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v3.25.3

Revenue from Contracts with Customers (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] |  |
Contract with Customer, Liability, Increase from Deferral Of Revenue | $ 9.5 | $ 12.2
Contract with Customer, Liability, Revenue Recognized | $ 10.2 | $ 8.6

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- Definition Contract with Customer, Liability, Increase from Deferral Of Revenue + References No definition available. + Details
Name: | mwa_ContractWithCustomerLiabilityIncreaseFromDeferralOfRevenue
Namespace Prefix: | mwa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 606 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479806/606-10-50-8 + Details
Name: | us-gaap_ContractWithCustomerLiabilityRevenueRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration