Commitments and Contingencies - Additional Information (Details) $ in Millions	3 Months Ended
	Dec. 31, 2024 USD ($)
Long-Term Purchase Commitment [Line Items]
Long-term purchase commitment, amount	$ 1,576.0
Capital committed to contribute to partnership	25.3
Remaining unfunded capital commitment	16.3
Spire Missouri [Member]
Long-Term Purchase Commitment [Line Items]
Long-term purchase commitment, amount	1,575.3
Spire Alabama Inc [Member]
Long-Term Purchase Commitment [Line Items]
Long-term purchase commitment, amount	$ 309.9