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Cover - USD ($)
 12 Months Ended
Sep. 30, 2020
Nov. 06, 2020
Mar. 31, 2020
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Sep. 30, 2020    
Document Transition Report false    
Entity File Number 1-10042    
Entity Registrant Name Atmos Energy Corp    
Entity Incorporation, State or Country Code TX    
Entity Tax Identification Number 75-1743247    
Entity Address, Address Line One 1800 Three Lincoln Centre    
Entity Address, Address Line Two 5430 LBJ Freeway    
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 934-9227    
Title of 12(b) Security Common stock    
Trading Symbol ATO    
Security Exchange Name NYSE    
Entity Well Known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
ICFR Auditor Attestation Flag true    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 11,938,304,144
Entity Common Stock Shares Outstanding   125,889,456  
Documents Incorporated by Reference
Portions of the registrant’s Definitive Proxy Statement to be filed for the Annual Meeting of Shareholders on February 3, 2021 are incorporated by reference into Part III of this report.
   
Entity Central Index Key 0000731802    
Current Fiscal Year End Date --09-30    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Amendment Flag false