Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	MUTUAL OF AMERICA INVESTMENT CORP
Prospectus Date	rr_ProspectusDate	May 01, 2018
Small Cap Equity Index Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Small Cap Equity Index Fund May 1, 2018
Objective [Heading]	rr_ObjectiveHeading	Investment Objective.
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks investment results that correspond to the investment performance of the S&P SmallCap 600® Index.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund.
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. Other Expenses are estimated, as the Fund will commence operations on or after July 1, 2018.
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	April 30, 2021
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover.
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. Because the Fund is expected to commence operations on or after July 1, 2018, information regarding portfolio turnover is not available as of the date of this prospectus.
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	Other Expenses are estimated, as the Fund will commence operations on or after July 1, 2018.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example.
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 all of your shares at the end of those periods, (b) a 5% return each year and (c) operating expenses remain the same. The Example reflects the expense reimbursement for the first year. 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	Principal Investment Strategies.
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The Fund invests primarily in the 600 common stocks included in the S&P SmallCap 600® Index to replicate, to the extent practicable, the weightings of such stocks in the Index. The components of the index are market capitalization weighted, adjusted for free float. The Fund also purchases shares in an exchange-traded fund designed to replicate the performance of the index to invest available cash in an attempt to efficiently and cost effectively keep the Fund fully invested on a daily basis to attempt to minimize deviation from the performance of the S&P SmallCap 600® Index. Under normal circumstances, at least 80% of the Fund’s total assets are invested in securities included in the S&P SmallCap 600® Index, which are typically companies with market capitalizations in the range of $450 million to $2.1 billion. The Fund is rebalanced at approximately the same time that the S&P SmallCap 600® Index to which the Fund is benchmarked is rebalanced and reconstituted, which currently occurs on the third Friday of the last month of each quarter.
Risk [Heading]	rr_RiskHeading	Principal Investment Risks.
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. 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. The prices of equity securities of smaller companies may fluctuate more than for more established companies. The equity securities of smaller companies may not be traded as often as for larger companies, therefore it may be difficult to trade securities at a desirable price. Investments in companies with small market capitalizations generally offer greater opportunities for appreciation, but are associated with more risks than for established companies. 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. Concentration risk: The chance that the stocks of a particular industry or group of industries will decline because of adverse developments affecting that industry. Because the fund concentrates its assets in certain industries to the same extent that the S&P SmallCap 600® Index does, the fund bears concentration risk Index risk: The Fund’s investment performance may not precisely duplicate the performance of the S&P SmallCap 600® Index due to factors such as operating and transaction costs, as well as weighting of each security in the index. Small-Cap risk: Small-cap stocks generally are subject to greater, less predictable price changes than the securities of companies with larger market capitalizations. Futures risk: The Fund’s investments in futures contracts may not exactly match the performance of the underlying index. 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. It may be more difficult for the Fund to sell a small-capitalization stock or any stock that trades “over-the-counter,” than a larger capitalization stock or stocks that trade on a national or regional stock exchange.
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	Performance/Annual Return.
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	Because the Fund is expected to commence operations on or after July 1, 2018, information regarding performance for a full calendar year is not available as of the date of this prospectus.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	Because the Fund is expected to commence operations on or after July 1, 2018, information regarding performance for a full calendar year is not available as of the date of this prospectus.
Small Cap Equity Index Fund | Small Cap Equity Index 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	1.42%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.50%
Expense Reimbursement	rr_FeeWaiverOrReimbursementOverAssets	(1.35%)	[1]
Total Annual Fund Operating Expenses After Expense Reimbursement	rr_NetExpensesOverAssets	0.15%
1 Year	rr_ExpenseExampleYear01	$ 15
3 Years	rr_ExpenseExampleYear03	$ 49

[1] The Adviser has contractually agreed beginning as of the inception of the Fund to reimburse the Fund’s direct operating expenses to the extent such operating expenses exceed 0.07% (excluding any extraordinary expenses that may arise and charges incurred in trading portfolio securities). This contractual obligation continues in effect until April 30, 2021, and will continue for each succeeding 12 month period thereafter, unless either the Investment Company (at the direction of its Board of Directors) gives not less than 30 days’ notice of termination to the Adviser or the Adviser gives written notice of termination to the Investment Company within a 45 calendar day period prior to the next May 1.