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Acquisitions and Divestitures - Narrative (Details)
$ in Millions
6 Months Ended
Mar. 31, 2020
USD ($)
service_center_store
Mar. 31, 2019
USD ($)
service_center_store
Business Acquisition [Line Items]    
Number of service center stores acquired | service_center_store 14 40
Consideration for acquisition | $ $ 11 $ 35
Finite-Lived Intangible Assets [Line Items]    
Gain on sale | $ $ 0  
Acquired Finite-Lived Intangible Assets [Line Items]    
Business Disposition, Number of Service Centers Sold | service_center_store 6  
Business Acquisition, Number of Former Franchise Service Centers | service_center_store 6  
Proceeds from sale of operations | $ $ 3