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v3.25.1

Nature of Business (Details) customer in Millions | Mar. 31, 2025 state customer regulated_distribution_division
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Organization, Consolidation and Presentation of Financial Statements [Abstract] |
Number of customers serviced (over) | customer | 3.3
Number of regulated distribution divisions | regulated_distribution_division | 6
Number of states with service areas | state | 8

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- Definition Number Of Customers, Regulated Distribution + References No definition available. + Details
Name: | ato_NumberOfCustomersRegulatedDistribution
Namespace Prefix: | ato_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Represents the number of regulated distribution divisions. + References No definition available. + Details
Name: | ato_NumberOfDivisionsRegulatedDistribution
Namespace Prefix: | ato_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition The number of states the entity operates in as of the balance sheet date. + References No definition available. + Details
Name: | us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
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