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Note 13 - Pension Plans and Other Postretirement Benefits - PBO, ABO, and Fair Value of Plan Assets for Plans in Excess of Plan Assets (Details) - USD ($) $ in Millions | Sep. 30, 2022 | Sep. 30, 2021
--- | --- | ---
Projected benefit obligation | $ 464.4 | $ 689.6
Accumulated benefit obligation | 457.1 | 673.3
Fair value of plan assets | 332.7 | 498.9
Spire Missouri [Member] |  |
Projected benefit obligation | 320.6 | 479.0
Accumulated benefit obligation | 315.0 | 465.4
Fair value of plan assets | 235.9 | 364.0
Spire Alabama Inc [Member] |  |
Projected benefit obligation | 97.8 | 149.4
Accumulated benefit obligation | 96.2 | 146.9
Fair value of plan assets | $ 57.3 | $ 82.8

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