Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	GMO TRUST
Prospectus Date	rr_ProspectusDate	Jun. 30, 2013
GMO Trust | GMO Alpha Only Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	GMO ALPHA ONLY FUND
Objective [Heading]	rr_ObjectiveHeading	Investment objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Total return greater than that of its benchmark, the Citigroup 3-Month Treasury Bill Index.
Expense [Heading]	rr_ExpenseHeading	Fees and expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The table below describes the fees and expenses that you may pay for each class of shares if you buy and hold shares of the Fund.
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 104% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	104.00%
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, regardless of whether or not you redeem your shares at the end of such periods. The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses 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:
Strategy [Heading]	rr_StrategyHeading	Principal investment strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund’s investment program involves having both long and short investment exposures. The Fund seeks to construct a portfolio in which it has long investment exposure to asset classes and sub-asset classes that it expects will outperform relative to the asset classes and sub-asset classes to which it has short investment exposure. To gain long investment exposure, the Fund may invest in securities directly or in shares of the Equity Funds and Emerging Country Debt Fund (collectively, the “underlying Funds”) (see “Additional Information About the Funds’ Investment Strategies, Risks, and Expenses — Asset Allocation Funds”). To gain short investment exposure, the Fund may use over-the-counter (OTC) and exchange-traded derivatives (including futures, swap contracts and currency forwards) and make short sales of securities, including short sales of securities the Fund does not own. The Fund is not limited in its use of derivatives or in the absolute face value of its derivative positions. As a result of its derivative positions, the Fund will typically have gross investment exposures in excess of its net assets (i.e., the Fund will be leveraged) and therefore is subject to heightened risk of loss. The Fund’s performance can depend substantially, if not primarily, on the performance of assets or indices underlying its derivatives even though it does not own those assets or indices. The Manager uses multi-year forecasts of returns and risk among asset classes to determine the Fund’s long and short positions. An important component of those forecasts is the expectation that valuation reversion ultimately drives market returns. The Manager changes the Fund’s holdings 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 factors considered and investment methods used by the Manager can change over time. 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. References to investments include those held directly by the Fund and indirectly through the Fund’s investments in the underlying Funds. The Fund and 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 price of a particular security held by the Fund or those underlying Funds may affect the Fund’s or an underlying Fund’s performance more than if the Fund or the underlying Fund were a diversified investment company. 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.” 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, credit risk, and counterparty risk. 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. 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 or an underlying 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 or an underlying 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. In addition, the value of the Fund’s shares will be adversely affected if the equities that are the subject of the Fund’s short positions appreciate in value. 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 – Low trading volume, lack of a market maker, large position size, or legal restrictions may limit or prevent a Fund from selling particular securities or unwinding derivative positions at desirable prices. 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 underlying Funds will not perform as expected or that the Fund will invest in underlying funds with higher fees or expenses. Leveraging Risk – The use of reverse repurchase agreements and other derivatives creates leverage. The Fund and some underlying Funds are not limited in their use of derivatives or in the absolute face value of their derivative positions. Leverage increases the Fund’s losses when the value of its investments (including derivatives) declines. 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. In addition, hedging a non-U.S. currency can have a negative effect on performance if the U.S. dollar declines in value relative to that currency. 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. Credit Risk – The Fund runs the risk that the issuer or guarantor of a fixed income investment or the obligor of an obligation underlying an asset-backed security will be unable or unwilling to satisfy its obligation to pay principal and interest or otherwise to honor its obligations in a timely manner. The market price of a fixed income investment will normally decline as a result of the issuer’s, guarantor’s, or obligor’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. 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. 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- and mid-cap 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. Short Sales Risk – The Fund runs the risk that the Fund’s loss on a short sale of securities that the Fund does not own is unlimited. 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. 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 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. 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 interest rates and widening credit spreads, or decreased liquidity stemming from 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 reduction in the payment stream the Manager expected the Fund to receive at the time the Fund purchased the asset-backed security.
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	The Fund and 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 price of a particular security held by the Fund or those underlying Funds may affect the Fund’s or an underlying Fund’s performance more than if the Fund or the underlying Fund were a diversified investment company.
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. 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). After-tax returns are shown for Class III shares only; after-tax returns for other classes will vary. 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.
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 Closing [Text Block]	rr_BarChartClosingTextBlock	Highest Quarter: 5.32% (4Q2008) Lowest Quarter: – 4.81% (2Q2009) Year-to-Date (as of 3/31/13): – 0.33%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns Periods Ending December 31, 2012
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 Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are shown for Class III shares only; after-tax returns for other classes will vary.
GMO Trust | GMO Alpha Only Fund | Class III
Risk/Return:	rr_RiskReturnAbstract
Management fee	rr_ManagementFeesOverAssets	0.50%	[1]
Shareholder service fee	rr_DistributionOrSimilarNon12b1FeesOverAssets	0.15%	[1]
Other expenses	rr_OtherExpensesOverAssets	0.02%
Acquired fund fees and expenses (underlying fund expenses)	rr_AcquiredFundFeesAndExpensesOverAssets	0.43%	[2]
Total annual operating expenses	rr_ExpensesOverAssets	1.10%
Expense reimbursement/waiver	rr_FeeWaiverOrReimbursementOverAssets	(0.44%)	[1]
Total annual operating expenses after expense reimbursement/waiver	rr_NetExpensesOverAssets	0.66%
1 Year	rr_ExpenseExampleYear01	$ 67	[3]
3 Years	rr_ExpenseExampleYear03	312
5 Years	rr_ExpenseExampleYear05	577
10 Years	rr_ExpenseExampleYear10	1,333
1 Year	rr_ExpenseExampleNoRedemptionYear01	67	[3]
3 Years	rr_ExpenseExampleNoRedemptionYear03	312
5 Years	rr_ExpenseExampleNoRedemptionYear05	577
10 Years	rr_ExpenseExampleNoRedemptionYear10	1,333
2003	rr_AnnualReturn2003	2.71%
2004	rr_AnnualReturn2004	2.64%
2005	rr_AnnualReturn2005	4.95%
2006	rr_AnnualReturn2006	3.34%
2007	rr_AnnualReturn2007	7.60%
2008	rr_AnnualReturn2008	12.08%
2009	rr_AnnualReturn2009	(7.93%)
2010	rr_AnnualReturn2010	(4.02%)
2011	rr_AnnualReturn2011	4.73%
2012	rr_AnnualReturn2012	(1.21%)
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	(0.33%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Highest Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2008
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	5.32%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Lowest Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Jun. 30, 2009
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(4.81%)
1 Year	rr_AverageAnnualReturnYear01	(1.21%)
5 Years	rr_AverageAnnualReturnYear05	0.49%
10 Years	rr_AverageAnnualReturnYear10	2.34%
Incept.	rr_AverageAnnualReturnSinceInception	3.91%
Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 29, 1994
GMO Trust | GMO Alpha Only Fund | Class IV
Risk/Return:	rr_RiskReturnAbstract
Management fee	rr_ManagementFeesOverAssets	0.50%	[1]
Shareholder service fee	rr_DistributionOrSimilarNon12b1FeesOverAssets	0.10%	[1]
Other expenses	rr_OtherExpensesOverAssets	0.02%
Acquired fund fees and expenses (underlying fund expenses)	rr_AcquiredFundFeesAndExpensesOverAssets	0.43%	[2]
Total annual operating expenses	rr_ExpensesOverAssets	1.05%
Expense reimbursement/waiver	rr_FeeWaiverOrReimbursementOverAssets	(0.44%)	[1]
Total annual operating expenses after expense reimbursement/waiver	rr_NetExpensesOverAssets	0.61%
1 Year	rr_ExpenseExampleYear01	62	[3]
3 Years	rr_ExpenseExampleYear03	297
5 Years	rr_ExpenseExampleYear05	550
10 Years	rr_ExpenseExampleYear10	1,275
1 Year	rr_ExpenseExampleNoRedemptionYear01	62	[3]
3 Years	rr_ExpenseExampleNoRedemptionYear03	297
5 Years	rr_ExpenseExampleNoRedemptionYear05	550
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,275
1 Year	rr_AverageAnnualReturnYear01	(1.15%)
5 Years	rr_AverageAnnualReturnYear05	0.53%
10 Years	rr_AverageAnnualReturnYear10
Incept.	rr_AverageAnnualReturnSinceInception	1.79%
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 02, 2006
GMO Trust | GMO Alpha Only Fund | Return After Taxes on Distributions | Class III
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(1.15%)
5 Years	rr_AverageAnnualReturnYear05	(3.62%)
10 Years	rr_AverageAnnualReturnYear10	0.05%
Incept.	rr_AverageAnnualReturnSinceInception	1.65%
Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 29, 1994
GMO Trust | GMO Alpha Only Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class III
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(0.62%)
5 Years	rr_AverageAnnualReturnYear05	(1.31%)
10 Years	rr_AverageAnnualReturnYear10	1.05%
Incept.	rr_AverageAnnualReturnSinceInception	2.20%
Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 29, 1994
GMO Trust | GMO Alpha Only Fund | Citigroup 3-Month Treasury Bill Index (reflects no deduction for fees, expenses, or taxes) | Class III
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.07%
5 Years	rr_AverageAnnualReturnYear05	0.45%
10 Years	rr_AverageAnnualReturnYear10	1.69%
Incept.	rr_AverageAnnualReturnSinceInception	3.07%
Inception Date	rr_AverageAnnualReturnInceptionDate	Jul. 29, 1994
GMO Trust | GMO Alpha Only Fund | Citigroup 3-Month Treasury Bill Index (reflects no deduction for fees, expenses, or taxes) | Class IV
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	0.07%
5 Years	rr_AverageAnnualReturnYear05	0.45%
10 Years	rr_AverageAnnualReturnYear10
Incept.	rr_AverageAnnualReturnSinceInception	1.59%
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 02, 2006

[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] These indirect expenses include commissions paid to broker-dealers by the Fund for executing transactions in unaffiliated underlying funds ("transaction fees"). Net fees and expenses of underlying funds (before addition of transaction fees) and indirect transaction fees were approximately 0.43% and less than 0.01%, respectively.

[3] After reimbursement