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Document and Entity Information - shares
 9 Months Ended
May 31, 2019
Jun. 28, 2019
Document and Entity Information [Abstract]    
Entity Registrant Name ACUITY BRANDS INC  
Entity Central Index Key 0001144215  
Document Type 10-Q  
Document Period End Date May 31, 2019  
Amendment Flag false  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Current Fiscal Year End Date --08-31  
Entity Current Reporting Status Yes  
Entity Filer Category Large Accelerated Filer  
Entity Common Stock, Shares Outstanding   39,899,076
Entity Shell Company false  
Entity Small Business false  
Entity Emerging Growth Company false