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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName MUTUAL OF AMERICA INVESTMENT CORP
Prospectus Date rr_ProspectusDate May 01, 2019
International Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading <b>International Fund May 1, 2019</b>
Objective [Heading] rr_ObjectiveHeading <b>Investment Objective.</b>
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The Fund seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading <b>Fees and Expenses of the Fund.</b>
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The table below describes the fees and expenses you may pay if you buy and hold Fund shares. The expenses shown do not include Separate Account expenses which would increase costs if included.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption <b>Shareholder Fees </b> (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption <b>Annual Fund Operating Expenses</b><br/><b>(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 Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may result in higher transaction costs. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the Fund’s most recently completed fiscal year, the Fund’s portfolio turnover rate was 0.00% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate none
Expense Example [Heading] rr_ExpenseExampleHeading <b>Example.</b>
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes: (a) that you invest $10,000 in the Fund for the time periods indicated and then redeem or hold all of your shares at the end of those periods, (b) a 5% return each year and (c) operating expenses remain the same. The expenses shown do not include Separate Account expenses which would increase costs if included. Although your actual costs may be higher or lower, your cost based on these assumptions would be:
Strategy [Heading] rr_StrategyHeading <b>Principal Investment Strategies.</b>
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock Under normal circumstances, at least 80% of the Fund’s total assets are invested, directly or indirectly, in stocks of large and mid-cap companies in developed market countries located outside the United States and Canada represented in the Morgan Stanley Capital International, Inc. Europe, Australasia, and Far East Index (the “MSCI EAFE Index”) through the purchase of such stocks or exchange traded funds designed to track the MSCI EAFE Index. The Fund also invests in exchange traded funds that own emerging market securities.
Risk [Heading] rr_RiskHeading <b>Principal Investment Risks.</b>
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock An investment in the Fund is subject to the following risks which are described in more detail in the Prospectus.
  • General risk: The Fund may not achieve its investment objective. An investment in the Fund could decline in value, and you could lose money by investing in the Fund.
  • Active Management risk: The portfolio manager’s judgments about the attractiveness, value or potential appreciation of the Fund’s investments may prove to be incorrect. The Fund could underperform in comparison to other funds with a similar benchmark or similar objectives and investment strategies if the Fund’s overall investment selections or strategies fail to produce the intended results.
  • Company risk: The price of the stock of a particular company can vary based on a variety of factors, such as the company’s financial performance, changes in management and product trends, and the potential for takeover and acquisition.
  • Market risk: The risk that prices of securities will go down because of the interplay of market forces may affect a single issuer, industry or sector of the economy or may affect the market as a whole.
  • Stock risk: The value of your investment will go up or down, depending on movements in the stock markets. The investment results may be better or worse than the results for the stock markets taken as a whole, or than the results of other funds that invest in the same types of securities.
  • Foreign Investment risk: Foreign markets are subject to the risk of change in currency or exchange rates, economic and political trends in foreign countries, less liquidity, more volatility, more difficulty in enforcing contractual obligations, higher transaction costs and less government supervision and other reporting regulations and requirements than domestic markets. Foreign investment risks are greater in emerging markets than in developed markets. Domestic equities indices could outperform the MSCI EAFE Index for periods of time.
  • Emerging Markets risk: Foreign investment risks are greater in emerging markets than in developed markets. Investments in emerging markets are often considered speculative.
  • Eurozone Investment risk: The United Kingdom’s intended departure from the European Union, commonly known as “Brexit,” may have significant political and financial consequences for Eurozone markets, including greater market volatility and illiquidity, currency fluctuations, deterioration in economic activity, a decrease in business confidence and an increased likelihood of a recession in the United Kingdom.
  • ETF risk: ETFs generally invest substantially all of their assets in securities and are traded on stock exchanges. Their net asset values may differ from the prices of the ETF shares offered on the exchanges.
  • Depositary Receipts Risk: The underlying ETF may invest in securities of foreign issuers in the form of depositary receipts, some of which are not obligated to disclose material information.
  • Trading Risk: ETF shares are listed on exchanges for which there can be no assurance that they will maintain the listing. Also there is no assurance that an active trading market will develop, creating illiquidity and resulting in price volatility. The market price of an ETF may trade at a premium or discount to its net asset value. Trading in ETFs may be halted because of market conditions or extraordinary market volatility.
  • Investment Company Risk: The cost of investing in the Fund is higher because in addition to the Fund’s direct fees and expenses, it also indirectly bears fees and expenses charged by the underlying ETFs. The underlying ETFs may change their investment objectives or policies without the approval of the Fund, causing the Fund to withdraw its investment at a possibly inopportune time.
  • Leveraging Risk: ETFs may borrow money or otherwise leverage their holdings by investing in collateral from securities loans and by borrowing money to meet redemption requests. This leveraging results in more volatility and a compounding of all other risks.
  • Passive Investment Risk: Many ETFs are not actively managed; rather the underlying ETF invests in securities that represent its underlying Index, regardless of its investment merit or market trends. Also, an underlying ETF is more susceptible to declines in the market because the underlying ETFs generally do not change their investment strategies to respond to changes in the economy.
  • Tracking Error Risk: Imperfect correlation between the securities of an ETF and those in the Index it intends to track, rounding of prices, changes to the indices and regulatory policies may cause the performance of an ETF to not match the performance of its Index.
  • Valuation Risk: An underlying ETF may value certain securities at higher prices than the prices at which it can sell them.
Risk Lose Money [Text] rr_RiskLoseMoney An investment in the Fund could decline in value, and you could lose money by investing in the Fund.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading <b>Performance/Annual Return.</b>
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The bar chart and table below show the annual return and average annual returns of the Fund.

Below the bar chart are the Fund’s highest and lowest total returns for any calendar quarter during the period covered by the chart, showing the volatility of the Fund’s total returns. The numbers in parentheses are negative, representing a loss of principal.

The information indicates some of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual returns for one year and the life of the Fund compare to those of a broad-based, unmanaged index for those periods. A fund’s past performance does not necessarily indicate how it will perform in the future.

The total returns and average annual total returns shown do not include charges against the assets of the Separate Accounts that purchase Fund shares. If these charges were reflected, returns would be less than those shown. Updated performance information is available at no cost online at http://www.mutualofamerica.com or by calling 1-800-468-3785.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table below show the annual return and average annual returns of the Fund. <br/><br/>The information indicates some of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual returns for one year and the life of the Fund compare to those of a broad-based, unmanaged index for those periods.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-468-3785
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress http://www.mutualofamerica.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture A fund’s past performance does not necessarily indicate how it will perform in the future.
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The total returns and average annual total returns shown do not include charges against the assets of the Separate Accounts that purchase Fund shares. If these charges were reflected, returns would be less than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock Best and Worst Performing Quarters

     Quarter/Year    Total Return  
Best   
Second quarter 2009
      23.90 % 
Worst   
Third quarter 2011
      (20.43 )% 
Performance Table Heading rr_PerformanceTableHeading <b>Average Annual Total Returns (for periods ended December 31, 2018) </b>
International Fund | International Fund Class  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther
Management Fees rr_ManagementFeesOverAssets 0.08%
Other Expenses rr_OtherExpensesOverAssets 0.05%
Acquired Fund Fees & Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.22%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.35%
1 Year rr_ExpenseExampleYear01 $ 36
3 Years rr_ExpenseExampleYear03 113
5 Years rr_ExpenseExampleYear05 198
10 Years rr_ExpenseExampleYear10 451
1 Year rr_ExpenseExampleNoRedemptionYear01 36
3 Years rr_ExpenseExampleNoRedemptionYear03 113
5 Years rr_ExpenseExampleNoRedemptionYear05 198
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 451
2009 rr_AnnualReturn2009 25.22%
2010 rr_AnnualReturn2010 8.32%
2011 rr_AnnualReturn2011 (12.60%)
2012 rr_AnnualReturn2012 18.24%
2013 rr_AnnualReturn2013 21.00%
2014 rr_AnnualReturn2014 (6.03%)
2015 rr_AnnualReturn2015 (0.63%)
2016 rr_AnnualReturn2016 1.69%
2017 rr_AnnualReturn2017 24.47%
2018 rr_AnnualReturn2018 (13.36%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel <b>Best</b>
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 23.90%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel <b>Worst</b>
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (20.43%)
Past One Year rr_AverageAnnualReturnYear01 (13.36%)
Past Five Years rr_AverageAnnualReturnYear05 0.48%
For Ten Years rr_AverageAnnualReturnYear10 5.68%
International Fund | MSCI EAFE Index (Index reflects no deduction for fees and expenses)  
Risk/Return: rr_RiskReturnAbstract  
Past One Year rr_AverageAnnualReturnYear01 (13.79%)
Past Five Years rr_AverageAnnualReturnYear05 0.53%
For Ten Years rr_AverageAnnualReturnYear10 6.32%