Summary of Significant Accounting Policies (Policies)	6 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]
Basis of presentation	These consolidated interim-period financial statements have been prepared in accordance with accounting principles generally accepted in the United States on the same basis as those used for the Company’s audited consolidated financial statements included in our Annual Report on Form 10-K for the fiscal year ended September 30, 2025. In the opinion of management, all material adjustments (consisting of normal recurring accruals) necessary for a fair presentation have been made to the unaudited consolidated interim-period financial statements. These consolidated interim-period financial statements are condensed as permitted by the instructions to Form 10-Q and should be read in conjunction with the audited consolidated financial statements of Atmos Energy Corporation included in our Annual Report on Form 10-K for the fiscal year ended September 30, 2025. Because of seasonal and other factors, the results of operations for the six-month period ended March 31, 2026 are not indicative of our results of operations for the full 2026 fiscal year, which ends September 30, 2026.
Goodwill imapairment	During the second quarter of fiscal 2026, we completed our annual goodwill impairment assessment using a qualitative assessment, as permitted under U.S. GAAP. We test for goodwill at the reporting unit level on an annual basis and between annual tests if an event occurs or circumstances change that would more likely than not reduce the fair value of the reporting unit. Based on the assessment performed, we determined that our goodwill was not impaired.
Recently issued accounting pronouncements	In November 2024, the FASB issued guidance that will require more detailed information about the types of expenses in commonly presented expense captions. The amendment is effective for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. This amendment will be effective for our Form 10-K for fiscal 2028 and our Form 10-Q for the first quarter of fiscal 2029. We are currently evaluating the impact this may have on our financial statement disclosures. In September 2025, the FASB issued guidance which provides qualitative updates to the determination of capitalizing internal-use software costs by expanding the scope to allow for various software development methods. The amendment is effective for fiscal years beginning after December 15, 2027. Early adoption is permitted, and the amendment may be applied prospectively, retrospectively, or with a modified transition approach. This amendment will be effective for our Form 10-K for fiscal 2029 and our Form 10-Q for the first quarter of fiscal 2029. We are currently evaluating the impact this may have on our financial statement disclosures.
Earnings per share	We use the two-class method of computing earnings per share because we have participating securities in the form of non-vested restricted stock units with a nonforfeitable right to dividend equivalents, for which vesting is predicated solely on the passage of time. The calculation of earnings per share using the two-class method excludes income attributable to these participating securities from the numerator and excludes the dilutive impact of those shares from the denominator. Basic weighted average shares outstanding is calculated based upon the weighted average number of common shares outstanding during the periods presented. Also, this calculation includes fully vested stock awards that have not yet been issued as common stock.
Fair value measurements	We report certain assets and liabilities at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). We record cash and cash equivalents, restricted cash and cash equivalents, accounts receivable, accounts payable, and short-term debt at carrying value, which substantially approximates fair value due to the short-term nature of these assets and liabilities. For other financial assets and liabilities, we primarily use quoted market prices and other observable market pricing information to minimize the use of unobservable pricing inputs in our measurements when determining fair value. The methods used to determine fair value for our assets and liabilities are fully described in Note 2 to the consolidated financial statements in our Annual Report on Form 10-K for the fiscal year ended September 30, 2025. During the six months ended March 31, 2026, there were no changes in these methods.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Mar. 31, 2026

These consolidated interim-period financial statements have been prepared in accordance with accounting principles generally accepted in the United States on the same basis as those used for the Company’s audited consolidated financial statements included in our Annual Report on Form 10-K for the fiscal year ended September 30, 2025. In the opinion of management, all material adjustments (consisting of normal recurring accruals) necessary for a fair presentation have been made to the unaudited consolidated interim-period financial statements. These consolidated interim-period financial statements are condensed as permitted by the instructions to Form 10-Q and should be read in conjunction with the audited consolidated financial statements of Atmos Energy Corporation included in our Annual Report on Form 10-K for the fiscal year ended September 30, 2025. Because of seasonal and other factors, the results of operations for the six-month period ended March 31, 2026 are not indicative of our results of operations for the full 2026 fiscal year, which ends September 30, 2026.

Goodwill imapairment

During the second quarter of fiscal 2026, we completed our annual goodwill impairment assessment using a qualitative assessment, as permitted under U.S. GAAP. We test for goodwill at the reporting unit level on an annual basis and between annual tests if an event occurs or circumstances change that would more likely than not reduce the fair value of the reporting unit. Based on the assessment performed, we determined that our goodwill was not impaired.

Recently issued accounting pronouncements

In November 2024, the FASB issued guidance that will require more detailed information about the types of expenses in commonly presented expense captions. The amendment is effective for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. This amendment will be effective for our Form 10-K for fiscal 2028 and our Form 10-Q for the first quarter of fiscal 2029. We are currently evaluating the impact this may have on our financial statement disclosures.

In September 2025, the FASB issued guidance which provides qualitative updates to the determination of capitalizing internal-use software costs by expanding the scope to allow for various software development methods. The amendment is effective for fiscal years beginning after December 15, 2027. Early adoption is permitted, and the amendment may be applied prospectively, retrospectively, or with a modified transition approach. This amendment will be effective for our Form 10-K for fiscal 2029 and our Form 10-Q for the first quarter of fiscal 2029. We are currently evaluating the impact this may have on our financial statement disclosures.

Earnings per share

We use the two-class method of computing earnings per share because we have participating securities in the form of non-vested restricted stock units with a nonforfeitable right to dividend equivalents, for which vesting is predicated solely on the passage of time. The calculation of earnings per share using the two-class method excludes income attributable to these participating securities from the numerator and excludes the dilutive impact of those shares from the denominator. Basic weighted average shares outstanding is calculated based upon the weighted average number of common shares outstanding during the periods presented. Also, this calculation includes fully vested stock awards that have not yet been issued as common stock.

Fair value measurements

We report certain assets and liabilities at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). We record cash and cash equivalents, restricted cash and cash equivalents, accounts receivable, accounts payable, and short-term debt at carrying value, which substantially approximates fair value due to the short-term nature of these assets and liabilities. For other financial assets and liabilities, we primarily use quoted market prices and other observable market pricing information to minimize the use of unobservable pricing inputs in our measurements when determining fair value. The methods used to determine fair value for our assets and liabilities are fully described in Note 2 to the consolidated financial statements in our Annual Report on Form 10-K for the fiscal year ended September 30, 2025. During the six months ended March 31, 2026, there were no changes in these methods.