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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName DIMENSIONAL INVESTMENT GROUP INC
Prospectus Date rr_ProspectusDate Feb. 28, 2019
U.S. LARGE COMPANY PORTFOLIO  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading U.S. Large Company Portfolio
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The U.S. Large Company Portfolio seeks, as its investment objective, to approximate the total investment return of the S&P 500® Index.
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. Large Company Portfolio.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption <b>Shareholder Fees (fees paid directly from your investment): </b>
Operating Expenses Caption [Text] rr_OperatingExpensesCaption <b>Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment) </b>
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading <b>PORTFOLIO TURNOVER </b>
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The U.S. Large Company 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 Portfolio’s performance. During the most recent fiscal year, the U.S. Large Company Portfolio’s portfolio turnover rate was 5% of the average value of its investment portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 5.00%
Expense Example [Heading] rr_ExpenseExampleHeading <b>EXAMPLE </b>
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock This Example is meant to help you compare the cost of investing in the U.S. Large 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. 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. Large Company Portfolio generally invests in the stocks that comprise the S&P 500® Index in approximately the proportions they are represented in the S&P 500® Index. The S&P 500® Index comprises a broad and diverse group of stocks. Generally, these are the U.S. stocks with the largest market capitalizations and, as a group, they generally represent approximately 80% of the total market capitalization of all publicly traded U.S. stocks. For the U.S. Large Company Portfolio, Dimensional Fund Advisors LP (the “Advisor”) considers the stocks that comprise the S&P 500® Index to be those of large companies. Under normal market conditions, at least 95% of the U.S. Large Company Portfolio’s net assets will be invested in the stocks that comprise the S&P 500® Index. As a non-fundamental policy, under normal circumstances, the U.S. Large Company Portfolio will invest at least 80% of its net assets in securities of large U.S. companies.

Ordinarily, portfolio companies will not be sold except to reflect additions or deletions of the companies that comprise the S&P 500® Index, including as a result of mergers, reorganizations and similar transactions and, to the extent necessary, to provide cash to pay redemptions of the U.S. Large Company Portfolio’s shares. Given the impact on prices of securities affected by the reconstitution of the S&P 500® Index around the time of a reconstitution date, the U.S. Large Company Portfolio may purchase or sell securities that may be impacted by the reconstitution before or after the reconstitution date of the S&P 500® Index. In seeking to approximate the total investment return of the S&P 500® Index, the Advisor may also adjust the representation of securities in the U.S. Large Company Portfolio after considering such securities’ characteristics and other factors the Advisor determines to be appropriate.

The U.S. Large Company 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 U.S. Large Company 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 U.S. Large Company Portfolio may lend its portfolio securities to generate additional income.

About the S&P 500® Index: The Standard & Poor’s 500 Composite Stock Price Index® is market capitalization weighted (adjusted for free float). Its performance is usually cyclical because it reflects periods when stock prices generally rise or fall. For information concerning S&P Global Ratings, a division of The McGraw Hill Companies (“S&P”), and disclaimers of S&P with respect to the U.S. Large Company Portfolio, see “Standard & Poor’s—Information and Disclaimers.”
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.

Derivatives Risk: Derivatives are instruments, such as futures contracts, and options thereon, 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 U.S. Large Company 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, as well as 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. Large Company Portfolio may lose money and there may be a delay in recovering the loaned securities. The U.S. Large Company 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 U.S. Large 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.
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 The bar chart and table immediately following illustrate the variability of the U.S. Large Company 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 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 U.S. Large Company 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 U.S. Large Company 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-advantaged arrangements, such as 401(k) plans or individual retirement accounts.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table immediately following illustrate the variability of the U.S. Large Company 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] rr_PerformanceAvailabilityWebSiteAddress http://us.dimensional.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The U.S. Large Company Portfolio’s past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading <b>U.S. Large Company Portfolio Institutional Class Shares—Total Returns </b>
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock January 2009-December  2018

Highest Quarter    Lowest Quarter
15.93% (4/09–6/09)
    -13.86% (7/11–9/11)
Performance Table Heading rr_PerformanceTableHeading <b>Annualized Returns (%) </b><br/>Periods ending December 31, 2018
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate The after-tax returns presented in the table for the U.S. Large Company 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 rr_PerformanceTableNotRelevantToTaxDeferred In addition, the after-tax returns shown are not relevant to investors who hold shares of the Portfolio through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts.
U.S. LARGE COMPANY PORTFOLIO | U.S. Large Company Portfolio  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fee rr_ManagementFeesOverAssets 0.06%
Other Expenses rr_OtherExpensesOverAssets 0.02%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.08%
1 Year rr_ExpenseExampleYear01 $ 8
3 Years rr_ExpenseExampleYear03 26
5 Years rr_ExpenseExampleYear05 45
10 Years rr_ExpenseExampleYear10 103
1 Year rr_ExpenseExampleNoRedemptionYear01 8
3 Years rr_ExpenseExampleNoRedemptionYear03 26
5 Years rr_ExpenseExampleNoRedemptionYear05 45
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 103
2009 rr_AnnualReturn2009 26.62%
2010 rr_AnnualReturn2010 14.99%
2011 rr_AnnualReturn2011 2.10%
2012 rr_AnnualReturn2012 15.82%
2013 rr_AnnualReturn2013 32.33%
2014 rr_AnnualReturn2014 13.53%
2015 rr_AnnualReturn2015 1.38%
2016 rr_AnnualReturn2016 11.90%
2017 rr_AnnualReturn2017 21.73%
2018 rr_AnnualReturn2018 (4.43%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.93%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (13.86%)
1 Year rr_AverageAnnualReturnYear01 (4.43%)
5 Years rr_AverageAnnualReturnYear05 8.42%
10 Years rr_AverageAnnualReturnYear10 13.07%
U.S. LARGE COMPANY PORTFOLIO | Return After Taxes on Distributions | U.S. Large Company Portfolio  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (4.99%)
5 Years rr_AverageAnnualReturnYear05 7.76%
10 Years rr_AverageAnnualReturnYear10 12.50%
U.S. LARGE COMPANY PORTFOLIO | Return After Taxes on Distributions and Sale of Portfolio Shares | U.S. Large Company Portfolio  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (2.18%)
5 Years rr_AverageAnnualReturnYear05 6.55%
10 Years rr_AverageAnnualReturnYear10 10.86%
U.S. LARGE COMPANY PORTFOLIO | S&P 500® Index (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 (4.38%) [1]
5 Years rr_AverageAnnualReturnYear05 8.49% [1]
10 Years rr_AverageAnnualReturnYear10 13.12% [1]
[1] Copyright© 2010 Standard & Poor’s Financial Services LLC, a subsidiary of The McGraw-Hill Companies, Inc. All rights reserved.