<?xml version="1.0" encoding="utf-8"?>
<FilingSummary xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Version>2.2.0.7</Version>
  <MyReports>
    <Report>
      <IsDefault>true</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>00090 - Document - Document and Entity Information</LongName>
      <ShortName>Document and Entity Information</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/DocumentDocumentAndEntityInformationNew</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R1.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>00100 - Statement - Consolidated Balance Sheets</LongName>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/StatementOfFinancialPositionClassified</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R2.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>00105 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/StatementOfFinancialPositionClassifiedParenthetical</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R3.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>00200 - Statement - Consolidated Statements of Operations and Comprehensive Income</LongName>
      <ShortName>Consolidated Statements of Operations and Comprehensive Income</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/StatementOfIncomeAlternative</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R4.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>00205 - Statement - Consolidated Statements of Operations and Comprehensive Income (Parenthetical)</LongName>
      <ShortName>Consolidated Statements of Operations and Comprehensive Income (Parenthetical)</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/StatementOfOtherComprehensiveIncomeParenthetical</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R5.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>00300 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/StatementOfCashFlowsIndirect</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R6.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>00305 - Statement - Consolidated Statements of Cash Flows (Parenthetical)</LongName>
      <ShortName>Consolidated Statements of Cash Flows (Parenthetical)</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/StatementOfCashFlowsIndirectParenthetical</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R7.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>00400 - Statement - Consolidated Statement of Changes in Stockholders' Equity</LongName>
      <ShortName>Consolidated Statement of Changes in Stockholders' Equity</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/StatementOfShareholdersEquityAndOtherComprehensiveIncome</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R8.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>00405 - Statement - Consolidated Statement of Changes in Stockholders' Equity (Parenthetical)</LongName>
      <ShortName>Consolidated Statement of Changes in Stockholders' Equity (Parenthetical)</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/StatementOfShareholdersEquityAndOtherComprehensiveIncomeParenthetical</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R9.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>10101 - Disclosure - Basis of Presentation</LongName>
      <ShortName>Basis of Presentation</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsOrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R10.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>10201 - Disclosure - New Accounting Pronouncements</LongName>
      <ShortName>New Accounting Pronouncements</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R11.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>10301 - Disclosure - Goodwill</LongName>
      <ShortName>Goodwill</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsScheduleOfGoodwillTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R12.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>10401 - Disclosure - Stockholders' Equity</LongName>
      <ShortName>Stockholders' Equity</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsStockholdersEquityNoteDisclosureTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R13.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>10501 - Disclosure - Long-Term Debt</LongName>
      <ShortName>Long-Term Debt</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsLongTermDebtTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R14.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>10601 - Disclosure - Short-Term Debt</LongName>
      <ShortName>Short-Term Debt</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsShortTermDebtTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R15.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>10701 - Disclosure - Income Taxes</LongName>
      <ShortName>Income Taxes</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsIncomeTaxDisclosureTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R16.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>10801 - Disclosure - Pension and Other Postretirement Benefits</LongName>
      <ShortName>Pension and Other Postretirement Benefits</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsPensionAndOtherPostretirementBenefitsDisclosureTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R17.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>10901 - Disclosure - Commitments and Contingencies</LongName>
      <ShortName>Commitments and Contingencies</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsCommitmentsAndContingenciesDisclosureTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R18.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>11001 - Disclosure - Environmental Matters</LongName>
      <ShortName>Environmental Matters</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsEnvironmentalLossContingencyDisclosureTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R19.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>11101 - Disclosure - Net Income (Loss) per Common Share</LongName>
      <ShortName>Net Income (Loss) per Common Share</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsEarningsPerShareTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R20.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>11201 - Disclosure - Fair Value of Assets and Liabilities</LongName>
      <ShortName>Fair Value of Assets and Liabilities</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsFairValueDisclosuresTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R21.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Sheet</ReportType>
      <LongName>11301 - Disclosure - Segment Information</LongName>
      <ShortName>Segment Information</ShortName>
      <Role>http://www.amwater.com/taxonomy/role/NotesToFinancialStatementsSegmentReportingDisclosureTextBlock</Role>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName>R22.xml</XmlFileName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ReportType>Book</ReportType>
      <LongName>All Reports</LongName>
      <ShortName>All Reports</ShortName>
      <Role />
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <XmlFileName />
    </Report>
  </MyReports>
  <EntityCount>1</EntityCount>
  <ContextCount>45</ContextCount>
  <SegmentCount>6</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <UnitCount>3</UnitCount>
  <ElementCount>156</ElementCount>
  <FootnotesReported>false</FootnotesReported>
  <TuplesReported>false</TuplesReported>
  <ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_20087</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2010_To_9_30_20105</ContextName>
      <ElementCount>3</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2009_To_9_30_20092</ContextName>
      <ElementCount>3</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_20106</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_7_1_2009_To_9_30_2009</ContextName>
      <ElementCount>29</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_20092</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_20085</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_20104</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_20082</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2009_To_12_31_2009</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2010_To_9_30_2010</ContextName>
      <ElementCount>97</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2010_To_9_30_20103</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_20096</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2010_To_9_30_20102</ContextName>
      <ElementCount>4</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_2008</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_2010</ContextName>
      <ElementCount>53</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2009_To_9_30_20095</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_200922</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2010_To_9_30_20107</ContextName>
      <ElementCount>3</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2010_To_9_30_20104</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_200924</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_20093</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_10_29_2010</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_20086</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_20105</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2009_To_9_30_2009</ContextName>
      <ElementCount>74</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_20102</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_200923</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_20107</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2010_To_9_30_20106</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2009_To_9_30_20094</ContextName>
      <ElementCount>4</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_20095</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_20092</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_20103</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_2009</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2009_To_9_30_20096</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_20094</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_20093</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_200922</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_20084</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_9_30_200925</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_7_1_2010_To_9_30_2010</ContextName>
      <ElementCount>29</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>Duration_1_1_2009_To_9_30_20093</ContextName>
      <ElementCount>1</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_20083</ContextName>
      <ElementCount>2</ElementCount>
    </ContextSummary>
    <ContextSummary>
      <ContextName>As_Of_12_31_2009</ContextName>
      <ElementCount>53</ElementCount>
    </ContextSummary>
  </ContextSummary>
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
