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Note 15 - Regulatory Matters - Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions | Sep. 30, 2023 | Sep. 30, 2022
--- | --- | ---
Regulatory assets | $ 348.3 | $ 355.4
Regulatory Assets Noncurrent | 1,249.2 | 1,112.4
Total Regulatory Assets | 1,597.5 | 1,467.8
Regulatory Liability Current | 7.3 | 3.7
Regulatory Liability Noncurrent | 472.4 | 418.2
Total Regulatory Liabilities | 479.7 | 421.9
Spire Missouri [Member] |  |
Regulatory assets | 293.1 | 288.1
Regulatory Assets Noncurrent | 617.6 | 547.6
Total Regulatory Assets | 910.7 | 835.7
Regulatory Liability Current | 0.0 | 0.0
Regulatory Liability Noncurrent | 389.4 | 331.8
Total Regulatory Liabilities | 389.4 | 331.8
Spire Alabama Inc [Member] |  |
Regulatory assets | 41.6 | 56.9
Regulatory Assets Noncurrent | 606.9 | 538.2
Total Regulatory Assets | 648.5 | 595.1
Regulatory Liability Current | 0.0 | 0.0
Regulatory Liability Noncurrent | 21.2 | 23.0
Total Regulatory Liabilities | 21.2 | 23.0
Unamortized Purchased Gas Adjustments Asset [Member] |  |
Regulatory assets | 293.2 | 322.2
Regulatory Assets Noncurrent | 23.0 | 0.0
Regulatory Liability Current | 11.2 | 53.0
Unamortized Purchased Gas Adjustments Asset [Member] | Spire Missouri [Member] |  |
Regulatory assets | 269.4 | 275.1
Regulatory Assets Noncurrent | 23.0 | 0.0
Regulatory Liability Current | 11.2 | 53.0
Unamortized Purchased Gas Adjustments Asset [Member] | Spire Alabama Inc [Member] |  |
Regulatory assets | 21.7 | 43.8
Regulatory Assets Noncurrent | 0.0 | 0.0
Regulatory Liability Current | 0.0 | 0.0
Other Regulatory Assets (Liabilities) [Member] |  |
Regulatory assets | 55.1 | 33.2
Regulatory Assets Noncurrent | 131.2 | 129.2
Regulatory Liability Current | 7.3 | 3.7
Regulatory Liability Noncurrent | 21.4 | 14.4
Other Regulatory Assets (Liabilities) [Member] | Spire Missouri [Member] |  |
Regulatory assets | 23.7 | 13.0
Regulatory Assets Noncurrent | 116.0 | 113.1
Regulatory Liability Current | 0.0 | 0.0
Regulatory Liability Noncurrent | 16.5 | 7.3
Other Regulatory Assets (Liabilities) [Member] | Spire Alabama Inc [Member] |  |
Regulatory assets | 19.9 | 13.1
Regulatory Assets Noncurrent | 0.9 | 1.0
Regulatory Liability Current | 0.0 | 0.0
Regulatory Liability Noncurrent | 3.3 | 3.6
Deferred Income Tax Charge [Member] |  |
Regulatory Assets Noncurrent | 144.5 | 137.8
Deferred Income Tax Charge [Member] | Spire Missouri [Member] |  |
Regulatory Assets Noncurrent | 136.2 | 129.2
Deferred Income Tax Charge [Member] | Spire Alabama Inc [Member] |  |
Regulatory Assets Noncurrent | 2.0 | 2.2
Pension and Other Postretirement Plans Costs [Member] |  |
Regulatory assets | 261.0 | 294.5
Regulatory Assets Noncurrent | 185.2 | 172.6
Pension and Other Postretirement Plans Costs [Member] | Spire Missouri [Member] |  |
Regulatory assets | 189.1 | 222.9
Regulatory Assets Noncurrent | 156.5 | 143.6
Pension and Other Postretirement Plans Costs [Member] | Spire Alabama Inc [Member] |  |
Regulatory assets | 67.8 | 66.5
Regulatory Assets Noncurrent | 17.9 | 19.4
Removal Costs [Member] |  |
Regulatory Assets Noncurrent | 633.2 | 493.7
Regulatory Liability Noncurrent | 126.6 | 32.9
Removal Costs [Member] | Spire Missouri [Member] |  |
Regulatory Assets Noncurrent | 97.0 | 25.2
Regulatory Liability Noncurrent | 90.4 | 0.0
Removal Costs [Member] | Spire Alabama Inc [Member] |  |
Regulatory Assets Noncurrent | 536.2 | 468.5
Regulatory Liability Noncurrent | 0.0 | 0.0
Renewable Energy Program [Member] |  |
Regulatory Assets Noncurrent | 56.3 | 57.2
Renewable Energy Program [Member] | Spire Missouri [Member] |  |
Regulatory Assets Noncurrent | 56.3 | 57.2
Renewable Energy Program [Member] | Spire Alabama Inc [Member] |  |
Regulatory Assets Noncurrent | 0.0 | 0.0
Estimated Deferred Taxes Due to Customers [Member] |  |
Regulatory Liability Noncurrent | 128.0 | 145.3
Estimated Deferred Taxes Due to Customers [Member] | Spire Missouri [Member] |  |
Regulatory Liability Noncurrent | 114.8 | 127.9
Estimated Deferred Taxes Due to Customers [Member] | Spire Alabama Inc [Member] |  |
Regulatory Liability Noncurrent | $ 0.0 | $ 0.0

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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 340 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481878/980-340-50-1 + Details
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 340 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481878/980-340-50-1 + Details
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