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v3.25.3

Commitments and Contingencies - Additional Information (Details) $ in Millions | 12 Months Ended
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Sep. 30, 2025 USD ($)
Long-Term Purchase Commitment [Line Items] |
Long-term purchase commitment, amount | $ 1,762.8
Capital committed to contribute to partnership | 25.0
Remaining unfunded capital commitment | 15.4
Spire Missouri [Member] |
Long-Term Purchase Commitment [Line Items] |
Long-term purchase commitment, amount | 1,388.9
Spire Alabama Inc [Member] |
Long-Term Purchase Commitment [Line Items] |
Long-term purchase commitment, amount | $ 557.2

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 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
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_LongTermPurchaseCommitmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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: |