Label Element Value
Prospectus [Line Items] rr_ProspectusLineItems  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Dec. 31, 2019
Entity Registrant Name dei_EntityRegistrantName ELFUN TRUSTS
Entity Central Index Key dei_EntityCentralIndexKey 0000032339
Amendment Flag dei_AmendmentFlag false
Entity Inv Company Type dei_EntityInvCompanyType N-1A
Document Creation Date dei_DocumentCreationDate Apr. 24, 2020
Document Effective Date dei_DocumentEffectiveDate Apr. 30, 2020
Prospectus Date rr_ProspectusDate Apr. 30, 2020
ELFUN TRUSTS  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Elfun Trusts
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

Elfun Trusts (the “Fund”) seeks long-term growth of capital and future income rather than current income.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
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 (“Fund Shares”).

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)
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 (or “turns over” its portfolio). 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 the most recent fiscal year, the Fund's portfolio turnover rate was 17% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 17.00%
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, and then sell or hold all of your Fund Shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. 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 seeks to achieve its investment objectives by investing in equity securities of U.S. companies. The Fund considers a company to be a U.S. company if it generates at least 50% of its revenues or profits from business activities in the U.S., has at least 50% of its assets situated in the U.S. or has the principal trading market for its securities in the U.S. The Fund also may invest, generally to a lesser extent, in securities of foreign (non-U.S.) issuers, including securities of issuers located in emerging markets.

 

SSGA Funds Management, Inc. (“SSGA FM” or the “Adviser”), the investment adviser to the Fund, selects equity securities from a number of industries based on the merits of individual companies. In seeking to achieve the Fund's investment objective with respect to future income, the Adviser will also consider companies that have the potential to pay dividends in the future. While the Fund may invest in companies of any market capitalization, it expects to primarily invest in large capitalization companies. The Fund may invest a substantial portion of its assets within one or more economic sectors or industries, which may change from time to time.

 

The Adviser seeks to identify securities of issuers with characteristics such as:

 

above-average annual growth rates;

 

appropriate capital structures;

 

leadership in their respective industries; and/or

 

high quality management focused on generating shareholder value.

 

The Adviser may consider selling a security when one of these characteristics no longer applies, when valuation has become excessive, or when more attractive alternatives are identified.

 

Equity securities may include common stocks, preferred stocks, other securities convertible into common stock or rights and warrants. Equity securities held by the Fund may be denominated in non-U.S. currencies and may be held outside the United States.

 

The Fund may invest to a lesser extent in debt securities. The Fund is permitted to invest up to 5% of its total assets (including any borrowings) in high yield securities (also known as below investment-grade bonds or “junk bonds”). The Fund is subject to no limitation with respect to the maturities of the debt instruments in which it may invest. The Adviser may also use various types of derivative instruments (such as options, futures and options on futures) to gain or hedge exposure to certain types of securities as an alternative to investing directly in or selling securities.

 

The Fund may invest in depositary receipts, repurchase agreements, when-issued and delayed delivery securities, mortgage-related securities, and may hold securities that are restricted as to resale. The Fund may invest in other investment companies, including exchange-traded funds (“ETFs”), to the extent permitted by applicable law (including those advised by SSGA FM). The Fund also may lend its securities.

Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

The Fund is subject to the following principal risks. You could lose money by investing in the Fund. Certain risks relating to instruments and strategies used in the management of the Fund are placed first. The significance of any specific risk to an investment in the Fund will vary over time, depending on the composition of the Fund's portfolio, market conditions, and other factors. You should read all of the risk information presented below carefully, because any one or more of these risks may result in losses to the Fund. An investment in the Fund is subject to investment risks, including possible loss of principal, is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund may not achieve its investment objective. The Fund is not intended to be a complete investment program, but rather is intended for investment as part of a diversified investment portfolio. Investors should consult their own advisers as to the role of the Fund in their overall investment programs.

 

Market Risk: The Fund's investments are subject to changes in general economic conditions, general market fluctuations and the risks inherent in investment in securities markets. Investment markets can be volatile and prices of investments can change substantially due to various factors including, but not limited to, economic growth or recession, changes in interest rates, changes in the actual or perceived creditworthiness of issuers, and general market liquidity. The Fund is subject to the risk that geopolitical events will disrupt securities markets and adversely affect global economies and markets. Local, regional or global events such as war, acts of terrorism, the spread of infectious illness or other public health issues, or other events could have a significant impact on the Fund and its investments.

 

Equity Investing Risk: The market prices of equity securities owned by the Fund may go up or down, sometimes rapidly or unpredictably. The value of a security may decline for a number of reasons that may directly relate to the issuer and also may decline due to general industry or market conditions that are not specifically related to a particular company. In addition, equity markets tend to move in cycles, which may cause stock prices to fall over short or extended periods of time.

 

Growth Stock Risk: The prices of growth stocks may be based largely on expectations of future earnings, and their prices can decline rapidly and significantly in reaction to negative news. Growth stocks may underperform value stocks and stocks in other broad style categories (and the stock market as a whole) over any period of time and may shift in and out of favor with investors generally, sometimes rapidly, depending on changes in market, economic, and other factors.

 

Counterparty Risk: The Fund will be subject to credit risk with respect to the counterparties with which the Fund enters into derivatives contracts, repurchase agreements, reverse repurchase agreements, and other transactions. If a counterparty fails to meet its contractual obligations, the Fund may be unable to terminate or realize any gain on the investment or transaction, or to recover collateral posted to the counterparty, resulting in a loss to the Fund. If the Fund holds collateral posted by its counterparty, it may be delayed or prevented from realizing on the collateral in the event of a bankruptcy or insolvency proceeding relating to the counterparty.

 

Currency Risk: The value of the Fund's assets may be affected favorably or unfavorably by currency exchange rates, currency exchange control regulations, and delays, restrictions or prohibitions on the repatriation of foreign currencies. Foreign currency exchange rates may have significant volatility, and changes in the values of foreign currencies against the U.S. dollar may result in substantial declines in the values of the Fund's assets denominated in foreign currencies.

 

Debt Securities Risk: The values of debt securities may increase or decrease as a result of the following: market fluctuations, increases in interest rates, actual or perceived inability or unwillingness of issuers, guarantors or liquidity providers to make scheduled principal or interest payments or illiquidity in debt securities markets; the risk of low rates of return due to reinvestment of securities during periods of falling interest rates or repayment by issuers with higher coupon or interest rates; and/or the risk of low income due to falling interest rates. To the extent that interest rates rise, certain underlying obligations may be paid off substantially slower than originally anticipated and the value of those securities may fall sharply. A rising interest rate environment may cause the value of the Fund's fixed income securities to decrease, an adverse impact on the liquidity of the Fund's fixed income securities, and increased volatility of the fixed income markets. If the principal on a debt obligation is prepaid before expected, the prepayments of principal may have to be reinvested in obligations paying interest at lower rates. During periods of falling interest rates, the income received by the Fund may decline. Changes in interest rates will likely have a greater effect on the values of debt securities of longer durations. Returns on investments in debt securities could trail the returns on other investment options, including investments in equity securities.

 

Derivatives Risk: Derivative transactions can create investment leverage and may have significant volatility. It is possible that a derivative transaction will result in a much greater loss than the principal amount invested, and the Fund may not be able to close out a derivative transaction at a favorable time or price. The counterparty to a derivatives contract may be unable or unwilling to make timely settlement payments, return the Fund's margin, or otherwise honor its obligations. A derivatives transaction may not behave in the manner anticipated by the Adviser or may not have the effect on the Fund anticipated by the Adviser.

 

Emerging Markets Risk: Risks of investing in emerging markets include, among others, greater political and economic instability, greater volatility in currency exchange rates, less developed securities markets, possible trade barriers, currency transfer restrictions, a more limited number of potential buyers and issuers, an emerging market country's dependence on revenue from particular commodities or international aid, less governmental supervision and regulation, unavailability of currency hedging techniques, differences in auditing and financial reporting standards, and less developed legal systems. There is also the potential for unfavorable action such as expropriation, nationalization, embargo, and acts of war. The securities of emerging market companies may trade less frequently and in smaller volumes than more widely held securities. Market disruptions or substantial market corrections may limit very significantly the liquidity of securities of certain companies in a particular country or geographic region, or of all companies in the country or region. The Fund may be unable to liquidate its positions in such securities at any time, or at a favorable price, in order to meet the Fund's obligations. These risks are generally greater for investments in frontier market countries, which typically have smaller economies or less developed capital markets than traditional emerging market countries.

 

Hedging Risk: The success of the Fund's hedging strategies will depend, in part, upon the Adviser's ability to assess correctly the degree of correlation between the performance of the instruments used in a hedging strategy and the performance of the investments being hedged. There is no guarantee that any hedging strategy used by the Fund will be successful in hedging the subject risks. It is possible that the Fund will lose money on a hedging transaction and on the asset of the Fund that was the subject of the hedge. Hedging transactions may have the effect of creating investment leverage in the Fund.

 

Large-Capitalization Securities Risk: Returns on investments in securities of large companies could trail the returns on investments in securities of smaller and mid-sized companies. Larger companies may be unable to respond as quickly as smaller and mid-sized companies to competitive challenges or to changes in business, product, financial, or other market conditions. Larger companies may not be able to maintain growth at the high rates that may be achieved by well-managed smaller and mid-sized companies.

 

Management Risk: The Fund is actively managed. The Adviser's judgments about the attractiveness, relative value, or potential appreciation of a particular sector, security, commodity or investment strategy or as to a hedging strategy may prove to be incorrect, and may cause the Fund to incur losses. There can be no assurance that the Adviser's investment techniques and decisions will produce the desired results.

 

Non-U.S. Securities Risk: Non-U.S. securities (including depositary receipts) are subject to political, regulatory, and economic risks not present in domestic investments. There may be less information publicly available about a non-U.S. entity than about a U.S. entity, and many non-U.S. entities are not subject to accounting, auditing, legal and financial report standards comparable to those in the United States. Further, such entities and/or their securities may be subject to risks associated with currency controls; expropriation; changes in tax policy; greater market volatility; differing securities market structures; higher transaction costs; and various administrative difficulties, such as delays in clearing and settling portfolio transactions or in receiving pay-ment of dividends. Securities traded on foreign markets may be less liquid (harder to sell) than securities traded domestically. Foreign governments may impose restrictions on the repatriation of capital to the U.S. In addition, to the extent that the Fund buys securities denominated in a foreign currency, there are special risks such as changes in currency exchange rates and the risk that a foreign government could regulate foreign exchange transactions. In addition, to the extent investments are made in a limited number of countries, events in those countries will have a more significant impact on the Fund. Investments in depositary receipts may be less liquid and more volatile than the underlying shares in their primary trading market.

 

Preferred Securities Risk: Generally, preferred security holders have no or limited voting rights with respect to the issuing company. In addition, preferred securities are subordinated to bonds and other debt instruments in a company's capital structure and therefore will be subject to greater credit risk than those debt instruments. Dividend payments on a preferred security typically must be declared by the issuer's board of directors. In the event an issuer of preferred securities experiences economic difficulties, the issuer's preferred securities may lose substantial value due to the reduced likelihood that the issuer's board of directors will declare a dividend and the fact that the preferred security may be subordinated to other securities of the same issuer. Further, because many preferred securities pay dividends at a fixed rate, their market price can be sensitive to changes in interest rates in a manner similar to bonds — that is, as interest rates rise, the value of the preferred securities held by the Fund are likely to decline. In addition, because many preferred securities allow holders to convert the preferred securities into common stock of the issuer, their market price can be sensitive to changes in the value of the issuer's common stock and, therefore, declining common stock values may also cause the value of the Fund's investments to decline. Preferred securities often have call features which allow the issuer to redeem the security at its discretion. The redemption of a preferred security having a higher than average yield may cause a decrease in the Fund's yield.

 

Unconstrained Sector Risk: The Fund may invest a substantial portion of its assets within one or more economic sectors or industries, which may change from time to time. Greater investment focus on one or more sectors or industries increases the potential for volatility and the risk that events negatively affecting such sectors or industries could reduce returns, potentially causing the value of the Fund's Shares to decrease, perhaps significantly.

Risk Lose Money [Text] rr_RiskLoseMoney You could lose money by investing in the Fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the Fund is subject to investment risks, including possible loss of principal, is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
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 illustrating the variability of the Fund's returns from year-to-year and by showing how the Fund's average annual returns for the periods indicated compared with those of a broad measure of market performance. The Fund's past performance does not necessarily indicate how the Fund will perform in the future. Current performance information for the Fund is available toll free by calling (800)-242-0134 or by visiting our website at www.ssga.com/geam.

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 illustrating the variability of the Fund's returns from year-to-year and by showing how the Fund's average annual returns for the periods indicated compared with those of a broad measure of market performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone (800)-242-0134
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.ssga.com/geam
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund's past performance does not necessarily indicate how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns (years ended 12/31)*
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Highest Quarterly Return: 15.86% (Q1, 2012)
Lowest Quarterly Return: -15.40% (Q3, 2011)

Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for periods ended 12/31/19)
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 After-tax returns depend on an investor's tax situation and may differ from those shown below, and after-tax returns are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (“IRAs”). The returns after taxes can exceed the returns before taxes due to an assumed tax benefit for a shareholder from realizing a capital loss on a sale of Fund shares.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

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. After-tax returns depend on an investor's tax situation and may differ from those shown below, and after-tax returns are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (“IRAs”). The returns after taxes can exceed the returns before taxes due to an assumed tax benefit for a shareholder from realizing a capital loss on a sale of Fund shares.

ELFUN TRUSTS | Elfun Trusts Shares  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol ELFNX
Maximum Sales Charge (Load) Imposed On Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of the net asset value) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fees rr_ManagementFeesOverAssets 0.14%
Distribution and Shareholder Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets
Other Expenses rr_OtherExpensesOverAssets 0.04%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.18%
One Year rr_ExpenseExampleYear01 $ 18
Three Years rr_ExpenseExampleYear03 58
Five Years rr_ExpenseExampleYear05 101
Ten Years rr_ExpenseExampleYear10 $ 230
Annual Return 2010 rr_AnnualReturn2010 13.07%
Annual Return 2011 rr_AnnualReturn2011 1.33%
Annual Return 2012 rr_AnnualReturn2012 21.27%
Annual Return 2013 rr_AnnualReturn2013 34.98%
Annual Return 2014 rr_AnnualReturn2014 13.13%
Annual Return 2015 rr_AnnualReturn2015 1.70%
Annual Return 2016 rr_AnnualReturn2016 6.08%
Annual Return 2017 rr_AnnualReturn2017 25.61%
Annual Return 2018 rr_AnnualReturn2018 (3.39%)
Annual Return 2019 rr_AnnualReturn2019 35.57%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.86%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (15.40%)
1 Year rr_AverageAnnualReturnYear01 35.57%
5 Years rr_AverageAnnualReturnYear05 12.16%
10 Years rr_AverageAnnualReturnYear10 14.18%
Inception Date rr_AverageAnnualReturnInceptionDate May 27, 1935
ELFUN TRUSTS | After Taxes on Distributions | Elfun Trusts Shares  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 32.72%
5 Years rr_AverageAnnualReturnYear05 9.51%
10 Years rr_AverageAnnualReturnYear10 11.93%
Inception Date rr_AverageAnnualReturnInceptionDate May 27, 1935
ELFUN TRUSTS | After Taxes on Distributions and Sales | Elfun Trusts Shares  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 22.96%
5 Years rr_AverageAnnualReturnYear05 9.10%
10 Years rr_AverageAnnualReturnYear10 11.20%
Inception Date rr_AverageAnnualReturnInceptionDate May 27, 1935
ELFUN TRUSTS | S&P 500 Index (reflects no deduction for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 31.49%
5 Years rr_AverageAnnualReturnYear05 11.70%
10 Years rr_AverageAnnualReturnYear10 13.56%
Inception Date rr_AverageAnnualReturnInceptionDate May 27, 1935