<?xml version="1.0" encoding="utf-8"?>
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  xmlns:afg="http://afginc.com/20191121"
  xmlns:dei="http://xbrl.sec.gov/dei/2019-01-31"
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        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001042046</identifier>
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        <period>
            <startDate>2019-11-21</startDate>
            <endDate>2019-11-21</endDate>
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    <context id="c20191121to20191121_StatementClassOfStockAxis_SixSubordinatedDebenturesDueNovember152055Member">
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        <period>
            <startDate>2019-11-21</startDate>
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            <startDate>2019-11-21</startDate>
            <endDate>2019-11-21</endDate>
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            <endDate>2019-11-21</endDate>
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    <context id="c20191121to20191121_StatementClassOfStockAxis_Five125SubordinatedDebenturesDueDecember152059Member">
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        <period>
            <startDate>2019-11-21</startDate>
            <endDate>2019-11-21</endDate>
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    <dei:AmendmentFlag
      contextRef="c20191121to20191121"
      id="Fact_d293496c437b49ce914319292812284c">false</dei:AmendmentFlag>
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      contextRef="c20191121to20191121"
      id="Fact_7d9d0b5831d14b829700f19c3615ca87">0001042046</dei:EntityCentralIndexKey>
    <dei:DocumentType
      contextRef="c20191121to20191121"
      id="Fact_e0d584727ef74aaf9f96bb00c3286ec1">8-K</dei:DocumentType>
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      contextRef="c20191121to20191121"
      id="Fact_af9d3e2c1e4b457c8319e61d3a186766">2019-11-21</dei:DocumentPeriodEndDate>
    <dei:EntityRegistrantName
      contextRef="c20191121to20191121"
      id="Fact_3a16ec736cd641e6936d78cf193a04c4">AMERICAN FINANCIAL GROUP, INC.</dei:EntityRegistrantName>
    <dei:EntityIncorporationStateCountryCode
      contextRef="c20191121to20191121"
      id="Fact_ba2c7ac4453a4d08b37e203c36c55e8d">OH</dei:EntityIncorporationStateCountryCode>
    <dei:EntityFileNumber
      contextRef="c20191121to20191121"
      id="Fact_ba51f5a1542b4ab3a47670cb849dbb62">001-13653</dei:EntityFileNumber>
    <dei:EntityTaxIdentificationNumber
      contextRef="c20191121to20191121"
      id="Fact_4332adff33c84422ad91d3e45c6e30be">31-1544320</dei:EntityTaxIdentificationNumber>
    <dei:EntityAddressAddressLine1
      contextRef="c20191121to20191121"
      id="Fact_f20fe11cc0794a6f879ea657fd8288bf">301 East Fourth Street</dei:EntityAddressAddressLine1>
    <dei:EntityAddressCityOrTown
      contextRef="c20191121to20191121"
      id="Fact_ba6c1dcc4aae4859a2fe847124bb683d">Cincinnati</dei:EntityAddressCityOrTown>
    <dei:EntityAddressStateOrProvince
      contextRef="c20191121to20191121"
      id="Fact_166db0c5234640a7a4ac5e83e8cb5788">OH</dei:EntityAddressStateOrProvince>
    <dei:EntityAddressPostalZipCode
      contextRef="c20191121to20191121"
      id="Fact_a90eec9b36c34c63a7e27ff2cfa96ccc">45202</dei:EntityAddressPostalZipCode>
    <dei:CityAreaCode
      contextRef="c20191121to20191121"
      id="Fact_baa3c440246b4eea9ad02f5d44eee832">513</dei:CityAreaCode>
    <dei:LocalPhoneNumber
      contextRef="c20191121to20191121"
      id="Fact_745df2357c6243aeba5ab835c2e50bee">579-2121</dei:LocalPhoneNumber>
    <dei:WrittenCommunications
      contextRef="c20191121to20191121"
      id="Fact_40353774bd1543c790fd2b08373d8dfb">false</dei:WrittenCommunications>
    <dei:SolicitingMaterial
      contextRef="c20191121to20191121"
      id="Fact_cdaa509159e640edb20e12a10eca8488">false</dei:SolicitingMaterial>
    <dei:PreCommencementTenderOffer
      contextRef="c20191121to20191121"
      id="Fact_88d953df3b294926ab1c9015450072dc">false</dei:PreCommencementTenderOffer>
    <dei:PreCommencementIssuerTenderOffer
      contextRef="c20191121to20191121"
      id="Fact_0edb0b145c5a4bcdbb98f159d07ed71d">false</dei:PreCommencementIssuerTenderOffer>
    <dei:EntityEmergingGrowthCompany
      contextRef="c20191121to20191121"
      id="Fact_22f02efaf86f450b80a89629921bffe9">false</dei:EntityEmergingGrowthCompany>
    <dei:Security12bTitle
      contextRef="c20191121to20191121_StatementClassOfStockAxis_CommonStockMember"
      id="Fact_385b3b8ec9014bffb4c3b7aa3c536131">Common Stock</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="c20191121to20191121_StatementClassOfStockAxis_CommonStockMember"
      id="Fact_15c9ebc854884377881d2b60fc5b111c">AFG</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="c20191121to20191121_StatementClassOfStockAxis_CommonStockMember"
      id="Fact_3b686ed2b79240739eb45e231c41b2f0">NYSE</dei:SecurityExchangeName>
    <dei:Security12bTitle
      contextRef="c20191121to20191121_StatementClassOfStockAxis_Six14SubordinatedDebenturesDueSeptember302054Member"
      id="Fact_6aa0fa6ae82c43babe0d37b7871e9f5a">6 1/4% Subordinated Debentures due September 30, 2054</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="c20191121to20191121_StatementClassOfStockAxis_Six14SubordinatedDebenturesDueSeptember302054Member"
      id="Fact_c79bae1d19164bc499cd06fcbf7dcf66">AFGE</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="c20191121to20191121_StatementClassOfStockAxis_Six14SubordinatedDebenturesDueSeptember302054Member"
      id="Fact_527741c3d8a44d908b02f46cefb82394">NYSE</dei:SecurityExchangeName>
    <dei:Security12bTitle
      contextRef="c20191121to20191121_StatementClassOfStockAxis_SixSubordinatedDebenturesDueNovember152055Member"
      id="Fact_4f4cd8f4edce479f8ac5dc9fc38b4114">6% Subordinated Debentures due November 15, 2055</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="c20191121to20191121_StatementClassOfStockAxis_SixSubordinatedDebenturesDueNovember152055Member"
      id="Fact_13aa2fa31b20479586faf5cd04e39adf">AFGH</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="c20191121to20191121_StatementClassOfStockAxis_SixSubordinatedDebenturesDueNovember152055Member"
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    <dei:Security12bTitle
      contextRef="c20191121to20191121_StatementClassOfStockAxis_Five875SubordinatedDebenturesDueMarch302059Member"
      id="Fact_9172b44b09384125b9f17423ea33c8c1">5.875% Subordinated Debentures due March 30, 2059</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="c20191121to20191121_StatementClassOfStockAxis_Five875SubordinatedDebenturesDueMarch302059Member"
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    <dei:SecurityExchangeName
      contextRef="c20191121to20191121_StatementClassOfStockAxis_Five875SubordinatedDebenturesDueMarch302059Member"
      id="Fact_9b2d4f7ffd6348d3920bdc886d50e958">NYSE</dei:SecurityExchangeName>
    <dei:Security12bTitle
      contextRef="c20191121to20191121_StatementClassOfStockAxis_Five125SubordinatedDebenturesDueDecember152059Member"
      id="Fact_d39df3cfb9ca40b891ffe97fb9b1496c">5.125% Subordinated Debentures due December 15, 2059</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="c20191121to20191121_StatementClassOfStockAxis_Five125SubordinatedDebenturesDueDecember152059Member"
      id="Fact_06e8346cc6b24c9981896cde5d687782">AFGC</dei:TradingSymbol>
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      contextRef="c20191121to20191121_StatementClassOfStockAxis_Five125SubordinatedDebenturesDueDecember152059Member"
      id="Fact_495a1db4520a42b58851586a2e01fbb6">NYSE</dei:SecurityExchangeName>
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