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Organization (Details)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Jul. 31, 2014
Mar. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Mar. 31, 2017
USD ($)
Mar. 31, 2018
USD ($)
Mar. 31, 2017
USD ($)
Sep. 30, 2019
Sep. 30, 2017
Segment Reporting Information [Line Items]                
Beginning balance   $ 3.0 $ 3.3   $ 3.3      
Restructuring   1.9   $ 2.5 5.8 $ 3.8    
Payments     $ 3.9          
Number of Reportable Segments     2          
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage 49.00%              
Payments for (Proceeds from) Other Investing Activities           26.6    
Defined Benefit Plan, Net Periodic Benefit Cost other than Service Cost   0.3   0.4 0.5 0.7    
Revenue, Net   $ 233.2   $ 199.7 $ 411.5 $ 366.9    
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent   24.50%   35.00% 24.50% 35.00%   35.00%
Mueller Co. [Member]                
Segment Reporting Information [Line Items]                
Restructuring   $ 0.1   $ 1.6 $ 0.1 $ 1.7    
Revenue, Net   $ 211.1   181.6 $ 371.2 327.9    
General and Administrative Expense [Member] | Mueller Co. [Member]                
Segment Reporting Information [Line Items]                
Defined Benefit Plan, Net Periodic Benefit Cost other than Service Cost       0.3   0.5    
Cost of Sales [Member] | Mueller Co. [Member]                
Segment Reporting Information [Line Items]                
Defined Benefit Plan, Net Periodic Benefit Cost other than Service Cost       $ 0.1   $ 0.2    
Scenario, Forecast [Member]                
Segment Reporting Information [Line Items]                
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent             21.00%