Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date	rr_ProspectusDate	Apr. 17, 2017
U.S. High Relative Profitability Portfolio
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	U.S. High Relative Profitability Portfolio
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of the U.S. High Relative Profitability Portfolio (the "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. High Relative Profitability 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)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	February 28, 2019
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	PORTFOLIO TURNOVER
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	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. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Portfolio's performance. Because the Portfolio is new, information about portfolio turnover rate is not yet available.
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	The U.S. High Relative Profitability Portfolio is a new portfolio, so the "Other Expenses" shown are based on anticipated fees and expenses for the first full fiscal year.
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example is meant to help you compare the cost of investing in the U.S. High Relative Profitability 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. 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]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The U.S. High Relative Profitability Portfolio purchases a broad and diverse group of readily marketable securities of large U.S. companies that Dimensional Fund Advisors LP (the "Advisor") determines to have high profitability relative to other U.S. large cap companies at the time of purchase. 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 Advisor may also adjust the representation in the Portfolio of an eligible company, or exclude a company, after considering such factors as market capitalization, free float, valuation ratios, profitability, momentum, trading strategies, liquidity management and other factors that the Advisor determines to be appropriate, given market conditions. As a non-fundamental policy, under normal circumstances, the Portfolio will invest at least 80% of its net assets in securities of 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®, Nasdaq Capital Market®, or such other securities exchanges deemed appropriate by the Advisor. Under the Advisor's market capitalization guidelines described above, based on market capitalization data as of December 31, 2016, the market capitalization of a large cap company would be $4,230 million or above. This dollar amount will change due to market conditions. The Portfolio may purchase or sell 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 sell futures contracts to establish short positions in individual securities or to use derivatives for purposes of speculation or leveraging investment returns.  The Portfolio may invest in exchange-traded funds ("ETFs") and similarly structured pooled investments for the purpose of gaining exposure to the U.S. stock market while maintaining liquidity. The Portfolio may lend its portfolio securities to generate additional income.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Because the value of your investment in the Portfolio will fluctuate, there is the risk that you will lose money. An investment in the Portfolio is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The following is a description of principal risks of investing in the Portfolio. Equity Market Risk: Even a long-term investment approach cannot guarantee a profit. Economic, market, political, and issuer-specific conditions and events will cause the value of equity securities, and the Portfolio that owns them, to rise or fall. Stock markets tend to move in cycles, with periods of rising prices and periods of falling prices. Investment Strategy Risk: Securities that have high profitability may perform differently from the market as a whole and an investment strategy emphasizing these securities 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 to carry more risk than other types of investments. When the Portfolio uses derivatives, the Portfolio will be directly exposed to the risks of those derivatives. 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 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. Cyber Security Risk: The 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.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Portfolio is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	Performance information is not available for the U.S. High Relative Profitability Portfolio because it has not yet commenced operations. Updated performance information for the Portfolio can be obtained in the future by visiting http://us.dimensional.com.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	Performance information is not available for the U.S. High Relative Profitability Portfolio because it has not yet commenced operations.
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	http://us.dimensional.com
U.S. High Relative Profitability Portfolio | Institutional Class
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fee	rr_ManagementFeesOverAssets	0.20%
Other Expenses	rr_OtherExpensesOverAssets	0.09%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.29%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	0.04%	[2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	0.25%
1 YEAR	rr_ExpenseExampleYear01	$ 26
3 YEARS	rr_ExpenseExampleYear03	89
1 YEAR	rr_ExpenseExampleNoRedemptionYear01	26
3 YEARS	rr_ExpenseExampleNoRedemptionYear03	$ 89

[1] The U.S. High Relative Profitability Portfolio is a new portfolio, so the "Other Expenses" shown are based on anticipated fees and expenses for the first full fiscal year.

[2] Dimensional Fund Advisors LP (the "Advisor") has agreed to waive all or a portion of its management fee and to assume the ordinary operating expenses of a class of the U.S. High Relative Profitability Portfolio (including the expenses that the Portfolio bears as a shareholder of other funds managed by the Advisor, excluding money market funds, but excluding the expenses that the Portfolio incurs indirectly through its investment in unaffiliated investment companies) ("Portfolio Expenses") to the extent necessary to limit the Portfolio Expenses of a class of the Portfolio to 0.25% of the average net assets of a class of the Portfolio on an annualized basis. The Fee Waiver and Expense Assumption Agreement for the Portfolio will remain in effect through February 28, 2019, 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.