Note 12 - Income Taxes - Summary of Federal and State Loss and Contribution and Tax Credit Carryforwards (Details) $ in Millions	Sep. 30, 2023 USD ($)
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

Amount of charitable contribution carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

No definition available.

+ Details

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Namespace Prefix:	sr_
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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

+ Details

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- Details

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Namespace Prefix:
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- Details

Name:	dei_LegalEntityAxis=sr_SpireAlabamaIncMember
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