Divestitures - Schedule of Cash Flows From Discontinued Operations (Details) - Discontinued Operations, Held-for-Sale [Member] - USD ($) $ in Millions |
9 Months Ended | |
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Jun. 30, 2026 |
Jun. 30, 2025 |
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| Spire Marketing [Member] | ||
| Disposal Group, Including Discontinued Operations [Line Items] | ||
| Net cash provided by operating activities | $ 31.6 | $ 24.5 |
| Net cash provided by (used in) investing activities | 80.4 | (24.6) |
| Spire Storage [Member] | ||
| Disposal Group, Including Discontinued Operations [Line Items] | ||
| Net cash provided by operating activities | 567.0 | 36.1 |
| Net cash provided by (used in) investing activities | $ (13.3) | $ (91.5) |
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- Definition Amount of cash inflow (outflow) from investing activity attributable to discontinued operation. Investing activity includes, but is not limited to, making and collecting loan, acquiring and disposing of debt and equity instruments, property, plant, and equipment, and other productive assets. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of cash inflow (outflow) from operating activity attributable to discontinued operation. Operating activity includes, but is not limited to, transaction, adjustment, and change in value not defined as investing or financing activity. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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