Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

DFA INVESTMENT DIMENSIONS GROUP INC

Prospectus Date

rr_ProspectusDate

Feb. 28, 2015

R SHARES | U.S. Targeted Value Portfolio

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

U.S. Targeted Value Portfolio

Objective [Heading]

rr_ObjectiveHeading

INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The investment objective of the U.S. Targeted Value Portfolio is to achieve 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. Targeted Value 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. Targeted 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 U.S. Targeted Value Portfolio’s performance. During the most recent fiscal year, the U.S. Targeted Value Portfolio’s portfolio turnover rate was 10% of the average value of its investment portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

10.00%

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees

Since the “Acquired Fund Fees and Expenses” are not directly borne by the Portfolio, they are not reflected in the Portfolio’s financial statements, and therefore, the amounts listed in “Total Annual Fund Operating Expenses” will differ from those presented in the Financial Highlights.

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. Targeted Value 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 the operating expenses remain the same. 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. Targeted Value Portfolio, using a market capitalization weighted approach, purchases a broad and diverse group of the readily marketable securities of U.S. small and mid cap 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 eligible 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, profitability and 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, the U.S. Targeted Value Portfolio will invest at least 80% of its net assets in securities of U.S. companies. As of the date of this Prospectus, the Advisor considers for investment companies whose market capitalization are generally smaller than the 500th largest U.S. company. As of December 31, 2014, companies smaller than the 500th largest U.S. company fall in lowest 17% of total U.S. market capitalization. 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. As of December 31, 2014, the market capitalization of a company smaller than the 500th largest U.S. company was approximately $8,020 million or below. This dollar amount will change due to market conditions.

The U.S. Targeted 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 derivatives for purposes of speculation or leveraging investment returns.

The U.S. Targeted Value Portfolio may lend its portfolio securities to generate additional income.

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. Targeted 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.

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.

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 U.S. Targeted 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 U.S. Targeted Value Portfolio may lose money and there may be a delay in recovering the loaned securities. The U.S. Targeted Value 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. Targeted Value Portfolio’s returns and are meant to provide some indication of the risks of investing in the Portfolio. The bar charts show the changes in the performance of U.S. Targeted Value Portfolio’s Class R1 shares and Class R2 shares from year to year. The table illustrates how annualized one year, five year and since inception returns of the Class R1 shares and Class R2 shares compare with those of a broad measure of market performance. The past performance of the U.S. Targeted Value Portfolio is not an indication of future results. Updated performance information for the Portfolio can be obtained by visiting http://us.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. Targeted Value Portfolio’s returns and are meant to provide some indication of the risks of investing in the Portfolio. The bar charts show the changes in the performance of U.S. Targeted Value Portfolio’s Class R1 shares and Class R2 shares 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 past performance of the U.S. Targeted Value Portfolio is not an indication of future results.

Bar Chart [Heading]

rr_BarChartHeading

US Targeted Value Portfolio Class R1 Shares
Total Returns (%)

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

January 2009-December 2014

Highest Quarter	Lowest Quarter
24.44 (7/09-9/09)	-23.98 (7/11-9/11)

Performance Table Heading

rr_PerformanceTableHeading

Periods ending December 31, 2014
Annualized Returns (%)

Bar Chart [Heading]

didgi_BarChartHeadingOne

U.S. Targeted Value Portfolio Class R2 Shares
Total Returns (%)

Bar Chart Closing [TextBlock]

didgi_BarChartClosingTextBlockOne

January 2009-December 2014

Highest Quarter	Lowest Quarter
24.37 (7/09-9/09)	-24.03 (7/11-9/11)

Performance Table Heading

didgi_PerformanceTableHeadingOne

Periods ending December 31, 2014
Annualized Returns (%)

R SHARES | U.S. Targeted Value Portfolio | Class R1

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees (fees paid directly from your investment)

rr_ShareholderFeeOther

none

Management Fee

rr_ManagementFeesOverAssets

0.35%

Shareholder Services Fees

rr_Component1OtherExpensesOverAssets

0.10%

^[1]

Other Expenses

rr_Component2OtherExpensesOverAssets

0.02%

Total Other Expenses

rr_OtherExpensesOverAssets

0.12%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.03%

^[2]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.50%

1 Year

rr_ExpenseExampleYear01

51

3 Years

rr_ExpenseExampleYear03

160

5 Years

rr_ExpenseExampleYear05

280

10 Years

rr_ExpenseExampleYear10

628

2009

rr_AnnualReturn2009

31.73%

2010

rr_AnnualReturn2010

29.02%

2011

rr_AnnualReturn2011

(6.40%)

2012

rr_AnnualReturn2012

19.06%

2013

rr_AnnualReturn2013

42.95%

2014

rr_AnnualReturn2014

2.89%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

24.44%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(23.98%)

One Year

rr_AverageAnnualReturnYear01

2.89%

Five Years

rr_AverageAnnualReturnYear05

16.16%

Since Inception

rr_AverageAnnualReturnSinceInception

10.01%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 31, 2008

R SHARES | U.S. Targeted Value Portfolio | Class R2

Risk/Return:

rr_RiskReturnAbstract

Shareholder Fees (fees paid directly from your investment)

rr_ShareholderFeeOther

none

Management Fee

rr_ManagementFeesOverAssets

0.35%

Shareholder Services Fees

rr_Component1OtherExpensesOverAssets

0.25%

^[1]

Other Expenses

rr_Component2OtherExpensesOverAssets

0.02%

Total Other Expenses

rr_OtherExpensesOverAssets

0.27%

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.03%

^[2]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

0.65%

1 Year

rr_ExpenseExampleYear01

66

3 Years

rr_ExpenseExampleYear03

208

5 Years

rr_ExpenseExampleYear05

362

10 Years

rr_ExpenseExampleYear10

810

2009

rr_AnnualReturn2009

31.54%

2010

rr_AnnualReturn2010

28.64%

2011

rr_AnnualReturn2011

(6.48%)

2012

rr_AnnualReturn2012

18.83%

2013

rr_AnnualReturn2013

42.68%

2014

rr_AnnualReturn2014

2.75%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

24.37%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(24.03%)

One Year

rr_AverageAnnualReturnYear01

2.75%

Five Years

rr_AverageAnnualReturnYear05

15.95%

Since Inception

rr_AverageAnnualReturnSinceInception

11.29%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 30, 2008

R SHARES | U.S. Targeted Value Portfolio | Russell 2000® Value Index (reflects no deduction for fees, expenses, or taxes) | Class R1

Risk/Return:

rr_RiskReturnAbstract

One Year

rr_AverageAnnualReturnYear01

4.22%

Five Years

rr_AverageAnnualReturnYear05

14.26%

Since Inception

rr_AverageAnnualReturnSinceInception

8.98%

R SHARES | U.S. Targeted Value Portfolio | Russell 2000® Value Index (reflects no deduction for fees, expenses, or taxes) | Class R2

Risk/Return:

rr_RiskReturnAbstract

One Year

rr_AverageAnnualReturnYear01

4.22%

Five Years

rr_AverageAnnualReturnYear05

14.26%

Since Inception

rr_AverageAnnualReturnSinceInception

9.93%

[1] An amount up to 0.10% of the average net assets of the Portfolio's Class R1 shares and an amount up to 0.25% of the average net assets of the Portfolio's Class R2 shares may be used to compensate service agents that provide shareholder servicing, record keeping, account maintenance and other services to investors in the Portfolio's Class R1 shares and Class R2 shares ("Shareholder Services Agent").

[2] Since the “Acquired Fund Fees and Expenses” are not directly borne by the Portfolio, they are not reflected in the Portfolio’s financial statements, and therefore, the amounts listed in “Total Annual Fund Operating Expenses” will differ from those presented in the Financial Highlights.