Revenue - Schedule of Gross Receipts Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Scheduleof Gross Receipts Taxes [Line Items]
Gross receipts taxes recorded in regulated gas distribution operating revenues	$ 21.9	$ 21.7
Spire Missouri
Scheduleof Gross Receipts Taxes [Line Items]
Gross receipts taxes recorded in regulated gas distribution operating revenues	14.9	15.2
Spire Alabama
Scheduleof Gross Receipts Taxes [Line Items]
Gross receipts taxes recorded in regulated gas distribution operating revenues	$ 5.7	$ 5.3