v3.26.3
Label Element Value
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk/Return [Heading] oef_RiskReturnHeading ​  GMO OPPORTUNISTIC INCOME FUND   ​
Objective [Heading] oef_ObjectiveHeading Investment objective
Objective, Primary [Text Block] oef_ObjectivePrimaryTextBlock
Capital appreciation and current income.
Expense Heading [Optional Text] oef_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] oef_ExpenseNarrativeTextBlock
The table below describes the fees and expenses that you may bear for each class of shares if you buy, hold, and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and example below.
Operating Expenses Caption [Optional Text] oef_OperatingExpensesCaption Annual Fund operating expenses (expenses that you bear each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination Sep. 30, 2027
Other Expenses, New Fund, Based on Estimates [Text] oef_OtherExpensesNewFundBasedOnEstimates Because ETF Class shares of the Fund are new, “Other expenses” are estimated amounts for the current fiscal year based on the expenses of Class R6 shares of the Fund.
Expense Example [Heading] oef_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] oef_ExpenseExampleNarrativeTextBlock
This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated, regardless of whether or not you sell your shares at the end of such periods. The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses with respect to ETF Class shares remain the same as those shown in the table. The one year amounts shown reflect the expense reimbursement and waiver noted in the expense table. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Portfolio Turnover [Heading] oef_PortfolioTurnoverHeading Portfolio turnover
Portfolio Turnover [Text Block] oef_PortfolioTurnoverTextBlock
The Fund pays transaction costs, such as commissions, when it buys and sells securities. A higher portfolio turnover rate may result in higher transaction costs and, for holders of Fund shares subject to U.S. taxes, higher income taxes. These transaction costs, which are not reflected in Annual Fund operating expenses or in the Example, affect the Fund’s performance. During its fiscal year ended February 28, 2026, the Fund’s portfolio turnover rate (excluding short-term investments) was 274% of the average value of its portfolio securities. That portfolio turnover rate includes investments in U.S. Treasury Fund, which the Fund uses as a short-term investment vehicle for cash management. The Fund’s portfolio turnover rate during its fiscal year ended February 28, 2026, excluding transactions in U.S. Treasury Fund and other short-term investments, was 277% of the average value of its portfolio securities.
Portfolio Turnover, Rate oef_PortfolioTurnoverRate 274.00%
Strategy [Heading] oef_StrategyHeading Principal investment strategies
Strategy Narrative [Text Block] oef_StrategyNarrativeTextBlock
The Fund invests primarily in securitized credit securities. Securitized credit securities include, but are not limited to, commercial and residential (non-agency and agency) mortgage-backed securities, small balance commercial mortgages, collateralized loan obligations, collateralized debt obligations, and securities backed by pools of receivables in various industries. The interest rates for these securities may be fixed or variable. The Fund also may invest in other fixed-income instruments, including, without limitation, bonds and other similar instruments issued or guaranteed by the U.S. government and its agencies and instrumentalities, by non-U.S. governments and their agencies and instrumentalities and by private sector entities.
The Fund also may invest in the following: interest-only, principal-only, or inverse floating rate debt; mortgage dollar rolls; securities on a when-issued, delayed delivery or forward commitment basis through the “to-be-announced” market; mortgage loans; securities of any
maturity or duration with fixed, floating, or variable rates; equity and debt securities issued by real estate investment trusts; debt securities issued by business development companies; corporate debt securities of any quality and maturity, including high-yield securities (commonly referred to as “junk bonds”); and securities that are not rated by any rating agency.
GMO utilizes both a top-down and bottom-up security selection approach. GMO allocates Fund assets among various asset classes within the structured fixed income market based on its views regarding the best value relative to what is currently available in the market. In managing the Fund’s portfolio, GMO typically analyzes a variety of factors including, among others, maturity, yield and ratings information, opportunities for price appreciation, collateral quality, credit support, structure, and market conditions. GMO attempts to diversify risks that arise from position sizes, sectors and geographies, ratings, duration, deal structure and collateral values and seeks to further limit risk of principal loss by causing the Fund to invest in securities or other instruments that it considers undervalued. To a lesser extent, GMO may use quantitative models to capitalize on price momentum across fixed income sectors. GMO does not manage the Fund to, or control the Fund’s risk relative to, any securities index or securities benchmark.
From time to time, the Fund may have some direct or indirect exposure to equities. The Fund may invest in securities of companies of any market capitalization, as well as in securities of any maturity, duration, or credit quality.
The Fund also may invest in exchange-traded funds (ETFs) and exchange-traded and over-the-counter (OTC) derivatives, including swap contracts (such as credit default swaps, swaps on securities and securities indices, total return swaps and interest rate swaps), futures contracts, forward currency contracts, currency and interest rate options, swaptions (including credit default swaptions), reverse repurchase agreements, and repurchase agreements. In addition, the Fund may lend its portfolio securities. The Fund is not limited in its use of derivatives or in the total notional value of its derivative positions. Leverage is not a principal component of the Fund’s investment strategy. However, because of its derivative positions, the Fund may at times have gross investment exposure in excess of its net assets (i.e., the Fund may be leveraged) and, therefore, may be subject to higher risk of loss during those times than if the Fund were not leveraged. The Fund’s performance can depend substantially on the performance of assets or indices underlying its derivatives even though it does not own those assets or indices.
In seeking to achieve the Fund’s investment objective, GMO may invest a significant portion of the Fund’s net assets in cash and cash equivalents.
The Fund also may invest in U.S. Treasury Fund, in money market funds unaffiliated with GMO, and directly in the types of investments typically held by money market funds. The Fund may, but is not required to, hedge part or all of its net foreign currency exposure into U.S. dollars.
The Fund’s ETF Class operates as an actively managed exchange-traded fund (“ETF”).
Bar Chart and Performance Table [Heading] oef_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] oef_PerformanceNarrativeTextBlock
The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s annual total returns from year to year for the periods indicated and by comparing the Fund’s average annual total returns for different calendar periods with those of the Bloomberg U.S. Securitized Index and an additional comparative index intended solely to represent, in satisfaction of regulatory requirements, the overall fixed income market. The Fund’s ETF Class shares are a new class and, as of the date of this Prospectus, had not commenced operations. Returns shown are those of Class VI shares of the Fund, a mutual fund class of shares of the Fund not offered in this Prospectus, and have not been adjusted to reflect the fees and expenses attributable to ETF Class shares. Class VI shares would have substantially similar annual returns to ETF Class shares because the shares are invested in the same portfolio of securities, and the annual returns at NAV (assuming ETF Class shares are bought and sold without any premium or discount) would differ only to the extent that Class VI shares do not have the same expenses as ETF Class shares. Share classes that bear higher expenses than the share classes shown below would have lower returns. 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 your tax situation and may differ from those shown. After-tax returns shown are not relevant if you are tax-exempt or if you hold your Fund shares through tax-advantaged arrangements (such as a 401(k) plan or individual retirement account). After-tax returns are shown for Class VI shares only; after-tax returns for other classes will vary. Updated performance information for the Fund is available at https://www.gmo.com/americas/investment-capabilities/etfs/. Past performance (before and after taxes) is not an indication of future performance.
Performance Information Illustrates Variability of Returns [Text] oef_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s annual total returns from year to year for the periods indicated and by comparing the Fund’s average annual total returns for different calendar periods with those of the Bloomberg U.S. Securitized Index and an additional comparative index intended solely to represent, in satisfaction of regulatory requirements, the overall fixed income market.
Performance One Year or Less [Text] oef_PerformanceOneYearOrLess The Fund’s ETF Class shares are a new class and, as of the date of this Prospectus, had not commenced operations.
Performance Availability Website Address [Text] oef_PerformanceAvailabilityWebSiteAddress https://www.gmo.com/americas/investment-capabilities/etfs/
Performance Past Does Not Indicate Future [Text] oef_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not an indication of future performance.
Bar Chart [Heading] oef_BarChartHeading Annual Total Returns/Class VI Shares1 Years Ending December 31
Bar Chart Footnotes [Text Block] oef_BarChartFootnotesTextBlock

1. The Fund is the accounting and performance successor to GMO Debt Opportunities Fund, a former series of GMO Trust (the “Predecessor Fund”). The Predecessor Fund merged into the Fund (which was known as “GMO Short-Duration Collateral Fund” prior to the merger) on February 12, 2014. Performance of the Fund for periods prior to February 12, 2014 is that of the Predecessor Fund and reflects the Predecessor Fund’s annual operating expenses (0.01% lower than those of the Fund immediately following the merger). From February 12, 2014 through December 31, 2016, the Fund operated as “GMO Debt Opportunities Fund” and had the same investment objective and pursued substantially identical investment strategies as the Predecessor Fund. Effective January 1, 2017, the Fund’s investment objective changed from “positive total return” to “capital appreciation and current income” and, in conjunction with a change in the Fund’s name from “GMO Debt Opportunities Fund” to “GMO Opportunistic Income Fund,” the Fund eliminated its name policy that required the Fund to invest at least 80% of its assets in debt investments. Also effective January 1, 2017, the Fund’s investment management fee increased from 0.25% to 0.40% of the Fund’s average daily net assets. Performance of the Fund for periods prior to January 1, 2017 reflects the Fund’s annual operating expenses during those periods, and would have been lower if the current management fee were in effect.
Bar Chart Closing [Text Block] oef_BarChartClosingTextBlock
Highest Quarter: 4.55% 2Q 2020
Lowest Quarter: -4.05% 1Q 2020
Year-to-Date: 1.34% As of 6/30/2026
Year to Date Return, Label [Optional Text] oef_YearToDateReturnLabel Year-to-Date:
Bar Chart, Year to Date Return, Date oef_BarChartYearToDateReturnDate Jun. 30, 2026
Bar Chart, Year to Date Return oef_BarChartYearToDateReturn 1.34%
Highest Quarterly Return, Label [Optional Text] oef_HighestQuarterlyReturnLabel Highest Quarter:
Highest Quarterly Return, Date oef_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return oef_BarChartHighestQuarterlyReturn 4.55%
Lowest Quarterly Return, Label [Optional Text] oef_LowestQuarterlyReturnLabel Lowest Quarter:
Lowest Quarterly Return, Date oef_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return oef_BarChartLowestQuarterlyReturn (4.05%)
Performance Table Heading oef_PerformanceTableHeading Average Annual Total Returns1,2 Periods Ending December 31, 2025
Index No Deduction for Fees, Expenses, or Taxes [Text] oef_IndexNoDeductionForFeesExpensesTaxes (returns reflect no deduction for fees, expenses, or taxes)
Performance Table Uses Highest Federal Rate oef_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 oef_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on your tax situation and may differ from those shown. After-tax returns shown are not relevant if you are tax-exempt or if you hold your Fund shares through tax-advantaged arrangements (such as a 401(k) plan or individual retirement account).
Performance Table One Class of after Tax Shown [Text] oef_PerformanceTableOneClassOfAfterTaxShown After-tax returns are shown for Class VI shares only; after-tax returns for other classes will vary.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Risk Lose Money [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock Many factors can affect this value, and you may lose money by investing in the Fund.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Risk Not Insured [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock An investment in the Fund is not a bank deposit and is not insured or guaranteed by the FDIC or any government agency.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Credit Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Credit Risk – The Fund runs the risk that the issuer or guarantor of a fixed income investment (including a sovereign or quasi-sovereign debt issuer) or the obligor of an obligation underlying an asset-backed security will be unable or unwilling to satisfy its obligation to pay principal and interest or otherwise to honor its obligations in a timely manner or at all. The market price of a fixed income investment will normally decline as a result of the failure of an issuer, guarantor, or obligor to meet its payment obligations or in anticipation of such a failure. Below investment grade investments (commonly referred to as high yield or “junk” bonds) have speculative characteristics and are subject to greater credit risk than other fixed income investments. Negative changes in economic conditions or other circumstances are more likely to impair the ability of issuers of below investment grade investments to make principal and interest payments than issuers of investment grade investments. In addition, investments in emerging country sovereign or quasi-sovereign debt are subject to a heightened risk that the issuer responsible for repayment of the debt may be unable or unwilling to pay interest and repay principal when due, and the Fund may lack recourse against the issuer in the event of a default. Investments in quasi-sovereign debt also are subject to the risk that the issuer will default independently of its sovereign. Investments in distressed or defaulted or other low quality debt investments generally are considered speculative and are subject to substantial risks not normally associated with investments in higher quality securities, including adverse business, financial or economic conditions that lead to their issuers’ payment defaults and insolvency proceedings. In particular, distressed or defaulted obligations might be repaid, if at all, only after lengthy workout or bankruptcy proceedings during which the issuer might not make any interest or other payments, and the Fund may incur additional expenses in its effort to be repaid. If GMO’s assessment of the eventual recovery value of a distressed or defaulted debt investment proves incorrect, the Fund may lose a substantial portion or all of its original investment or may be required to accept cash or instruments worth less than its original investment.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Market Risk – Asset-Backed Securities [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Market Risk – Asset-Backed Securities – The market price of asset-backed securities, like that of other fixed income investments, can decline for a variety of reasons, including increases in interest rates. In addition, the market price can decrease due to a reduction in or decrease in the reliability of their payment streams. Payment streams associated with asset-backed securities held by the Fund depend on
many factors (e.g., the cash flow generated by the assets backing the securities, deal structure, and creditworthiness of any credit-support provider), and a problem in any of these factors can lead to a reduction in the payment stream GMO expected the Fund to receive when the Fund purchased the asset-backed security. The liquidity of asset-backed securities (particularly below investment grade asset-backed securities) may change over time. During periods of deteriorating economic conditions, such as recessions, or periods of rising unemployment, delinquencies and losses generally increase, sometimes dramatically, for asset-backed securities whose underlying assets consist of loans, sales contracts, receivables and other obligations.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Illiquidity Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Illiquidity Risk – Low trading volume, lack of a market maker, large position size, or legal restrictions increase the risk that the Fund or an underlying fund is limited or prevented from selling particular securities or closing derivative positions at desirable prices at a particular time or at all.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Focused Investment Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Focused Investment Risk – Investments in countries, regions, asset classes, sectors, industries, currencies, or issuers that are subject to the same or similar risk factors and investments whose market prices are closely correlated, such as the Fund’s investments in non-U.S. government bonds and asset-backed securities secured by different types of consumer debt (e.g., credit-card receivables, automobile loans, and home equity loans), are subject to higher overall risk than investments that are more diversified or whose market prices are not as closely correlated.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Market Risk – Fixed Income [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Market Risk – Fixed Income – The market price of a fixed income investment can decline due to market-related factors, including rising interest or inflation rates and widening credit spreads, or decreased liquidity due, for example, to market uncertainty about the value of a fixed income investment (or class of fixed income investments).
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Derivatives and Short Sales Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Derivatives and Short Sales Risk – The use of derivatives involves the risk that their value may not change as expected relative to changes in the value of the underlying assets, pools of assets, rates, currencies or indices. Derivatives also present other risks, including market risk, illiquidity risk, currency risk, credit risk, leveraging risk, commodities risk and counterparty risk. The market price of an option is affected by many factors, including changes in the market prices or dividend rates of underlying securities (or in the case of indices, the securities in such indices); the time remaining before expiration; changes in interest rates or exchange rates; and changes in the actual or perceived volatility of the relevant index or underlying securities. The Fund typically creates short investment exposure by selling securities short or by taking a derivative position in which the value of the derivative moves in the opposite direction from the price of an underlying asset, pool of assets, rate, currency or index. Specifically, the net asset value of the Fund’s shares will be adversely affected if the securities or other assets that are the subject of the Fund’s short exposures appreciate in value. The risk of loss associated with derivatives that provide short investment exposure and short sales of securities is theoretically unlimited.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Futures Contracts Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Futures Contracts Risk – The loss to the Fund resulting from its use of futures contracts is potentially unlimited. Futures markets are highly volatile, and the use of futures contracts increases the volatility of the Fund’s net asset value. A liquid market may not exist for any particular futures contract at any particular time, and the Fund may be unable when it wishes to terminate its exposure under that contract. When the Fund uses futures contracts for hedging purposes, it runs the risk that changes in the prices of the contracts will not correlate perfectly with changes in the securities, index, or other asset underlying the contracts or movements in the prices of the Fund’s investments that are subject to the hedge. In addition, the Fund may be unable to recover or may be delayed in recovering margin or other amounts deposited with a futures commission merchant or futures clearinghouse. Foreign futures contracts are often less liquid and more volatile than U.S. futures contracts.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Leveraging Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Leveraging Risk – The use of derivatives, short sales and securities lending can create leverage. Leverage increases the Fund’s losses when the value of its investments (including derivatives) declines. In addition, the Fund’s portfolio will be leveraged if it exercises its right to delay payment on a redemption and the value of the Fund’s assets declines between the time a redemption request is treated as being received by the Fund and the time the Fund liquidates assets to fund that redemption.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Counterparty Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Counterparty Risk – The Fund runs the risk that the counterparty to a derivatives contract or a clearing member used by the Fund to hold a cleared derivatives contract is unable or unwilling to make timely settlement payments, return the Fund’s collateral or otherwise honor its obligations.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Management and Operational Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Management and Operational Risk – The Fund runs the risk that GMO’s investment techniques will fail to produce intended results. The Fund also runs the risk that GMO’s assessment of an investment, including a security’s fundamental fair (or intrinsic) value, is wrong or that deficiencies in GMO’s or another service provider’s internal systems or controls will cause losses for the Fund or impair Fund operations.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Large Transactions Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Large Transactions Risk – To the extent that a large number of shares of the Fund is held by a single shareholder (e.g., an institutional investor or another GMO Fund) or a group of shareholders with a common investment strategy (e.g., GMO asset allocation accounts), the Fund is subject to the risk that a redemption by (or caused by) that shareholder or group will require the Fund to sell investments at disadvantageous prices, disrupt the Fund’s operations, lead to temporary overexposure to the Fund’s intended investment program or force the Fund’s liquidation. The Fund also may be subject to these effects when a number of shareholders collectively redeem or sell a large amount of Fund shares.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Market Disruption and Geopolitical Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Market Disruption and Geopolitical Risk – Geopolitical and other events (e.g., wars, pandemics, sanctions, terrorism, diplomatic tensions, dramatic changes in regulatory and/or foreign policy, cyberattacks, and rapid technological developments such as artificial intelligence) often disrupt securities markets and adversely affect the general economy or particular economies and markets. Those events, as well as other changes in non-U.S. and U.S. economic and political conditions, could exacerbate other risks or otherwise reduce the value of the Fund’s investments.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Smaller Company Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Smaller Company Risk – Smaller companies may have limited product lines, markets, or financial resources, lack the competitive strength of larger companies, have less experienced managers or depend on a few key employees. The securities of companies with smaller market capitalizations often are less widely held and trade less frequently and in lesser quantities, and their market prices often fluctuate more, than the securities of companies with larger market capitalizations.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Non-U.S. Investment Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Non-U.S. Investment Risk – The market prices of many non-U.S. securities fluctuate more than those of U.S. securities. Many non-U.S. securities markets are less stable, smaller, less liquid, and less regulated than U.S. securities markets, and the cost of trading in those markets often is higher than in U.S. securities markets. In addition, non-U.S. securities issuers often are not subject to as much regulation as U.S. issuers, and the reporting, recordkeeping, accounting, custody, and auditing standards to which those issuers are subject often are not as rigorous as U.S. standards. In addition, the Fund is subject to taxation by countries other than the United States, including potentially on a retroactive basis, on (i) capital gains it realizes or dividends, interest, or other amounts it realizes or accrues in respect of non-U.S. investments; (ii) transactions in those investments; and (iii) repatriation of proceeds generated from the sale or other disposition of those investments. Also, the Fund needs a license to invest directly in securities traded in many non-U.S. securities markets, and the Fund is subject to the risk that its license is terminated or suspended. In some non-U.S. securities markets, prevailing custody and trade settlement practices (e.g., the requirement to pay for securities prior to receipt) expose the Fund to credit and other risks. Further, adverse changes in investment regulations, capital requirements or exchange controls could adversely affect the value of the Fund’s investments. The risks above (such as substantial price fluctuations and market instability, illiquidity and lack of regulation) and other risks (e.g., nationalization, expropriation or other confiscation of assets of non-U.S. issuers, difficulties enforcing legal judgments or contractual rights and geopolitical risks) tend to be higher for investments in the securities of issuers tied economically to emerging countries. The economies of emerging countries often depend predominantly on only a few industries or commodities and often are more volatile than the economies of developed countries.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | Currency Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
Currency Risk – Fluctuations in exchange rates can adversely affect the market value of the Fund’s foreign currency holdings and investments denominated in foreign currencies.
GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | ETF Risks [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock
ETF Risks – The Fund’s ETF Class operates as an ETF and, as a result of this structure, ETF Class shares are exposed to the following risks:
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Costs of Buying or Selling Shares Risk.   Due to the costs of buying or selling the Fund’s ETF Class shares, including brokerage commissions imposed by brokers and the variance in bid-ask spreads, frequent trading of ETF Class shares may significantly reduce investment results and an investment in ETF Class shares may not be advisable for investors who anticipate regularly making small investments.
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Limited Authorized Participants, Market Makers and Liquidity Providers Risk.   Because the Fund’s ETF Class operates as an ETF, typically only a limited number of institutional investors (known as “Authorized Participants”) are authorized to purchase and redeem shares ETF Class shares directly from the Fund. Retail investors cannot transact in ETF Class shares directly with the Fund. In addition, there may be a limited number of market makers and/or liquidity providers in the marketplace to transact in ETF Class shares, there may be demand for ETF Class shares, thereby increasing the market price above net asset value (“NAV”), or lack of demand, which may decrease the market price below NAV, or in stressed market conditions, the market for ETF Class shares may become less liquid in response to deteriorating liquidity in the markets for the Fund’s underlying portfolio holdings. As a result of these considerations, ETF Class shares may trade at a material premium or discount to their NAV or these factors may, in turn, lead to wider spreads between the bid and ask price of ETF Class shares. In addition, the ETF Class shares may face possible delisting if: (i) Authorized Participants exit the business or otherwise become unable to process creation and/or redemption orders and no other Authorized Participants step forward to perform these services, or (ii) market makers and/or liquidity providers exit the business or significantly reduce their business activities and no other entities step forward to perform their functions.
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Trading Risk.   The Fund’s ETF Class shares may trade on the NYSE Arca, Inc. (the “Exchange”) above (premium) or below (discount) their NAV. In stressed market conditions, the market for ETF Class shares may become less liquid in response to deteriorating liquidity in the markets for the Fund’s underlying portfolio holdings, which may increase the variance between the market price of the ETF Class shares and the value of the Fund’s underlying holdings attributable to ETF Class shares. This can be reflected as a spread between the bid and ask prices for the ETF Class shares quoted during the day or a premium or discount in the closing price from their NAV. In addition, although the Fund’s ETF Class shares are currently listed on the Exchange, there can be no assurance that an active trading market for ETF Class shares will develop or be maintained. Trading in ETF Class shares may be halted due to market conditions or for reasons that, in the view of the Exchange, make trading in ETF Class shares of the Fund inadvisable.
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Cash Transactions Risk.   The Fund may effect some of its creations and redemptions of ETF Class shares for cash, rather than in-kind securities. As a result, the Fund may have to sell portfolio securities at inopportune times in order to obtain the cash needed to meet redemption orders. This may cause the Fund to sell a security and recognize ordinary income, or a capital gain or loss that might not have been incurred if it had made a redemption in-kind. The use of cash creations and redemptions may also cause the Fund’s ETF Class shares to trade in the market at wider bid-ask spreads or greater premiums or discounts to their NAV. In effecting creations and redemptions in ETF Class shares in exchange for cash, the Fund may incur certain costs, including brokerage costs in connection with investing cash received and may recognize capital gains in connection with cash redemptions, unlike an ETF that effects creations and redemptions only in-kind. In addition, costs could be imposed on the Fund which would have the effect of decreasing the Fund’s NAV to the extent the costs are not offset by a transaction fee payable by an Authorized Participant.
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National Closed Market Trading Risk.   To the extent that the underlying securities or other instruments held by the Fund trade on foreign exchanges or in foreign markets that may be closed when the securities exchange on which the Fund’s ETF Class shares trade is open, there are likely to be deviations between the current price of such an underlying security and the last quoted price for the underlying security (i.e., the Fund’s quote from the closed foreign market). The impact of a closed foreign market on the Fund is likely to be greater where a large portion of the Fund’s underlying securities or other instruments trade on that closed foreign market or when the foreign market is closed for unscheduled reasons. These deviations could result in premiums or discounts to the NAV of the Fund’s ETF Class shares that may be greater than those experienced by other ETFs.
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GMO Opportunistic Income Fund | GMO Opportunistic Income Fund | ETF Class  
Prospectus [Line Items] oef_ProspectusLineItems  
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.55% [1]
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.20% [2]
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.75%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.17%) [1]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.58%
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 59
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 223
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 400
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 914
GMO Opportunistic Income Fund | Bloomberg U.S. Aggregate Index (returns reflect no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] oef_ProspectusLineItems  
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.30% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct (0.36%) [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.01% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.05% [3],[4]
GMO Opportunistic Income Fund | Bloomberg U.S. Securitized Index (returns reflect no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] oef_ProspectusLineItems  
Average Annual Return, Percent oef_AvgAnnlRtrPct 8.49% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 0.22% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.68% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.86% [3],[4]
GMO Opportunistic Income Fund | Class VI  
Prospectus [Line Items] oef_ProspectusLineItems  
Annual Return [Percent] oef_AnnlRtrPct 5.14%
Annual Return [Percent] oef_AnnlRtrPct 6.41%
Annual Return [Percent] oef_AnnlRtrPct 4.02%
Annual Return [Percent] oef_AnnlRtrPct 3.83%
Annual Return [Percent] oef_AnnlRtrPct 3.33%
Annual Return [Percent] oef_AnnlRtrPct 2.83%
Annual Return [Percent] oef_AnnlRtrPct (2.08%)
Annual Return [Percent] oef_AnnlRtrPct 7.08%
Annual Return [Percent] oef_AnnlRtrPct 6.11%
Annual Return [Percent] oef_AnnlRtrPct 6.47%
Average Annual Return, Percent oef_AvgAnnlRtrPct 6.47% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.02% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.28% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.64% [3],[4]
Performance Inception Date oef_PerfInceptionDate Oct. 03, 2011
GMO Opportunistic Income Fund | Class VI | After Taxes on Distributions  
Prospectus [Line Items] oef_ProspectusLineItems  
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.33% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.08% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.49% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 3.01% [3],[4]
GMO Opportunistic Income Fund | Class VI | After Taxes on Distributions and Sales  
Prospectus [Line Items] oef_ProspectusLineItems  
Average Annual Return, Percent oef_AvgAnnlRtrPct 3.80% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.24% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.52% [3],[4]
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.94% [3],[4]
[1] Includes both management fee of 0.40% and class-specific service and supplemental support fee of 0.15% for ETF Class shares. Grantham, Mayo, Van Otterloo & Co. LLC (“GMO”) has contractually agreed to reimburse the Fund for the portion of its “Specified Operating Expenses” ​(as defined below) that exceeds 0.02% of the Fund’s average daily net assets. If the Fund has outstanding ETF Class shares, the reimbursement will be implemented at the share class level. “Specified Operating Expenses” means only the following expenses: audit expenses, fund accounting and administration expenses, pricing service expenses, expenses of non-investment related tax services, transfer agency expenses (excluding, in the case of Class I shares, any amounts paid for sub-transfer agency, recordkeeping and other administrative services provided by financial intermediaries for the benefit of Class I shareholders), expenses of non-investment related legal services provided to the Fund by or at the direction of GMO, federal securities law filing expenses, printing expenses, state and federal registration fees, custody expenses and exchange listing fees. GMO also has contractually agreed to waive or reduce the Fund’s management fees and service and supplemental support fees to the extent necessary to offset the management fees and service and supplemental support fees paid to GMO that are directly or indirectly borne by the Fund or a class of shares of the Fund as a result of the Fund’s direct or indirect investments in other series of GMO Trust and GMO-managed ETFs (“GMO Funds”). Management fees and service and supplemental support fees will not be waived below zero. These reimbursements and waivers will continue through at least September 30, 2027 and may not be terminated prior to this date without the action or consent of the Trust’s Board of Trustees.
[2] Because ETF Class shares of the Fund are new, “Other expenses” are estimated amounts for the current fiscal year based on the expenses of Class R6 shares of the Fund.
[3] On December 21, 2015, GMO changed the primary pricing source for certain fixed income asset-backed securities held by the Fund, which resulted in an increase of  $0.04 to the December 21, 2015 net asset value of Class VI shares of the Fund.
[4] The Fund is the accounting and performance successor to GMO Debt Opportunities Fund, a former series of GMO Trust (the “Predecessor Fund”). The Predecessor Fund merged into the Fund (which was known as “GMO Short-Duration Collateral Fund” prior to the merger) on February 12, 2014. Performance of the Fund for periods prior to February 12, 2014 is that of the Predecessor Fund and reflects the Predecessor Fund’s annual operating expenses (0.01% lower than those of the Fund immediately following the merger). From February 12, 2014 through December 31, 2016, the Fund operated as “GMO Debt Opportunities Fund” and had the same investment objective and pursued substantially identical investment strategies as the Predecessor Fund. Effective January 1, 2017, the Fund’s investment objective changed from “positive total return” to “capital appreciation and current income” and, in conjunction with a change in the Fund’s name from “GMO Debt Opportunities Fund” to “GMO Opportunistic Income Fund,” the Fund eliminated its name policy that required the Fund to invest at least 80% of its assets in debt investments. Also effective January 1, 2017, the Fund’s investment management fee increased from 0.25% to 0.40% of the Fund’s average daily net assets. Performance of the Fund for periods prior to January 1, 2017 reflects the Fund’s annual operating expenses during those periods, and would have been lower if the current management fee were in effect.