Segment Information (Schedule Of Selected Supplemental Balance Sheet Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Segment Reporting Information [Line Items]
Net sales	$ 237.4	$ 212.6
Operating income	27.8	20.3
Depreciation and amortization	14.7	14.0
Restructuring and other charges	1.4	2.4
Payments to Acquire Productive Assets	15.6	15.2
Total assets	1,397.5		$ 1,395.0
Intangible intangible assets, net	403.8		$ 408.9
Mueller Co. [Member]
Segment Reporting Information [Line Items]
Net sales	215.9	192.3
Operating income	41.6	35.5
Depreciation and amortization	12.5	12.0
Restructuring and other charges	0.1	0.0
Payments to Acquire Productive Assets	14.7	14.5
Mueller Co. [Member] | Central Region [Member]
Segment Reporting Information [Line Items]
Net sales	56.9	46.4
Mueller Co. [Member] | Northeast Region [Member] [Member]
Segment Reporting Information [Line Items]
Net sales	45.8	41.7
Mueller Co. [Member] | Southeast Region [Member]
Segment Reporting Information [Line Items]
Net sales	38.4	39.4
Mueller Co. [Member] | Western Region [Member]
Segment Reporting Information [Line Items]
Net sales	53.4	46.0
Mueller Co. [Member] | CANADA
Segment Reporting Information [Line Items]
Net sales	12.1	11.6
Mueller Co. [Member] | Other International Locations [Member]
Segment Reporting Information [Line Items]
Net sales	9.3	7.2
Mueller Co. [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Net sales	194.5	173.5
Mueller Technologies [Member]
Segment Reporting Information [Line Items]
Net sales	21.5	20.3
Operating income	(1.5)	(1.8)
Depreciation and amortization	2.1	2.0
Restructuring and other charges	0.0	0.0
Payments to Acquire Productive Assets	0.8	0.6
Mueller Technologies [Member] | Central Region [Member]
Segment Reporting Information [Line Items]
Net sales	4.9	4.8
Mueller Technologies [Member] | Northeast Region [Member] [Member]
Segment Reporting Information [Line Items]
Net sales	3.5	6.3
Mueller Technologies [Member] | Southeast Region [Member]
Segment Reporting Information [Line Items]
Net sales	7.3	6.0
Mueller Technologies [Member] | Western Region [Member]
Segment Reporting Information [Line Items]
Net sales	5.0	2.0
Mueller Technologies [Member] | CANADA
Segment Reporting Information [Line Items]
Net sales	0.3	0.6
Mueller Technologies [Member] | Other International Locations [Member]
Segment Reporting Information [Line Items]
Net sales	0.5	0.6
Mueller Technologies [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Net sales	$ 20.7	$ 19.1