Label		Element	Value
Risk/Return:		rr_RiskReturnAbstract
Registrant Name		dei_EntityRegistrantName	DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date		rr_ProspectusDate	Feb. 28, 2015
DFA Municipal Real Return Portfolio
Risk/Return:		rr_RiskReturnAbstract
Risk/Return [Heading]		rr_RiskReturnHeading	DFA Municipal Real Return Portfolio
Objective [Heading]		rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]		rr_ObjectivePrimaryTextBlock	The investment objective of the DFA Municipal Real Return Portfolio (the “Municipal Real Return Portfolio”) is to seek inflation protection and to provide current income from municipal securities.
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 Municipal Real Return 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, 2016
Portfolio Turnover [Heading]		rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]		rr_PortfolioTurnoverTextBlock	The Municipal Real Return 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 Municipal Real Return Portfolio’s performance. Because the Municipal Real Return Portfolio is new, information about portfolio turnover rate is not yet available.
Other Expenses, New Fund, Based on Estimates [Text]		rr_OtherExpensesNewFundBasedOnEstimates	The Municipal Real Return 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 [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 Municipal Real Return 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 Municipal Real Return 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 Municipal Real Return Portfolio seeks its investment objective by investing primarily in a universe of investment grade municipal securities, including inflation-protected municipal securities, and in derivative instruments to provide inflation protection. Municipal securities include bonds, notes, commercial paper and other instruments (including participation interests in such securities) issued by or on behalf of the states, territories and possessions of the United States (including the District of Columbia) and their political subdivisions, agencies and instrumentalities. The interest on the municipal securities purchased by the Portfolio, in the opinion of bond counsel for the issuers, is exempt from federal income tax (i.e., excludable from gross income for individuals for federal income tax purposes but not necessarily exempt from state or local taxes). As a fundamental investment policy, under normal market conditions, the Portfolio will invest at least 80% of its net assets in municipal securities that pay interest exempt from federal income tax. The Portfolio does not currently intend to invest its assets in municipal securities whose interest is subject to the federal alternative minimum tax. Under normal circumstances, the Municipal Real Return Portfolio will maintain an average portfolio duration of no greater than five years. If a security has been redeemed by the issuer at a date prior to the stated final maturity date for the purposes of the above maturity restriction, the early redemption date shall be considered the maturity date regardless of the stated final maturity. At least 75% of the assets of the Municipal Real Return Portfolio will be invested in municipal securities that, at the time of purchase, are rated in the top three credit-rating categories (i.e., Aaa, Aa and A for Moody’s Investor’s Service, Inc. (“Moody’s”) or AAA, AA and A for Standard & Poor’s Rating Group (“S&P”) or AAA, AA and A for Fitch Ratings Ltd. (“Fitch”)). No more than 25% of the Portfolio’s assets will be invested in municipal securities that, at the time of purchase, are rated in the lowest quarter of the investment grade spectrum (i.e., rated Baa3 to Baa1 (by Moody’s) or BBB- to BBB+ (by S&P or Fitch), or that are unrated but have been determined by the Dimensional Fund Advisors LP (the “Advisor”) to be of comparable quality). The fixed income securities in which the Municipal Real Return Portfolio invests are considered investment grade at the time of purchase. The Municipal Real Return Portfolio may (1) purchase certain municipal securities that are insured, (2) invest in municipal securities secured by mortgages on single-family homes and multi-family projects, (3) invest in pre-refunded municipal securities, (4) purchase tax-exempt municipal securities on a “when-issued” basis, and (5) use bond (interest rate) futures and options contracts, credit default swaps and interest rate swaps to hedge against changes in interest rates. The Municipal Real Return Portfolio may enter into swaps, such as inflation swaps, to seek inflation protection. The Portfolio also may enter into credit default swaps on issuers or indices to buy or sell credit protection to hedge its credit exposure; gain market or issuer exposure without owning the underlying securities; or increase the Portfolio’s total return. The Portfolio also may use derivatives, such as futures contracts and options on futures contracts, for non-hedging purposes as a substitute for direct investment or to allow the Portfolio to remain fully invested while maintaining the liquidity required to pay redemptions. The Municipal Real Return 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 Municipal Real Return 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. Interest Rate Risk: Fixed income securities are subject to interest rate risk because the prices of fixed income securities tend to move in the opposite direction of interest rates. When interest rates rise, fixed income security prices fall. When interest rates fall, fixed income security prices rise. In general, fixed income securities with longer maturities are more sensitive to changes in interest rates. Credit Risk: Credit risk is the risk that the issuer of a security, including a governmental entity, may be unable to make interest payments and/or repay principal when due. A downgrade to an issuer’s credit rating or a perceived change in an issuer’s financial strength may affect a security’s value, and thus, impact the Portfolio’s performance. The ability of a municipal securities issuer to make payments could be affected by litigation, legislation or other political events or the bankruptcy of the issuer. Inflation-Protected Securities Interest Rate Risk: Inflation-protected securities may react differently from other fixed income securities to changes in interest rates. Because interest rates on inflation-protected securities are adjusted for inflation, the values of these securities are not materially affected by inflation expectations. Therefore, the value of inflation-protected securities are anticipated to change in response to changes in “real” interest rates, which represent nominal (stated) interest rates reduced by the expected impact of inflation. Generally, the value of an inflation-protected security will fall when real interest rates rise and will rise when real interest rates fall. Risks of Investing for Inflation Protection: Because the interest and/or principal payments on an inflation-protected security are adjusted periodically for changes in inflation, the income distributed by the Portfolio may be irregular. Although the U.S. Treasury guarantees to pay at least the original face value of any inflation-protected securities the Treasury issues, other issuers may not offer the same guarantee. Also, inflation-protected securities, including those issued by the U.S. Treasury, are not protected against deflation. As a result, in a period of deflation, the principal and income of inflation-protected securities held by the Portfolio will decline and the Portfolio may suffer a loss during such periods. While inflation-protected securities are expected to be protected from long-term inflationary trends, short-term increases in inflation may lead to a decline in the Portfolio’s value. For example, if interest rates rise due to reasons other than inflation, the Portfolio’s investment in these securities may not be protected to the extent that the increase is not reflected in the securities’ inflation measures. In addition, positive adjustments to principal generally will result in taxable income to the Portfolio at the time of such adjustments (which generally would be distributed by the Portfolio as part of its taxable dividends), even though the principal amount is not paid until maturity. The current market value of inflation-protected securities is not guaranteed and will fluctuate. Income Risk: Income risk is the risk that falling interest rates will cause the Portfolio’s income to decline because, among other reasons, the proceeds from maturing short-term securities in its portfolio may be reinvested in lower-yielding securities. Tax Liability Risk: Tax liability risk is the risk that distributions by the Municipal Real Return Portfolio become taxable to shareholders due to noncompliant conduct by a municipal bond issuer, unfavorable changes in federal or state tax laws, or adverse interpretations of tax laws by the Internal Revenue Service or state tax authorities or other factors. Such adverse interpretations or actions could cause interest from a security to become taxable, possibly retroactively, subjecting, shareholders to increased tax liability. In addition, such adverse interpretations or actions could cause the value of a security, and therefore, the value of the Portfolio’s shares, to decline. Additionally, if the Portfolio’s use of derivative instruments for hedging and non-hedging purposes cause the Portfolio to invest less than 50% of its assets in municipal securities in any quarter, which the Portfolio does not anticipate, the Portfolio may fail to qualify to pay exempt-interest dividends to its shareholders, resulting in the distributions by the Municipal Real Return Portfolio becoming taxable to shareholders as ordinary income. Derivatives Risk: Derivatives are instruments, such as swaps and futures contracts, whose value is derived from that of other assets, rates or indices. Derivatives can be used for hedging (attempting to reduce risk by offsetting one investment position with another) or non-hedging purposes. Hedging with derivatives may increase expenses, and there is no guarantee that a hedging strategy will work. While hedging can reduce or eliminate losses, it can also reduce or eliminate gains or cause losses if the market moves in a manner different from that anticipated by the Portfolio or if the cost of the derivative outweighs the benefit of the hedge. The use of derivatives for non-hedging purposes may be considered more speculative than other types of investments. When the Portfolio uses derivatives, the Municipal Real Return 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. Additional risks are associated with the use of credit default swaps including counterparty and credit risk (the risk that the other party to a swap agreement will not fulfill its contractual obligations, whether because of bankruptcy or other default) and liquidity risk (the possible lack of a secondary market for the swap agreement). Credit risk increases when the Portfolio is the seller of credit default swaps and counterparty risk increases when the Portfolio is a buyer of credit default swaps. In addition, where the Portfolio is the seller of credit default swaps, it may be required to liquidate portfolio securities at inopportune times in order to meet payment obligations or segregation requirements. Credit default swaps may be illiquid or difficult to value. Additionally, payments made or received by the Portfolio under such derivatives may increase the amount of distributions taxable to you as ordinary income, increase or decrease the amount of capital gain distributions to you and/or decrease the amount available for distribution to you as exempt-interest dividends. Liquidity Risk: Liquidity risk exists when particular portfolio investments are difficult to purchase or sell. To the extent that the Municipal Real Return Portfolio holds illiquid investments, the Portfolio’s performance may be reduced due to an inability to sell the investments at opportune prices or times. Liquid portfolio investments may become illiquid or less liquid after purchase by the Municipal Real Return Portfolio due to low trading volume, adverse investor perceptions and/or other market developments. Liquidity risk includes the risk that the Municipal Real Return Portfolio will experience significant net redemptions at a time when it cannot find willing buyers for its portfolio securities or can only sell its portfolio securities at a material loss. Liquidity risk can be more pronounced in periods of market turmoil. 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 Municipal Real Return 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 Municipal Real Return 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.
Bar Chart and Performance Table [Heading]		rr_BarChartAndPerformanceTableHeading	PERFORMANCE
Performance Narrative [Text Block]		rr_PerformanceNarrativeTextBlock	Performance information is not available for the Municipal Real Return Portfolio because it has not yet completed a full calendar year of 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 Municipal Real Return Portfolio because it has not yet completed a full calendar year of operations.
Performance Availability Website Address [Text]		rr_PerformanceAvailabilityWebSiteAddress	http://us.dimensional.com
DFA Municipal Real Return 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	[1]	rr_OtherExpensesOverAssets	0.09%
Total Annual Fund Operating Expenses		rr_ExpensesOverAssets	0.29%
Fee Waiver and/or Expense Reimbursement	[2]	rr_FeeWaiverOrReimbursementOverAssets	0.02%
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		rr_NetExpensesOverAssets	0.27%
1 Year		rr_ExpenseExampleYear01	$ 28
3 Years		rr_ExpenseExampleYear03	$ 91

[1] The Municipal Real Return Portfolio is a new portfolio, so the "Other Expenses" shown are based on anticipated fees and expenses for the first full fiscal year.

[2] The Advisor has agreed to waive certain fees and in certain instances, assume certain expenses of the Municipal Real Return Portfolio. The Fee Waiver and Expense Assumption Agreement for the Municipal Real Return 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.