Note 16 - Commitments and Contingencies (Details Textual) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	May 31, 2023	Sep. 30, 2023
Long-Term Purchase Commitment, Amount		$ 1,613.2
Capital Committed to Contribute to Partnership		10.0
Remaining Unfunded Capital Commitment		4.9
MoGas Pipeline and Omega Pipeline [Member]
Business Combination, Price of Acquisition, Expected	$ 175.0
Spire Missouri [Member]
Long-Term Purchase Commitment, Amount		1,182.0
Spire Alabama Inc [Member]
Long-Term Purchase Commitment, Amount		$ 251.6