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Document and Entity Information - shares
 9 Months Ended
Jun. 30, 2024
Aug. 01, 2024
Document and Entity Information    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2024  
Document Transition Report false  
Securities Act File Number 000-52423  
Entity Registrant Name AECOM  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 61-1088522  
Entity Address, Address Line One 13355 Noel Road  
Entity Address, City or Town Dallas  
Entity Address, State or Province TX  
Entity Address, Postal Zip Code 75240  
City Area Code 972  
Local Phone Number 788-1000  
Title of 12(b) Security Common Stock, $0.01 par value  
Trading Symbol ACM  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   134,066,746
Entity Central Index Key 0000868857  
Current Fiscal Year End Date --09-30  
Document Fiscal Year Focus 2024  
Document Fiscal Period Focus Q3  
Amendment Flag false