Segment Information - Additional Information (Details) - Segment |
3 Months Ended | 6 Months Ended |
|---|---|---|
Dec. 31, 2025 |
Mar. 31, 2026 |
|
| Segment Reporting Information [Line Items] | ||
| Number of reportable segments | 3 | 1 |
| 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 evaluates the performance of the segments based on the computation of net income. The CODM uses net income to allocate resources and determine reinvestment for each segment, predominantly in the annual budget and forecasting process. Net Income 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 segment. | |
| Spire Missouri [Member] | ||
| Segment Reporting Information [Line Items] | ||
| Number of reportable segments | 1 | |
| Segment Reporting, CODM, Individual Title and Position or Group Name [Extensible Enumeration] | srt:ChiefExecutiveOfficerMember | |
| Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description | The chief executive officer is the CODM, who assesses performance and decides how to allocate resources based on net income. The CODM uses comparisons of actual results with budgeted and prior year results to assess performance of Spire Missouri and in establishing management’s compensation. The CODM does not receive asset information other than asset information reported on the Spire Missouri Balance Sheets. Financial data related to income and expenses, including gross receipt taxes which are disclosed separately, for the single reportable segment are reported on Spire Missouri’s Statements of Comprehensive Income. | |
| Spire Alabama Inc [Member] | ||
| Segment Reporting Information [Line Items] | ||
| Number of reportable segments | 1 | |
| Segment Reporting, CODM, Individual Title and Position or Group Name [Extensible Enumeration] | srt:ChiefExecutiveOfficerMember | |
| Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description | The chief executive officer is the CODM, who assesses performance and decides how to allocate resources based on net income. The CODM uses comparisons of actual results with budgeted and prior year results to assess performance of each company and in establishing management’s compensation. The CODM does not receive asset information other than asset information reported on the Spire Alabama Balance Sheets. Financial data related to income and expenses, including gross receipts taxes which are disclosed separately, for the single reportable segment are reported on Spire Alabama’s Statements of Income. |