Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	GMO TRUST
Prospectus Date	rr_ProspectusDate	Jun. 30, 2016
GMO Foreign Small Companies Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	GMO FOREIGN SMALL COMPANIES FUND
Objective [Heading]	rr_ObjectiveHeading	Investment objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Total return in excess of that of its benchmark, the S&P Developed ex-U.S. Small Cap Index.
Expense [Heading]	rr_ExpenseHeading	Fees and expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The tables below describe the fees and expenses that you may bear 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 bear each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	June 30, 2017
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 transaction costs, which are not reflected in Annual Fund operating expenses or in the Example, affect the Fund’s performance. During its fiscal year ended February 29, 2016, the Fund’s portfolio turnover rate was 44% of the average value of its portfolio. That portfolio turnover rate excludes investments in U.S. Treasury Fund, which the Fund uses as a short-term investment vehicle for cash management, and other short-term investments. The Fund’s portfolio turnover rate during its fiscal year ended February 29, 2016, including transactions in U.S. Treasury Fund, was 60% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	44.00%
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. The one year amounts shown reflect the expense reimbursement and waiver noted in the expense table. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
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 typically invests directly and indirectly in equities of companies tied economically to countries other than the United States whose outstanding publicly traded equities are in the lowest 25% of publicly traded market capitalization (float) in a particular country at the time of investment ("small companies"). The term "equities" refers to direct and indirect investments in common and preferred stocks and other stock-related securities, such as convertible securities, depositary receipts, and equity real estate investment trusts (REITs) and income trusts. The market capitalization range of companies whose equities are held by the Fund is generally within the market capitalization range of companies in the Fund's benchmark, which represents the lowest 15% of publicly traded market capitalization (float) of the S&P Broad Market Index in each country. Depending on the country, as of May 31, 2016, the market capitalization of the outstanding common stock and other stock-related securities of the largest company in a particular country included in the S&P Developed ex-U.S. Small Cap Index ranged from approximately $410 million (Argentina) to $14.4 billion (Switzerland) (based on exchange rates as of May 31, 2016). As of May 31, 2016, the publicly traded market capitalization of the largest small company (as defined by the Fund) ranged from approximately $519 million (Egypt) to $17.6 billion (Switzerland) (based on exchange rates as of May 31, 2016). Under normal circumstances, the Fund invests directly and indirectly (e.g., through underlying funds or derivatives) at least 80% of its assets in securities of small companies that are tied economically to countries other than the United States, including both developed and emerging countries (see "Name Policies"). GMO selects investments using value-based fundamental analysis that is informed by a disciplined quantitative screening process. GMO analyzes companies for financial, operational, and managerial strength and compares them to their global, regional, and industry peers. GMO also considers a company's accounting and governance practices. As part of the investment process, GMO frequently meets with management and visits companies. The factors GMO considers and investment methods GMO uses can change over time. In pursuing its investment objective, the Fund may (but is not obligated to) invest in a wide variety of exchange-traded and over-the-counter (OTC) derivatives, including, without limitation, forward currency contracts, futures and options, as well as exchange-traded funds (ETFs). The Fund's foreign currency exposure may differ from the currency exposure of its equity investments. In addition, the Fund may lend its portfolio securities. The Fund also may invest in U.S. Treasury Fund, in money market funds unaffiliated with GMO, or directly in the types of investments typically held by 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. The principal risks of investing in the Fund are summarized below. For a more complete discussion of these risks, see “Description of Principal Risks.” Small Company Risk – Smaller companies may have limited product lines, markets, or financial resources, may lack the competitive strength of larger companies, may have inexperienced managers or may depend on a few key employees. The securities of companies with smaller market capitalizations often are less widely held and trade less frequently and in lesser quantities, and their market prices often fluctuate more, than the securities of companies with larger market capitalizations. Market Risk – Equities – The market price of an equity may decline due to factors affecting the issuer, its industry or the economy and equity markets generally. If the Fund purchases an equity for less than its fundamental fair (or intrinsic) value as determined by GMO, the Fund runs the risk that the market price of the equity will not appreciate or will decline due to GMO’s incorrect assessment of the equity’s fundamental fair (or intrinsic) value. The Fund also may purchase equities that typically trade at higher multiples of current earnings than other securities, and the market prices of these equities 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. Non-U.S. Investment Risk – The market prices of many non-U.S. securities fluctuate more than those of U.S. securities. Many non-U.S. securities markets are less stable, smaller, less liquid, and less regulated than U.S. securities markets, and the cost of trading in those markets often is higher than in U.S. securities markets. Transactions in non-U.S. securities generally involve higher commission rates, transfer taxes, and custodial costs than similar transactions in U.S. securities. 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, interest, or other amounts it realizes or accrues in respect of non-U.S. investments; (ii) transactions in those investments; and (iii) repatriation of proceeds generated from the sale or other disposition of those investments. Also, the Fund needs a license to invest directly in many non-U.S. securities 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. securities markets, prevailing custody and trade settlement practices (e.g., the requirement to pay for securities prior to receipt) expose the Fund to credit and other risks. Further, adverse changes in investment regulations, capital requirements or exchange controls could adversely affect the value of the Fund’s investments. 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 may be predominantly based on only a few industries or dependent on revenues from particular commodities and which often are more volatile than the economies of developed countries. Currency Risk – Fluctuations in exchange rates can adversely affect the market value of the Fund’s foreign currency holdings and investments denominated in foreign currencies. Illiquidity Risk – Low trading volume, lack of a market maker, large position size, or legal restrictions may limit or prevent the Fund from selling particular securities or closing derivative positions at desirable prices. Management and Operational Risk – The Fund runs the risk that GMO’s investment techniques will fail to produce desired results. GMO often uses quantitative models as part of its investment process. GMO’s models are not necessarily predictive of future market events and use simplifying assumptions that can limit their effectiveness. In addition, the data on which the models are based is subject to limitations (e.g., inaccuracies, staleness) that could adversely affect the Fund’s performance. The Fund also runs the risk that GMO’s assessment of an investment (including a company’s fundamental fair (or intrinsic) value) 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. Focused Investment Risk – Investments focused in countries, regions, sectors, industries, or issuers (or in sectors within a country or region) that are subject to the same or similar risk factors and investments whose prices are closely correlated are subject to greater overall risk than investments that are more diversified or whose prices are not as closely 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. 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 reverse repurchase agreements and other derivatives and securities lending creates leverage. Leverage increases the Fund’s losses when the value of its investments (including derivatives) declines. Derivatives and Short Sales Risk – The use of derivatives involves the risk that their value may not change as expected relative to changes in the value of the underlying assets, rates, or indices. Derivatives also present other risks, including market risk, illiquidity risk, currency risk, credit risk, and counterparty risk. The market price of an option is affected by many factors, including changes in the market prices or dividend rates of underlying securities (or in the case of indices, the securities in such indices); the time remaining before expiration; changes in interest rates or exchange rates; and changes in the actual or perceived volatility of the relevant stock market and underlying securities. The Fund may create short investment exposure by taking a derivative position in which the value of the derivative moves in the opposite direction from the price of an underlying investment, pool of investments, index or currency. The risks of loss associated with derivatives that provide short investment exposure and short sales of securities are theoretically unlimited. 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 require the Fund to sell securities at disadvantageous prices or otherwise 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 a broad-based 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-advantaged 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. Updated performance information for the Fund is available at www.gmo.com. 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 Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.gmo.com
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: 31.25% (2Q2009) Lowest Quarter: – 24.05% (3Q2008) Year-to-Date (as of 3/31/16): – 1.83%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns Periods Ending December 31, 2015
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-advantaged 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 Foreign 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	0.70%	[1]
Shareholder service fee	rr_DistributionOrSimilarNon12b1FeesOverAssets	0.15%	[1]
Other expenses	rr_OtherExpensesOverAssets	0.07%
Total annual fund operating expenses	rr_ExpensesOverAssets	0.92%
Expense reimbursement/waiver	rr_FeeWaiverOrReimbursementOverAssets	(0.06%)	[1]
Total annual fund operating expenses	rr_NetExpensesOverAssets	0.86%	[2]
1 Year	rr_ExpenseExampleYear01	$ 189
3 Years	rr_ExpenseExampleYear03	392
5 Years	rr_ExpenseExampleYear05	612
10 Years	rr_ExpenseExampleYear10	1,244
1 Year	rr_ExpenseExampleNoRedemptionYear01	137
3 Years	rr_ExpenseExampleNoRedemptionYear03	336
5 Years	rr_ExpenseExampleNoRedemptionYear05	551
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,170
2006	rr_AnnualReturn2006	35.83%
2007	rr_AnnualReturn2007	7.85%
2008	rr_AnnualReturn2008	(44.68%)
2009	rr_AnnualReturn2009	44.58%
2010	rr_AnnualReturn2010	24.83%
2011	rr_AnnualReturn2011	(15.25%)
2012	rr_AnnualReturn2012	22.57%
2013	rr_AnnualReturn2013	28.25%
2014	rr_AnnualReturn2014	(10.17%)
2015	rr_AnnualReturn2015	6.18%
Year to Date Return, Label	rr_YearToDateReturnLabel	Year-to-Date
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2016
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	(1.83%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Highest Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	31.25%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Lowest Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(24.05%)
1 Year	rr_AverageAnnualReturnYear01	5.12%	[3],[4]
5 Years	rr_AverageAnnualReturnYear05	4.70%	[3],[4]
10 Years	rr_AverageAnnualReturnYear10	6.29%	[3],[4]
Incept.	rr_AverageAnnualReturnSinceInception	10.34%	[3],[4]
Inception Date	rr_AverageAnnualReturnInceptionDate	Jan. 04, 1995	[3],[4]
GMO Foreign Small Companies Fund | Class IV
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	0.70%	[1]
Shareholder service fee	rr_DistributionOrSimilarNon12b1FeesOverAssets	0.10%	[1]
Other expenses	rr_OtherExpensesOverAssets	0.07%
Total annual fund operating expenses	rr_ExpensesOverAssets	0.87%
Expense reimbursement/waiver	rr_FeeWaiverOrReimbursementOverAssets	(0.06%)	[1]
Total annual fund operating expenses	rr_NetExpensesOverAssets	0.81%	[2]
1 Year	rr_ExpenseExampleYear01	$ 184
3 Years	rr_ExpenseExampleYear03	376
5 Years	rr_ExpenseExampleYear05	585
10 Years	rr_ExpenseExampleYear10	1,186
1 Year	rr_ExpenseExampleNoRedemptionYear01	132
3 Years	rr_ExpenseExampleNoRedemptionYear03	320
5 Years	rr_ExpenseExampleNoRedemptionYear05	524
10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 1,112
1 Year	rr_AverageAnnualReturnYear01	5.11%	[3],[5]
5 Years	rr_AverageAnnualReturnYear05	4.75%	[3],[5]
10 Years	rr_AverageAnnualReturnYear10	6.32%	[3],[5]
Incept.	rr_AverageAnnualReturnSinceInception	10.54%	[3],[5]
Inception Date	rr_AverageAnnualReturnInceptionDate	Jun. 14, 2002	[3],[5]
GMO Foreign Small Companies Fund | Return After Taxes on Distributions | Class III
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	3.97%	[3],[4]
5 Years	rr_AverageAnnualReturnYear05	3.84%	[3],[4]
10 Years	rr_AverageAnnualReturnYear10	4.85%	[3],[4]
Incept.	rr_AverageAnnualReturnSinceInception		[3],[4]
Inception Date	rr_AverageAnnualReturnInceptionDate	Jan. 04, 1995	[3],[4]
GMO Foreign Small Companies Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class III
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	4.11%	[3],[4]
5 Years	rr_AverageAnnualReturnYear05	3.74%	[3],[4]
10 Years	rr_AverageAnnualReturnYear10	5.15%	[3],[4]
Incept.	rr_AverageAnnualReturnSinceInception		[3],[4]
Inception Date	rr_AverageAnnualReturnInceptionDate	Jan. 04, 1995	[3],[4]
GMO Foreign Small Companies Fund | S&P Developed ex-U.S. Small Cap Index (reflects no deduction for fees, expenses, or taxes) | Class III
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	5.92%	[3],[4]
5 Years	rr_AverageAnnualReturnYear05	5.51%	[3],[4]
10 Years	rr_AverageAnnualReturnYear10	5.33%	[3],[4]
Incept.	rr_AverageAnnualReturnSinceInception	6.94%	[3],[4]
Inception Date	rr_AverageAnnualReturnInceptionDate	Jan. 04, 1995	[3],[4]
GMO Foreign Small Companies Fund | S&P Developed ex-U.S. Small Cap Index (reflects no deduction for fees, expenses, or taxes) | Class IV
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	5.92%	[3],[5]
5 Years	rr_AverageAnnualReturnYear05	5.51%	[3],[5]
10 Years	rr_AverageAnnualReturnYear10	5.33%	[3],[5]
Incept.	rr_AverageAnnualReturnSinceInception	9.73%	[3],[5]
Inception Date	rr_AverageAnnualReturnInceptionDate	Jun. 14, 2002	[3],[5]

[1] Grantham, Mayo, Van Otterloo & Co. LLC ("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 GMO, federal securities law filing expenses, printing expenses, state and federal registration fees and custody expenses. GMO also has contractually 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 paid to GMO that are directly or indirectly borne by the Fund or a class of shares of the Fund as a result of the Fund's direct or indirect investments in other series of GMO Trust ("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, 2017, and may not be terminated prior to this date without the action or consent of the Fund's Board of Trustees.

[2] after expense reimbursement/waiver

[3] Information on the Fund's return after taxes is unavailable prior to June 30, 2000, the date the Fund commenced operations as a registered investment company. Prior to that date, the Fund operated as a private investment pool with investment objectives, policies, and guidelines that were substantially the same as those of the Fund.

[4] Performance of Class III shares prior to June 30, 2000 is that of the private investment pool, restated to reflect the Fund's higher annual operating expenses. The pool was not registered as an investment company and therefore was not subject to certain restrictions imposed on the Fund by the Investment Company Act of 1940, as amended, and the Internal Revenue Code of 1986, as amended. Had the pool been subject to these restrictions, its performance may have been adversely affected.

[5] For the period from March 16, 2009 to August 12, 2009, no Class IV shares were outstanding. The returns shown in the table for that period are those of Class III shares, which have higher expenses.