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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName GMO TRUST
Prospectus Date rr_ProspectusDate Jun. 30, 2012
GMO Trust | GMO Benchmark-Free Allocation Fund
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading GMO BENCHMARK-FREE ALLOCATION FUND
Objective [Heading] rr_ObjectiveHeading Investment objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock Positive total return not “relative” return.
Expense [Heading] rr_ExpenseHeading Fees and expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The tables below describe the fees and expenses that you may pay for each class of shares if you buy and hold shares of the Fund.
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 June 30, 2013
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. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when 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 fiscal year ended February 29, 2012, the Fund’s portfolio turnover rate (excluding short-term investments) was 33% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 33.00%
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent “Other expenses” have been restated to reflect current fees.

The amount has been restated to reflect current fees of certain underlying funds.
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. The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same as those shown in the table. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption If you sell your shares
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If you do not sell your shares
Strategy [Heading] rr_StrategyHeading Principal investment strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock The Fund is a fund of funds and invests primarily in shares of other GMO Funds, which may include the International Equity Funds, the U.S. Equity Funds, the Fixed Income Funds, Alpha Only Fund, Alternative Asset Opportunity Fund, Debt Opportunities Fund, High Quality Short-Duration Bond Fund, Special Situations Fund, World Opportunity Overlay Fund, Implementation Fund and U.S. Flexible Equities Fund (collectively, the “underlying Funds”) (see “Additional Information About the Funds’ Investment Strategies, Risks, and Expenses – Asset Allocation Funds”). In addition, the Fund may invest in securities directly.

The Manager does not seek to manage the Fund to, or control the Fund’s risk relative to, any index or benchmark. The Manager seeks to achieve the Fund’s investment objective (positive total return) by allocating the Fund’s assets among asset classes represented by the underlying Funds (e.g., non-U.S. equity, U.S. equity, emerging country equity, emerging country debt, non-U.S. fixed income, U.S. fixed income and commodities). The Fund is not restricted in its exposure to any particular asset class, and at times may be substantially invested in underlying Funds that primarily invest in a single asset class (e.g., GMO Real Estate Fund and the Fixed Income Funds). In addition, the Fund is not restricted in its exposure to any particular market and may invest in securities of companies of any market capitalization. Although the Fund generally will have exposure to both emerging countries and developed countries, including the U.S., at times, it also may have substantial exposure to a particular country or type of country (e.g., emerging countries). The Fund may have indirect exposure to derivatives and short sales through its investment in the underlying Funds.

The Manager uses multi-year forecasts of returns and risk among asset classes (e.g., non-U.S. equity, U.S. equity, emerging country equity, emerging country debt, non-U.S. fixed income, U.S. fixed income and commodities) to select the underlying Funds in which the Fund invests and to decide how much to invest in each. An important component of those forecasts is the expectation that valuation reversion ultimately drives market returns. The Manager changes the Fund’s holdings of underlying Funds in response to changes in its investment outlook and market valuations and may use redemptions or purchases of Fund shares to rebalance the Fund’s investments. The Manager’s ability to shift investments among the underlying Funds is not subject to any limits. The Fund may invest substantially all of its assets in a few underlying Funds that primarily invest in the same asset class and may, at times, also invest a substantial portion of its assets in a single underlying Fund. The Fund also reserves the right to invest directly in asset classes, or to adjust its exposure to asset classes, through direct investments.

Prior to January 1, 2012, the Fund served as a principal component of a broader GMO real return strategy, and the Fund’s investors were principally separate account clients of the Manager who participated in that strategy. Shares of the Fund also were offered on a standalone basis to the Manager’s partners and employees. Beginning on January 1, 2012, the Fund has been managed as a standalone investment. The Manager expects that the Fund’s investment exposures will not differ significantly from those the Fund would have had as a component of the broader real return strategy, although the Manager will likely allocate a greater percentage of the Fund’s assets to strategies that have cash-like benchmarks.

For cash management purposes, the Fund may invest in U.S. Treasury Fund and unaffiliated money market funds.
Risk [Heading] rr_RiskHeading Principal risks of investing in the Fund
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock The value of the Fund’s shares changes with the value of the Fund’s investments. Many factors can affect this value, and you may lose money by investing in the Fund. References to investments include those held directly by the Fund and indirectly through the Fund’s investments in the underlying Funds. Some of the underlying Funds are non-diversified investment companies under the Investment Company Act of 1940, as amended, and therefore a decline in the market value of a particular security held by those Funds may affect their performance more than if they were diversified investment companies. The principal risks of investing in the Fund are summarized below. For a more complete discussion of these risks, including those risks to which the Fund is exposed as a result of its investments in the underlying Funds, see “Description of Principal Risks.”
  • Market Risk – Equity Securities – The market price of equity investments may decline due to factors affecting the issuing companies, their industries, or the economy and equity markets generally. If an underlying Fund purchases equity investments at a discount from their value as determined by the Manager, the Fund runs the risk that the market prices of these investments will not appreciate to or decline from that value for a variety of reasons, one of which may be the Manager’s overestimation of the value of those investments. An underlying Fund also may purchase equity investments that typically trade at higher multiples of current earnings than other securities, and the market prices of these investments often are more sensitive to changes in future earnings expectations than those other securities. Declines in stock market prices generally are likely to reduce the net asset value of the Fund’s shares.
  • Management and Operational Risk – The Fund runs the risk that GMO’s investment techniques will fail to produce the desired results. The Fund’s portfolio managers may use quantitative analyses and models, and any imperfections or limitations in those analyses and models could affect the ability of the portfolio managers to implement the strategies they wish to pursue. By necessity, these analyses and models make simplifying assumptions that limit their efficacy. Models that appear to explain prior market data can fail to predict future market events. Further, the data used in models may be inaccurate and may not include the most recent information about a company or a security. The Fund also runs the risk that GMO’s fundamental assessment of an investment may be 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.
  • 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. markets are less stable, smaller, less liquid, and less regulated than U.S. markets, and the cost of trading in those markets often is higher than in U.S. markets. Non-U.S. portfolio transactions generally involve higher commission rates, transfer taxes, and custodial costs than similar transactions in the U.S. In addition, the Fund may be subject to non-U.S. taxes, including potentially on a retroactive basis, on (i) capital gains it realizes or dividends or interest it receives on non-U.S. securities, (ii) transactions in those securities and (iii) the repatriation of proceeds generated from the sale of those securities. Also, many non-U.S. markets require a license for the Fund to invest directly in those markets, and the Fund is subject to the risk that it could not invest if its license were terminated or suspended. In some non-U.S. 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 with respect to participating brokers, custodians, clearing banks or other clearing agents, escrow agents and issuers. Further, adverse changes in investment regulations, capital requirements or exchange controls could adversely affect the value of the Fund’s investments. These and other risks (e.g., nationalization, expropriation or other confiscation of assets of non-U.S. issuers) tend to be greater for investments in companies tied economically to emerging countries, the economies of which tend to be more volatile than the economies of developed countries.
  • Market Risk – Fixed Income Investments – The market price of a fixed income investment can decline due to a number of market-related factors, including rising (or, in some limited cases, declining) interest rates and widening credit spreads, or decreased liquidity that reflect the market’s uncertainty about the value of a fixed income investment (or class of fixed income investments).
  • Market Risk – Asset-Backed Securities – The market price of fixed income investments with complex structures, such as asset-backed securities, can decline due to a number of factors, including market uncertainty about their credit quality and 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, the deal structure, the credit worthiness of any credit-support provider, and the reliability of various other service providers with access to the payment stream) and a problem in any one of these areas can lead to a decrease in the payment stream expected by the Fund at the time it purchased the asset-backed security.
  • Smaller Company Risk – Smaller companies may have limited product lines, markets, or financial resources, may lack the competitive strength of larger companies, or may lack managers with experience 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 capitalization.
  • Liquidity Risk – Low trading volume, lack of a market maker, large position size, or legal restrictions may limit or prevent the Fund or an underlying Fund from selling particular securities or unwinding derivative positions at desirable prices.
  • Derivatives Risk – The use of derivatives involves the risk that their value may not move as expected relative to the value of the relevant underlying assets, rates, or indices. Derivatives also present other risks, including market risk, liquidity risk, currency risk and counterparty risk.
  • Currency Risk – Fluctuations in exchange rates can adversely affect the market value of non-U.S. currency holdings and investments denominated in non-U.S. currencies.
  • Fund of Funds Risk – The Fund is indirectly exposed to all of the risks of an investment in the underlying Funds in which it invests, including the risk that those Funds will not perform as expected.
  • Credit Risk – The Fund runs the risk that the issuer or guarantor of a fixed income investment will be unable or unwilling to satisfy its obligation to pay principal and interest or otherwise to honor its obligations in a timely manner. The market price of a fixed income investment will normally decline as a result of the issuer’s or guarantor’s failure to meet its payment obligations. Below investment grade securities have speculative characteristics, and changes in economic conditions or other circumstances are more likely to impair the capacity of issuers to make principal and interest payments than is the case with issuers of investment grade securities.
  • Counterparty Risk – The Fund runs the risk that the counterparty to an over-the-counter (OTC) derivatives contract or a borrower of the Fund’s securities will be unable or unwilling to make timely settlement payments or otherwise honor its obligations.
  • Natural Resources Risk – To the extent an underlying Fund concentrates its assets in the natural resources sector, the value of its portfolio is subject to factors affecting the natural resources industry and may fluctuate more than the value of a portfolio that consists of securities of companies in a broader range of industries.
  • Commodities Risk – Commodities prices can be extremely volatile and exposure to commodities can cause the price of the Fund’s shares to decline and fluctuate more than the price of shares of a fund with a broader range of investments.
  • Leveraging Risk – The use of reverse repurchase agreements and other derivatives and securities lending creates leverage. Leverage increases the magnitude of the Fund’s losses when the value of its investments (including derivatives) declines.
  • Real Estate Risk – To the extent an underlying Fund concentrates its assets in real estate-related investments, the value of its portfolio is subject to factors affecting the real estate industry and may fluctuate more than the value of a portfolio that consists of securities of companies in a broader range of industries.
  • Market Disruption and Geopolitical Risk – Geopolitical and other events may disrupt securities markets and adversely affect global economies and markets. Those events, as well as other changes in non-U.S. and U.S. economic and political conditions, could adversely affect the value of the Fund’s investments.
  • Short Sales Risk – The Fund runs the risk that an underlying Fund’s loss on a short sale of securities that the underlying Fund does not own is unlimited.
  • Focused Investment Risk – Focusing investments in countries, regions, sectors, companies, or industries with high positive correlations to one another creates more risk than if the Fund’s investments were less correlated.
  • Large Shareholder Risk – To the extent that a large number of shares of the Fund is held by a single shareholder (e.g., an institutional investor), the Fund is subject to the risk that a redemption by that shareholder of all or a large portion of its Fund shares will disrupt the Fund’s operations.
Risk Lose Money [Text] rr_RiskLoseMoney Many factors can affect this value, and you may lose money by investing in the Fund.
Risk Nondiversified Status [Text] rr_RiskNondiversifiedStatus Some of the underlying Funds are non-diversified investment companies under the Investment Company Act of 1940, as amended, and therefore a decline in the market value of a particular security held by those Funds may affect their performance more than if they were diversified investment companies.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance
Performance Narrative [Text Block] rr_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 a broad-based index and the Consumer Price Index. Purchase premiums and redemption fees are not reflected in the bar chart, but are reflected in the table; as a result, the returns in the table are lower than the returns in the bar chart. Returns in the table reflect current purchase premiums and redemption fees. 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-deferred arrangements (such as a 401(k) plan or individual retirement account). Past performance (before and after taxes) is not an indication of future performance.
Performance Information Illustrates Variability of Returns [Text] rr_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 a broad-based index and the Consumer Price Index.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not an indication of future performance.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns/Class III Shares
Years Ending December 31
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Purchase premiums and redemption fees are not reflected in the bar chart, but are reflected in the table; as a result, the returns in the table are lower than the returns in the bar chart.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Highest Quarter: 9.19% (2Q2009)
Lowest Quarter: –6.90% (4Q2008)
Year-to-Date (as of 3/31/12): 5.89%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns
Periods Ending December 31, 2011
Performance Table Does Reflect Sales Loads rr_PerformanceTableDoesReflectSalesLoads Returns in the table reflect current purchase premiums and redemption fees.
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on 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-deferred arrangements (such as a 401(k) plan or individual retirement account).
GMO Trust | GMO Benchmark-Free Allocation Fund | Class III
  
Risk/Return: rr_RiskReturnAbstract  
Purchase premium (as a percentage of amount invested) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.12%
Redemption fee (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption 0.12%
Management fee rr_ManagementFeesOverAssets 0.65% [1]
Shareholder service fee rr_DistributionOrSimilarNon12b1FeesOverAssets 0.15% [1]
Supplemental support fee rr_Component1OtherExpensesOverAssets   
Other expenses rr_OtherExpensesOverAssets 0.02% [2]
Acquired fund fees and expenses (underlying fund expenses) rr_AcquiredFundFeesAndExpensesOverAssets 0.35% [3]
Total annual operating expenses rr_ExpensesOverAssets 1.17%
Expense reimbursement/waiver rr_FeeWaiverOrReimbursementOverAssets (0.19%) [1]
Total annual operating expenses after expense reimbursement rr_NetExpensesOverAssets 0.98% [4]
1 Year rr_ExpenseExampleYear01 124 [5]
3 Years rr_ExpenseExampleYear03 344 [6]
5 Years rr_ExpenseExampleYear05 581 [6]
10 Years rr_ExpenseExampleYear10 1,262 [6]
1 Year rr_ExpenseExampleNoRedemptionYear01 112 [5]
3 Years rr_ExpenseExampleNoRedemptionYear03 330 [6]
5 Years rr_ExpenseExampleNoRedemptionYear05 566 [6]
10 Years rr_ExpenseExampleNoRedemptionYear10 1,244 [6]
2004 rr_AnnualReturn2004 18.15% [7]
2005 rr_AnnualReturn2005 16.44% [7]
2006 rr_AnnualReturn2006 12.93% [7]
2007 rr_AnnualReturn2007 11.28% [7]
2008 rr_AnnualReturn2008 (11.23%) [7]
2009 rr_AnnualReturn2009 20.65% [7]
2010 rr_AnnualReturn2010 4.91% [7]
2011 rr_AnnualReturn2011 3.86% [7]
Year to Date Return, Label rr_YearToDateReturnLabel Year-to-Date
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2012
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 5.89% [7]
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 9.19% [7]
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (6.90%) [7]
1 Year rr_AverageAnnualReturnYear01 3.62% [7]
5 Years rr_AverageAnnualReturnYear05 5.32% [7]
10 Years rr_AverageAnnualReturnYear10    [7]
Incept. rr_AverageAnnualReturnSinceInception 11.00% [7]
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 23, 2003 [7]
GMO Trust | GMO Benchmark-Free Allocation Fund | Class IV
  
Risk/Return: rr_RiskReturnAbstract  
Purchase premium (as a percentage of amount invested) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.12%
Redemption fee (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption 0.12%
Management fee rr_ManagementFeesOverAssets 0.65% [1]
Shareholder service fee rr_DistributionOrSimilarNon12b1FeesOverAssets 0.10% [1]
Supplemental support fee rr_Component1OtherExpensesOverAssets   
Other expenses rr_OtherExpensesOverAssets 0.02% [2]
Acquired fund fees and expenses (underlying fund expenses) rr_AcquiredFundFeesAndExpensesOverAssets 0.35% [3]
Total annual operating expenses rr_ExpensesOverAssets 1.12%
Expense reimbursement/waiver rr_FeeWaiverOrReimbursementOverAssets (0.19%) [1]
Total annual operating expenses after expense reimbursement rr_NetExpensesOverAssets 0.93% [4]
1 Year rr_ExpenseExampleYear01 119 [5]
3 Years rr_ExpenseExampleYear03 328 [6]
5 Years rr_ExpenseExampleYear05 554 [6]
10 Years rr_ExpenseExampleYear10 1,204 [6]
1 Year rr_ExpenseExampleNoRedemptionYear01 107 [5]
3 Years rr_ExpenseExampleNoRedemptionYear03 314 [6]
5 Years rr_ExpenseExampleNoRedemptionYear05 539 [6]
10 Years rr_ExpenseExampleNoRedemptionYear10 1,186 [6]
GMO Trust | GMO Benchmark-Free Allocation Fund | Class MF
  
Risk/Return: rr_RiskReturnAbstract  
Purchase premium (as a percentage of amount invested) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.12%
Redemption fee (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption 0.12%
Management fee rr_ManagementFeesOverAssets 0.65% [1]
Shareholder service fee rr_DistributionOrSimilarNon12b1FeesOverAssets    [1]
Supplemental support fee rr_Component1OtherExpensesOverAssets 0.10% [1]
Other expenses rr_OtherExpensesOverAssets 0.02% [2]
Acquired fund fees and expenses (underlying fund expenses) rr_AcquiredFundFeesAndExpensesOverAssets 0.35% [3]
Total annual operating expenses rr_ExpensesOverAssets 1.12%
Expense reimbursement/waiver rr_FeeWaiverOrReimbursementOverAssets (0.19%) [1]
Total annual operating expenses after expense reimbursement rr_NetExpensesOverAssets 0.93% [4]
1 Year rr_ExpenseExampleYear01 119 [5]
3 Years rr_ExpenseExampleYear03 328 [6]
5 Years rr_ExpenseExampleYear05 554 [6]
10 Years rr_ExpenseExampleYear10 1,204 [6]
1 Year rr_ExpenseExampleNoRedemptionYear01 107 [5]
3 Years rr_ExpenseExampleNoRedemptionYear03 314 [6]
5 Years rr_ExpenseExampleNoRedemptionYear05 539 [6]
10 Years rr_ExpenseExampleNoRedemptionYear10 1,186 [6]
GMO Trust | Return After Taxes on Distributions | GMO Benchmark-Free Allocation Fund | Class III
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 3.19% [7]
5 Years rr_AverageAnnualReturnYear05 3.09% [7]
10 Years rr_AverageAnnualReturnYear10    [7]
Incept. rr_AverageAnnualReturnSinceInception 8.55% [7]
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 23, 2003 [7]
GMO Trust | Return After Taxes on Distributions and Sale of Fund Shares | GMO Benchmark-Free Allocation Fund | Class III
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.38% [7]
5 Years rr_AverageAnnualReturnYear05 3.45% [7]
10 Years rr_AverageAnnualReturnYear10    [7]
Incept. rr_AverageAnnualReturnSinceInception 8.44% [7]
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 23, 2003 [7]
GMO Trust | MSCI World Index (returns reflect no deduction for fees or expenses, but are net of withholding tax on dividend reinvestments) | GMO Benchmark-Free Allocation Fund
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (5.54%) [7]
5 Years rr_AverageAnnualReturnYear05 (2.37%) [7]
10 Years rr_AverageAnnualReturnYear10    [7]
Incept. rr_AverageAnnualReturnSinceInception 5.55% [7]
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 23, 2003 [7]
GMO Trust | Consumer Price Index (reflects no deduction for fees, expenses, or taxes) | GMO Benchmark-Free Allocation Fund
  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 2.95% [7]
5 Years rr_AverageAnnualReturnYear05 2.26% [7]
10 Years rr_AverageAnnualReturnYear10    [7]
Incept. rr_AverageAnnualReturnSinceInception 2.52% [7]
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 23, 2003 [7]
[1] Grantham, Mayo, Van Otterloo & Co. LLC (the "Manager" or "GMO") has contractually agreed to reimburse the Fund for the following expenses to the extent that they are borne by the Fund: audit expenses, fund accounting expenses, pricing service expenses, non-investment related tax expenses, transfer agency expenses, non-investment related legal expenses provided to the Fund by or at the direction of the Manager, federal securities law filing expenses, printing expenses, state and federal registration fees and custody expenses. This reimbursement will continue through at least June 30, 2013, and may not be terminated prior to this date without the action or consent of the Fund's Board of Trustees. The Manager also has agreed to waive and/or reduce the Fund's management, shareholder service, and supplemental support fees to the extent necessary to offset the management fees and shareholder service fees directly or indirectly paid to the Manager as a result of the Fund's direct or indirect investments in other GMO Funds.
[2] "Other expenses" have been restated to reflect current fees.
[3] The amount has been restated to reflect current fees of certain underlying funds. These indirect expenses include interest expense that may be incurred by certain underlying funds and also include, to the extent applicable, purchase premiums and redemption fees ("transaction fees") charged by certain underlying funds. Net fees and expenses of underlying funds (before addition of interest expense and transaction fees and as restated), indirect interest expense, and indirect transaction fees were approximately 0.27%, less than 0.01%, and 0.08%, respectively.
[4] Total annual operating expenses after expense reimbursement/waiver (Fund and underlying fund expenses)
[5] After expense reimbursements/waivers noted in the expense table
[6] Reflects fee reductions set forth in the Fund's management contract and servicing and supplemental support agreement.
[7] The returns are for Class III shares of the Fund under the Fund's prior fee arrangement. Under the Fund's current fee arrangement, the returns would have been lower.