption proceeds, as applicable)	none
Redemption fees	none

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses - (Gateway Fund)	Class T
Management fees	0.63%
Distribution and/or service (12b-1) fees	0.25%
Other expenses	0.14%	[1]
Total annual fund operating expenses	1.02%
Fee waiver and/or expense reimbursement	0.08%	[2]
Total annual fund operating expenses after fee waiver and/or expense reimbursement	0.94%

Example

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same, except that the example is based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement assuming that such waiver and/or reimbursement will only be in place through the date noted above and on the Total Annual Fund Operating Expenses for the remaining periods. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example - (Gateway Fund)	1 Year	3 Years	5 Years	10 Years
Class T | USD ($)	344	558	791	1,459

Portfolio Turnover

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 14% of the average value of its portfolio.

Investments, Risks and Performance

Principal Investment Strategies

Under normal circumstances, the Fund invests in a broadly diversified portfolio of common stocks, while also selling index call options and purchasing index put options. Writing index call options reduces the Fund's volatility, provides steady cash flow and is an important source of the Fund's return, although it also reduces the Fund's ability to profit from increases in the value of its equity portfolio. The Fund also buys index put options, which can protect the Fund from a significant market decline that may occur over a short period of time. The value of an index put option generally increases as the prices of the stocks constituting the index decrease, and decreases as those stocks increase in price. From time to time, the Fund may reduce its holdings of put options, resulting in an increased exposure to a market decline. The combination of the diversified stock portfolio, the steady cash flow from the sale of index call options and the downside protection from index put options is intended to provide the Fund with the majority of the returns associated with equity market investments while exposing investors to less risk than other equity investments. The Fund may invest in companies with small, medium or large market capitalizations. Equity securities purchased by the Fund may include U.S. exchange-listed common stocks, American Depositary Receipts ("ADRs"), which are securities issued by a U.S. bank that represent interests in foreign equity securities, and interests in real estate investment trusts ("REITs").

The Fund strives not only for the majority of the returns associated with equity market investments, but also for returns in excess of those available from other investments comparable in volatility. Because, as described above, the Fund writes index call options and purchases index put options in addition to investing in equity securities, the Fund's historical volatility has been closer to intermediate-to long-term fixed-income investments (intermediate-term are those with approximately five-year maturities and long-term are those with maturities of ten or more years) and hybrid investments (blends of equity and short-term fixed-income securities) than to equity investments. With its core investment in equities, the Fund is significantly less vulnerable to fluctuations in value caused by interest rate volatility, a risk factor present in both fixed-income investments and "hybrid investments" (blends of equity and short-term fixed-income), although the Fund expects to generally have lower long-term returns than a fund consisting solely of equity securities. Through the use of index options, the Fund intends that its risk management strategy will reduce the volatility inherent in equity investments while also allowing for more participation in equity returns than hybrid investments. Thus, the Fund seeks to provide an efficient trade-off between risk and reward where risk is characterized by volatility or fluctuations in value over time.

Purchasing Stocks

The Fund invests in a diversified stock portfolio, generally consisting of approximately 200 to 400 stocks, designed to support the Fund's index option based risk management strategy as efficiently as possible while seeking to enhance the Fund's after tax total return. The Adviser uses a multifactor quantitative model to construct the stock portfolio. The model evaluates approximately 9,000 equity securities to construct a portfolio of U.S.-exchange-traded equities that meets criteria and constraints established by the Adviser. Generally, the Adviser tries to minimize the difference between the performance of the stock portfolio and that of the index or indices underlying the Fund's option strategies while also considering other factors, such as predicted dividend yield. The Adviser monitors this difference and the other factors, and rebalances and adjusts the stock portfolio from time to time, by purchasing and selling stocks. To the extent consistent with the Fund's investment goal, the Adviser may also sell stocks to realize capital losses in an effort to minimize any required capital gain distributions. The Adviser expects the portfolio to generally represent the broad U.S. equity market.

Writing Index Call Options

The Fund continuously writes index call options, typically on broad-based securities market indices, on the full value of its broadly diversified stock portfolio. As the seller of the index call option, the Fund receives cash (the "premium") from the purchaser. The purchaser of an index call option has the right to any appreciation in the value of the index over a fixed price (the "exercise price") on a certain date in the future (the "expiration date"). If the purchaser does not exercise the option, the Fund retains the premium. If the purchaser exercises the option, the Fund pays the purchaser the difference between the value of the index and the exercise price of the option. The premium, the exercise price and the value of the index determine the gain or loss realized by the Fund as the seller of the index call option. The Fund can also repurchase the call option prior to the expiration date, ending its obligation. In this case, the difference between the cost of repurchasing the option and the premium received will determine the gain or loss realized by the Fund.

Purchasing Index Put Options

The Fund may buy index put options in an attempt to protect the Fund from a significant market decline that may occur over a short period of time. The value of an index put option generally increases as stock prices (and the value of the index) decrease and decreases as those stocks (and the index) increase in price. The Fund may not spend at any time more than 5% of its assets to purchase index put options.

Other Investments

The Fund may invest in foreign securities traded in U.S. markets (through ADRs or stocks traded in U.S. dollars). The Fund may enter into repurchase agreements and/or hold cash and cash equivalents.

Principal Investment Risks

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.

Correlation Risk: The effectiveness of the Fund's index option-based risk management strategy may be reduced if the performance of the Fund's equity portfolio does not correlate to that of the indices underlying its option positions.

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. Small- and mid-capitalization and emerging growth companies may be subject to more abrupt price movements, limited markets and less liquidity than larger, more established companies, which could adversely affect the value of the Fund's equity portfolio.

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.

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.

Options Risk: The value of the Fund's positions in index options will fluctuate in response to changes in the value of the underlying index. Writing index call options limits the opportunity to profit from an increase in the market value of stocks in exchange for up-front cash at the time of selling the call option. The Fund also risks losing all or part of the cash paid for purchasing index put options. Unusual market conditions or the lack of a ready market for any particular option at a specific time may reduce the effectiveness of the Fund's option strategies, and for these and other reasons the Fund's option strategies may not reduce the Fund's volatility to the extent desired.

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/Return Bar Chart and Table

The following bar chart and table 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 and ten-year periods compare to those of two broad measures 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 ngam.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.

Total Returns for Class T Shares

Highest Quarterly Return:
Second Quarter 2009, 6.06%

Lowest Quarterly Return:
Fourth Quarter 2008, -11.15%

Average Annual Total Returns

(for the periods ended December 31, 2016)

Average Annual Total Returns - (Gateway Fund)	Past 1 Year	Past 5 Years	Past 10 Years
Class T	2.60%	4.21%	2.77%
Class T | Return After Taxes on Distributions	2.26%	3.86%	2.42%
Class T | Return After Taxes on Distributions and Sale of Fund Shares	1.74%	3.27%	2.17%
S&P 500® Index	11.96%	14.66%	6.95%
Bloomberg Barclays U.S. Aggregate Bond Index	2.65%	2.23%	4.34%

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 are offered in a separate prospectus and have the same expenses as Class T shares, restated in the table to reflect the different sales load applicable to Class T shares. The returns shown in the bar chart and the table for periods before February 15, 2008 is that of the Fund's predecessor (the "Gateway Predecessor Fund"), restated to reflect the expenses of Class A 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.

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

[2] Gateway Investment Advisers, LLC ("Gateway" 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 1.20% of the Fund's average daily net assets for Class T 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 April 30, 2018 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 T 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 fee/expense was waived/reimbursed.

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

[2] Gateway Investment Advisers, LLC ("Gateway" or the "Adviser") has given a binding contractual undertaking to the Fund to limit the amount of the Fund's total annual fund operating expenses to 0.94% of the Fund's average daily net assets for Class T 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 April 30, 2018 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 T 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 fee/expense was waived/reimbursed.

XML

Label

Element

Value

(Gateway Equity Call Premium Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

rr_ObjectiveHeading

Investment Goal

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks total return with less risk than U.S. equity markets.

Expense [Heading]

rr_ExpenseHeading

Fund Fees & Expenses

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for a sales charge discount if you invest at least $250,000 in the Fund. More information about this and other discounts is available from your financial professional and in the section "How Sales Charges Are Calculated" on page 77 of the Prospectus.

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for a sales charge discount if you invest at least $250,000 in the Fund.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

$ 250,000

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees

(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

April 30, 2018

Other Expenses, New Fund, Based on Estimates [Text]

rr_OtherExpensesNewFundBasedOnEstimates

Other expenses are estimated for the current fiscal year.

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same, except that the example is based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement assuming that such waiver and/or reimbursement will only be in place through the date noted above and on the Total Annual Fund Operating Expenses for the remaining periods. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes for you if your Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During its most recently ended fiscal year, the Fund's portfolio turnover rate was 24% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

24.00%

Strategy [Heading]

rr_StrategyHeading

Investments, Risks and Performance

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal market conditions, the Fund will invest at least 80% of its net assets (plus any borrowings made for investment purposes) in equity securities. Equity securities purchased by the Fund may include the following U.S. exchange-listed securities: common stocks; American Depositary Receipts ("ADRs"), which are securities issued by a U.S. bank that represent interests in foreign equity securities; and interests in real estate investment trusts ("REITs"). The Fund ordinarily invests in a broadly diversified equity portfolio, while also writing (selling) index call options with an aggregate notional value approximately equal to the market value of the equity portfolio. Writing index call options is intended to reduce the Fund's volatility and provide steady cash flow. Cash flow from call option writing is intended to be an important source of the Fund's return, although the Fund's option writing activity reduces the Fund's ability to profit from increases in the value of its equity portfolio. The combination of a diversified stock portfolio and the steady cash flow from the sale of index call options is intended to moderate the volatility of returns relative to an all-equity portfolio. The Fund may invest in companies with small, medium or large market capitalizations.

The Fund's combination of a broadly diversified portfolio of common stocks and written index call options is similar to the components of the CBOE S&P 500 BuyWrite Index (the "BXM℠"). The BXM℠ is a passive total return index based on (1) buying an S&P 500® stock index portfolio, and (2) writing (selling) the near-term S&P 500® Index "covered" call option. The Fund's more flexible, active option management approach creates the potential for it to achieve higher long-term returns than the BXM℠ while exhibiting a similar level of volatility, as defined by standard deviation of returns. The similarities between the BXM℠ and the Fund's equity investment strategy are expected to result in the Fund exhibiting a positive correlation to the broad U.S. equity markets similar to that exhibited by the BXM℠.

With its core investment in equities, the Fund is intended to be significantly less vulnerable to fluctuations in value caused by interest rate volatility, a risk factor present in both fixed-income investments and "hybrid investments" (blends of equity and fixed-income securities). Through the use of index options, the Fund intends that its risk management strategy will reduce the volatility inherent in equity investments while also allowing for more participation in equity returns than hybrid investments. Thus, the Fund seeks to provide an efficient trade-off between risk and reward, where risk is characterized by volatility or fluctuations in value over time.

Purchasing Stocks

The Fund invests in a diversified stock portfolio, generally consisting of approximately 200 to 400 stocks (including ADRs and REITs), designed to support the Fund's index option-based risk management strategy as efficiently as possible while seeking to enhance the Fund's after-tax total return. The Adviser uses a multifactor quantitative model to construct the stock portfolio. The model evaluates approximately 9,000 equity securities to construct a portfolio of U.S.-exchange-traded equities that meets the criteria and constraints established by the Adviser. Generally, the Adviser tries to minimize the difference between the performance of the Fund's stock portfolio and the performance of the index or indices underlying the Fund's option strategies while also considering other factors, such as predicted dividend yield. The Adviser monitors this difference and other factors, and rebalances and adjusts the stock portfolio from time to time, by purchasing and selling stocks. To the extent consistent with the Fund's investment goal, the Adviser may also sell stocks to realize capital losses in an effort to minimize any required capital gain distributions. The Adviser expects the portfolio to generally represent the broad U.S. equity market.

Writing Index Call Options

The Fund continuously writes index call options, typically on broad-based securities market indices, with an aggregate notional value approximately equal to the market value of its broadly diversified stock portfolio. As the seller of the index call option, the Fund receives cash (the "premium") from the purchaser. The purchaser of an index call option has the right to any appreciation in the value of the index over a fixed price (the "exercise price") on a certain date in the future (the "expiration date"). If the purchaser does not exercise the option, the Fund retains the premium. If the purchaser exercises the option, the Fund pays the purchaser the difference between the value of the index and the exercise price of the option. The premium, the exercise price and the value of the index determine the gain or loss realized by the Fund as the seller of the index call option. The Fund can also repurchase the call option prior to the expiration date, ending its obligation. In such a case, the difference between the cost of repurchasing the option and the premium received will determine the gain or loss realized by the Fund.

Other Investments

The Fund may invest in foreign securities traded in U.S. markets (through ADRs or stocks traded in U.S. dollars). The Fund may enter into repurchase agreements and/or hold cash and cash equivalents.

Risk [Heading]

rr_RiskHeading

Principal Investment Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The principal risks of investing in the Fund are summarized below. The Fund does not represent a complete investment program. You may lose money by investing in the Fund.

Call Options Risk: The value of the Fund's positions in index options will fluctuate in response to changes in the value of the underlying index. Writing index call options limits the opportunity to profit from an increase in the market value of stocks in exchange for up-front cash at the time of selling the call option. Unusual market conditions or the lack of a ready market for any particular option at a specific time may reduce the effectiveness of the Fund's option-based risk management strategy, and for these and other reasons the Fund's option strategy may not reduce the Fund's volatility to the extent desired.

Correlation Risk: The Fund's ability to manage the volatility of its equity portfolio by writing index call options depends on the correlation between the returns of the equity portfolio and those of the index on which the call options are written. Accordingly, the effectiveness of the Fund's index option-based risk management strategy may be reduced to the extent the performance of the Fund's equity portfolio does not correlate to that of the indices underlying its option positions.

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. Small- and mid-capitalization and emerging growth companies may be subject to more abrupt price movements, limited markets and less liquidity than larger, more established companies, which could adversely affect the value of the Fund's equity portfolio.

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.

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.

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.

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]

rr_RiskLoseMoney

You may lose money by investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Risk/Return Bar Chart and Table

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The bar chart and table shown below provide some indication of the risks of investing in the Fund by showing the Fund's performance in the first full year and by showing how the Fund's average annual returns for the one-year and Life-of-Fund periods compare to those of two broad measures 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 ngam.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

Total Returns for Class T Shares

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

The chart does not reflect any sales charge that you may be required to pay when you buy or redeem the Fund's shares. A sales charge will reduce your return.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

Highest Quarterly Return:
Fourth Quarter 2015, 4.00%

Lowest Quarterly Return:
Third Quarter 2015, -3.59%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns

(for the periods ended December 31, 2016)

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 are offered in a separate prospectus and have the same expenses as Class T shares, restated in the table 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

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 the Fund's performance in the first full year and by showing how the Fund's average annual returns for the one-year and Life-of-Fund periods 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.

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

ngam.natixis.com

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-225-5478

(Gateway Equity Call Premium Fund) | CBOE S&P 500 BuyWrite Index (BXM℠)

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

7.07%

Life of Fund (9/30/14)

rr_AverageAnnualReturnSinceInception

5.05%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2014

(Gateway Equity Call Premium Fund) | S&P 500® Index

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

11.96%

Life of Fund (9/30/14)

rr_AverageAnnualReturnSinceInception

8.07%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2014

(Gateway Equity Call Premium 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

0.65%

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

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.41%

^[1]

Total annual fund operating expenses

rr_ExpensesOverAssets

1.31%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.11%

^[2]

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

rr_NetExpensesOverAssets

1.20%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 369

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

643

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

939

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,779

Annual Return 2015

rr_AnnualReturn2015

3.90%

Annual Return 2016

rr_AnnualReturn2016

7.58%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Return: Fourth Quarter 2015, 4.00%

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

4.00%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2015

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return: Third Quarter 2015, -3.59%

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(3.59%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2015

Past 1 Year

rr_AverageAnnualReturnYear01

4.91%

Life of Fund (9/30/14)

rr_AverageAnnualReturnSinceInception

3.88%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2014

(Gateway Equity Call Premium Fund) | Class T | Return After Taxes on Distributions

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

4.67%

Life of Fund (9/30/14)

rr_AverageAnnualReturnSinceInception

3.59%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2014

(Gateway Equity Call Premium Fund) | Class T | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

rr_ProspectusTable

Past 1 Year

rr_AverageAnnualReturnYear01

2.96%

Life of Fund (9/30/14)

rr_AverageAnnualReturnSinceInception

2.95%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2014

(Gateway Fund)

Prospectus:

rr_ProspectusTable

Objective [Heading]

rr_ObjectiveHeading

Investment Goal

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks to capture the majority of the returns associated with equity market investments, while exposing investors to less risk than other equity investments.

Expense [Heading]

rr_ExpenseHeading

Fund Fees & Expenses

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for a sales charge discount if you invest at least $250,000 in the Fund. More information about this and other discounts is available from your financial professional and in the section "How Sales Charges Are Calculated" on page 77 of the Prospectus.

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for a sales charge discount if you invest at least $250,000 in the Fund.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

$ 250,000

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees

(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

April 30, 2018

Other Expenses, New Fund, Based on Estimates [Text]

rr_OtherExpensesNewFundBasedOnEstimates

Other expenses are estimated for the current fiscal year.

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods (except where indicated). The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same, except that the example is based on the Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement assuming that such waiver and/or reimbursement will only be in place through the date noted above and on the Total Annual Fund Operating Expenses for the remaining periods. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes for you if your Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund's performance. During its most recently ended fiscal year, the Fund's portfolio turnover rate was 14% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

14.00%

Strategy [Heading]

rr_StrategyHeading

Investments, Risks and Performance

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Under normal circumstances, the Fund invests in a broadly diversified portfolio of common stocks, while also selling index call options and purchasing index put options. Writing index call options reduces the Fund's volatility, provides steady cash flow and is an important source of the Fund's return, although it also reduces the Fund's ability to profit from increases in the value of its equity portfolio. The Fund also buys index put options, which can protect the Fund from a significant market decline that may occur over a short period of time. The value of an index put option generally increases as the prices of the stocks constituting the index decrease, and decreases as those stocks increase in price. From time to time, the Fund may reduce its holdings of put options, resulting in an increased exposure to a market decline. The combination of the diversified stock portfolio, the steady cash flow from the sale of index call options and the downside protection from index put options is intended to provide the Fund with the majority of the returns associated with equity market investments while exposing investors to less risk than other equity investments. The Fund may invest in companies with small, medium or large market capitalizations. Equity securities purchased by the Fund may include U.S. exchange-listed common stocks, American Depositary Receipts ("ADRs"), which are securities issued by a U.S. bank that represent interests in foreign equity securities, and interests in real estate investment trusts ("REITs").

The Fund strives not only for the majority of the returns associated with equity market investments, but also for returns in excess of those available from other investments comparable in volatility. Because, as described above, the Fund writes index call options and purchases index put options in addition to investing in equity securities, the Fund's historical volatility has been closer to intermediate-to long-term fixed-income investments (intermediate-term are those with approximately five-year maturities and long-term are those with maturities of ten or more years) and hybrid investments (blends of equity and short-term fixed-income securities) than to equity investments. With its core investment in equities, the Fund is significantly less vulnerable to fluctuations in value caused by interest rate volatility, a risk factor present in both fixed-income investments and "hybrid investments" (blends of equity and short-term fixed-income), although the Fund expects to generally have lower long-term returns than a fund consisting solely of equity securities. Through the use of index options, the Fund intends that its risk management strategy will reduce the volatility inherent in equity investments while also allowing for more participation in equity returns than hybrid investments. Thus, the Fund seeks to provide an efficient trade-off between risk and reward where risk is characterized by volatility or fluctuations in value over time.

Purchasing Stocks

The Fund invests in a diversified stock portfolio, generally consisting of approximately 200 to 400 stocks, designed to support the Fund's index option based risk management strategy as efficiently as possible while seeking to enhance the Fund's after tax total return. The Adviser uses a multifactor quantitative model to construct the stock portfolio. The model evaluates approximately 9,000 equity securities to construct a portfolio of U.S.-exchange-traded equities that meets criteria and constraints established by the Adviser. Generally, the Adviser tries to minimize the difference between the performance of the stock portfolio and that of the index or indices underlying the Fund's option strategies while also considering other factors, such as predicted dividend yield. The Adviser monitors this difference and the other factors, and rebalances and adjusts the stock portfolio from time to time, by purchasing and selling stocks. To the extent consistent with the Fund's investment goal, the Adviser may also sell stocks to realize capital losses in an effort to minimize any required capital gain distributions. The Adviser expects the portfolio to generally represent the broad U.S. equity market.

Writing Index Call Options

The Fund continuously writes index call options, typically on broad-based securities market indices, on the full value of its broadly diversified stock portfolio. As the seller of the index call option, the Fund receives cash (the "premium") from the purchaser. The purchaser of an index call option has the right to any appreciation in the value of the index over a fixed price (the "exercise price") on a certain date in the future (the "expiration date"). If the purchaser does not exercise the option, the Fund retains the premium. If the purchaser exercises the option, the Fund pays the purchaser the difference between the value of the index and the exercise price of the option. The premium, the exercise price and the value of the index determine the gain or loss realized by the Fund as the seller of the index call option. The Fund can also repurchase the call option prior to the expiration date, ending its obligation. In this case, the difference between the cost of repurchasing the option and the premium received will determine the gain or loss realized by the Fund.

Purchasing Index Put Options

The Fund may buy index put options in an attempt to protect the Fund from a significant market decline that may occur over a short period of time. The value of an index put option generally increases as stock prices (and the value of the index) decrease and decreases as those stocks (and the index) increase in price. The Fund may not spend at any time more than 5% of its assets to purchase index put options.

Other Investments

The Fund may invest in foreign securities traded in U.S. markets (through ADRs or stocks traded in U.S. dollars). The Fund may enter into repurchase agreements and/or hold cash and cash equivalents.

Risk [Heading]

rr_RiskHeading

Principal Investment Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

The principal risks of investing in the Fund are summarized below. The Fund does not represent a complete investment program. You may lose money by investing in the Fund.

Correlation Risk: The effectiveness of the Fund's index option-based risk management strategy may be reduced if the performance of the Fund's equity portfolio does not correlate to that of the indices underlying its option positions.

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. Small- and mid-capitalization and emerging growth companies may be subject to more abrupt price movements, limited markets and less liquidity than larger, more established companies, which could adversely affect the value of the Fund's equity portfolio.

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.

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.

Options Risk: The value of the Fund's positions in index options will fluctuate in response to changes in the value of the underlying index. Writing index call options limits the opportunity to profit from an increase in the market value of stocks in exchange for up-front cash at the time of selling the call option. The Fund also risks losing all or part of the cash paid for purchasing index put options. Unusual market conditions or the lack of a ready market for any particular option at a specific time may reduce the effectiveness of the Fund's option strategies, and for these and other reasons the Fund's option strategies may not reduce the Fund's volatility to the extent desired.

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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Risk/Return Bar Chart and Table

Performance Narrative [Text Block]

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The following bar chart and table 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 and ten-year periods compare to those of two broad measures 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 ngam.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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Total Returns for Class T Shares

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, 6.06%

Lowest Quarterly Return:
Fourth Quarter 2008, -11.15%

Performance Table Heading

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Average Annual Total Returns

(for the periods ended December 31, 2016)

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 are offered in a separate prospectus and have the same expenses as Class T shares, restated in the table to reflect the different sales load applicable to Class T shares. The returns shown in the bar chart and the table for periods before February 15, 2008 is that of the Fund's predecessor (the "Gateway Predecessor Fund"), restated to reflect the expenses of Class A 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.

Performance Table Does Reflect Sales Loads

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The returns shown in the bar chart and the table for periods before February 15, 2008 is that of the Fund's predecessor (the "Gateway Predecessor Fund"), restated to reflect the expenses of Class A shares.

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

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

Performance Table Uses Highest Federal Rate

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

Performance Table Not Relevant to Tax Deferred

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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]

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The following bar chart and table 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 and ten-year periods 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.

Performance Availability Website Address [Text]

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ngam.natixis.com

Performance Availability Phone [Text]

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800-225-5478

(Gateway Fund) | S&P 500® Index

Prospectus:

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Past 1 Year

rr_AverageAnnualReturnYear01

11.96%

Past 5 Years

rr_AverageAnnualReturnYear05

14.66%

Past 10 Years

rr_AverageAnnualReturnYear10

6.95%

(Gateway Fund) | Bloomberg Barclays U.S. Aggregate Bond Index

Prospectus:

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Past 1 Year

rr_AverageAnnualReturnYear01

2.65%

Past 5 Years

rr_AverageAnnualReturnYear05

2.23%

Past 10 Years

rr_AverageAnnualReturnYear10

4.34%

(Gateway Fund) | Class T

Prospectus:

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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)

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none

Redemption fees

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none

Management fees

rr_ManagementFeesOverAssets

0.63%

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

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.14%

^[1]

Total annual fund operating expenses

rr_ExpensesOverAssets

1.02%

Fee waiver and/or expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.08%

^[3]

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

rr_NetExpensesOverAssets

0.94%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 344

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

558

Expense Example, with Redemption, 5 Years

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791

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,459

Annual Return 2007

rr_AnnualReturn2007

7.94%

Annual Return 2008

rr_AnnualReturn2008

(13.92%)

Annual Return 2009

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6.57%

Annual Return 2010

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4.83%

Annual Return 2011

rr_AnnualReturn2011

2.99%

Annual Return 2012

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4.51%

Annual Return 2013

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8.39%

Annual Return 2014

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3.33%

Annual Return 2015

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2.34%

Annual Return 2016

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5.23%

Highest Quarterly Return, Label

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Highest Quarterly Return: Second Quarter 2009, 6.06%

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

6.06%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Return: Fourth Quarter 2008, -11.15%

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(11.15%)

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Past 1 Year

rr_AverageAnnualReturnYear01

2.60%

Past 5 Years

rr_AverageAnnualReturnYear05

4.21%

Past 10 Years

rr_AverageAnnualReturnYear10

2.77%

(Gateway Fund) | Class T | Return After Taxes on Distributions

Prospectus:

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Past 1 Year

rr_AverageAnnualReturnYear01

2.26%

Past 5 Years

rr_AverageAnnualReturnYear05

3.86%

Past 10 Years

rr_AverageAnnualReturnYear10

2.42%

(Gateway Fund) | Class T | Return After Taxes on Distributions and Sale of Fund Shares

Prospectus:

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Past 1 Year

rr_AverageAnnualReturnYear01

1.74%

Past 5 Years

rr_AverageAnnualReturnYear05

3.27%

Past 10 Years

rr_AverageAnnualReturnYear10

2.17%

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

[2] Gateway Investment Advisers, LLC ("Gateway" 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 1.20% of the Fund's average daily net assets for Class T 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 April 30, 2018 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 T 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 fee/expense was waived/reimbursed.

[3] Gateway Investment Advisers, LLC ("Gateway" or the "Adviser") has given a binding contractual undertaking to the Fund to limit the amount of the Fund's total annual fund operating expenses to 0.94% of the Fund's average daily net assets for Class T 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 April 30, 2018 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 T 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 fee/expense was waived/reimbursed.