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Fair Value Measurements - Additional Information (Details) - USD ($) | Sep. 30, 2020 | Sep. 30, 2019
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Spire Alabama |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Outstanding derivative contracts | $ 0 | $ 0

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- Definition Derivative contracts outstanding. + References No definition available. + Details
Name: | sr_DerivativeContractsOutstanding
Namespace Prefix: | sr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- 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_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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