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Segment Information - Additional Information (Details) | 12 Months Ended
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Sep. 30, 2025 Segment
Segment Reporting Information [Line Items] |
Number of reportable segments | 3
Segment Reporting, CODM, Individual Title and Position or Group Name [Extensible Enumeration] | srt:ChiefExecutiveOfficerMember
Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description | The CODM and management evaluate the performance of the segments based on the computation of adjusted earnings. Adjusted earnings excludes from reported net income, as applicable, the after-tax impacts of fair value accounting and timing adjustments associated with energy-related transactions, the impacts of acquisition, divestiture and restructuring activities, and the largely non-cash impacts of other non-recurring or unusual items such as certain regulatory, legislative or GAAP standard-setting actions. For each of the Company’s segments, the CODM uses adjusted earnings to allocate resources and determine reinvestment for each segment, predominantly in the annual budget and forecasting process. Adjusted earnings is also used to monitor budget versus actual results to assess performance of the segment and establish management compensation. The CODM does not receive asset information for the individual reportable segments.
Spire Missouri [Member] |
Segment Reporting Information [Line Items] |
Number of reportable segments | 1
Spire Alabama Inc [Member] |
Segment Reporting Information [Line Items] |
Number of reportable segments | 1

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- Definition Indicates title and position of individual or name of group identified as chief operating decision maker (CODM) for segment reporting. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 54 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-54 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 47 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-47 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 21 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-21 + Details
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- Definition Description of how chief operating decision maker (CODM) uses reported segment profit (loss) measure to assess performance and allocate resource. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 47 -Subparagraph (bb) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-47 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 54 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-54 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 29 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-29 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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