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v3.23.1

Note 1 - Summary of Significant Accounting Policies - Transactions With Affiliates (Details) - Affiliated Entity [Member] - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2020
Regulated Operation [Member] | Spire Marketing [Member] | Spire Missouri [Member] |  |  |
Natural gas purchases from Spire Marketing | $ 86.3 | $ 92.5 | $ 56.9
Natural gas sales to Spire Marketing | 0.0 | 1.1 | 0.1
Regulated Operation [Member] | Spire Marketing [Member] | Spire Alabama Inc [Member] |  |  |
Natural gas purchases from Spire Marketing | 3.2 | 10.4 | 6.3
Natural gas sales to Spire Marketing | 0.5 | 0.1 | 0.3
Unregulated Operation [Member] | Spire S T L Pipeline L L C [Member] | Spire Missouri [Member] |  |  |
Transportation services expense | 32.0 | 32.0 | 27.9
Unregulated Operation [Member] | Spire S T L Pipeline L L C [Member] | Spire Alabama Inc [Member] |  |  |
Transportation services expense | 0.0 | 0.0 | 0.0
Unregulated Operation [Member] | Spire N G L Inc [Member] | Spire Missouri [Member] |  |  |
Transportation services expense | 0.0 | 0.5 | 1.0
Unregulated Operation [Member] | Spire N G L Inc [Member] | Spire Alabama Inc [Member] |  |  |
Transportation services expense | $ 0.0 | $ 0.0 | $ 0.0

X
- Definition Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party. + References No definition available. + Details
Name: | us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party. + References No definition available. + Details
Name: | us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | us-gaap_RelatedPartyTransactionAxis=srt_AffiliatedEntityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis=us-gaap_RegulatedOperationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_CounterpartyNameAxis=sr_SpireMarketingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

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- Details
Name: | us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis=us-gaap_UnregulatedOperationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_CounterpartyNameAxis=sr_SpireSTLPipelineLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_CounterpartyNameAxis=sr_SpireNGLIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |