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Note 12 - Income Taxes - Summary of Federal and State Loss and Contribution and Tax Credit Carryforwards (Details) $ in Millions | Sep. 30, 2023 USD ($)
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Federal and state loss carryforwards | $ 1,000.3
Contribution carryforwards | 6.1
Tax credit carryforwards | 13.1
Spire Missouri [Member] |
Federal and state loss carryforwards | 352.4
Contribution carryforwards | 5.6
Tax credit carryforwards | 8.5
Spire Alabama Inc [Member] |
Federal and state loss carryforwards | 624.1
Contribution carryforwards | 0.0
Tax credit carryforwards | $ 1.6

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- Definition Amount of charitable contribution carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
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Period Type: | instant

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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482685/740-10-50-3 + Details
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- Definition The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482685/740-10-50-3 + Details
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |