<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.22.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>105</ContextCount>
  <ElementCount>354</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>39</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>6</UnitCount>
  <MyReports>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001001 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/DocumentandEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>0002002 - Document - Cover Page Document</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/CoverPageDocument</Role>
      <ShortName>Cover Page Document</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1001003 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/ConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1002004 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/ConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1003005 - Statement - Consolidated Statements Of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/ConsolidatedStatementsOfOperations</Role>
      <ShortName>Consolidated Statements Of Operations</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1004006 - Statement - Consolidated Statement of Comprehensive Income Statement</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/ConsolidatedStatementofComprehensiveIncomeStatement</Role>
      <ShortName>Consolidated Statement of Comprehensive Income Statement</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1005007 - Statement - Consolidated Statement Of Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/ConsolidatedStatementOfStockholdersEquity</Role>
      <ShortName>Consolidated Statement Of Stockholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>1006008 - Statement - Consolidated Statements Of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/ConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements Of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>1107109 - Statement - Accumulated Other Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/AccumulatedOtherComprehensiveLoss</Role>
      <ShortName>Accumulated Other Comprehensive Loss</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>1308309 - Statement - Accumulated Other Comprehensive Loss (Tabular)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/AccumulatedOtherComprehensiveLossTabular</Role>
      <ShortName>Accumulated Other Comprehensive Loss (Tabular)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>1409415 - Statement - Accumulated Other Comprehensive Loss (Schedule Of Accumulated Other Comprehensive Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveLoss</Role>
      <ShortName>Accumulated Other Comprehensive Loss (Schedule Of Accumulated Other Comprehensive Loss)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2101101 - Disclosure - Organization</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/Organization</Role>
      <ShortName>Organization</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2105102 - Disclosure - Revenue from Contracts with Customers (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/RevenuefromContractswithCustomersNotes</Role>
      <ShortName>Revenue from Contracts with Customers (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2108103 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2112104 - Disclosure - Borrowing Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/BorrowingArrangements</Role>
      <ShortName>Borrowing Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2116105 - Disclosure - Derivative Financial Instruments (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/DerivativeFinancialInstrumentsNotes</Role>
      <ShortName>Derivative Financial Instruments (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2119106 - Disclosure - Retirement Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/RetirementPlans</Role>
      <ShortName>Retirement Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2123107 - Disclosure - Stock-based Compensation Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/StockbasedCompensationPlans</Role>
      <ShortName>Stock-based Compensation Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2127108 - Disclosure - Supplemental Balance Sheet Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/SupplementalBalanceSheetInformation</Role>
      <ShortName>Supplemental Balance Sheet Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2131110 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/SegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2135111 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/CommitmentsandContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2137112 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/SubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2139113 - Disclosure - Business Combinations and Asset Acquisitions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/BusinessCombinationsandAssetAcquisitions</Role>
      <ShortName>Business Combinations and Asset Acquisitions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2302301 - Disclosure - Organization Restructuring Rollforward (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/OrganizationRestructuringRollforwardTables</Role>
      <ShortName>Organization Restructuring Rollforward (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2306302 - Disclosure - Revenue from Contracts with Customers (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/RevenuefromContractswithCustomersTables</Role>
      <ShortName>Revenue from Contracts with Customers (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/RevenuefromContractswithCustomersNotes</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2309303 - Disclosure - Income Taxes Rate Reconciliation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/IncomeTaxesRateReconciliationTables</Role>
      <ShortName>Income Taxes Rate Reconciliation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2313304 - Disclosure - Borrowing Arrangements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/BorrowingArrangementsTables</Role>
      <ShortName>Borrowing Arrangements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/BorrowingArrangements</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2320306 - Disclosure - Retirement Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/RetirementPlansTables</Role>
      <ShortName>Retirement Plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/RetirementPlans</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2324307 - Disclosure - Stock-based Compensation Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/StockbasedCompensationPlansTables</Role>
      <ShortName>Stock-based Compensation Plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/StockbasedCompensationPlans</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2328308 - Disclosure - Supplemental Balance Sheet Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/SupplementalBalanceSheetInformationTables</Role>
      <ShortName>Supplemental Balance Sheet Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/SupplementalBalanceSheetInformation</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2332310 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/SegmentInformationTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/SegmentInformation</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2340311 - Disclosure - Business Combinations and Asset Acquisitions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/BusinessCombinationsandAssetAcquisitionsTables</Role>
      <ShortName>Business Combinations and Asset Acquisitions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/BusinessCombinationsandAssetAcquisitions</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2403401 - Disclosure - Organization (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/OrganizationDetails</Role>
      <ShortName>Organization (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/OrganizationRestructuringRollforwardTables</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2404402 - Disclosure - Organization Restructuring (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/OrganizationRestructuringDetails</Role>
      <ShortName>Organization Restructuring (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/OrganizationRestructuringRollforwardTables</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2407403 - Disclosure - Revenue from Contracts with Customers (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/RevenuefromContractswithCustomersDetails</Role>
      <ShortName>Revenue from Contracts with Customers (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/RevenuefromContractswithCustomersTables</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2410404 - Disclosure - Income Taxes (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/IncomeTaxesNarrativeDetails</Role>
      <ShortName>Income Taxes (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/IncomeTaxesRateReconciliationTables</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2411405 - Disclosure - Income Taxes Income Tax Rate Reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/IncomeTaxesIncomeTaxRateReconciliationDetails</Role>
      <ShortName>Income Taxes Income Tax Rate Reconciliation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2414406 - Disclosure - Borrowing Arrangements (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/BorrowingArrangementsNarrativeDetails</Role>
      <ShortName>Borrowing Arrangements (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/BorrowingArrangementsTables</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2415407 - Disclosure - Borrowing Arrangements (Components Of Long-Term Debt) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/BorrowingArrangementsComponentsOfLongTermDebtDetails</Role>
      <ShortName>Borrowing Arrangements (Components Of Long-Term Debt) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/BorrowingArrangementsTables</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2418408 - Disclosure - Derivative Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/DerivativeFinancialInstrumentsDetails</Role>
      <ShortName>Derivative Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/DerivativeFinancialInstrumentsNotes</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2422410 - Disclosure - Retirement Plans (Net Periodic Benefit Cost) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/RetirementPlansNetPeriodicBenefitCostDetails</Role>
      <ShortName>Retirement Plans (Net Periodic Benefit Cost) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/RetirementPlansTables</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2425411 - Disclosure - Stock-based Compensation Plans (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/StockbasedCompensationPlansNarrativeDetails</Role>
      <ShortName>Stock-based Compensation Plans (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/StockbasedCompensationPlansTables</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2426412 - Disclosure - Stock-based Compensation Plans Grants Table (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/StockbasedCompensationPlansGrantsTableDetails</Role>
      <ShortName>Stock-based Compensation Plans Grants Table (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2429413 - Disclosure - Supplemental Balance Sheet Information (Schedule Of Selected Supplemental Balance Sheet Information) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/SupplementalBalanceSheetInformationScheduleOfSelectedSupplementalBalanceSheetInformationDetails</Role>
      <ShortName>Supplemental Balance Sheet Information (Schedule Of Selected Supplemental Balance Sheet Information) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/SupplementalBalanceSheetInformationTables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2430414 - Disclosure - Schedule of Accrued Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/ScheduleofAccruedLiabilitiesDetails</Role>
      <ShortName>Schedule of Accrued Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2433416 - Disclosure - Segment Information (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/SegmentInformationNarrativeDetails</Role>
      <ShortName>Segment Information (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/SegmentInformationTables</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2434417 - Disclosure - Segment Information (Schedule Of Selected Supplemental Balance Sheet Information) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/SegmentInformationScheduleOfSelectedSupplementalBalanceSheetInformationDetails</Role>
      <ShortName>Segment Information (Schedule Of Selected Supplemental Balance Sheet Information) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/SegmentInformationTables</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2436418 - Disclosure - Commitments and Contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/CommitmentsandContingenciesDetails</Role>
      <ShortName>Commitments and Contingencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/CommitmentsandContingencies</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2438419 - Disclosure - Subsequent Events (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/SubsequentEventsDetails</Role>
      <ShortName>Subsequent Events (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/SubsequentEvents</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="mwa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2441420 - Disclosure - Business Combinations and Asset Acquisitions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.muellerwaterproducts.com/role/BusinessCombinationsandAssetAcquisitionsDetails</Role>
      <ShortName>Business Combinations and Asset Acquisitions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.muellerwaterproducts.com/role/BusinessCombinationsandAssetAcquisitionsTables</ParentRole>
      <Position>50</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" original="mwa-20211231.htm">mwa-20211231.htm</File>
    <File>exhibit311ceo302certificat.htm</File>
    <File>exhibit312cfo302certificat.htm</File>
    <File>exhibit321ceo906certificat.htm</File>
    <File>exhibit322cfo906certificat.htm</File>
    <File>mwa-20211231.xsd</File>
    <File>mwa-20211231_cal.xml</File>
    <File>mwa-20211231_def.xml</File>
    <File>mwa-20211231_lab.xml</File>
    <File>mwa-20211231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="534">http://fasb.org/us-gaap/2021-01-31</BaseTaxonomy>
    <BaseTaxonomy items="31">http://xbrl.sec.gov/dei/2021</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
