<?xml version="1.0" encoding="utf-8"?>
<xbrl
  xml:lang="en-US"
  xmlns="http://www.xbrl.org/2003/instance"
  xmlns:dei="http://xbrl.sec.gov/dei/2020-01-31"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="awk-20220126.xsd" xlink:type="simple"/>
    <context id="i62c1955185f542849ff27421d38e3a90_D20220126-20220126">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001410636</identifier>
        </entity>
        <period>
            <startDate>2022-01-26</startDate>
            <endDate>2022-01-26</endDate>
        </period>
    </context>
    <dei:DocumentPeriodEndDate
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl80L2ZyYWc6M2U3OTgyNjQ0MjgxNGNhZWEzZDdhMTE1NGUwNzE0MzEvdGFibGU6OTRiOTJlN2U2Y2EzNGUwMGJmNzgyZGQzMjE4Mzc4OWEvdGFibGVyYW5nZTo5NGI5MmU3ZTZjYTM0ZTAwYmY3ODJkZDMyMTgzNzg5YV8xLTEtMS0xLTY4NjIz_3ee8e9c9-0741-46a9-8432-7e412f9097e9">2022-01-26</dei:DocumentPeriodEndDate>
    <dei:DocumentPeriodEndDate
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl80L2ZyYWc6M2U3OTgyNjQ0MjgxNGNhZWEzZDdhMTE1NGUwNzE0MzEvdGFibGU6OTRiOTJlN2U2Y2EzNGUwMGJmNzgyZGQzMjE4Mzc4OWEvdGFibGVyYW5nZTo5NGI5MmU3ZTZjYTM0ZTAwYmY3ODJkZDMyMTgzNzg5YV8xLTEtMS0xLTY4NjIz_ecfcb11d-142d-4d0e-bc38-14fa7aabfe5f">2022-01-26</dei:DocumentPeriodEndDate>
    <dei:EntityRegistrantName
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl80L2ZyYWc6M2U3OTgyNjQ0MjgxNGNhZWEzZDdhMTE1NGUwNzE0MzEvdGFibGU6OTRiOTJlN2U2Y2EzNGUwMGJmNzgyZGQzMjE4Mzc4OWEvdGFibGVyYW5nZTo5NGI5MmU3ZTZjYTM0ZTAwYmY3ODJkZDMyMTgzNzg5YV8yLTEtMS0xLTY4NjIz_d865e7b0-b1c7-417b-a045-5b6c0d256308">American Water Works Company, Inc.</dei:EntityRegistrantName>
    <dei:EntityCentralIndexKey
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl80L2ZyYWc6M2U3OTgyNjQ0MjgxNGNhZWEzZDdhMTE1NGUwNzE0MzEvdGFibGU6OTRiOTJlN2U2Y2EzNGUwMGJmNzgyZGQzMjE4Mzc4OWEvdGFibGVyYW5nZTo5NGI5MmU3ZTZjYTM0ZTAwYmY3ODJkZDMyMTgzNzg5YV8zLTEtMS0xLTY4NjIz_a7a47cd9-1306-49c1-adae-1ace8b8ea24d">0001410636</dei:EntityCentralIndexKey>
    <dei:AmendmentFlag
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl80L2ZyYWc6M2U3OTgyNjQ0MjgxNGNhZWEzZDdhMTE1NGUwNzE0MzEvdGFibGU6OTRiOTJlN2U2Y2EzNGUwMGJmNzgyZGQzMjE4Mzc4OWEvdGFibGVyYW5nZTo5NGI5MmU3ZTZjYTM0ZTAwYmY3ODJkZDMyMTgzNzg5YV80LTEtMS0xLTY4NjIz_76d3e4a1-ebe7-4408-abd0-6af2a3854e29">false</dei:AmendmentFlag>
    <dei:DocumentType
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjgy_8f795131-ba3b-4abe-8fa1-cf75c734273f">8-K</dei:DocumentType>
    <dei:DocumentPeriodEndDate
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18yMzA_3ee8e9c9-0741-46a9-8432-7e412f9097e9">2022-01-26</dei:DocumentPeriodEndDate>
    <dei:DocumentPeriodEndDate
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18yMzA_ecfcb11d-142d-4d0e-bc38-14fa7aabfe5f">2022-01-26</dei:DocumentPeriodEndDate>
    <dei:EntityFileNumber
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjgz_88b6cd49-9779-4f22-8e8f-7b823807f8e5">001-34028</dei:EntityFileNumber>
    <dei:EntityIncorporationStateCountryCode
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGFibGU6OTEyZTBiNDY3NDBlNDg1MmI0YjlhZDQ0OWIxM2MyN2QvdGFibGVyYW5nZTo5MTJlMGI0Njc0MGU0ODUyYjRiOWFkNDQ5YjEzYzI3ZF8wLTAtMS0xLTY4NjIz_01668725-3004-40b6-bc41-0678f89adfe1">DE</dei:EntityIncorporationStateCountryCode>
    <dei:EntityTaxIdentificationNumber
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGFibGU6OTEyZTBiNDY3NDBlNDg1MmI0YjlhZDQ0OWIxM2MyN2QvdGFibGVyYW5nZTo5MTJlMGI0Njc0MGU0ODUyYjRiOWFkNDQ5YjEzYzI3ZF8wLTEtMS0xLTY4NjIz_1717f608-dcf4-4f85-a991-35a8fc14087b">51-0063696</dei:EntityTaxIdentificationNumber>
    <dei:EntityAddressAddressLine1
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjg4_813ccaf9-ccb4-4949-9bad-725970dba7ab">1 Water Street</dei:EntityAddressAddressLine1>
    <dei:EntityAddressCityOrTown
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjg5_4c0eb1ae-5a64-4599-8f36-b7c3e240a6cc">Camden</dei:EntityAddressCityOrTown>
    <dei:EntityAddressStateOrProvince
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjg0_af77753f-8d33-4494-b083-0c7270dd0a91">NJ</dei:EntityAddressStateOrProvince>
    <dei:EntityAddressPostalZipCode
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjg1_85dd45f5-3a83-43cd-8993-d7c4e6f43762">08102-1658</dei:EntityAddressPostalZipCode>
    <dei:CityAreaCode
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjg2_76c29b98-0e19-4558-8212-cc123bc79a2d">856</dei:CityAreaCode>
    <dei:LocalPhoneNumber
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjkw_4253ff7b-4191-43e7-b1c6-93073569855c">955-4001</dei:LocalPhoneNumber>
    <dei:WrittenCommunications
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjkx_709d5b15-df5b-45e1-be25-e4708d651661">false</dei:WrittenCommunications>
    <dei:SolicitingMaterial
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjky_213b898c-80c0-4911-9217-2251cead1cf2">false</dei:SolicitingMaterial>
    <dei:PreCommencementTenderOffer
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjkz_436858e0-510c-4707-850f-ebc21538c9a9">false</dei:PreCommencementTenderOffer>
    <dei:PreCommencementIssuerTenderOffer
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjg3_3874f2ac-3312-433e-a23c-efede82cd686">false</dei:PreCommencementIssuerTenderOffer>
    <dei:Security12bTitle
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGFibGU6NTk3MzU1YjI3YTMxNGQyNDg4ZGViMWJmYTc3NjI3YTYvdGFibGVyYW5nZTo1OTczNTViMjdhMzE0ZDI0ODhkZWIxYmZhNzc2MjdhNl8xLTAtMS0xLTY4NjIz_efd16fef-9dbf-4680-b472-1fa30bfe7944">Common stock, par value $0.01 per share</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGFibGU6NTk3MzU1YjI3YTMxNGQyNDg4ZGViMWJmYTc3NjI3YTYvdGFibGVyYW5nZTo1OTczNTViMjdhMzE0ZDI0ODhkZWIxYmZhNzc2MjdhNl8xLTItMS0xLTY4NjIz_f2abac7c-ecb0-45eb-a99e-ca3babe4fb4b">AWK</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGFibGU6NTk3MzU1YjI3YTMxNGQyNDg4ZGViMWJmYTc3NjI3YTYvdGFibGVyYW5nZTo1OTczNTViMjdhMzE0ZDI0ODhkZWIxYmZhNzc2MjdhNl8xLTQtMS0xLTY4NjIz_7c822388-f3dd-4680-a845-24ff09da3693">NYSE</dei:SecurityExchangeName>
    <dei:EntityEmergingGrowthCompany
      contextRef="i62c1955185f542849ff27421d38e3a90_D20220126-20220126"
      id="id3VybDovL2RvY3MudjEvZG9jOjYyMzI0M2E1MGJjNTQzMDhhOWZjNGNmNmU5ODY3YTdmL3NlYzo2MjMyNDNhNTBiYzU0MzA4YTlmYzRjZjZlOTg2N2E3Zl8xL2ZyYWc6MDllZGM4NGEwYjM2NDVmNzliZWIwOTdiZDExMjMxYjcvdGV4dHJlZ2lvbjowOWVkYzg0YTBiMzY0NWY3OWJlYjA5N2JkMTEyMzFiN18xNjk0_1460b7c7-3313-4651-8b16-da05a8d256b6">false</dei:EntityEmergingGrowthCompany>
</xbrl>
