Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date	rr_ProspectusDate	Jan. 10, 2017
Global Small Company Portfolio
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Global Small Company Portfolio
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of the Global Small Company 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 Global Small Company 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, 2018
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. The Global Small Company 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 portfolio. 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. 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 Global Small Company Portfolio is a new portfolio, so the "Other Expenses" and "Acquired Fund Fees and Expenses" shown are based on anticipated fees and expenses for the current fiscal year.
Acquired Fund Fees and Expenses, Based on Estimates [Text]	rr_AcquiredFundFeesAndExpensesBasedOnEstimates	"Acquired Fund Fees and Expenses" shown are based on anticipated fees and expenses for the current 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 Global Small Company 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 Global Small Company Portfolio is a "fund of funds," which means the Portfolio generally allocates its assets among other funds managed by the Advisor (the "Underlying Funds"), although it has the ability to invest directly in securities and derivatives. The Portfolio seeks to achieve its investment objective of providing investors with access to securities portfolios consisting of a broad range of equity securities of primarily small companies in developed and emerging markets. The Portfolio pursues its investment objective by investing substantially all of its assets in the following Underlying Funds: The Asia Pacific Small Company Series, The Canadian Small Company Series, The Continental Small Company Series, The Emerging Markets Small Cap Series, The Japanese Small Company Series, The United Kingdom Small Company Series (each a series of The DFA Investment Trust Company), and U.S. Small Cap Portfolio (a series of DFA Investment Dimensions Group Inc.). The Global Small Company Portfolio typically allocates its investments among the Underlying Funds in the following manner: 30% to 60% in the U.S. Small Cap Portfolio; 5% to 30% in The Continental Small Company Series; 5% to 25% in The Emerging Markets Small Cap Series; 0% to 20% in The Japanese Small Company Series; 0% to 20% in The United Kingdom Small Company Series; 0% to 15% in The Asia Pacific Company Series; and 0% to 10% in The Canadian Small Company Series.  When deciding allocations to the Underlying Funds, the Global Small Company Portfolio takes into account, among other factors, the aggregate market capitalizations and adjustments for free float of the eligible universe of securities within each region.  Periodically, the Advisor will review the allocations for the 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. Certain Underlying Funds invest in small companies using a market capitalization weighted approach in each country or region designated by the Advisor as an approved market for investment. 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 a small company within an eligible country or region, the greater its representation in the Underlying Fund. The Advisor may adjust the representation in the Underlying Funds of an eligible company, or exclude a company, 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. In assessing profitability, the Advisor may consider different ratios, such as that of earnings or profits from operations relative to book value or assets. Under normal circumstances, the Portfolio, directly or through its investments in the Underlying Funds, may invest up to 60% of its net assets in U.S. companies (unless market conditions are not deemed favorable by the Advisor, in which case the Portfolio, directly or through its investments in the Underlying Funds, may invest up to 70% of its net assets in U.S. companies). As a non-fundamental policy, under normal circumstances, the Portfolio, directly or through its investments in the Underlying Funds, will invest at least 80% of its net assets in securities of small companies. The Advisor determines the maximum market capitalization of a small company with respect to each country in which the Portfolio or Underlying Fund invests. In the countries or regions authorized for investment, the Advisor first ranks eligible companies listed on selected exchanges based on the companies' market capitalizations. The Advisor then determines the universe of eligible stocks by defining the maximum market capitalization of a small company that may be purchased by the Portfolio or Underlying Fund with respect to each country or region. As of November 30, 2016, for the Global Small Company Portfolio, the highest maximum market capitalization of a small company in any country in which the Global Small Company Portfolio or its Underlying Funds would invest was $5,631 million. This threshold will vary by country or region. For example, as of November 30, 2016, the Advisor considered a small company in Switzerland to have a market capitalization below $5,179 million, a small company in the United States to have a market capitalization below $4,145 million, a small company in Norway to have a market capitalization below $2,096 million, and a small company in Japan to have a market capitalization below $2,097 million. This threshold will change due to market conditions. The Portfolio and each Underlying Fund may invest in affiliated and unaffiliated registered and unregistered money market funds to manage its cash pending investment in other securities or to maintain liquidity for the payment of redemptions or other purposes. Investments in money market funds may involve a duplication of certain fees and expenses. The Portfolio and each Underlying Fund 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 and each Underlying Fund may use derivatives, such as futures contracts and options on futures contracts for equity securities and indices of its approved markets or other equity market securities or indices, including those of the United States, to adjust market exposure based on actual or expected cash inflows to or outflows from the Portfolio or Underlying Fund. The Portfolio and Underlying Funds do not intend to use derivatives for purposes of speculation or leveraging investment returns. The Portfolio and Underlying Funds may lend their 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. The following is a description of principal risks of investing in the Portfolio. Fund of Funds Risk: The investment performance of the Global Small Company Portfolio is affected by the investment performance of the Underlying Funds in which the Global Small Company Portfolio invests. The ability of the Global Small Company 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. There can be no assurance that the investment objective of the Global Small Company 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 Global Small Company Portfolio is subject to the risks of the Underlying Funds' investments. The risks of the Global Small Company Portfolio's and Underlying Funds' investments are described below. 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 Underlying Funds do 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. 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. 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 Global Small Company Portfolio or Underlying Fund that owns them, to rise or fall. Stock markets tend to move in cycles, with periods of rising prices and periods of falling prices. 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. 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 Global Small Company Portfolio or an Underlying Fund uses derivatives, the Portfolio or Underlying Fund 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 or Underlying Fund 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 Global Small Company Portfolio or an Underlying Fund may lose money and there may be a delay in recovering the loaned securities. The Portfolio or Underlying Fund 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 Global Small Company 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 Global Small Company 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 Global Small Company Portfolio because it has not yet commenced operations.
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	http://us.dimensional.com
Global Small Company Portfolio | Institutional Class Shares
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fee	rr_ManagementFeesOverAssets	0.45%
Other Expenses	rr_OtherExpensesOverAssets	0.03%	[1]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.27%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.75%
Fee Waiver and/or Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	0.26%	[2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement	rr_NetExpensesOverAssets	0.49%
1 Year	rr_ExpenseExampleYear01	$ 50
3 Years	rr_ExpenseExampleYear03	$ 214

[1] The Global Small Company Portfolio is a new portfolio, so the "Other Expenses" and "Acquired Fund Fees and Expenses" shown are based on anticipated fees and expenses for the current 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 Global Small Company 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 0.49% 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, 2018, 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.