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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date rr_ProspectusDate Feb. 28, 2014
R10R25 SHARES | U.S. Sustainability Core 1 Portfolio
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading U.S. Sustainability Core 1 Portfolio
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The investment objective of the U.S. Sustainability Core 1 Portfolio is long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock This table describes the fees and expenses you may pay if you buy and hold Class R25 shares of the U.S. Sustainability Core 1 Portfolio.
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 February 28, 2015
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The U.S. Sustainability Core 1 Portfolio pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Portfolio shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the U.S. Sustainability Core 1 Portfolio’s performance. During the most recent fiscal year, the U.S. Sustainability Core 1 Portfolio’s portfolio turnover rate was 2% of the average value of its investment portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 2.00%
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates The Class R25 shares are a new class of shares of the Portfolio, so the "Other Expenses" shown for the class are based on anticipated fees and expenses for the first full fiscal year.
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock This Example is meant to help you compare the cost of investing in the U.S. Sustainability Core 1 Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The costs for the Portfolio reflect the net expenses that result from the contractual expense waiver and assumption in the first year only. 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 Dimensional Fund Advisors LP (the “Advisor”) believes that equity investing should involve a long-term view and a systematic focus on sources of expected returns, not on stock picking or market timing. In constructing an investment portfolio, the Advisor identifies a broadly diversified universe of eligible securities with precisely-defined risk and return characteristics. It then places priority on efficiently managing portfolio turnover and keeping trading costs low. In general, the Advisor does not intend to purchase or sell securities for the investment portfolio based on prospects for the economy, the securities markets or the individual issuers whose shares are eligible for purchase.

The U.S. Sustainability Core 1 Portfolio purchases a broad and diverse group of securities of U.S. companies with a greater emphasis on small capitalization and value companies as compared to their representation in the U.S. Universe, while adjusting the composition of the Portfolio based on environmental impact considerations. The Advisor generally defines the U.S. Universe as a free float adjusted market capitalization weighted portfolio of U.S. operating companies listed on the New York Stock Exchange (“NYSE”), NYSE MKT LLC or Nasdaq Global Market® or such other securities exchanges deemed appropriate by the Advisor. The Portfolio’s increased exposure to small and value companies may be achieved by decreasing the allocation of the Portfolio’s assets to the largest U.S. growth companies relative to their weight in the U.S. Universe. An equity issuer is considered a growth company primarily because it has a low, non-negative book value in relation to its market capitalization. An equity issuer is considered a value company primarily because it has a high book value in relation to its market capitalization.

As a non-fundamental policy, under normal circumstances, U.S. Sustainability Core 1 Portfolio will invest at least 80% of its net assets in equity securities of U.S. companies. The percentage allocation of the assets of the U.S. Sustainability Core 1 Portfolio to securities of the largest U.S. growth companies as defined above will generally be reduced from between 2.5% and 25% of their percentage weight in the U.S. Universe. For example, as of December 31, 2013, securities of the largest U.S. growth companies comprised 25% of the U.S. Universe and the Advisor allocated approximately 16% of the U.S. Sustainability Core 1 Portfolio to securities of the largest U.S. growth companies. The percentage by which the U.S. Sustainability Core 1 Portfolio’s allocation to securities of the largest U.S. growth companies is reduced will change due to market movements, environmental impact considerations and other factors. Additionally, the range by which the U.S. Sustainability Core 1 Portfolio’s percentage allocation to all securities as compared to the U.S. Universe may be impacted by the Portfolio’s investment strategies with respect to environmental impact considerations or modified after considering other factors the Advisor determines to be appropriate, such as free float, momentum, trading strategies, liquidity management, and expected profitability. In assessing expected profitability, the Advisor may consider different ratios, such as that of earnings or profits from operations relative to book value or assets.

The U.S. Sustainability Core 1 Portfolio also may use derivatives, such as futures contracts and options on futures contracts for U.S. equity securities and indices, to gain market exposure on its uninvested cash pending investment in securities or to maintain liquidity to pay redemptions. The above-referenced investments are not subject to, although they may incorporate, the U.S. Sustainability Core 1 Portfolio’s environmental impact considerations.

The U.S. Sustainability Core 1 Portfolio may lend its portfolio securities to generate additional income.

The Advisor intends to take into account the impact that companies have on the environment when making investment decisions for the U.S. Sustainability Core 1 Portfolio by adjusting the composition of the Portfolio based on environmental impact considerations. Relative to a portfolio without environmental impact considerations, the U.S. Sustainability Core 1 Portfolio will exclude or underweight securities of companies that, according to the Portfolio’s environmental impact considerations, may have a relatively negative impact on the environment as compared either to other companies in the Portfolio’s entire investment universe or other companies with similar business lines. Similarly, relative to a portfolio without environmental impact considerations, the U.S. Sustainability Core 1 Portfolio will overweight securities of companies that, according to the Portfolio’s environmental impact considerations, may have a relatively positive impact on the environment as compared either to other companies in the Portfolio’s entire investment universe or other companies with similar business lines. Negative factors include issues relating to agricultural chemicals, climate change, hazardous waste, ozone depleting chemicals, regulatory problems, substantial emissions, negative economic impact, and other environmental concerns. Positive factors include issues relating to beneficial products and services, clean energy, environmental management systems, pollution prevention, recycling and other strengths. The Advisor has engaged a third party service provider to provide research and ratings information relating to the U.S. Sustainability Core 1 Portfolio’s environmental impact considerations with respect to securities in the portfolio, where information is available from such provider.
Risk [Heading] rr_RiskHeading PRINCIPAL RISKS
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock Market Risk: Even a long-term investment approach cannot guarantee a profit. Economic, political, and issuer-specific events will cause the value of securities, and the U.S. Sustainability Core 1 Portfolio that owns them, to rise or fall. Because the value of your investment in the Portfolio will fluctuate, there is the risk that you will lose money.

Value Investment Risk: Value stocks may perform differently from the market as a whole and following a value-oriented investment strategy may cause the Portfolio to at times underperform equity funds that use other investment strategies.

Small Company Risk: Securities of small companies are often less liquid than those of large companies and this could make it difficult to sell a small company security at a desired time or price. As a result, small company stocks may fluctuate relatively more in price. In general, smaller capitalization companies are also more vulnerable than larger companies to adverse business or economic developments and they may have more limited resources.

Environmental Impact Consideration Investment Risk: The U.S. Sustainability Core 1 Portfolio’s environmental impact considerations may limit the number of investment opportunities available to the Portfolio, and as a result, at times, the Portfolio may produce more modest gains than funds that are not subject to such special investment considerations. For example, the Portfolio may decline to purchase, or underweight its investment in, certain securities due to environmental impact considerations when other investment considerations would suggest that a more significant investment in such securities would be advantageous. In addition, the Portfolio may sell certain securities due to environmental impact considerations when it is otherwise disadvantageous to do so. The environmental impact considerations may cause the Portfolio’s industry allocation to deviate from that of funds without these considerations and of conventional benchmarks.

Derivatives Risk: Derivatives are instruments, such as futures contracts, whose value is derived from that of other assets, rates or indices. The use of derivatives for non-hedging purposes may be considered more speculative than other types of investments. When the U.S. Sustainability Core 1 Portfolio uses derivatives, the Portfolio will be directly exposed to the risks of that derivative. Derivative instruments are subject to a number of risks including counterparty, liquidity, interest rate, market, credit and management risks, and the risk of improper valuation. Changes in the value of a derivative may not correlate perfectly with the underlying asset, rate or index, and the Portfolio could lose more than the principal amount invested.

Securities Lending Risk: Securities lending involves the risk that the borrower may fail to return the securities in a timely manner or at all. As a result, the U.S. Sustainability Core 1 Portfolio may lose money and there may be a delay in recovering the loaned securities. The U.S. Sustainability Core 1 Portfolio could also lose money if it does not recover the securities and/or the value of the collateral falls, including the value of investments made with cash collateral. Securities lending also may have certain adverse tax consequences.
Risk Lose Money [Text] rr_RiskLoseMoney Because the value of your investment in the Portfolio will fluctuate, there is the risk that you will lose money.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading PERFORMANCE
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The bar chart and table immediately following illustrate the variability of the U.S. Sustainability Core 1 Portfolio’s returns and are meant to provide some indication of the risks of investing in the Portfolio. The Class R25 shares of the Portfolio are a new class of shares for which performance information is not available, therefore, the bar chart and table show performance information for the Institutional Class shares of the Portfolio, another class of shares of the Portfolio not offered in this Prospectus. The bar chart shows the changes in performance of the Institutional Class shares of the Portfolio from year to year. The table illustrates how annualized one year, five year and since inception returns of the Institutional Class shares of the Portfolio compare with those of a broad measure of market performance. The U.S. Sustainability Core 1 Portfolio’s past performance (before and after taxes) is not an indication of future results. Updated performance information for the Portfolio can be obtained by visiting www.dimensional.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table immediately following illustrate the variability of the U.S. Sustainability Core 1 Portfolio’s returns and are meant to provide some indication of the risks of investing in the Portfolio. The Class R25 shares of the Portfolio are a new class of shares for which performance information is not available, therefore, the bar chart and table show performance information for the Institutional Class shares of the Portfolio, another class of shares of the Portfolio not offered in this Prospectus. The bar chart shows the changes in performance of the Institutional Class shares of the Portfolio from year to year.
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess The Class R25 shares of the Portfolio are a new class of shares for which performance information is not available
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.dimensional.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The U.S. Sustainability Core 1 Portfolio’s past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading U.S. Sustainability Core 1 Portfolio Institutional Class Shares
Total Returns (%)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock January 2009-December 2013

Highest Quarter    Lowest Quarter
18.89 (4/09-6/09)    -17.51 (7/11-9/11)
Bar Chart, Returns for Class Not Offered in Prospectus [Text] rr_BarChartReturnsForClassNotOfferedInProspectus The Class R25 shares of the Portfolio are a new class of shares for which performance information is not available, therefore, the bar chart and table show performance information for the Institutional Class shares of the Portfolio, another class of shares of the Portfolio not offered in this Prospectus.
Performance Table Heading rr_PerformanceTableHeading Periods ending December 31, 2013
Annualized Returns (%)
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock The implementation and management of the Advisor’s “Sustainability” portfolios, including without limitation, the U.S. Sustainability Core 1 Portfolio, is protected by U.S. Patent Nos. 7,596,525 B1 and 7,599,874 B1 and 8,438,092 B2.
R10R25 SHARES | U.S. Sustainability Core 1 Portfolio | Class R25
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fee rr_ManagementFeesOverAssets 0.29%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.62% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.16%
Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.54% [2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 0.62%
1 Year rr_ExpenseExampleYear01 63
3 Years rr_ExpenseExampleYear03 $ 315
R10R25 SHARES | U.S. Sustainability Core 1 Portfolio | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
2009 rr_AnnualReturn2009 31.36% [3]
2010 rr_AnnualReturn2010 18.68% [3]
2011 rr_AnnualReturn2011 (0.66%) [3]
2012 rr_AnnualReturn2012 17.05% [3]
2013 rr_AnnualReturn2013 36.69% [3]
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.89%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (17.51%)
One Year rr_AverageAnnualReturnYear01 36.69% [3]
Five Years rr_AverageAnnualReturnYear05 19.90% [3]
Since Inception rr_AverageAnnualReturnSinceInception 9.83% [3]
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 12, 2008 [3]
R10R25 SHARES | U.S. Sustainability Core 1 Portfolio | Russell 3000® Index (reflects no deduction for fees, expenses, or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 33.55%
Five Years rr_AverageAnnualReturnYear05 18.71%
Since Inception rr_AverageAnnualReturnSinceInception 9.05%
[1] The Class R25 shares are a new class of shares of the Portfolio, so the "Other Expenses" shown for the class are based on anticipated fees and expenses for the first full fiscal year.
[2] The Advisor has agreed to waive certain fees and in certain instances, assume certain expenses of the Portfolio. The Fee Waiver and Expense Assumption Agreement for the Portfolio will remain in effect through February 28, 2015, and may only be terminated by the Fund's Board of Directors prior to that date. Under certain circumstances, the Advisor retains the right to seek reimbursement for any fees previously waived and/or expenses previously assumed up to thirty-six months after such fee waiver and/or expense assumption.
[3] The Institutional Class shares of the Portfolio would have substantially similar annual returns as the Class R25 shares because the shares are invested in the same portfolio securities. Returns for the Class R25 shares and Institutional Class shares will differ to the extent that the classes will have different expenses, and returns for the Class R25 shares would be expected to be lower than the returns of the Institutional Class shares to the extent that the Class R25 shares have higher expenses than the Institutional Class shares.