Segment Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Restructuring and other charges	$ 8.6	$ 2.5	$ 11.9	$ 12.6
Operating income	20.0	47.2	76.1	85.3
Depreciation, Depletion and Amortization	14.5	13.3	42.8	38.8
Payments to Acquire Productive Assets	13.9	22.4	51.2	52.9
Net sales	228.5	274.3	698.8	701.1
Mueller Co. [Member]
Segment Reporting Information [Line Items]
Restructuring and other charges	0.0	0.0	0.4	1.1
Operating income	43.8	60.6	129.9	131.6
Depreciation, Depletion and Amortization	12.2	11.3	36.3	32.8
Payments to Acquire Productive Assets	13.4	18.9	49.1	46.7
Net sales	209.9	250.2	643.0	636.3
Mueller Co. [Member] | Central Region [Member]
Segment Reporting Information [Line Items]
Net sales	57.5	58.8	163.9	154.1
Corporate
Segment Reporting Information [Line Items]
Restructuring and other charges	8.6	2.5	11.5	11.5
Operating income	(20.0)	(11.2)	(43.3)	(36.8)
Depreciation, Depletion and Amortization	0.0	0.0	0.1	0.1
Payments to Acquire Productive Assets	0.0	1.7	0.3	1.7
Mueller Technologies [Member]
Segment Reporting Information [Line Items]
Restructuring and other charges	0.0	0.0	0.0	0.0
Operating income	(3.8)	(2.2)	(10.5)	(9.5)
Depreciation, Depletion and Amortization	2.3	2.0	6.4	5.9
Payments to Acquire Productive Assets	0.5	1.8	1.8	4.5
Net sales	18.6	24.1	55.8	64.8
Mueller Technologies [Member] | Central Region [Member]
Segment Reporting Information [Line Items]
Net sales	$ 5.0	$ 6.6	$ 13.3	$ 20.5