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Segment Information (Narrative) (Details) $ in Millions	12 Months Ended
	Sep. 30, 2021 USD ($) business_segments	Sep. 30, 2020 USD ($)	Sep. 30, 2019
Segment Reporting [Abstract]
Number of Reportable Segments | business_segments	2
Revenue, Major Customer [Line Items]
Receivables, net	$ 212.2	$ 180.8
Intangible Assets, Net (Including Goodwill)	507.6	508.7
Total assets	$ 1,518.0	1,395.0
Document Period End Date	Sep. 30, 2021
Mueller Co. [Member]
Revenue, Major Customer [Line Items]
Intangible Assets, Net (Including Goodwill)	$ 473.2	490.8
Mueller Technologies [Member]
Revenue, Major Customer [Line Items]
Intangible Assets, Net (Including Goodwill)	$ 34.4	$ 17.9
Customer Concentration Risk [Member] | Major Customers, Group One | Sales Revenue, Goods, Gross [Member]
Revenue, Major Customer [Line Items]
10 largest customers	58.00%	53.00%	53.00%
Customer Concentration Risk [Member] | Major Customers, Group Two | Sales Revenue, Goods, Gross [Member]
Revenue, Major Customer [Line Items]
10 largest customers	37.00%	34.00%	34.00%
Customer Concentration Risk [Member] | Ferguson Enterprises | Sales Revenue, Goods, Gross [Member]
Revenue, Major Customer [Line Items]
10 largest customers	19.00%	17.00%	18.00%
Customer Concentration Risk [Member] | Ferguson Enterprises | Sales Revenue, Goods, Gross [Member] | Mueller Co. [Member]
Revenue, Major Customer [Line Items]
10 largest customers	18.00%	16.00%	17.00%
Customer Concentration Risk [Member] | Ferguson Enterprises | Sales Revenue, Goods, Gross [Member] | Mueller Technologies [Member]
Revenue, Major Customer [Line Items]
10 largest customers	33.00%	22.00%	30.00%
Customer Concentration Risk [Member] | HDS IP Holdings, LLC [Member] | Sales Revenue, Goods, Gross [Member]
Revenue, Major Customer [Line Items]
10 largest customers	18.00%	17.00%	16.00%
Customer Concentration Risk [Member] | HDS IP Holdings, LLC [Member] | Sales Revenue, Goods, Gross [Member] | Mueller Co. [Member]
Revenue, Major Customer [Line Items]
10 largest customers	20.00%	19.00%	18.00%

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