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Note 16 - Commitments and Contingencies (Details Textual) - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
May 31, 2023 | Sep. 30, 2023
Long-Term Purchase Commitment, Amount |  | $ 1,613.2
Capital Committed to Contribute to Partnership |  | 10.0
Remaining Unfunded Capital Commitment |  | 4.9
MoGas Pipeline and Omega Pipeline [Member] |  |
Business Combination, Price of Acquisition, Expected | $ 175.0 |
Spire Missouri [Member] |  |
Long-Term Purchase Commitment, Amount |  | 1,182.0
Spire Alabama Inc [Member] |  |
Long-Term Purchase Commitment, Amount |  | $ 251.6

X
- Definition Amount of capital committed to partnership. + References No definition available. + Details
Name: | sr_CapitalCommittedToContributeToPartnership
Namespace Prefix: | sr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of unfunded capital remaining. + References No definition available. + Details
Name: | sr_RemainingUnfundedCapitalCommitment
Namespace Prefix: | sr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Purchase price of expected business acquisition prior to consideration being transferred. Excludes asset acquisition. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name Accounting Standards Codification -Section 15 -Paragraph 3 -SubTopic 10 -Topic 805 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479455/805-10-15-3 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The minimum amount the entity agreed to spend under the long-term purchase commitment. + References No definition available. + Details
Name: | us-gaap_LongTermPurchaseCommitmentAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=sr_MogasPipelineAndOmegaPipelineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=sr_SpireMissouriMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=sr_SpireAlabamaIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |