Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	GMO TRUST
Prospectus Date	rr_ProspectusDate	Jun. 30, 2013
GMO Trust | GMO International Small Companies Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	GMO INTERNATIONAL SMALL COMPANIES FUND
Objective [Heading]	rr_ObjectiveHeading	Investment objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	High total 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 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, 2014
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 result in higher transaction costs and, when Fund shares are held in a taxable account, higher taxes. 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, 2013, the Fund’s portfolio turnover rate (excluding short-term investments) was 76% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	76.00%
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 Manager seeks to achieve the Fund’s investment objective by investing the Fund’s portfolio primarily in equity securities that the Manager believes will provide a higher return than the MSCI EAFE Small Cap Index. The Manager determines which securities the Fund should buy or sell based on its evaluation of companies’ published financial information and corporate behavior, securities’ prices, equity and bond markets, and the overall economy. In selecting securities for the Fund, the Manager uses a combination of investment methods to identify securities that the Manager believes have positive return potential relative to other securities in the Fund’s investment universe. Some of these methods evaluate individual securities or groups of securities based on the ratio of their price to historical financial information and forecasted financial information, such as book value, cash flow and earnings, and a comparison of these ratios to industry or market averages or to their own history. Other methods focus on patterns of information, such as price movement or volatility of a security or groups of securities relative to the Fund’s investment universe or corporate behavior of an issuer. The Manager also uses multi-year return forecasts for asset classes and other groups of securities as an input to the investment process and may adjust the Fund’s portfolio for factors such as position size, market capitalization, and exposure to factors such as industry, sector, country, or currency. The factors considered and investment methods used by the Manager can change over time. The Manager does not manage the Fund to, or control the Fund’s risk relative to, any securities index or securities benchmark. As a substitute for direct investments in equity securities, the Fund may use exchange-traded and over-the-counter (OTC) derivatives and exchange-traded funds (“ETFs”). The Fund also may use derivatives and ETFs: (i) in an attempt to reduce investment exposures (which may result in a reduction below zero); (ii) in an attempt to adjust elements of the Fund’s investment exposure; and (iii) as a substitute for securities lending. Derivatives used may include futures, options, forward currency contracts, and swap contracts. In addition, the Fund may lend its portfolio securities. The Fund typically invests directly and indirectly (e.g., through underlying funds or derivatives) in equity securities of non-U.S. small companies. Under normal circumstances, the Fund invests directly and indirectly at least 80% of its assets in securities of small companies (see “Name Policies”). For these purposes, non-U.S. companies are companies tied economically to countries other than the U.S., including both developed and emerging countries (“Non-U.S. Companies”). The Manager considers “small companies” to be all Non-U.S. Companies other than (i) the largest 500 companies in developed countries based on full, non-float adjusted market capitalization and (ii) any company in an emerging country with a full, non-float adjusted market capitalization that is greater than or equal to that of the smallest excluded developed country companies. A company’s full, non-float adjusted market capitalization includes all of the company’s outstanding equity securities. As of May 31, 2013, the market capitalization of the outstanding common stock and other stock-related securities of the largest company included within the Fund’s definition of small companies was approximately $6.0 billion. For purposes of the Fund’s investments, the term “equity securities” refers to direct and indirect investments in common stocks and other stock-related securities, such as preferred stocks, convertible securities, depositary receipts, and exchange-traded equity real estate investment trusts (REITs) and income trusts. The Fund also may invest in U.S. Treasury Fund and money market funds that are unaffiliated with GMO.
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. The principal risks of investing in the Fund are summarized below. For a more complete discussion of these risks, see “Description of Principal Risks.” Market Risk – Equities – The market prices of equities may decline due to factors affecting the issuing companies, their industries, or the economy and equity markets generally. If the Fund purchases equities 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 or will decline for a variety of reasons, one of which may be the Manager’s overestimation of the value of those investments. The Fund also may purchase equities 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 the market prices of equities trading at lower multiples. 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 desired results. The Fund’s portfolio managers may use quantitative analyses and models, and any imperfections, errors, or limitations in those analyses and models could affect the ability of the portfolio managers to implement the Fund’s 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 may not include the most recent information about a company or a security. The Fund also runs the risk that GMO’s 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. Liquidity Risk – Shares of small- and mid-cap companies often have lower trading volumes than those of larger companies and a limited number or no market makers. Thus, the Fund may be unable to sell a large position in shares of small- and mid-cap companies or unwind derivative positions on them at desirable prices. 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. investments, (ii) transactions in those investments, and (iii) the repatriation of proceeds generated from the sale of those investments. 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. Currency Risk – Fluctuations in exchange rates can adversely affect the market value of the Fund’s non-U.S. currency holdings and investments denominated in non-U.S. currencies. Derivatives Risk – The use of derivatives involves the risk that their value may not move as expected relative to the value of the underlying assets, rates, or indices. Derivatives also present other risks, including market risk, liquidity risk, currency risk, and counterparty risk. 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 small companies 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. Counterparty Risk – The Fund runs the risk that the counterparty to a derivatives contract, a clearing member used by the Fund to hold a cleared derivatives contract, or a borrower of the Fund’s securities will be unable or unwilling to make timely settlement payments, return the Fund’s margin or otherwise honor its obligations. Leveraging Risk – The use of derivatives and securities lending creates leverage. Leverage increases the Fund’s losses when the value of its investments (including derivatives) declines. 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. 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. 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 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 those shareholders of all or a large portion of their 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.
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 the Fund’s benchmark (which is a broad-based index) and a composite index computed by the Manager. 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 the Fund’s benchmark (which is a broad-based index) and a composite index computed by the Manager.
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: 32.07% (2Q2009) Lowest Quarter: – 21.36% (3Q2011) Year-to-Date (as of 3/31/13): 8.69%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns Periods Ending December 31, 2012
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 International Small Companies Fund | Class III
Risk/Return:	rr_RiskReturnAbstract
Purchase premium (as a percentage of amount invested)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	0.50%
Redemption fee (as a percentage of amount redeemed)	rr_RedemptionFeeOverRedemption	0.50%
Management fee	rr_ManagementFeesOverAssets	0.60%	[1]
Shareholder service fee	rr_DistributionOrSimilarNon12b1FeesOverAssets	0.15%	[1]
Other expenses	rr_OtherExpensesOverAssets	0.18%
Total annual operating expenses	rr_ExpensesOverAssets	0.93%
Expense reimbursement/waiver	rr_FeeWaiverOrReimbursementOverAssets	(0.17%)	[1]
Total annual operating expenses after expense reimbursement/waiver	rr_NetExpensesOverAssets	0.76%
1 Year	rr_ExpenseExampleYear01	$ 179	[2]
3 Years	rr_ExpenseExampleYear03	384
5 Years	rr_ExpenseExampleYear05	606
10 Years	rr_ExpenseExampleYear10	1,246
1 Year	rr_ExpenseExampleNoRedemptionYear01	127	[2]
3 Years	rr_ExpenseExampleNoRedemptionYear03	328
5 Years	rr_ExpenseExampleNoRedemptionYear05	546
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,172
2003	rr_AnnualReturn2003	67.44%
2004	rr_AnnualReturn2004	27.04%
2005	rr_AnnualReturn2005	24.66%
2006	rr_AnnualReturn2006	27.36%
2007	rr_AnnualReturn2007	7.63%
2008	rr_AnnualReturn2008	(42.37%)
2009	rr_AnnualReturn2009	33.44%
2010	rr_AnnualReturn2010	21.18%
2011	rr_AnnualReturn2011	(14.55%)
2012	rr_AnnualReturn2012	23.98%
Year to Date Return, Label	rr_YearToDateReturnLabel	Year-to-Date
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2013
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	8.69%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Highest Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	32.07%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Lowest Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(21.36%)
1 Year	rr_AverageAnnualReturnYear01	22.75%
5 Years	rr_AverageAnnualReturnYear05	(0.45%)
10 Years	rr_AverageAnnualReturnYear10	13.52%
Incept.	rr_AverageAnnualReturnSinceInception	9.16%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 14, 1991
GMO Trust | GMO International Small Companies Fund | Return After Taxes on Distributions | Class III
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	21.81%
5 Years	rr_AverageAnnualReturnYear05	(1.14%)
10 Years	rr_AverageAnnualReturnYear10	10.63%
Incept.	rr_AverageAnnualReturnSinceInception	6.99%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 14, 1991
GMO Trust | GMO International Small Companies Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class III
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	15.47%
5 Years	rr_AverageAnnualReturnYear05	(0.55%)
10 Years	rr_AverageAnnualReturnYear10	11.28%
Incept.	rr_AverageAnnualReturnSinceInception	7.30%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 14, 1991
GMO Trust | GMO International Small Companies Fund | MSCI EAFE Small Cap Index (Fund benchmark) (returns reflect no deductions for fees or expenses, but are net of withholding tax on dividend reinvestments)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	20.00%
5 Years	rr_AverageAnnualReturnYear05	(0.86%)
10 Years	rr_AverageAnnualReturnYear10	11.93%
Incept.	rr_AverageAnnualReturnSinceInception
GMO Trust | GMO International Small Companies Fund | MSCI EAFE Small Cap + Index (Composite index)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	20.00%
5 Years	rr_AverageAnnualReturnYear05	(0.85%)
10 Years	rr_AverageAnnualReturnYear10	12.39%
Incept.	rr_AverageAnnualReturnSinceInception	6.55%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 14, 1991

[1] Grantham, Mayo, Van Otterloo & Co. LLC (the “Manager” or “GMO”) has contractually agreed to reimburse the Fund for the following expenses: audit expenses, fund accounting expenses, pricing service expenses, expenses of non-investment related tax services, transfer agency expenses, expenses of non-investment related legal services 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. The Manager also has agreed to waive or reduce the Fund’s management fees and shareholder service 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. Management fees and shareholder service fees will not be waived below zero. This reimbursement and waiver will continue through at least June 30, 2014, and may not be terminated prior to this date without the action or consent of the Fund’s Board of Trustees.

[2] After reimbursement