Label

Element

Value

Risk/Return:

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Registrant Name

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DFA INVESTMENT DIMENSIONS GROUP INC

Prospectus Date

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Feb. 28, 2015

Emerging Markets Social Core Equity Portfolio

Risk/Return:

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Risk/Return [Heading]

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Emerging Markets Social Core Equity Portfolio

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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The investment objective of the Emerging Markets Social Core Equity Portfolio is long-term capital appreciation.

Expense [Heading]

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FEES AND EXPENSES OF THE PORTFOLIO

Expense Narrative [Text Block]

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This table describes the fees and expenses you may pay if you buy and hold shares of the Emerging Markets Social Core Equity Portfolio.

Shareholder Fees Caption [Text]

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Shareholder Fees (fees paid directly from your investment):

Operating Expenses Caption [Text]

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Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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The Emerging Markets Social Core Equity 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 Emerging Markets Social Core Equity Portfolio’s performance. During the most recent fiscal year, the Emerging Markets Social Core Equity Portfolio’s portfolio turnover rate was 10% of the average value of its investment portfolio.

Portfolio Turnover, Rate

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10.00%

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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This Example is meant to help you compare the cost of investing in the Emerging Markets Social Core Equity 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. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Strategy [Heading]

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PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Emerging Markets Social Core Equity Portfolio purchases a broad and diverse group of securities associated with emerging markets, which may include frontier markets (emerging market countries in an earlier stage of development), authorized for investment by Dimensional Fund Advisors LP’s (the “Advisor”) Investment Committee (“Approved Markets”), with an increased exposure to small capitalization and value companies while excluding securities of certain emerging markets companies based upon the Portfolio’s social issue screens. In assessing value, the Advisor may consider factors such as the issuer’s securities having a high book value in relation to their market value, as well as price to cash flow or price to earnings ratios. The criteria the Advisor uses for assessing value are subject to change from time to time. In addition, the Advisor may adjust the representation in the Portfolio of an eligible company, or exclude a company, after considering the profitability relative to other eligible companies. In assessing profitability, the Advisor may consider different ratios, such as that of earnings or profits from operations relative to book value or assets.

As a non-fundamental policy, under normal circumstances, the Emerging Markets Social Core Equity Portfolio will invest at least 80% of its net assets in emerging markets equity securities that are defined in the prospectus as Approved Markets securities.

The Emerging Markets Social Core Equity Portfolio may gain exposure to companies in Approved Markets by purchasing equity securities in the form of depositary receipts, which may be listed or traded outside the issuer’s domicile country. The Emerging Markets Social Core Equity Portfolio may use derivatives, such as futures contracts and options on futures contracts for Approved Market or other equity market securities and indices, including those of the United States, to adjust market exposure based on actual or expected cash inflows to or outflows from the Portfolio. The Portfolio does not intend to use derivative for purposes of speculation or leveraging investment returns. The above-referenced investments are not subject to, though they may incorporate, the Portfolio’s social criteria.

The Emerging Markets Social Core Equity Portfolio may lend its portfolio securities to generate additional income.

The Emerging Markets Social Core Equity Portfolio seeks to purchase securities that are consistent with the Portfolio’s social issue screens, which are monitored by an independent third party. The Portfolio seeks to exclude from its investment portfolio those companies that are identified by the Portfolio’s social issue screens, as further discussed below. The Portfolio’s social issue screens are designed to identify companies that: (1) earn at least 20% of their total annual revenue through the production and/or sale of conventional or nuclear weapons, their weapon systems, or critical components of these products, or the provision of weapon systems support and service; (2) are engaged in certain for profit business activities in or with the Republic of the Sudan; (3) earn at least 15% of their total annual revenue through the production and/or sale of tobacco or alcohol products, or key products or raw materials necessary for their production; (4) earn at least 20% of their total annual revenue from certain gambling activities, the production of goods used exclusively for gambling, or the provision of certain services in casinos that are fundamental to gambling operations; (5) directly participate in abortions, or develop or manufacture abortive agents or contraceptives; (6) earn at least 15% of their total annual revenue from the rental, sale, distribution or production of pornographic materials, or the ownership or operation of adult entertainment establishments; (7) are involved in the production or manufacture of landmines, cluster munitions, or the essential components of these products; and/or (8) are involved in stem cell research.

The Portfolio may modify this list of social issue screens, at any time, without prior shareholder approval or notice.

Risk [Heading]

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PRINCIPAL RISKS

Risk Narrative [Text Block]

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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 Emerging Markets Social Core Equity 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.

Emerging Markets Risk: Numerous emerging market countries have a history of, and continue to experience serious, and potentially continuing, economic and political problems. Stock markets in many emerging market countries are relatively small, expensive to trade in and generally have higher risks than those in developed markets. Securities in emerging markets also may be less liquid than those in developed markets and foreigners are often limited in their ability to invest in, and withdraw assets from, these markets. Additional restrictions may be imposed under other conditions. Frontier market countries generally have smaller economies or less developed capital markets and, as a result, the risks of investing in emerging market countries are magnified in frontier market countries.

Foreign Securities and Currencies Risk: Foreign securities prices may decline or fluctuate because of: (a) economic or political actions of foreign governments, and/or (b) less regulated or liquid securities markets. Investors holding these securities may also be exposed to foreign currency risk (the possibility that foreign currency will fluctuate in value against the U.S. dollar or that a foreign government will convert, or be forced to convert, its currency to another currency, changing its value against the U.S. dollar). The Emerging Markets Social Core Equity Portfolio does not hedge foreign currency risk.

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.

Social Investment Risk: The Emerging Markets Social Core Equity Portfolio’s social issue screens may limit the number of investment opportunities available to the Portfolio, and as a result, at times the Portfolio may produce different returns than funds that are not subject to such special investment conditions. For example, the Portfolio may decline to purchase certain securities when it is otherwise advantageous to do so, or the Portfolio may sell certain securities for social reasons when it is otherwise disadvantageous to do so.

Derivatives Risk: Derivatives are instruments, such as swaps, futures and foreign exchange forward 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 Emerging Markets Social Core Equity 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 Emerging Markets Social Core Equity Portfolio may lose money and there may be a delay in recovering the loaned securities. The Emerging Markets Social Core Equity 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]

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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]

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PERFORMANCE

Performance Narrative [Text Block]

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The bar chart and table immediately following illustrate the variability of the Emerging Markets Social Core Equity 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 Portfolio’s performance from year to year. The table illustrates how annualized one year, five year and since inception returns, both before and after taxes, compare with those of a broad measure of market performance. The Emerging Markets Social Core Equity 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 Emerging Markets Social Core Equity 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.

Performance Information Illustrates Variability of Returns [Text]

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The bar chart and table immediately following illustrate the variability of the Emerging Markets Social Core Equity 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 Portfolio’s performance from year to year.

Performance Availability Website Address [Text]

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http://us.dimensional.com

Performance Past Does Not Indicate Future [Text]

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The Emerging Markets Social Core Equity Portfolio’s past performance (before and after taxes) is not an indication of future results.

Bar Chart [Heading]

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Emerging Markets Social Core Equity Portfolio
Total Returns (%)

Bar Chart Closing [Text Block]

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January 2007-December 2014

Highest Quarter	Lowest Quarter
40.60 (4/09-6/09)	-27.29 (10/08-12/08)

Performance Table Heading

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Periods ending December 31, 2014
Annualized Returns (%)

Performance Table Uses Highest Federal Rate

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The after-tax returns presented in the table for the Emerging Markets Social Core Equity 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

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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.

Emerging Markets Social Core Equity Portfolio | Emerging Markets Social Core Equity Portfolio Shares

Risk/Return:

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Shareholder Fees (fees paid directly from your investment)

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none

Management Fee

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0.55%

Other Expenses

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0.08%

Total Annual Fund Operating Expenses

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0.63%

1 Year

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64

3 Years

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202

5 Years

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351

10 Years

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786

2007

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38.13%

2008

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(52.00%)

2009

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83.84%

2010

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23.42%

2011

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(21.27%)

2012

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20.36%

2013

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(3.15%)

2014

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(1.25%)

Highest Quarterly Return, Label

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Highest Quarter

Highest Quarterly Return, Date

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Jun. 30, 2009

Highest Quarterly Return

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40.60%

Lowest Quarterly Return, Label

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Lowest Quarter

Lowest Quarterly Return, Date

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Dec. 31, 2008

Lowest Quarterly Return

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(27.29%)

One Year

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(1.25%)

Five Years

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2.27%

Since Inception

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6.00%

Inception Date

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Aug. 31, 2006

Emerging Markets Social Core Equity Portfolio | Return After Taxes on Distributions | Emerging Markets Social Core Equity Portfolio Shares

Risk/Return:

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One Year

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(1.73%)

Five Years

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1.63%

Since Inception

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5.32%

Inception Date

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Aug. 31, 2006

Emerging Markets Social Core Equity Portfolio | Return After Taxes on Distributions and Sale of Portfolio Shares | Emerging Markets Social Core Equity Portfolio Shares

Risk/Return:

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One Year

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(0.34%)

Five Years

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1.90%

Since Inception

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4.96%

Inception Date

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Aug. 31, 2006

Emerging Markets Social Core Equity Portfolio | MSCI Emerging Markets Index (net dividends) (reflects no deduction for fees, expenses, or taxes on sales)

Risk/Return:

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One Year

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(2.19%)

Five Years

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1.78%

Since Inception

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4.91%