Revenue - Schedule of Gross Receipts Taxes Associated Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Disaggregation of Revenue [Line Items]
Gross receipts tax amounts	$ 29.9	$ 26.8
Spire Missouri [Member]
Disaggregation of Revenue [Line Items]
Gross receipts tax amounts	21.7	19.5
Spire Alabama Inc [Member]
Disaggregation of Revenue [Line Items]
Gross receipts tax amounts	$ 6.8	$ 5.7

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.

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+ Details

SPIRE INC 10-Q