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v3.23.1

Note 13 - Pension Plans and Other Postretirement Benefits (Details Textual) - USD ($) $ in Thousands |  |  | 12 Months Ended |
--- | --- | --- | --- | ---
Dec. 23, 2021 | Dec. 22, 2021 | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2020 | Apr. 18, 2018
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement |  |  |  | $ 0 | $ 0 |  |
Regulatory Asset, Total |  |  |  | $ 1,467,800 | 1,300,000 |  |
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% |  |  |
Postretirement Benefit Plans, Recovery in Rates Base Allowance |  |  |  |  |  |  | $ 8,600
Defined Contribution Plan, Cost |  |  |  | $ 15,500 | 15,500 | $ 13,600 |
Minimum [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, Actuarial Gains From Prior Years, Percent |  |  |  | 2.55% |  |  |
Maximum [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, Actuarial Gains From Prior Years, Percent |  |  |  | 2.80% |  |  |
Pension Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement |  |  |  | $ 109,300 | 67,600 |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  |  | 52,400 | 53,400 |  |
Other Postretirement Benefits Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  |  | 400 | 100 |  |
Spire Missouri [Member] |  |  |  |  |  |  |
Regulatory Asset, Total |  |  |  | 835,700 | 759,400 |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  |  |  | 42,200 |  |
Defined Contribution Plan, Cost |  |  |  | $ 10,900 | $ 10,900 | $ 9,500 |
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 | 32,400 | 29,000 |  |  |  |  |
Spire Missouri [Member] | Pension and Other Postretirement Plans Costs [Member] | Missouri West [Member] |  |  |  |  |  |  |
Regulatory Assets for Which No Return on Investment During Recovery Period Is Provided | $ 1,100 | $ 3,300 |  |  |  |  |
Remaining Recovery Period of Regulatory Assets 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 | $ 11,000 | $ 21,600 |  |  |  |  |
Remaining Recovery Period of Regulatory Assets for which No Return on Investment During Recovery Period is Provided (Year) | 8 years | 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% | 2.85% |
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement |  |  |  | $ 87,000 | $ 44,600 |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  |  | 37,800 |  |  |
Anticipated Contributions to Pension Plans Qualified Trusts |  |  |  | 44,500 |  |  |
Anticipated Contributions To Pension Plans Non Qualified Trusts |  |  |  | 1,100 |  |  |
Spire Missouri [Member] | Pension Plan [Member] | Nonqualified Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  |  | $ 0 |  |  |
Spire Missouri [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 5.80% | 2.95% |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  |  | $ 400 | $ 100 |  |
Spire Missouri [Member] | Other Postretirement Benefits Plan [Member] | Forecast [Member] |  |  |  |  |  |  |
Anticipated Contributions to Pension Plans Qualified Trusts |  |  | $ 0 |  |  |  |
Spire Alabama Inc [Member] |  |  |  |  |  |  |
Regulatory Asset, Total |  |  |  | 595,100 | 502,100 |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  |  |  | 11,100 |  |
Defined Contribution Plan, Cost |  |  |  | $ 3,600 | $ 2,900 | $ 3,400 |
Spire Alabama Inc [Member] | Pension Plan One [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 5.70% | 3.10% |  |
Spire Alabama Inc [Member] | Pension Plan Two [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 5.65% | 3.00% |  |
Spire Alabama Inc [Member] | Pension Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  |  | 3.10% | 2.95% |
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement |  |  |  | $ 22,300 | $ 22,900 |  |
Defined Benefit Plan, Benefit Obligation, Settlement Losses Amortized Over Remaining Actuarial Life (Year) |  |  |  | 12 years 3 months 18 days | 11 years 8 months 12 days | 11 years 4 months 24 days |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  |  | $ 14,400 |  |  |
Anticipated Contributions to Pension Plans Qualified Trusts |  |  |  | $ 13,800 |  |  |
Spire Alabama Inc [Member] | Pension Plan [Member] | Minimum [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 5.65% | 3.00% |  |
Spire Alabama Inc [Member] | Pension Plan [Member] | Maximum [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 5.70% | 3.10% |  |
Spire Alabama Inc [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  |  | 5.80% | 2.95% |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  |  | $ 0 | $ 0 |  |
Spire Alabama Inc [Member] | Other Postretirement Benefits Plan [Member] | Forecast [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 |  |  |  | $ 109,300 | $ 67,500 |  |

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