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Pension Plans and Other Postretirement Benefits - Expected Pension Benefit Payments for Succeeding Fiscal Years (Details) $ in Millions | Sep. 30, 2025 USD ($)
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Pension Plan [Member] |
2026 | $ 51.2
2027 | 46.0
2028 | 45.3
2029 | 42.9
2030 | 41.7
2031-2035 | 196.2
Pension Plan [Member] | Spire Missouri [Member] |
2026 | 38.5
2027 | 33.4
2028 | 32.6
2029 | 30.5
2030 | 29.1
2031-2035 | 133.5
Pension Plan [Member] | Spire Alabama Inc [Member] |
2026 | 8.8
2027 | 8.8
2028 | 8.5
2029 | 8.4
2030 | 8.5
2031-2035 | 42.8
Other Postretirement Benefits Plan [Member] |
2026 | 13.4
2027 | 13.0
2028 | 12.5
2029 | 12.0
2030 | 11.6
2031-2035 | 54.0
Other Postretirement Benefits Plan [Member] | Spire Missouri [Member] |
2026 | 10.1
2027 | 9.7
2028 | 9.3
2029 | 8.9
2030 | 8.5
2031-2035 | 38.3
Other Postretirement Benefits Plan [Member] | Spire Alabama Inc [Member] |
2026 | 3.2
2027 | 3.2
2028 | 3.1
2029 | 3.0
2030 | 3.0
2031-2035 | $ 15.2

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