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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date rr_ProspectusDate Feb. 28, 2016
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 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)
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 11% of the average value of its investment portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 11.00%
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 of the Portfolio 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 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 sustainability 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, Nasdaq Global Market®, Nasdaq Capital 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. Securities are considered to be value stocks primarily because a company’s shares have a high book value in relation to their market value.

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, 2015, securities of the largest U.S. growth companies comprised 33% of the U.S. Universe and the Advisor allocated approximately 24% 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, sustainability 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 sustainability impact considerations and the Advisor may also adjust the representation in the U.S. Sustainability Core 1 Portfolio of an eligible company, or exclude a company, after considering other factors the Advisor determines to be appropriate, such as free float, momentum, trading strategies, liquidity management, profitability, and other factors the Advisor determines to be appropriate, given market conditions. In assessing 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 adjust market exposure based on actual or expected cash inflows to or outflows from the Portfolio. The Portfolio does not intend to use derivatives for purposes of speculation or leveraging investment returns. The above-referenced investments are not subject to, although they may incorporate, the U.S. Sustainability Core 1 Portfolio’s sustainability 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 may have on the environment and other sustainability considerations when making investment decisions for the U.S. Sustainability Core 1 Portfolio. Relative to a portfolio without these considerations, the U.S. Sustainability Core 1 Portfolio will exclude or underweight securities of companies that, according to the Portfolio’s sustainability impact considerations, may be less sustainable as compared either to other companies in the Portfolio’s investment universe or other companies with similar business lines. Similarly, relative to a portfolio without sustainability impact considerations, the U.S. Sustainability Core 1 Portfolio will overweight securities of companies that, according to the Portfolio’s sustainability impact considerations, may be more sustainable as compared either to other companies in the Portfolio’s investment universe or other companies with similar business lines. In considering sustainability impact and other factors that the Advisor believes may be important to investors, the Advisor may consider carbon and other greenhouse emissions, or potential emissions, land use, cluster munitions manufacturing, biodiversity, involvement in toxic spills or releases, operational waste, water use, tobacco, child labor and factory farming activities, among other factors. In particular, the Portfolio may exclude companies the Advisor considers to have high carbon or greenhouse gas emissions or reserves that may produce those emissions. The Advisor may engage third party service providers to provide research and/or ratings information relating to the U.S. Sustainability Core 1 Portfolio’s sustainability impact considerations with respect to securities in the portfolio, where information is available from such providers.
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.

Sustainability Impact Consideration Investment Risk: The U.S. Sustainability Core 1 Portfolio’s sustainability 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 sustainability 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 sustainability impact considerations when it is otherwise disadvantageous to do so. The sustainability 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 swaps, 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.

Cyber Security Risk: The U.S. Sustainability Core 1 Portfolio’s and its service providers’ use of internet, technology and information systems may expose the Portfolio to potential risks linked to cyber security breaches of those technological or information systems. Cyber security breaches, amongst other things, could allow an unauthorized party to gain access to proprietary information, customer data, or fund assets, or cause the Portfolio and/or its service providers to suffer data corruption or lose operational functionality.
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 bar chart shows the changes in the U.S. Sustainability Core 1 Portfolio’s performance from year to year. The table illustrates how annualized one year and since inception returns, both before and after taxes, 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 http://us.dimensional.com.

The after-tax returns presented in the table for the U.S. Sustainability Core 1 Portfolio 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 an investor’s tax situation and may differ from those shown in the table. In addition, the after-tax returns shown are not relevant to investors who hold shares of the Portfolio through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. A negative pre-tax total return translates into a higher after-tax return because this calculation assumes that an investor received a tax deduction for the loss incurred on the sale.
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 bar chart shows the changes in the U.S. Sustainability Core 1 Portfolio’s performance from year to year.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress http://us.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—Total Returns
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock January 2009-December 2015

Highest Quarter    Lowest Quarter
18.89% (4/09–6/09)    -17.51% (7/11–9/11)
Performance Table Heading rr_PerformanceTableHeading Annualized Returns (%)
Periods ending December 31, 2015
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate The after-tax returns presented in the table for the U.S. Sustainability Core 1 Portfolio 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 In addition, the after-tax returns shown are not relevant to investors who hold shares of the Portfolio through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher A negative pre-tax total return translates into a higher after-tax return because this calculation assumes that an investor received a tax deduction for the loss incurred on the sale.
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, 7,599,874 B1 and, 8,438,092 B2.
U.S. Sustainability Core 1 Portfolio | U.S. Sustainability Core 1 Portfolio Shares  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fee rr_ManagementFeesOverAssets 0.29% [1]
Other Expenses rr_OtherExpensesOverAssets 0.03% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.32% [1]
Fee Waiver and/or Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets 0.07% [1]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement rr_NetExpensesOverAssets 0.25% [1]
1 YEAR rr_ExpenseExampleYear01 $ 26
3 YEARS rr_ExpenseExampleYear03 103
5 YEARS rr_ExpenseExampleYear05 180
10 YEARS rr_ExpenseExampleYear10 $ 406
2009 rr_AnnualReturn2009 31.36%
2010 rr_AnnualReturn2010 18.68%
2011 rr_AnnualReturn2011 (0.66%)
2012 rr_AnnualReturn2012 17.05%
2013 rr_AnnualReturn2013 36.69%
2014 rr_AnnualReturn2014 10.39%
2015 rr_AnnualReturn2015 (1.23%)
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%)
1 YEAR rr_AverageAnnualReturnYear01 (1.23%)
5 YEARS rr_AverageAnnualReturnYear05 11.62%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 8.42%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Mar. 12, 2008
U.S. Sustainability Core 1 Portfolio | Return After Taxes on Distributions | U.S. Sustainability Core 1 Portfolio Shares  
Risk/Return: rr_RiskReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (1.83%)
5 YEARS rr_AverageAnnualReturnYear05 11.09%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 7.97%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Mar. 12, 2008
U.S. Sustainability Core 1 Portfolio | Return After Taxes on Distributions and Sale of Portfolio Shares | U.S. Sustainability Core 1 Portfolio Shares  
Risk/Return: rr_RiskReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (0.20%)
5 YEARS rr_AverageAnnualReturnYear05 9.26%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 6.74%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Mar. 12, 2008
U.S. Sustainability Core 1 Portfolio | Russell 3000® Index (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 0.48%
5 YEARS rr_AverageAnnualReturnYear05 12.18%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 8.35%
[1] The "Annual Fund Operating Expenses" table reflects an amendment to the Portfolio's Fee Waiver and Expense Assumption Agreement with Dimensional Fund Advisors LP (the "Advisor"), effective as of February 28, 2016, which reduced the expense limitation amount for the Portfolio. The "Total Annual Fund Operating Expenses" of the Portfolio did not reach the previous expense limitation amount during the fiscal year ended October 31, 2015.