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Revenue - Schedule of Gross Receipts Taxes (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 2020 | Mar. 31, 2021 | Mar. 31, 2020
Scheduleof Gross Receipts Taxes [Line Items] |  |  |  |
Gross receipts taxes recorded in regulated gas distribution operating revenues | $ 42.2 | $ 37.9 | $ 63.9 | $ 62.5
Spire Missouri |  |  |  |
Scheduleof Gross Receipts Taxes [Line Items] |  |  |  |
Gross receipts taxes recorded in regulated gas distribution operating revenues | 28.6 | 26.2 | 43.8 | 43.4
Spire Alabama |  |  |  |
Scheduleof Gross Receipts Taxes [Line Items] |  |  |  |
Gross receipts taxes recorded in regulated gas distribution operating revenues | $ 11.8 | $ 9.9 | $ 17.1 | $ 16.1

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- 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
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- Definition [Line Items] for Schedule of Gross Receipts Taxes [Table] + References No definition available. + Details
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- Details
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- Details
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