<?xml version="1.0" encoding="utf-8"?>
<xbrl
  xmlns="http://www.xbrl.org/2003/instance"
  xmlns:dei="http://xbrl.sec.gov/dei/2019-01-31"
  xmlns:fisv="http://www.fiserv.com/20191031"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:us-gaap="http://fasb.org/us-gaap/2019-01-31"
  xmlns:xbrldi="http://xbrl.org/2006/xbrldi"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="fisv-20191031.xsd" xlink:type="simple"/>
    <context id="D2019Q4Nov6-Nov6">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000798354</identifier>
        </entity>
        <period>
            <startDate>2019-11-06</startDate>
            <endDate>2019-11-06</endDate>
        </period>
    </context>
    <context id="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2023Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000798354</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:StatementClassOfStockAxis">fisv:SeniorNotesDue2023Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2019-11-06</startDate>
            <endDate>2019-11-06</endDate>
        </period>
    </context>
    <context id="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2025Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000798354</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:StatementClassOfStockAxis">fisv:SeniorNotesDue2025Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2019-11-06</startDate>
            <endDate>2019-11-06</endDate>
        </period>
    </context>
    <context id="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_us-gaap_CommonStockMember">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000798354</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:StatementClassOfStockAxis">us-gaap:CommonStockMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2019-11-06</startDate>
            <endDate>2019-11-06</endDate>
        </period>
    </context>
    <context id="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2031Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000798354</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:StatementClassOfStockAxis">fisv:SeniorNotesDue2031Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2019-11-06</startDate>
            <endDate>2019-11-06</endDate>
        </period>
    </context>
    <context id="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2027Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000798354</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:StatementClassOfStockAxis">fisv:SeniorNotesDue2027Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2019-11-06</startDate>
            <endDate>2019-11-06</endDate>
        </period>
    </context>
    <context id="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2030Member">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0000798354</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:StatementClassOfStockAxis">fisv:SeniorNotesDue2030Member</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2019-11-06</startDate>
            <endDate>2019-11-06</endDate>
        </period>
    </context>
    <dei:AmendmentFlag
      contextRef="D2019Q4Nov6-Nov6"
      id="Fact-4376BB38EEA54F60B803F8A07EC70FEB-wk-Fact-4376BB38EEA54F60B803F8A07EC70FEB">false</dei:AmendmentFlag>
    <dei:EntityCentralIndexKey
      contextRef="D2019Q4Nov6-Nov6"
      id="Fact-5F56ED6B509C4E72EC5AF89FEECD7EC8-wk-Fact-5F56ED6B509C4E72EC5AF89FEECD7EC8">0000798354</dei:EntityCentralIndexKey>
    <dei:DocumentType
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e113-wk-Fact-9D31486339715A90ED07F823E903DE13">8-K</dei:DocumentType>
    <dei:DocumentPeriodEndDate
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e146-wk-Fact-11DABC273B61551DC826026FE8A56199">2019-11-06</dei:DocumentPeriodEndDate>
    <dei:EntityRegistrantName
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e165-wk-Fact-B525D7A9C774C85C42C6F88E8B477541">Fiserv, Inc.</dei:EntityRegistrantName>
    <dei:EntityIncorporationStateCountryCode
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e231-wk-Fact-A6F12C4FB67F6C4140A6F824B3A0D871">WI</dei:EntityIncorporationStateCountryCode>
    <dei:EntityFileNumber
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e241-wk-Fact-BB5B64DD9B64D84A73C1F82516DF7525">1-38962</dei:EntityFileNumber>
    <dei:EntityTaxIdentificationNumber
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e251-wk-Fact-8B610CBEBB1CE7AAEEF9F824E65E589F">39-1506125</dei:EntityTaxIdentificationNumber>
    <dei:EntityAddressAddressLine1
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e289-wk-Fact-A2D58547DD34414D6997F82545C65C4B">255 Fiserv Drive</dei:EntityAddressAddressLine1>
    <dei:EntityAddressCityOrTown
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e294-wk-Fact-96BE59901AAC32CCF8F1F825745C3897">Brookfield</dei:EntityAddressCityOrTown>
    <dei:EntityAddressStateOrProvince
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e299-wk-Fact-8C235F56AB6364A96256F825A13EE615">WI</dei:EntityAddressStateOrProvince>
    <dei:EntityAddressPostalZipCode
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e304-wk-Fact-30CB900E8F37F53150ABF825CDDE986E">53045</dei:EntityAddressPostalZipCode>
    <dei:CityAreaCode
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e315-wk-Fact-2EDBE3C344F4BEF31774F826E779ADFF">262</dei:CityAreaCode>
    <dei:LocalPhoneNumber
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e320-wk-Fact-367281B57B43F4E7A1FFF8272F58D5F9">879-5000</dei:LocalPhoneNumber>
    <dei:WrittenCommunications
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e359-wk-Fact-83D2561E354B41DA2D9EF8289F2F0BB6">false</dei:WrittenCommunications>
    <dei:SolicitingMaterial
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e379-wk-Fact-3C1ACFF151BBB62DADAAF82920FF5B23">false</dei:SolicitingMaterial>
    <dei:PreCommencementTenderOffer
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e399-wk-Fact-B626F67B9BB1FB1F6D57F829C4EEB3A8">false</dei:PreCommencementTenderOffer>
    <dei:PreCommencementIssuerTenderOffer
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e419-wk-Fact-53E388AB48925FEEFE10F82A3C5238A0">false</dei:PreCommencementIssuerTenderOffer>
    <dei:Security12bTitle
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_us-gaap_CommonStockMember"
      id="d58302302e475-wk-Fact-203371D8CB53A7F2ADFCF82B087E4C39">Common Stock, par value $0.01 per share</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_us-gaap_CommonStockMember"
      id="d58302302e485-wk-Fact-C78D89463DACCD75C479F82BAFE2E058">FISV</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_us-gaap_CommonStockMember"
      id="d58302302e495-wk-Fact-C0725BC967F7CE6F9C89F82C02907AB2">NASDAQ</dei:SecurityExchangeName>
    <dei:Security12bTitle
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2023Member"
      id="d58302302e501-wk-Fact-0DDD1A5B4D9EABDC7AB1F82B0C70ED5B">0.375% Senior Notes due 2023</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2023Member"
      id="d58302302e511-wk-Fact-2D9FF6AD1B9AFFA76A23F82BB27376A5">FISV23</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2023Member"
      id="d58302302e521-wk-Fact-8A17908372526FE48446F82C070F43E4">NASDAQ</dei:SecurityExchangeName>
    <dei:Security12bTitle
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2027Member"
      id="d58302302e527-wk-Fact-8B299ED2865E17278B83F82B0FD9FA67">1.125% Senior Notes due 2027</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2027Member"
      id="d58302302e537-wk-Fact-B0A5DBC322379D4266CDF82BB49282A0">FISV27</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2027Member"
      id="d58302302e547-wk-Fact-64245473A2B427A81ABDF82C092AA447">NASDAQ</dei:SecurityExchangeName>
    <dei:Security12bTitle
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2030Member"
      id="d58302302e553-wk-Fact-5E5B8CFDFE5CEC718F96F82B134CDF39">1.625% Senior Notes due 2030</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2030Member"
      id="d58302302e563-wk-Fact-180C35A7DA5DD9333116F82BB8A7AD2A">FISV30</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2030Member"
      id="d58302302e573-wk-Fact-553E2CF3C76C760988E1F82C0D15C03C">NASDAQ</dei:SecurityExchangeName>
    <dei:Security12bTitle
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2025Member"
      id="d58302302e579-wk-Fact-64484CC4828F1358EDF1F82B17154940">2.250% Senior Notes due 2025</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2025Member"
      id="d58302302e589-wk-Fact-7A16B2C06BADC90A33D4F82BBC8608DA">FISV25</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2025Member"
      id="d58302302e599-wk-Fact-22972B2884AA55D016AFF82C0EC87E07">NASDAQ</dei:SecurityExchangeName>
    <dei:Security12bTitle
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2031Member"
      id="d58302302e605-wk-Fact-D245470D19D2E8D09730F82B19EB51E3">3.000% Senior Notes due 2031</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2031Member"
      id="d58302302e615-wk-Fact-32A19665E64CC87A3CA1F82BBE9F3B35">FISV31</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="D2019Q4Nov6-Nov6_us-gaap_StatementClassOfStockAxis_fisv_SeniorNotesDue2031Member"
      id="d58302302e625-wk-Fact-7E332BF74980302523F5F82C10D839E6">NASDAQ</dei:SecurityExchangeName>
    <dei:EntityEmergingGrowthCompany
      contextRef="D2019Q4Nov6-Nov6"
      id="d58302302e636-wk-Fact-3E7826F99CF7D0109C98F894FDF9138F">false</dei:EntityEmergingGrowthCompany>
</xbrl>
