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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Document Type dei_DocumentType Other
Document Period End Date dei_DocumentPeriodEndDate Feb. 28, 2011
Registrant Name dei_EntityRegistrantName GMO TRUST
Central Index Key dei_EntityCentralIndexKey 0000772129
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Dec. 08, 2011
Document Effective Date dei_DocumentEffectiveDate Dec. 08, 2011
Prospectus Date rr_ProspectusDate Jun. 30, 2011
Supplement [Text Block] gmofx_SupplementTextBlock

GMO TRUST

Amended and Restated Supplement dated December 8, 2011 to

GMO Trust Prospectus and Statement of Additional Information,

each dated June 30, 2011
GMO BENCHMARK-FREE ALLOCATION FUND | GMO TRUST
  
Risk/Return: rr_RiskReturnAbstract  
Supplement [Text Block] gmofx_SupplementTextBlock

Benchmark-Free Allocation Fund

Effective January 1, 2012, the description of GMO Benchmark-Free Allocation Fund on pages 138-140 of the Prospectus is amended and restated as follows:
Objective [Heading] rr_ObjectiveHeading Investment objective
Objective Primary [Text Block] rr_ObjectivePrimaryTextBlock The Fund seeks a positive total return. The Fund does not have a particular securities market index as a benchmark and does not seek to outperform a particular index or blend of indices (i.e., the Fund seeks positive return, not “relative” return).
Fees and expenses gmofx_FundFeesAndExpensesAbstract  
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 rr_ShareholderFeesAbstract  
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder fees (fees paid directly from your investment)
Annual Fund operating expenses rr_OperatingExpensesAbstract  
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):
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent Restated as of June 2011. The amount includes purchase premiums and redemption fees of the underlying GMO Funds.
Example rr_ExpenseExampleAbstract  
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, With Redemption gmofx_ExpenseExampleWithRedemptionAbstract  
Expense Example by Year, Caption [Text] rr_ExpenseExampleByYearCaption If you sell your shares
Expense Example, No Redemption rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If you do not sell your shares
Portfolio turnover gmofx_PortfolioTurnoverAltAbstract  
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 28, 2011, the Fund’s portfolio turnover rate (excluding short-term investments) was 19% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 19.00%
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 and Implementation 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 Fund implements its strategy by allocating its assets among asset classes represented by the underlying Funds (e.g., foreign equity, U.S. equity, emerging country equity, emerging country debt, foreign 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., Fixed Income Funds). In addition, the Fund is not restricted in its exposure to any particular market. 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 Manager uses multi-year forecasts of relative value and risk among asset classes (e.g., foreign equity, U.S. equity, emerging country equity, emerging country debt, foreign 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. The Manager changes the Fund’s holdings of underlying Funds in response to changes in its investment outlook and market valuations and may use redemption/purchase activity 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 predominantly as the principal component of a broader real return strategy, and the Fund’s investors were predominantly separate account clients of the Manager. The Fund was also offered on a stand-alone basis to the Manager’s partners and employees. Beginning on January 1, 2012, the Fund will be managed as a stand-alone investment strategy. The Manager expects that the Fund’s investment exposures will not differ significantly from the allocations the Fund would have had as a component of the broader real return, although the Fund will likely allocate a greater percentage of its 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. 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 value 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 increase to 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 values 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.

• Foreign Investment Risk – The market prices of many foreign securities fluctuate more than those of U.S. securities. Many foreign 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. Foreign 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 foreign taxes on capital gains or other income payable on foreign securities, on transactions in those securities and on the repatriation of proceeds generated from those securities. Also, many foreign 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 foreign 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 foreign 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 Securities – Typically, the market value of fixed income securities will decline during periods of rising interest rates and widening of credit spreads.

• Market Risk – Asset-Backed Securities – Asset-backed securities are subject to severe credit downgrades, illiquidity, defaults and declines in market value.

• 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 size of position or legal restrictions may limit or prevent the Fund or an underlying Fund from selling particular securities or unwinding derivative positions at desirable prices. The more less-liquid securities the Fund holds, the more likely it is to honor a redemption request in-kind.

• 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 Fund risks, including market risk, liquidity risk, currency risk and counterparty risk.

• Currency Risk – Fluctuations in exchange rates can adversely affect the market value of foreign currency holdings and investments denominated in foreign currencies.

• Fund of Funds Risk – The Fund is indirectly exposed to all of the risks of an investment in the underlying Funds, including the risk that the underlying Funds in which it invests do not perform as expected.

• Management and Operational Risk – The Fund relies on GMO’s ability to achieve its investment objective by effectively implementing its investment approach. The Fund runs the risk that GMO’s proprietary investment techniques will fail to produce the desired results. The Fund’s portfolio managers may use quantitative analyses and/or models and any imperfections or limitations in such analyses and/or models could affect the ability of the portfolio managers to implement strategies. 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/or it may not include the most recent information about a company or a security. The Fund is also subject to the risk that deficiencies in the Manager’s or another service provider’s internal systems or controls will cause losses for the Fund or impair Fund operations.

• Credit Risk – The Fund runs the risk that the issuer or guarantor of a fixed income security or the obligor of an obligation underlying an asset-backed security will be unable or unwilling to satisfy its obligations to pay principal or interest payments or to otherwise honor its obligations. The market value of a fixed income security normally will decline as a result of the issuer’s failure to meet its payment obligations or the market’s expectation of a default, which may result from the downgrading of the issuer’s credit rating. 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.

• Commodities Risk – To the extent an underlying Fund has exposure to global commodity markets, the value of its shares is affected by factors particular to the commodity markets and may fluctuate more than the value 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 may cause the Fund’s portfolio to be leveraged. Leverage increases the Fund’s portfolio losses when the value of its investments decline.

• 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.

• 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.

• 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.

• Focused Investment Risk – Focusing investments in countries, regions, sectors or companies or in industries with high positive correlations to one another creates additional risk.

• 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 foreign and domestic economic and political conditions could adversely affect the value of the Fund’s investments.

• Large Shareholder Risk – To the extent that shares of the Fund are held by large shareholders (e.g., institutional investors), the Fund is subject to the risk that these shareholders will disrupt the Fund’s operations by purchasing or redeeming Fund shares in large amounts and/or on a frequent basis.
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.
Performance gmofx_FundPastPerformanceAbstract  
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.
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.
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).
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not an indication of future performance.
Annual Total Returns rr_BarChartTableAbstract  
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns/Class III Shares * Years Ending December 31
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Highest Quarter: 9.19% (2Q2009)

Lowest Quarter: -6.90% (4Q2008)

Year-to-Date (as of 3/31/11): 1.92%
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns * Periods Ending December 31, 2010 [1]
GMO BENCHMARK-FREE ALLOCATION FUND | Class III, GMO Benchmark-Free Allocation Fund
  
Shareholder fees rr_ShareholderFeesAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class III
Purchase premium (as a percentage of amount invested) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.09%
Redemption fee (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption 0.09%
Annual Fund operating expenses rr_OperatingExpensesAbstract  
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class III
Management fee rr_ManagementFeesOverAssets 0.65%
Shareholder service fee rr_DistributionOrSimilarNon12b1FeesOverAssets 0.15%
Other expenses rr_OtherExpensesOverAssets 0.02%
Acquired fund fees and expenses (underlying fund expenses) rr_AcquiredFundFeesAndExpensesOverAssets 0.57% [2]
Total annual operating expenses rr_ExpensesOverAssets 1.39%
Expense reimbursement/waiver rr_FeeWaiverOrReimbursementOverAssets (0.50%) [3]
Total annual operating expenses after expense reimbursement/waiver (Fund and underlying fund expenses) rr_NetExpensesOverAssets 0.89%
Expense Example, With Redemption gmofx_ExpenseExampleWithRedemptionAbstract  
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class III
1 Year rr_ExpenseExampleYear01 109 [4]
3 Years rr_ExpenseExampleYear03 350 [5]
5 Years rr_ExpenseExampleYear05 610 [5]
10 Years rr_ExpenseExampleYear10 1,353 [5]
Expense Example, No Redemption rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class III
1 Year rr_ExpenseExampleNoRedemptionYear01 100 [4]
3 Years rr_ExpenseExampleNoRedemptionYear03 340 [5]
5 Years rr_ExpenseExampleNoRedemptionYear05 599 [5]
10 Years rr_ExpenseExampleNoRedemptionYear10 1,340 [5]
Annual Total Returns rr_BarChartTableAbstract  
2004 rr_AnnualReturn2004 18.15% [1]
2005 rr_AnnualReturn2005 16.44% [1]
2006 rr_AnnualReturn2006 12.93% [1]
2007 rr_AnnualReturn2007 11.28% [1]
2008 rr_AnnualReturn2008 (11.23%) [1]
2009 rr_AnnualReturn2009 20.65% [1]
2010 rr_AnnualReturn2010 4.91% [1]
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter:
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 9.19%
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter:
Lowest Quarterly Return, Return rr_BarChartLowestQuarterlyReturn (6.90%)
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Year To Date Return, Label rr_YearToDateReturnLabel Year-to-Date
Bar Chart, Year To Date Return rr_BarChartYearToDateReturn 1.92%
Bar Chart, Year To Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2011
GMO BENCHMARK-FREE ALLOCATION FUND | Class IV, GMO Benchmark-Free Allocation Fund
  
Shareholder fees rr_ShareholderFeesAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class IV
Purchase premium (as a percentage of amount invested) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.09%
Redemption fee (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption 0.09%
Annual Fund operating expenses rr_OperatingExpensesAbstract  
Operating Expenses Column [Text] rr_OperatingExpensesColumnName Class IV
Management fee rr_ManagementFeesOverAssets 0.65%
Shareholder service fee rr_DistributionOrSimilarNon12b1FeesOverAssets 0.10%
Other expenses rr_OtherExpensesOverAssets 0.02%
Acquired fund fees and expenses (underlying fund expenses) rr_AcquiredFundFeesAndExpensesOverAssets 0.57% [2]
Total annual operating expenses rr_ExpensesOverAssets 1.34%
Expense reimbursement/waiver rr_FeeWaiverOrReimbursementOverAssets (0.50%) [3]
Total annual operating expenses after expense reimbursement/waiver (Fund and underlying fund expenses) rr_NetExpensesOverAssets 0.84%
Expense Example, With Redemption gmofx_ExpenseExampleWithRedemptionAbstract  
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class IV
1 Year rr_ExpenseExampleYear01 104 [4]
3 Years rr_ExpenseExampleYear03 334 [5]
5 Years rr_ExpenseExampleYear05 583 [5]
10 Years rr_ExpenseExampleYear10 1,295 [5]
Expense Example, No Redemption rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class IV
1 Year rr_ExpenseExampleNoRedemptionYear01 95 [4]
3 Years rr_ExpenseExampleNoRedemptionYear03 324 [5]
5 Years rr_ExpenseExampleNoRedemptionYear05 572 [5]
10 Years rr_ExpenseExampleNoRedemptionYear10 1,282 [5]
GMO BENCHMARK-FREE ALLOCATION FUND | Return Before Taxes | Class III, GMO Benchmark-Free Allocation Fund
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class III
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 4.72% [1]
5 Years rr_AverageAnnualReturnYear05 7.11% [1]
10 Years rr_AverageAnnualReturnYear10    [1]
Inception rr_AverageAnnualReturnSinceInception 12.00% [1]
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 23, 2003
GMO BENCHMARK-FREE ALLOCATION FUND | Return After Taxes on Distributions | Class III, GMO Benchmark-Free Allocation Fund
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class III
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 4.19% [1]
5 Years rr_AverageAnnualReturnYear05 4.42% [1]
10 Years rr_AverageAnnualReturnYear10    [1]
Inception rr_AverageAnnualReturnSinceInception 9.27% [1]
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 23, 2003
GMO BENCHMARK-FREE ALLOCATION FUND | Return After Taxes on Distributions and Sale of Fund Shares | Class III, GMO Benchmark-Free Allocation Fund
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class III
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 3.14% [1]
5 Years rr_AverageAnnualReturnYear05 4.86% [1]
10 Years rr_AverageAnnualReturnYear10    [1]
Inception rr_AverageAnnualReturnSinceInception 9.18% [1]
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 23, 2003
GMO BENCHMARK-FREE ALLOCATION FUND | MSCI World Index | Class III, GMO Benchmark-Free Allocation Fund
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class III
Label rr_AverageAnnualReturnLabel MSCI World Index
Index No Deduction For Fees, Expenses, Taxes (for MSCI World Index, returns are net of withholding tax) rr_IndexNoDeductionForFeesExpensesTaxes (returns reflect no deduction for fees or expenses, but are net of withholding tax on dividend reinvestments)
1 Year rr_AverageAnnualReturnYear01 11.76% [1]
5 Years rr_AverageAnnualReturnYear05 2.43% [1]
10 Years rr_AverageAnnualReturnYear10    [1]
Inception rr_AverageAnnualReturnSinceInception 7.14% [1]
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 23, 2003
GMO BENCHMARK-FREE ALLOCATION FUND | Consumer Price Index | Class III, GMO Benchmark-Free Allocation Fund
  
Average Annual Total Returns rr_AverageAnnualReturnAbstract  
Column rr_AverageAnnualReturnColumnName Class III
Label rr_AverageAnnualReturnLabel Consumer Price Index
Index No Deduction For Fees, Expenses, Taxes (for MSCI World Index, returns are net of withholding tax) rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses, or taxes)
1 Year rr_AverageAnnualReturnYear01 1.25% [1]
5 Years rr_AverageAnnualReturnYear05 2.18% [1]
10 Years rr_AverageAnnualReturnYear10    [1]
Inception rr_AverageAnnualReturnSinceInception 2.47% [1]
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 23, 2003
Performance Additional Market Index [Text] rr_PerformanceAdditionalMarketIndex Consumer Price Index
GMO U.S. SMALL/MID CAP VALUE FUND | GMO TRUST
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading GMO U.S. Small/Mid Cap Value Fund
Supplement Strategy Narrative [Text Block] gmofx_SupplementStrategyNarrativeTextBlock

Effective January 16, 2012, GMO U.S. Small/Mid Cap Value Fund is renamed “GMO U.S. Small/Mid Cap Fund” and the first paragraph of the section captioned “Principal investment strategies” on page 16 of the Prospectus is amended and restated as follows:

The Manager seeks to achieve the Fund’s investment objective by investing in equities or groups of equities that the Manager believes will provide higher returns than the Russell 2500 Index.

Effective January 16, 2012, the Fund’s benchmark is the Russell 2500 Index. The Russell 2500 Index is an independently maintained and widely published index that measures the performance of the small to mid-cap segment of the U.S. equity universe. The Russell 2500 is a subset of the Russell 3000 Index. It includes approximately 2500 of the smallest securities based on a combination of their market cap and current index membership. Russell Investment Group is the source and owner of the trademarks, service marks and copyrights related to the Russell Indexes. Russell® is a trademark of Russell Investment Group.
GMO TOBACCO-FREE CORE FUND AND GMO U.S. SMALL/MID CAP GROWTH FUND | GMO TRUST
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading GMO Tobacco-Free Core Fund and GMO U.S. Small/Mid Cap Growth Fund
Supplement [Text Block] gmofx_SupplementTextBlock The Board of Trustees of GMO Trust has approved the liquidation of GMO Tobacco-Free Core Fund and GMO U.S. Small/Mid Cap Growth Fund. It is expected that GMO Tobacco-Free Core Fund will be liquidated on or about December 31, 2011 and that GMO U.S. Small/Mid Cap Growth Fund will be liquidated on or about January 31, 2012. You may redeem from the Funds at any time, but if you are still a shareholder of a Fund on the date that the Fund is liquidated, your investment in the Fund will be liquidated and the proceeds will be transmitted to you.
GMO TAX-MANAGED U.S. EQUITIES FUND | GMO TRUST
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading GMO Tax-Managed U.S. Equities Fund
Supplement [Text Block] gmofx_SupplementTextBlock GMO Tax-Managed U.S. Equities Fund was liquidated on October 31, 2011.
GMO CURRENCY HEDGED INTERNATIONAL EQUITY FUND | GMO TRUST
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading GMO Currency Hedged International Equity Fund
Supplement Strategy Narrative [Text Block] gmofx_SupplementStrategyNarrativeTextBlock

The first two sentences of the section captioned “Principal investment strategies” on page 73 of the Prospectus are amended and restated as follows:

The Fund is a fund of funds and invests primarily in other GMO Funds. The Fund may invest in International Core Equity Fund, International Intrinsic Value Fund, International Large/Mid Cap Value Fund, International Growth Equity Fund, International Small Companies Fund, Asset Allocation International Small Companies Fund, and Flexible Equities Fund (collectively, the “underlying Funds”).
GMO STRATEGIC FIXED INCOME FUND | GMO TRUST
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading GMO Strategic Fixed Income Fund
Supplement [Text Block] gmofx_SupplementTextBlock Effective December 9, 2011, the Fund charges a purchase premium and a redemption fee, which will be paid to and retained by the Fund to help offset non-de minimis estimated portfolio transaction costs and other related costs incurred by the Fund as a result of a purchase or redemption of its shares by allocating estimated transaction costs to the purchasing or redeeming shareholder. The following table is added to the section captioned “Fees and expenses” on page 85 of the Prospectus:
Shareholder fees rr_ShareholderFeesAbstract  
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder fees (fees paid directly from your investment)
Example rr_ExpenseExampleAbstract  
Supplement Example Heading [Text Block] gmofx_SupplementExampleHeadingTextBlock In addition, the section captioned “Example” on page 85 is replaced with the following:
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, With Redemption gmofx_ExpenseExampleWithRedemptionAbstract  
Expense Example by Year, Caption [Text] rr_ExpenseExampleByYearCaption If you sell your shares
Expense Example, No Redemption rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption If you do not sell your shares
GMO STRATEGIC FIXED INCOME FUND | Class III, GMO Strategic Fixed Income Fund
  
Shareholder fees rr_ShareholderFeesAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class III
Purchase premium (as a percentage of amount invested) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.20%
Redemption fee (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption 0.20%
Expense Example, With Redemption gmofx_ExpenseExampleWithRedemptionAbstract  
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class III
1 Year rr_ExpenseExampleYear01 84 [6]
3 Years rr_ExpenseExampleYear03 193
5 Years rr_ExpenseExampleYear05 312
10 Years rr_ExpenseExampleYear10 659
Expense Example, No Redemption rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class III
1 Year rr_ExpenseExampleNoRedemptionYear01 63 [6]
3 Years rr_ExpenseExampleNoRedemptionYear03 170
5 Years rr_ExpenseExampleNoRedemptionYear05 287
10 Years rr_ExpenseExampleNoRedemptionYear10 628
GMO STRATEGIC FIXED INCOME FUND | Class VI, GMO Strategic Fixed Income Fund
  
Shareholder fees rr_ShareholderFeesAbstract  
Shareholder Fees Column [Text] rr_ShareholderFeesColumnName Class VI
Purchase premium (as a percentage of amount invested) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.20%
Redemption fee (as a percentage of amount redeemed) rr_RedemptionFeeOverRedemption 0.20%
Expense Example, With Redemption gmofx_ExpenseExampleWithRedemptionAbstract  
Expense Example, By Year, Column [Text] rr_ExpenseExampleByYearColumnName Class VI
1 Year rr_ExpenseExampleYear01 75 [6]
3 Years rr_ExpenseExampleYear03 162
5 Years rr_ExpenseExampleYear05 257
10 Years rr_ExpenseExampleYear10 537
Expense Example, No Redemption rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Column [Text] rr_ExpenseExampleNoRedemptionByYearColumnName Class VI
1 Year rr_ExpenseExampleNoRedemptionYear01 54 [6]
3 Years rr_ExpenseExampleNoRedemptionYear03 139
5 Years rr_ExpenseExampleNoRedemptionYear05 232
10 Years rr_ExpenseExampleNoRedemptionYear10 506
GMO GLOBAL BALANCED ASSET ALLOCATION FUND | GMO TRUST
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading GMO Global Balanced Asset Allocation Fund
Supplement [Text Block] gmofx_SupplementTextBlock Effective September 15, 2011 (the “Effective Date”), GMO Global Balanced Asset Allocation Fund was renamed “GMO Global Asset Allocation Fund.” In conjunction with the name change, as of the Effective Date, the Fund is no longer bound by its policy to invest at least 25% of its assets in fixed income investments and at least 25% of its assets in equity investments, and the description of the Fund’s principal investment strategies on page 132 of the Prospectus is replaced with the following:
Portfolio turnover gmofx_PortfolioTurnoverAltAbstract  
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 and World Opportunity Overlay Fund (collectively, the “underlying Funds”) (see “Additional Information About the Funds’ Investment Strategies, Risks, and Expenses – Asset Allocation Funds”). In addition, the Fund may hold securities (particularly asset-backed securities) directly or through one or more subsidiaries or other entities. The Fund may be exposed to foreign and U.S. equity investments (which may include emerging country equities, both growth and value style equities and equities of any market capitalization), U.S. and foreign fixed income securities (including asset-backed securities and other fixed income securities of any credit quality and having any maturity or duration), the investment returns of commodities and, from time to time, other alternative asset classes.

The Manager uses multi-year forecasts of relative value and risk among asset classes (e.g., foreign equity, U.S. equity, emerging country equity, emerging country debt, U.S. fixed income, foreign fixed income and commodities) to select the underlying Funds in which the Fund invests and to decide how much to invest in each. The Manager changes the Fund’s holdings of underlying Funds in response to changes in its investment outlook and market valuations and may use redemption/purchase activity to rebalance the Fund’s investments. Under normal circumstances, the Manager intends to invest not more than 85% of the Fund’s assets in the U.S. Equity and International Equity Funds.

For cash management purposes, the Fund may invest in U.S. Treasury Fund and unaffiliated money market funds.
GMO EMERGING DOMESTIC OPPORTUNITIES FUND | GMO TRUST
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading GMO Emerging Domestic Opportunities Fund
Supplement Annual Fund Operating Expenses Table Footnote [Text Block] gmofx_SupplementAnnualFundOperatingExpensesTableFootnoteTextBlock

Footnote 2 to the table captioned “Annual Fund operating expenses” on page 64 of the Prospectus is amended and restated as follows:

2 Subject to certain exclusions (“Excluded Fund Fees and Expenses), Grantham, Mayo, Van Otterloo & Co. LLC (the “Manager” or “GMO”) has contractually agreed to reimburse the Fund to the extent the Fund’s total annual operating expenses exceed 0.75% of the Fund’s average daily net assets. Excluded Fund Fees and Expenses include (i) shareholder service fees, (ii) underlying fund expenses, (iii) any portion of the Fund’s annual custodial fees that exceeds 0.10% of the Fund’s average daily net assets, (iv) independent Trustee expenses, (v) certain legal costs, (vi) investment-related costs (e.g., brokerage commissions and securities lending fees), (vii) extraordinary expenses, and other expenses described under “Expense Reimbursement” in this Prospectus. This expense limitation will continue through at least June 30, 2012, and may not be terminated prior to this date without the consent of the Fund’s Board of Trustees.
Annual Fund operating expenses rr_OperatingExpensesAbstract  
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination June 30, 2012
[1] 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.
[2] Restated as of June 2011. The amount includes purchase premiums and redemption fees of the underlying GMO Funds.
[3] The Manager has agreed to waive and/or reduce the Fund's management and shareholder service fees in order to offset the management and shareholder service fees charged by the underlying GMO Funds in which the Fund invests. In addition, the Manager has agreed to reimburse the Fund for certain of its operational expenses.
[4] After expense reimbursements/waivers noted in expense table
[5] Reflects fee reductions set forth in the Fund's management agreement and servicing and supplemental support agreement.
[6] After reimbursement