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

VA U.S. LARGE VALUE PORTFOLIO

Risk/Return:

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Risk/Return [Heading]

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VA U.S. Large Value Portfolio

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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The investment objective of the VA U.S. Large Value 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 VA U.S. Large Value Portfolio. The expenses in the table do not include any fees or charges imposed by the variable insurance contract. If such fees and charges were included, the expenses would be higher.

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 VA U.S. Large Value 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 VA U.S. Large Value Portfolio’s performance. During the most recent fiscal year, the VA U.S. Large Value Portfolio’s portfolio turnover rate was 19% of the average value of its investment portfolio.

Portfolio Turnover, Rate

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19.00%

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 VA U.S. Large Value Portfolio with the cost of investing in other mutual funds. The Example does not include any fees or charges imposed by the variable insurance contract and if such fees were included, expenses would be higher. 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 VA U.S. Large Value Portfolio, using a market capitalization weighted approach, purchases a broad and diverse group of readily marketable securities of large U.S. companies that Dimensional Fund Advisors LP (the “Advisor”) determines to be value stocks. A company’s market capitalization is the number of its shares outstanding times its price per share. In general, the higher the relative market capitalization of the U.S. large cap company, the greater its representation in the Portfolio. The Advisor may modify market capitalization weights and even exclude companies after considering such factors as free float, momentum, trading strategies, liquidity management, and profitability, as well as other factors that the Advisor determines to be appropriate, given market conditions. Securities are considered value stocks primarily because a company’s shares have a high book value in relation to their market value. 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, VA U.S. Large Value Portfolio will invest at least 80% of its net assets in securities of large cap U.S. companies. As of the date of this Prospectus, for purposes of the Portfolio, the Advisor considers large cap companies to be companies whose market capitalizations are generally in the highest 90% of total market capitalization or companies whose market capitalizations are larger than the 1,000th largest U.S. company, whichever results in the higher market capitalization break. Total market capitalization is based on the market capitalization of U.S. operating companies listed on the New York Stock Exchange (“NYSE”), NYSE MKT LLC, Nasdaq Global Market^® or such other securities exchanges deemed appropriate by the Advisor. Under the Advisor’s market capitalization guidelines described above, as of December 31, 2014, the market capitalization of a large cap company was $3,938 million or above. This dollar amount will change due to market conditions.

The VA U.S. Large Value Portfolio 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 derivative for purposes of speculation or leveraging investment returns.

The VA U.S. Large Value 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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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 VA U.S. Large Value 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.

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 VA U.S. Large Value 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 VA U.S. Large Value 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 VA U.S. Large Value 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 performance reflected in the bar chart for the Portfolio does not reflect any insurance company separate account charges, which if reflected would lower returns. The table illustrates how annualized one year, five year and ten year 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 VA U.S. Large Value 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 VA U.S. Large Value 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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VA U.S. Large Value Portfolio
Total Returns (%)

Bar Chart Closing [Text Block]

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January 2005-December 2014

Highest Quarter	Lowest Quarter
24.33 (4/09-6/09)	-27.59 (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 VA U.S. Large Value 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.

VA U.S. LARGE VALUE PORTFOLIO | VA U.S. Large Value Portfolio

Risk/Return:

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Management Fee

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0.25%

Other Expenses

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0.02%

Total Annual Fund Operating Expenses

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0.27%

1 Year

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28

3 Years

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87

5 Years

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152

10 Years

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343

2005

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9.68%

2006

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19.81%

2007

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(2.94%)

2008

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(39.90%)

2009

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29.93%

2010

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20.63%

2011

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(3.43%)

2012

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21.94%

2013

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40.82%

2014

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9.08%

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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24.33%

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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(27.59%)

One Year

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9.08%

Five Years

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16.89%

Ten Years

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8.07%

VA U.S. LARGE VALUE PORTFOLIO | Return After Taxes on Distributions | VA U.S. Large Value Portfolio

Risk/Return:

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One Year

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7.69%

Five Years

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15.64%

Ten Years

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7.19%

VA U.S. LARGE VALUE PORTFOLIO | Return After Taxes on Distributions and Sale of Portfolio Shares | VA U.S. Large Value Portfolio

Risk/Return:

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One Year

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5.46%

Five Years

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13.30%

Ten Years

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6.38%

VA U.S. LARGE VALUE PORTFOLIO | Russell 1000® Value Index (reflects no deduction for fees, expenses, or taxes)

Risk/Return:

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One Year

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13.45%

Five Years

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15.42%

Ten Years

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7.30%