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

World ex U.S. Core Equity Portfolio

Risk/Return:

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Risk/Return [Heading]

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World ex U.S. Core Equity Portfolio

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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The investment objective of the World ex U.S. Core Equity Portfolio is to achieve 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 World ex U.S. 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)

Fee Waiver or Reimbursement over Assets, Date of Termination

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February 28, 2016

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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A mutual fund generally 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 mutual fund shares are held in a taxable account. The World ex U.S. Core Equity Portfolio does not pay transaction costs when buying and selling shares of other mutual funds (the “Underlying Funds”); however, the Underlying Funds pay transaction costs when buying and selling securities for their portfolios. The transaction costs incurred by the Underlying Funds, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the World ex U.S. Core Equity Portfolio’s portfolio turnover rate was 6% based on the weighted average portfolio turnover ratios of each of the Portfolio’s underlying investments.

Portfolio Turnover, Rate

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6.00%

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 World ex U.S. 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. The costs for the Portfolio reflect the net expenses of the Portfolio that result from the contractual expense waiver in the first year only. 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 World ex U.S. Core Equity Portfolio seeks to achieve its investment objective through exposure to a broad and diverse group of securities of non-U.S. companies in countries with developed and emerging markets with a greater emphasis on small capitalization and value companies as compared to their representation in the Non-U.S. Universe. For purposes of the Portfolio, Dimensional Fund Advisors LP (the “Advisor”) defines the Non-U.S. Universe as a market capitalization weighted portfolio of non-U.S. companies in developed and emerging markets that have been authorized for investment as approved markets by the Advisor’s Investment Committee. The Portfolio’s increased exposure to small capitalization and value companies may be achieved by decreasing the allocation of the Portfolio’s assets to the largest growth companies relative to their weight in the Non-U.S. Universe, which would result in a greater weight allocation to small capitalization and value companies. 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 value stocks primarily because a company’s shares have a high book value in relation to their market value. The Advisor determines company size on a country or region specific basis and based primarily on market capitalization. When investing directly in securities of non-U.S. companies, the Advisor may adjust the representation in the Portfolio of an eligible company, or exclude a company, after considering different valuation ratios and/or profitability. 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 World ex U.S. Core Equity Portfolio may pursue its investment objective by investing its assets in the International Core Equity Portfolio, Emerging Markets Core Equity Portfolio (the “Underlying Funds”) and/or directly in securities of non-U.S. companies. Periodically, the Advisor will review the allocations for the World ex U.S. Core Equity Portfolio in each Underlying Fund and may adjust allocations to the Underlying Funds or may add or remove Underlying Funds in the Portfolio without notice to shareholders. As a non-fundamental policy, under normal circumstances, the Portfolio will invest at least 80% of its net assets in non-U.S. equity securities and/or investments that provide exposure to non-U.S. securities.

The World ex U.S. Core Equity Portfolio may gain exposure to companies associated with 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 Portfolio may use derivatives, such as futures contracts and options on futures contracts for foreign or 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 Portfolio may engage in spot foreign currency transactions for the purposes of settling the Portfolio’s purchases and sales of foreign securities.

The World ex U.S. Core Equity Portfolio may lend its portfolio securities to generate additional income.

Risk [Heading]

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PRINCIPAL RISKS

Risk Narrative [Text Block]

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Fund of Funds Risk: The investment performance of the World ex U.S. Core Equity Portfolio is affected by the investment performance of the Underlying Funds in which the Portfolio invests. The ability of the Portfolio to achieve its investment objective depends on the ability of the Underlying Funds to meet their investment objectives and on the Advisor’s decisions regarding the allocation of the Portfolio’s assets among the Underlying Funds. The Portfolio may allocate assets to an Underlying Fund that underperforms other funds. There can be no assurance that the investment objective of the Portfolio or any Underlying Fund will be achieved. When the Portfolio invests in Underlying Funds, investors are exposed to a proportionate share of the expenses of those Underlying Funds in addition to the expenses of the Portfolio. Through its investments in the Underlying Funds, the Portfolio is subject to the risks of the Underlying Funds’ investments. The risks listed below for the Portfolio include both the risks associated with direct investment in securities by the Portfolio and indirect investment in securities through the Portfolio’s investment in the Underlying Funds.

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 World ex U.S. 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 World ex U.S. Core Equity 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.

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 World ex U.S. Core Equity Portfolio does not hedge foreign currency risk.

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.

Derivatives Risk: Derivatives are instruments, such as 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 World ex U.S. 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 World ex U.S. Core Equity Portfolio may lose money and there may be a delay in recovering the loaned securities. The 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 World ex U.S. 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 and since inception returns, both before and after taxes, compare with those of a broad measure of market performance. The 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 World ex U.S. 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 World ex U.S. 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 Portfolio’s past performance (before and after taxes) is not an indication of future results.

Bar Chart [Heading]

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World ex U.S. Core Equity Portfolio Institutional Class Shares
Total Returns (%)

Bar Chart Closing [Text Block]

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January 2014-December 2014

Highest Quarter	Lowest Quarter
4.43 (4/14-6/14)	-6.25 (7/14-9/14)

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 World ex U.S. 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.

World ex U.S. Core Equity Portfolio | Institutional Class 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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0.40%

Other Expenses

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0.05%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.43%

Total Annual Fund Operating Expenses

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0.88%

Fee Waiver and/or Expense Reimbursement

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0.41%

^[1]

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement

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0.47%

1 Year

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48

3 Years

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240

5 Years

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447

10 Years

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1,046

2014

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(4.86%)

Highest Quarterly Return, Label

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Highest Quarter

Highest Quarterly Return, Date

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Jun. 30, 2014

Highest Quarterly Return

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4.43%

Lowest Quarterly Return, Label

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Lowest Quarter

Lowest Quarterly Return, Date

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Sep. 30, 2014

Lowest Quarterly Return

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(6.25%)

One Year

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(4.86%)

Since Inception

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3.23%

Inception Date

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Apr. 09, 2013

World ex U.S. Core Equity Portfolio | Return After Taxes on Distributions | Institutional Class Shares

Risk/Return:

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One Year

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(5.36%)

Since Inception

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2.48%

Inception Date

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Apr. 09, 2013

World ex U.S. Core Equity Portfolio | Return After Taxes on Distributions and Sale of Portfolio Shares | Institutional Class Shares

Risk/Return:

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One Year

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(2.29%)

Since Inception

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2.38%

Inception Date

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Apr. 09, 2013

World ex U.S. Core Equity Portfolio | MSCI All Country World ex USA 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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(3.87%)

Since Inception

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4.50%

[1] The Advisor has agreed to waive certain fees and in certain instances, assume certain expenses of the World ex U.S. Core Equity Portfolio. The Amended and Restated Fee Waiver and Expense Assumption Agreement for the Portfolio will remain in effect through February 28, 2016, 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.