| Document and Entity Information | Nov. 11, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Nov. 11, 2020 |
| Entity Registrant Name | ATMOS ENERGY CORP |
| Entity Incorporation, State or Country Code | TX |
| Entity File Number | 1-10042 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000731802 |
| Amendment Flag | false |
