Segment Information (Schedule Of Selected Supplemental Balance Sheet Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
Segment Reporting Information [Line Items]
Net sales	$ 228.5	$ 274.3	$ 698.8	$ 701.1
Operating income	20.0	47.2	76.1	85.3
Depreciation and amortization	14.5	13.3	42.8	38.8
Restructuring and other charges	8.6	2.5	11.9	12.6
Payments to Acquire Productive Assets	13.9	22.4	51.2	52.9
Total assets	1,340.6		1,340.6		$ 1,337.3
Intangible intangible assets, net	413.7		413.7		$ 433.7
Mueller Co. [Member]
Segment Reporting Information [Line Items]
Net sales	209.9	250.2	643.0	636.3
Operating income	43.8	60.6	129.9	131.6
Depreciation and amortization	12.2	11.3	36.3	32.8
Restructuring and other charges	0.0	0.0	0.4	1.1
Payments to Acquire Productive Assets	13.4	18.9	49.1	46.7
Mueller Co. [Member] | Central Region [Member]
Segment Reporting Information [Line Items]
Net sales	57.5	58.8	163.9	154.1
Mueller Co. [Member] | Northeast Region [Member] [Member]
Segment Reporting Information [Line Items]
Net sales	38.8	52.0	135.7	134.8
Mueller Co. [Member] | Southeast Region [Member]
Segment Reporting Information [Line Items]
Net sales	35.7	41.3	120.3	117.2
Mueller Co. [Member] | Western Region [Member]
Segment Reporting Information [Line Items]
Net sales	50.8	63.8	154.5	159.1
Mueller Co. [Member] | CANADA
Segment Reporting Information [Line Items]
Net sales	20.7	24.1	47.3	49.3
Mueller Co. [Member] | Other International Locations [Member]
Segment Reporting Information [Line Items]
Net sales	6.4	10.2	21.3	21.8
Mueller Co. [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Net sales	182.8	215.9	574.4	565.2
Mueller Technologies [Member]
Segment Reporting Information [Line Items]
Net sales	18.6	24.1	55.8	64.8
Operating income	(3.8)	(2.2)	(10.5)	(9.5)
Depreciation and amortization	2.3	2.0	6.4	5.9
Restructuring and other charges	0.0	0.0	0.0	0.0
Payments to Acquire Productive Assets	0.5	1.8	1.8	4.5
Mueller Technologies [Member] | Central Region [Member]
Segment Reporting Information [Line Items]
Net sales	5.0	6.6	13.3	20.5
Mueller Technologies [Member] | Northeast Region [Member] [Member]
Segment Reporting Information [Line Items]
Net sales	4.0	5.5	14.6	12.3
Mueller Technologies [Member] | Southeast Region [Member]
Segment Reporting Information [Line Items]
Net sales	5.1	8.0	16.1	21.7
Mueller Technologies [Member] | Western Region [Member]
Segment Reporting Information [Line Items]
Net sales	3.6	2.3	8.7	6.6
Mueller Technologies [Member] | CANADA
Segment Reporting Information [Line Items]
Net sales	0.3	0.5	1.2	0.8
Mueller Technologies [Member] | Other International Locations [Member]
Segment Reporting Information [Line Items]
Net sales	0.6	1.2	1.9	2.9
Mueller Technologies [Member] | UNITED STATES
Segment Reporting Information [Line Items]
Net sales	$ 17.7	$ 22.4	$ 52.7	$ 61.1