Note 10 - Commitments and Contingencies (Details Textual) $ in Millions	9 Months Ended
	Jun. 30, 2022 USD ($)
Long-Term Purchase Commitment, Amount	$ 1,998.9
Spire Missouri [Member]
Long-Term Purchase Commitment, Amount	1,178.9
Spire Alabama Inc [Member]
Long-Term Purchase Commitment, Amount	$ 707.2