<?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/2021q4"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="awk-20220616.xsd" xlink:type="simple"/>
    <context id="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001410636</identifier>
        </entity>
        <period>
            <startDate>2022-06-16</startDate>
            <endDate>2022-06-16</endDate>
        </period>
    </context>
    <dei:DocumentPeriodEndDate
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M180L2ZyYWc6MzcxOTFiODkzMDM2NDIwMDhiMjU0MDU4YjI1NDk1MzEvdGFibGU6OTZlNTFmMjJiNTYyNDAxODllZGI4YTFmNDIzMDI1ZTkvdGFibGVyYW5nZTo5NmU1MWYyMmI1NjI0MDE4OWVkYjhhMWY0MjMwMjVlOV8xLTEtMS0xLTEyMjQ4NQ_96398320-ddde-409a-9e0e-99c412be34be">2022-06-16</dei:DocumentPeriodEndDate>
    <dei:EntityCentralIndexKey
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M180L2ZyYWc6MzcxOTFiODkzMDM2NDIwMDhiMjU0MDU4YjI1NDk1MzEvdGFibGU6OTZlNTFmMjJiNTYyNDAxODllZGI4YTFmNDIzMDI1ZTkvdGFibGVyYW5nZTo5NmU1MWYyMmI1NjI0MDE4OWVkYjhhMWY0MjMwMjVlOV8zLTEtMS0xLTEyMjQ4NQ_6573b36e-0274-48f3-b347-3313012c35e0">0001410636</dei:EntityCentralIndexKey>
    <dei:AmendmentFlag
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M180L2ZyYWc6MzcxOTFiODkzMDM2NDIwMDhiMjU0MDU4YjI1NDk1MzEvdGFibGU6OTZlNTFmMjJiNTYyNDAxODllZGI4YTFmNDIzMDI1ZTkvdGFibGVyYW5nZTo5NmU1MWYyMmI1NjI0MDE4OWVkYjhhMWY0MjMwMjVlOV80LTEtMS0xLTEyMjQ4NQ_6694a7c0-b2fd-443c-982d-6621042f8df2">false</dei:AmendmentFlag>
    <dei:DocumentType
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjgy_0dae5bb9-b0d2-43c5-b79c-3ce90f6b965a">8-K</dei:DocumentType>
    <dei:DocumentPeriodEndDate
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8yMzA_96398320-ddde-409a-9e0e-99c412be34be">2022-06-16</dei:DocumentPeriodEndDate>
    <dei:EntityRegistrantName
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjg5_c6511408-ec0b-4b52-a1db-f95b5e40b973">American Water Works Company, Inc.</dei:EntityRegistrantName>
    <dei:EntityFileNumber
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjkz_e5eb7122-8a2f-439c-a83e-a363421ed736">001-34028</dei:EntityFileNumber>
    <dei:EntityIncorporationStateCountryCode
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGFibGU6ZTQyNjgxM2M3Mzg0NDIwY2FiMTZjZGI5NTMwNDcxOTEvdGFibGVyYW5nZTplNDI2ODEzYzczODQ0MjBjYWIxNmNkYjk1MzA0NzE5MV8wLTAtMS0xLTEyMjQ4NQ_9c0aa183-a199-4f2b-98dc-5b55740846e5">DE</dei:EntityIncorporationStateCountryCode>
    <dei:EntityTaxIdentificationNumber
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGFibGU6ZTQyNjgxM2M3Mzg0NDIwY2FiMTZjZGI5NTMwNDcxOTEvdGFibGVyYW5nZTplNDI2ODEzYzczODQ0MjBjYWIxNmNkYjk1MzA0NzE5MV8wLTEtMS0xLTEyMjQ4NQ_a3d8939d-ad75-4d27-937a-276ab137bde8">51-0063696</dei:EntityTaxIdentificationNumber>
    <dei:EntityAddressAddressLine1
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjk0_fa0d5c48-cdf0-42bf-a241-ad1e95bf2cb2">1 Water Street</dei:EntityAddressAddressLine1>
    <dei:EntityAddressCityOrTown
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjg0_ec0613c7-4126-4f54-9543-af2be5d58858">Camden</dei:EntityAddressCityOrTown>
    <dei:EntityAddressStateOrProvince
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjk1_a49a8a31-c329-4836-8b9f-fdfe86603ce3">NJ</dei:EntityAddressStateOrProvince>
    <dei:EntityAddressPostalZipCode
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjk2_0de297cc-1e02-4a5b-8c58-3d59397270c6">08102-1658</dei:EntityAddressPostalZipCode>
    <dei:CityAreaCode
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjkw_a28480ca-0c25-4329-a2ad-7db478e3b3d3">856</dei:CityAreaCode>
    <dei:LocalPhoneNumber
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjg1_85e46f3f-a1bd-4ca1-a6e4-35c2a34c48cf">955-4001</dei:LocalPhoneNumber>
    <dei:WrittenCommunications
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjkx_41521477-dc17-4f99-9b16-a98a48981af6">false</dei:WrittenCommunications>
    <dei:SolicitingMaterial
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjg2_c47f3267-d82b-4788-b519-5709bb8f005d">false</dei:SolicitingMaterial>
    <dei:PreCommencementTenderOffer
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjg3_6764ac4c-c319-4a95-af9b-c3e08e9b0e28">false</dei:PreCommencementTenderOffer>
    <dei:PreCommencementIssuerTenderOffer
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjky_493c4153-a79d-442e-8027-63ad1e095737">false</dei:PreCommencementIssuerTenderOffer>
    <dei:Security12bTitle
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGFibGU6ODcwMjkwYzNlZjJkNDZkNzkxYjMwYjk2OTIzZTI5MzgvdGFibGVyYW5nZTo4NzAyOTBjM2VmMmQ0NmQ3OTFiMzBiOTY5MjNlMjkzOF8xLTAtMS0xLTEyMjQ4NQ_bca2c88b-5c28-4696-af7b-59ec3e7f601f">Common stock, par value $0.01 per share</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGFibGU6ODcwMjkwYzNlZjJkNDZkNzkxYjMwYjk2OTIzZTI5MzgvdGFibGVyYW5nZTo4NzAyOTBjM2VmMmQ0NmQ3OTFiMzBiOTY5MjNlMjkzOF8xLTItMS0xLTEyMjQ4NQ_3691a2e5-bc71-442c-8781-e9bdeb509d48">AWK</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGFibGU6ODcwMjkwYzNlZjJkNDZkNzkxYjMwYjk2OTIzZTI5MzgvdGFibGVyYW5nZTo4NzAyOTBjM2VmMmQ0NmQ3OTFiMzBiOTY5MjNlMjkzOF8xLTQtMS0xLTEyMjQ4NQ_129b0288-af97-4426-ab24-7e7eab31e6f1">NYSE</dei:SecurityExchangeName>
    <dei:EntityEmergingGrowthCompany
      contextRef="i505d94193f3345229d2ef53c0a94d2a5_D20220616-20220616"
      id="id3VybDovL2RvY3MudjEvZG9jOmE0NjIyNWNkMDM0ODRhMzZiODg2YzdlYmFmNzJjYTczL3NlYzphNDYyMjVjZDAzNDg0YTM2Yjg4NmM3ZWJhZjcyY2E3M18xL2ZyYWc6M2VmYWNiMDc2ZGI2NGNlZGEyM2U5YTI5OTNmYjk5NDQvdGV4dHJlZ2lvbjozZWZhY2IwNzZkYjY0Y2VkYTIzZTlhMjk5M2ZiOTk0NF8xNjg4_c7a81246-eb27-4fb4-b9b2-8819427e3e1d">false</dei:EntityEmergingGrowthCompany>
</xbrl>
