NEW YORK--(BUSINESS WIRE)--Fitch Ratings has upgraded Atmos Energy Corporation's (Atmos) Long-Term Issuer Default Rating (IDR) to 'A-' from 'BBB+' and its Senior Unsecured Debt rating to 'A' from 'A-'. A complete list of rating actions is shown at the end of this press release. The Rating Outlook is Stable. These rating actions affect $2.46 billion of long-term debt. The upgrade reflects Fitch's expectation of continued strong financial performance, which has been driven primarily by organic gr