Note 11 - Commitments and Contingencies (Details Textual) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Long-Term Purchase Commitment, Amount	$ 1,551.7
Capital Committed to Contribute to Partnership		$ 10.0
Remaining Unfunded Capital Commitment	7.7
Spire Missouri [Member]
Long-Term Purchase Commitment, Amount	1,133.0
Spire Alabama Inc [Member]
Long-Term Purchase Commitment, Amount	$ 233.4