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Note 15 - Regulatory Matters - Regulatory Assets Not Earning a Return (Details) - USD ($) $ in Millions | Sep. 30, 2023 | Sep. 30, 2022
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Regulatory assets not earning a return | $ 672.5 | $ 686.3
Spire Missouri [Member] |  |
Regulatory assets not earning a return | 666.2 | 679.9
Pension and Other Postretirement Plans Costs [Member] |  |
Regulatory assets not earning a return | 133.4 | 152.9
Pension and Other Postretirement Plans Costs [Member] | Spire Missouri [Member] |  |
Regulatory assets not earning a return | 133.4 | 152.9
Deferred Income Tax Charge [Member] |  |
Regulatory assets not earning a return | 142.5 | 135.6
Deferred Income Tax Charge [Member] | Spire Missouri [Member] |  |
Regulatory assets not earning a return | 136.2 | 129.2
Unamortized Purchased Gas Adjustments Asset [Member] |  |
Regulatory assets not earning a return | 292.4 | 275.1
Unamortized Purchased Gas Adjustments Asset [Member] | Spire Missouri [Member] |  |
Regulatory assets not earning a return | 292.4 | 275.1
Other Regulatory Assets (Liabilities) [Member] |  |
Regulatory assets not earning a return | 104.2 | 122.7
Other Regulatory Assets (Liabilities) [Member] | Spire Missouri [Member] |  |
Regulatory assets not earning a return | $ 104.2 | $ 122.7

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- Definition Remaining balance of regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base. + 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 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 55 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481849/980-340-55-2 + Details
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- Details
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