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Note 2 - Revenue - Taxes Associated with Natural Gas Utility Services (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Gross Receipts Tax Amounts | $ 131.8 | $ 109.8 | $ 94.0
Spire Missouri [Member] |  |  |
Gross Receipts Tax Amounts | 96.7 | 79.6 | 64.3
Spire Alabama Inc [Member] |  |  |
Gross Receipts Tax Amounts | $ 29.9 | $ 25.5 | $ 25.1

X
- Definition Amount of gross receipts taxes associated with natural gas utility service, which are imposed on the Utility and billed to its customers. + References No definition available. + Details
Name: | sr_TaxesReceiptAmountsIncludedOperatingRevenues
Namespace Prefix: | sr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- 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: |