Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	AMG Funds IV
Prospectus Date	rr_ProspectusDate	Mar. 01, 2019
AMG Managers Montag & Caldwell Growth Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	<b>AMG Managers Montag & Caldwell Growth Fund</b>
Objective [Heading]	rr_ObjectiveHeading	<b>INVESTMENT OBJECTIVE</b>
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund seeks long-term capital appreciation and,
Objective, Secondary [Text Block]	rr_ObjectiveSecondaryTextBlock	secondarily, current income, by investing primarily in common stocks and convertible securities.
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)
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 33% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	33.00%
Expenses Restated to Reflect Current [Text]	rr_ExpensesRestatedToReflectCurrent	Expense information has been restated to reflect current fees.
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]	rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees	The Total Annual Fund Operating Expenses do not correlate to the ratios of expenses to average net assets in the Financial Highlights section of this Prospectus, which reflect only the operating expenses of the Fund and do not include fees and expenses of any acquired fund.
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. 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	The Fund invests primarily in common stocks, convertible preferred stocks, and convertible bonds. Montag & Caldwell, LLC, the subadviser to the Fund (“Montag & Caldwell” or the “Subadviser”), uses a bottom-up approach to stock selection and seeks high quality, well-established, large-cap companies that the Subadviser believes are growing their near-term earnings at an above average rate. The Fund defines a large-cap company as one having a market capitalization of $5 billion or more at the time of acquisition. The Subadviser emphasizes valuation to find companies selling at a discount to their intrinsic value. These companies must pass an initial capitalization screen and: Have a strong history of earnings growth Be attractively priced, relative to the company’s potential for above average long-term earnings and revenue growth Have strong balance sheets Have a sustainable competitive advantage Be currently, or have the potential to become, industry leaders The Fund may invest in foreign securities (directly and through depositary receipts). To manage risk, the Subadviser limits sector and individual security exposure, and adheres to a structured 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. 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. Large-Capitalization Stock Risk—the stocks of large-capitalization companies are generally more mature and may not be able to reach the same levels of growth as the stocks of small- or mid-capitalization companies. 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 information technology and consumer staples sectors may comprise a significant portion of the Fund's portfolio.  The information technology sector may be affected by technological obsolescence, short product cycles, falling prices and profits, competitive pressures and general market conditions.  The consumer staples sector may be significantly affected by demographic and product trends, competitive pricing, food fads, marketing campaigns, environmental factors, and government regulation, as well as the performance of the overall economy, interest rates, and consumer confidence.
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.  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: 14.92% (2nd Quarter 2009) Worst Quarter: -12.62% (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 and Class R 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 and Class R shares will vary.
AMG Managers Montag & Caldwell Growth Fund | Class N
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.70%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.19%
Other Expenses	rr_OtherExpensesOverAssets	0.27%	[1]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.17%	[2]
1 Year	rr_ExpenseExampleYear01	$ 119
3 Years	rr_ExpenseExampleYear03	372
5 Years	rr_ExpenseExampleYear05	644
10 Years	rr_ExpenseExampleYear10	$ 1,420
2009	rr_AnnualReturn2009	29.84%
2010	rr_AnnualReturn2010	8.28%
2011	rr_AnnualReturn2011	3.13%
2012	rr_AnnualReturn2012	12.70%
2013	rr_AnnualReturn2013	27.29%
2014	rr_AnnualReturn2014	7.35%
2015	rr_AnnualReturn2015	5.76%
2016	rr_AnnualReturn2016	(2.64%)
2017	rr_AnnualReturn2017	23.35%
2018	rr_AnnualReturn2018	(1.72%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	14.92%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2018
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(12.62%)
1 Year	rr_AverageAnnualReturnYear01	(1.72%)
5 Years	rr_AverageAnnualReturnYear05	6.03%
10 Years	rr_AverageAnnualReturnYear10	10.79%
AMG Managers Montag & Caldwell Growth Fund | Class I
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.70%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.27%	[1]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.98%	[2]
1 Year	rr_ExpenseExampleYear01	$ 100
3 Years	rr_ExpenseExampleYear03	312
5 Years	rr_ExpenseExampleYear05	542
10 Years	rr_ExpenseExampleYear10	$ 1,201
1 Year	rr_AverageAnnualReturnYear01	(1.52%)
5 Years	rr_AverageAnnualReturnYear05	6.27%
10 Years	rr_AverageAnnualReturnYear10	11.06%
AMG Managers Montag & Caldwell Growth Fund | Class R
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.70%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other Expenses	rr_OtherExpensesOverAssets	0.27%	[1]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.48%	[2]
1 Year	rr_ExpenseExampleYear01	$ 151
3 Years	rr_ExpenseExampleYear03	468
5 Years	rr_ExpenseExampleYear05	808
10 Years	rr_ExpenseExampleYear10	$ 1,768
1 Year	rr_AverageAnnualReturnYear01	(2.08%)
5 Years	rr_AverageAnnualReturnYear05	5.75%
10 Years	rr_AverageAnnualReturnYear10	10.51%
AMG Managers Montag & Caldwell Growth Fund | Return After Taxes on Distributions | Class N
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(6.65%)
5 Years	rr_AverageAnnualReturnYear05	1.88%
10 Years	rr_AverageAnnualReturnYear10	8.15%
AMG Managers Montag & Caldwell Growth Fund | Return After Taxes on Distributions and Sale of Fund Shares | Class N
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	2.16%
5 Years	rr_AverageAnnualReturnYear05	4.35%
10 Years	rr_AverageAnnualReturnYear10	8.72%
AMG Managers Montag & Caldwell Growth Fund | Russell 1000® Growth Index (reflects no deduction for fees, expenses, or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(1.51%)
5 Years	rr_AverageAnnualReturnYear05	10.40%
10 Years	rr_AverageAnnualReturnYear10	15.29%

[1] Expense information has been restated to reflect current fees.

[2] The Total Annual Fund Operating Expenses do not correlate to the ratios of expenses to average net assets in the Financial Highlights section of this Prospectus, which reflect only the operating expenses of the Fund and do not include fees and expenses of any acquired fund.