Segment Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Restructuring	$ 0.9	$ 6.9	$ 3.3	$ 10.1
Operating income	35.8	22.2	56.1	38.1
Depreciation, Depletion and Amortization	14.3	13.4	28.3	25.5
Payments to Acquire Productive Assets	22.1	14.6	37.3	30.5
Revenues	257.7	234.0	470.3	426.8
Mueller Co. [Member]
Segment Reporting Information [Line Items]
Restructuring	0.4	1.1	0.4	1.1
Operating income	50.4	40.1	86.1	71.0
Depreciation, Depletion and Amortization	12.1	11.4	24.1	21.5
Payments to Acquire Productive Assets	21.2	13.0	35.7	27.8
Revenues	240.3	214.1	433.1	386.1
Corporate [Member]
Segment Reporting Information [Line Items]
Restructuring	0.5	5.8	2.9	9.0
Operating income	(9.9)	(14.3)	(23.3)	(25.6)
Depreciation, Depletion and Amortization	0.1	0.1	0.1	0.1
Payments to Acquire Productive Assets	0.2	0.0	0.3	0.0
Mueller Technologies [Member]
Segment Reporting Information [Line Items]
Restructuring	0.0	0.0	0.0	0.0
Operating income	(4.7)	(3.6)	(6.7)	(7.3)
Depreciation, Depletion and Amortization	2.1	1.9	4.1	3.9
Payments to Acquire Productive Assets	0.7	1.6	1.3	2.7
Revenues	$ 17.4	$ 19.9	$ 37.2	$ 40.7