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Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions				12 Months Ended
	Nov. 22, 2021	Nov. 10, 2021	Oct. 22, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Subsequent Event [Line Items]
Dividends declared, in dollars per share				$ 0.22	$ 0.21	$ 0.2025
Stock Repurchased During Period, Shares				651,271	418,374	1,074,234
Stock Repurchased During Period, Value				$ 10.0	$ 5.0	$ 10.0
Intangible Assets, Net (Including Goodwill)				507.6	508.7
Inventories				184.7	162.5
Mueller Co. [Member]
Subsequent Event [Line Items]
Intangible Assets, Net (Including Goodwill)				473.2	490.8
Inventories				162.0	143.5
Mueller Technologies [Member]
Subsequent Event [Line Items]
Intangible Assets, Net (Including Goodwill)				34.4	17.9
Inventories				22.7	19.0
Corporate [Member]
Subsequent Event [Line Items]
Intangible Assets, Net (Including Goodwill)				0.0	0.0
Inventories				$ 0.0	$ 0.0
Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends Payable, Date Declared			Oct. 22, 2021
Dividends declared, in dollars per share			$ 0.0580
Dividends Payable, Date to be Paid	Nov. 22, 2021
Dividends Payable, Date of Record		Nov. 10, 2021

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Aggregate dividends declared during the period for each share of common stock outstanding.

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