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Segment Information (Schedule Of Selected Supplemental Balance Sheet Information) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Segment Reporting Information [Line Items]
Net sales	$ 267.5	$ 257.7	$ 504.9	$ 470.3
Operating income	33.4	35.8	61.2	56.1
Depreciation and amortization	14.7	14.3	29.4	28.3
Restructuring and other charges	0.8	0.9	2.2	3.3
Payments to Acquire Productive Assets	15.5	22.1	31.1	37.3
Total assets	1,435.8		1,435.8		$ 1,395.0
Intangible intangible assets, net	397.1		397.1		$ 408.9
Mueller Co. [Member]
Segment Reporting Information [Line Items]
Net sales	246.9	239.9	462.8	432.2
Operating income	52.6	50.3	94.2	85.8
Depreciation and amortization	12.7	12.1	25.2	24.1
Restructuring and other charges	(0.7)	0.4	(0.6)	0.4
Payments to Acquire Productive Assets	14.8	21.2	29.5	35.7
Mueller Co. [Member] \| Central Region [Member]
Segment Reporting Information [Line Items]
Net sales	64.1	59.8	121.1	106.2
Mueller Co. [Member] \| Northeast Region [Member] [Member]
Segment Reporting Information [Line Items]
Net sales	43.2	55.0	89.0	96.7
Mueller Co. [Member] \| Southeast Region [Member]
Segment Reporting Information [Line Items]
Net sales	48.1	44.8	86.6	84.2
Mueller Co. [Member] \| Western Region [Member]
Segment Reporting Information [Line Items]
Net sales	63.5	57.6	116.9	103.6
Mueller Co. [Member] \| CANADA
Segment Reporting Information [Line Items]
Net sales	20.4	15.0	32.5	26.6
Mueller Co. [Member] \| Other International Locations [Member]
Segment Reporting Information [Line Items]
Net sales	7.6	7.7	16.7	14.9
Mueller Co. [Member] \| UNITED STATES
Segment Reporting Information [Line Items]
Net sales	218.9	217.2	413.6	390.7
Mueller Technologies [Member]
Segment Reporting Information [Line Items]
Net sales	20.6	17.8	42.1	38.1
Operating income	(4.6)	(4.6)	(6.1)	(6.4)
Depreciation and amortization	2.0	2.1	4.1	4.1
Restructuring and other charges	0.0	0.0	0.0	0.0
Payments to Acquire Productive Assets	0.7	0.7	1.5	1.3
Mueller Technologies [Member] \| Central Region [Member]
Segment Reporting Information [Line Items]
Net sales	6.6	3.7	11.5	8.5
Mueller Technologies [Member] \| Northeast Region [Member] [Member]
Segment Reporting Information [Line Items]
Net sales	3.4	4.5	6.9	10.8
Mueller Technologies [Member] \| Southeast Region [Member]
Segment Reporting Information [Line Items]
Net sales	6.5	5.4	13.9	11.4
Mueller Technologies [Member] \| Western Region [Member]
Segment Reporting Information [Line Items]
Net sales	3.0	3.1	8.0	5.1
Mueller Technologies [Member] \| CANADA
Segment Reporting Information [Line Items]
Net sales	0.1	0.3	0.4	0.9
Mueller Technologies [Member] \| Other International Locations [Member]
Segment Reporting Information [Line Items]
Net sales	1.0	0.8	1.4	1.4
Mueller Technologies [Member] \| UNITED STATES
Segment Reporting Information [Line Items]
Net sales	$ 19.5	$ 16.7	$ 40.3	$ 35.8