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v3.23.3

Note 13 - Pension Plans and Other Postretirement Benefits (Details Textual) - USD ($) $ in Thousands |  |  |  | 12 Months Ended
--- | --- | --- | --- | ---
Dec. 26, 2022 | Dec. 23, 2021 | Dec. 22, 2021 | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement |  |  |  | $ 0 | $ 0 |
Regulatory Asset, Total |  |  |  | $ 1,597,500 | 1,467,800 |
Implementation Period Used To Calculate Return On Plan Assets (Year) |  |  |  | 4 years |  |
Gains Or Losses Includible In Cost Amortized To Extent Exceeds Projected Benefit Obligations or Market Related Value of Plan Assets Percentage |  |  |  | 10.00% |  |
Regulatory Liability |  |  |  | $ 479,700 | 421,900 |
Defined Contribution Plan, Cost |  |  |  | $ 15,500 | 15,500 | $ 15,500
Minimum [Member] |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, Actuarial Gains From Prior Years, Percent |  |  |  | 0.50% |  |
Maximum [Member] |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, Actuarial Gains From Prior Years, Percent |  |  |  | 0.55% |  |
Pension Plan [Member] |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement |  |  |  | $ 48,800 | $ 109,300 |
Spire Missouri [Member] |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 6.30% | 5.80% |
Regulatory Asset, Total |  |  |  | $ 910,700 | $ 835,700 |
Regulatory Liability |  |  |  | 389,400 | 331,800 |
Defined Contribution Plan, Cost |  |  |  | 9,100 | $ 10,900 | $ 10,900
Spire Missouri [Member] | Pension Costs [Member] | Missouri West [Member] |  |  |  |  |  |
Regulatory Asset, Total |  | $ 4,400 | $ 5,500 |  |  |
Spire Missouri [Member] | Pension Costs [Member] | Missouri East [Member] |  |  |  |  |  |
Regulatory Asset, Total | $ 29,900 | 32,400 | 29,000 |  |  |
Spire Missouri [Member] | Pension and Other Postretirement Plans Costs [Member] | Missouri West [Member] |  |  |  |  |  |
Regulatory Liabilities For Which No Return On Investment During Recovery Period Is Provided | 800 | $ 1,100 | $ 3,300 |  |  |
Remaining Recovery Period of Regulatory Liabilities for which No Return on Investment During Recovery Period is Provided (Year) |  | 8 years | 8 years |  |  |
Spire Missouri [Member] | Pension and Other Postretirement Plans Costs [Member] | Missouri East [Member] |  |  |  |  |  |
Regulatory Assets for Which No Return on Investment During Recovery Period Is Provided | 6,900 | $ 11,000 | $ 21,600 |  |  |
Remaining Recovery Period of Regulatory Assets for which No Return on Investment During Recovery Period is Provided (Year) |  |  | 8 years |  |  |
Additional Remaining Recovery Period of Regulatory Assets for Which No Return on Investment During Recovery Period Is Provided (Year) |  | 8 years |  |  |  |
Spire Missouri [Member] | Pension Plan One [Member] |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  |  | 5.70% |
Spire Missouri [Member] | Pension Plan Two [Member] |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  |  | 5.80% |
Spire Missouri [Member] | Pension Plan [Member] |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  |  |  | 3.00%
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement |  |  |  | 9,900 | $ 87,000 |
Anticipated Contributions to Pension Plans Qualified Trusts |  |  |  | 21,600 |  |
Anticipated Contributions To Pension Plans Non Qualified Trusts |  |  |  | 0 |  |
Spire Missouri [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |  |  |
Anticipated Contributions to Pension Plans Qualified Trusts |  |  |  | 0 |  |
Postretirement Benefit Plans, Recovery in Rates Base Allowance |  | $ 8,600 |  |  |  |
Spire Missouri [Member] | Other Postretirement Benefits Plan [Member] | Missouri West [Member] |  |  |  |  |  |
Regulatory Liability | 100 |  |  |  |  |
Spire Missouri [Member] | Other Postretirement Benefits Plan [Member] | Missouri East [Member] |  |  |  |  |  |
Regulatory Liability | $ 900 |  |  |  |  |
Spire Alabama Inc [Member] |  |  |  |  |  |
Regulatory Asset, Total |  |  |  | 648,500 | 595,100 |
Regulatory Liability |  |  |  | 21,200 | 23,000 |
Defined Contribution Plan, Cost |  |  |  | $ 3,100 | $ 3,600 | $ 2,900
Spire Alabama Inc [Member] | Pension Plan One [Member] |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 6.20% | 5.70% | 3.10%
Spire Alabama Inc [Member] | Pension Plan Two [Member] |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 6.25% | 5.65% | 3.00%
Spire Alabama Inc [Member] | Pension Plan [Member] |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement |  |  |  | $ 38,800 | $ 22,300 |
Anticipated Contributions to Pension Plans Qualified Trusts |  |  |  | $ 16,400 |  |
Spire Alabama Inc [Member] | Pension Plan [Member] | Minimum [Member] |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 6.25% | 5.65% |
Defined Benefit Plan, Benefit Obligation, Settlement Losses Amortized Over Remaining Actuarial Life (Year) |  |  |  | 11 years 9 months 18 days | 11 years 4 months 24 days |
Spire Alabama Inc [Member] | Pension Plan [Member] | Maximum [Member] |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 6.20% | 5.70% |
Defined Benefit Plan, Benefit Obligation, Settlement Losses Amortized Over Remaining Actuarial Life (Year) |  |  |  | 13 years 4 months 24 days | 12 years 3 months 18 days |
Spire Alabama Inc [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |  |  |
Anticipated Contributions to Pension Plans Qualified Trusts |  |  |  | $ 0 |  |
Spire Alabama And Spire Missouri [Member] | Pension Plan [Member] |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement |  |  |  | $ 48,700 | $ 109,300 |
Spire Alabama And Spire Missouri [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 6.30% | 5.80% |

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