Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	AMG Funds IV
Prospectus Date	rr_ProspectusDate	Mar. 01, 2019
AMG Managers Fairpointe ESG Equity Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	<b>AMG Managers Fairpointe ESG Equity Fund</b>
Objective [Heading]	rr_ObjectiveHeading	<b>INVESTMENT OBJECTIVE</b>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks long-term total return through 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 that you may pay if you buy and hold shares of the Fund. If you transact in Class I shares of the Fund through a financial intermediary, you may be required to pay a commission to the financial intermediary for effecting such transactions. Such commissions are charged by the financial intermediary and are not reflected in the table or Expense Example below.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses<br/>(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	March 1, 2020
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 indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 41% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	41.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	<b>EXPENSE EXAMPLE</b>
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example will help you compare the cost of investing in the Fund to the cost of investing in other mutual funds. The Example makes certain assumptions. It assumes that you invest $10,000 as an initial investment in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. It also assumes that your investment has a 5% total return each year and the Fund’s operating expenses remain the same. The Example includes the Fund’s contractual expense limitation through March 1, 2020. Although your actual costs may be higher or lower, based on the above assumptions, your costs would be:
Strategy [Heading]	rr_StrategyHeading	<b>PRINCIPAL INVESTMENT STRATEGIES</b>
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal conditions, the Fund will invest at least 80% of its assets in a select number of equity securities that Fairpointe Capital LLC, the subadviser to the Fund (“Fairpointe” or the “Subadviser”), believes to be trading at a significant discount to intrinsic value. In selecting stocks, the Subadviser prefers investment in companies it deems to have strong environmental, social and governance (ESG) records and seeks to avoid those with inferior ESG records relative to the market and peers. The Fund incorporates certain ESG guidelines in the selection of individual securities and in portfolio construction. The Subadviser uses internal guidelines as well as third-party research and databases to evaluate and rank a company’s record with respect to each ESG component, and then establishes an overall ranking of the company’s ESG record. In establishing an overall ESG ranking for a company, the Subadviser places a greater emphasis on the governance component of ESG, as it believes that good governance can also lead to more responsible behavior in the social and environmental components of ESG. The Fund also seeks to monitor and advocate for ESG accountability of portfolio companies through proxy voting and shareholder engagement. The Subadviser further evaluates stocks for selection based on bottom-up fundamental analysis, favoring companies with strong business models, effective management, strong or improving balance sheets and attractive valuations. The number of issuers in which the Fund invests varies based on the Subadviser’s investment outlook for the Fund and so, from time to time, the Fund’s holdings may be focused on a smaller number of issuers than at other times. The Subadviser takes a long-term approach to portfolio management, with a focus on maximizing after-tax returns. Once the Fund invests in a company, the Subadviser intends to monitor that company’s ESG record and, in some cases, the Fund may sell an investment in a company whose ESG ranking assigned by the Subadviser declines below that which it was at the time of purchase, even if the other investment fundamentals of the company are positive. In addition to value criteria, the Subadviser looks for companies with the following characteristics: Industry leaders with a focused business plan and the ability to grow their market share Proven, effective management The Fund typically expects to invest in companies having a market capitalization at the time of acquisition within the capitalization range of the Russell 1000 Index, which as of May 11, 2018, the date of the latest reconstitution of the Index (implemented by the Index on June 22, 2018), was approximately $2.5 billion to $926.9 billion. This capitalization range will change over time. The Fund may invest in equity securities outside of the capitalization range of the Russell 1000 Index (including small-cap companies), convertible securities (including convertible preferred stocks and convertible bonds), and foreign securities (directly and through American Depositary Receipts). To manage risk, the Subadviser employs a valuation discipline that attempts to purchase securities trading at a substantial discount to intrinsic value, limits position sizes and sector exposure, and adheres to a strong sell discipline.
Risk [Heading]	rr_RiskHeading	<b>PRINCIPAL RISKS</b>
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	There is the risk that you may lose money on your investment. All investments carry a certain amount of risk, and the Fund cannot guarantee that it will achieve its investment objective. An investment in the Fund is not a deposit or obligation of any bank, is not endorsed or guaranteed by any bank, and is not insured by the Federal Deposit Insurance Corporation (“FDIC”) or any other government agency. Below are some of the risks of investing in the Fund. The risks are described in alphabetical order and not in the order of importance or potential exposure. Convertible Securities Risk— convertible preferred stocks, which are convertible into shares of the issuer’s common stock and pay regular dividends, and convertible debt securities, which are convertible into shares of the issuer’s common stock and bear interest, are subject to the risks of equity securities and fixed income securities. The lower the conversion premium, the more likely the price of the convertible security will follow the price of the underlying common stock. Conversely, higher premium convertible securities are more likely to exhibit the behavior of bonds because the likelihood of conversion is lower, which may cause their prices to fall as interest rates rise. There is the risk that the issuer of convertible preferred stock will not be able to make dividend payments or that the issuer of a convertible bond will not be able to make principal and/or interest payments. Currency Risk—fluctuations in exchange rates may affect the total loss or gain on a non-U.S. dollar investment when converted back to U.S. dollars and exposure to non-U.S. currencies may subject the Fund to the risk that those currencies will decline in value relative to the U.S. dollar. ESG Investing Risk— because applying the Fund’s ESG investment criteria may result in the selection or exclusion of securities of certain issuers for reasons other than performance, the Fund may underperform funds that do not utilize an ESG investment strategy. The application of this strategy may affect the Fund’s exposure to certain companies, sectors, regions, countries or types of investments, which could negatively impact the Fund’s performance depending on whether such investments are in or out of favor. Applying ESG criteria to investment decisions is qualitative and subjective by nature, and there is no guarantee that the criteria utilized by the Subadviser or any judgment exercised by the Subadviser will reflect the beliefs or values of any particular investor. Focused Investment Risk—to the extent the Fund invests a substantial portion of its assets in a relatively small number of securities or a particular market, industry, group of industries, country, region, group of countries, asset class or sector, it generally will be subject to greater risk than a fund that invests in a more diverse investment portfolio. In addition, the value of the Fund would be more susceptible to any single economic, market, political or regulatory occurrence affecting, for example, that particular market, industry, region or sector. Foreign Investment Risk—investments in foreign issuers involve additional risks (such as risks arising from less frequent trading, changes in political or social conditions, and less publicly available information about non-U.S. issuers) that differ from those associated with investments in U.S. issuers and may result in greater price volatility. Growth Stock Risk—the prices of equity securities of companies that are expected to experience relatively rapid earnings growth, or “growth stocks,” may be more sensitive to market movements because the prices tend to reflect future investor expectations rather than just current profits. Liquidity Risk—the Fund may not be able to dispose of particular investments, such as illiquid securities, readily at favorable times or prices or the Fund may have to sell them at a loss. Management Risk—because the Fund is an actively managed investment portfolio, security selection or focus on securities in a particular style, market sector or group of companies may cause the Fund to incur losses or underperform relative to its benchmarks or other funds with a similar investment objective. There can be no guarantee that the Subadviser’s investment techniques and risk analysis will produce the desired result. Market Risk—market prices of investments held by the Fund may fall rapidly or unpredictably due to a variety of factors, including economic, political, or market conditions or in response to events that affect particular industries or companies. Sector Risk—issuers and companies that are in similar industry sectors may be similarly affected by particular economic or market events; to the extent the Fund has substantial holdings within a particular sector, the risks associated with that sector increase. Stocks in the consumer discretionary sector may comprise a significant portion of the Fund's portfolio.  The consumer discretionary sector may be affected by the performance of the overall economy, consumer confidence and spending, changes in demographics and consumer tastes, interest rates, and competitive pressures. Small- and Mid-Capitalization Stock Risk—the stocks of small- and mid-capitalization companies often have greater price volatility, lower trading volume, and less liquidity than the stocks of larger, more established companies. Value Stock Risk—value stocks may perform differently from the market as a whole and may be undervalued by the market for a long period of time.
Risk Lose Money [Text]	rr_RiskLoseMoney	There is the risk that you may lose money on your investment.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a deposit or obligation of any bank, is not endorsed or guaranteed by any bank, and is not insured by the Federal Deposit Insurance Corporation (“FDIC”) or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	<b>PERFORMANCE</b>
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following performance information illustrates 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 performance compares to that of a broad-based securities market index. As always, past performance of the Fund (before and after taxes) is not an indication of how the Fund will perform in the future. Effective October 1, 2017, the Fund changed its name from “AMG Managers Fairpointe Focused Equity Fund” to “AMG Managers Fairpointe ESG Equity Fund” and adopted the Fund’s current investment strategies. Prior to October 1, 2017, the Fund pursued a focused U.S. equity strategy and did not have a specific ESG mandate. To obtain updated performance information please visit www.amgfunds.com or call 800.548.4539.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following performance information illustrates 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 performance compares to that of a broad-based securities market index.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800.548.4539
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.amgfunds.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	As always, past performance of the Fund (before and after taxes) is not an indication of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Calendar Year Total Returns as of 12/31/18 (Class N)
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter: 10.23% (3rd Quarter 2016) Worst Quarter: -15.62% (4th Quarter 2018)
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns as of 12/31/18
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns 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	Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (“IRAs”).
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are shown for Class N shares only, and after-tax returns for Class I shares will vary.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	After-tax returns 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. After-tax returns are not relevant to investors who hold their Fund shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (“IRAs”). After-tax returns are shown for Class N shares only, and after-tax returns for Class I shares will vary.
AMG Managers Fairpointe ESG Equity Fund | Class N
Risk/Return:	rr_RiskReturnAbstract
Management Fees	rr_ManagementFeesOverAssets	0.70%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.21%
Other Expenses	rr_OtherExpensesOverAssets	1.05%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.96%
Fee Waiver and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.85%)	[1]
Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements	rr_NetExpensesOverAssets	1.11%	[1]
1 Year	rr_ExpenseExampleYear01	$ 113
3 Years	rr_ExpenseExampleYear03	533
5 Years	rr_ExpenseExampleYear05	979
10 Years	rr_ExpenseExampleYear10	$ 2,217
2015	rr_AnnualReturn2015	(10.96%)
2016	rr_AnnualReturn2016	20.91%
2017	rr_AnnualReturn2017	18.23%
2018	rr_AnnualReturn2018	(15.90%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2016
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	10.23%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2018
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(15.62%)
1 Year	rr_AverageAnnualReturnYear01	(15.90%)
Since Inception	rr_AverageAnnualReturnSinceInception	1.45%	[2]
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 24, 2014
AMG Managers Fairpointe ESG Equity Fund | Class I
Risk/Return:	rr_RiskReturnAbstract
Management Fees	rr_ManagementFeesOverAssets	0.70%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	1.05%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.75%
Fee Waiver and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.85%)	[1]
Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements	rr_NetExpensesOverAssets	0.90%	[1]
1 Year	rr_ExpenseExampleYear01	$ 92
3 Years	rr_ExpenseExampleYear03	468
5 Years	rr_ExpenseExampleYear05	869
10 Years	rr_ExpenseExampleYear10	$ 1,992
1 Year	rr_AverageAnnualReturnYear01	(15.77%)
Since Inception	rr_AverageAnnualReturnSinceInception	1.66%	[2]
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 24, 2014
AMG Managers Fairpointe ESG Equity Fund | Return After Taxes on Distributions | Class N
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(16.12%)
Since Inception	rr_AverageAnnualReturnSinceInception	1.25%	[2]
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 24, 2014
AMG Managers Fairpointe ESG Equity Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class N
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(9.26%)
Since Inception	rr_AverageAnnualReturnSinceInception	1.12%	[2]
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 24, 2014
AMG Managers Fairpointe ESG Equity Fund | Russell 1000® Index (reflects no deduction for fees, expenses, or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(4.78%)
Since Inception	rr_AverageAnnualReturnSinceInception	6.69%	[2]
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 24, 2014

[1] AMG Funds LLC (the “Investment Manager”) has contractually agreed, through at least March 1, 2020, to waive management fees and/or pay or reimburse the Fund’s expenses in order to limit Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements (exclusive of taxes, interest (including interest incurred in connection with bank and custody overdrafts and in connection with securities sold short), shareholder servicing fees, distribution and service (12b-1) fees, brokerage commissions and other transaction costs, dividends payable with respect to securities sold short, acquired fund fees and expenses, and extraordinary expenses) of the Fund to the annual rate of 0.82% of the Fund’s average daily net assets (this annual rate or such other annual rate that may be in effect from time to time, the “Expense Cap”), subject to later reimbursement by the Fund in certain circumstances. In general, for a period of up to 36 months after the date any amounts are paid, waived or reimbursed by the Investment Manager, the Investment Manager may recover such amounts from the Fund, provided that such repayment would not cause the Fund’s Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursements (exclusive of the items noted in the parenthetical above) to exceed either (i) the Expense Cap in effect at the time such amounts were paid, waived or reimbursed, or (ii) the Expense Cap in effect at the time of such repayment by the Fund. The contractual expense limitation may only be terminated in the event the Investment Manager or a successor ceases to be the investment manager of the Fund or a successor fund, by mutual agreement between the Investment Manager and the AMG Funds IV Board of Trustees or in the event of the Fund’s liquidation unless the Fund is reorganized or is a party to a merger in which the surviving entity is successor to the accounting and performance information of the Fund.

[2] Performance shown reflects performance since the inception date of the Fund on December 24, 2014.