Commitments and Contingencies - Additional Information - Contingencies (Details)	Sep. 30, 2021 site
Spire Missouri East
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP) sites in Missouri	3
Number of sites enrolled in Brownfields/Voluntary clean up program	2
Spire Missouri West | Previous Ownership
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)	6
Spire Alabama
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)	9
Number of former manufactured gas distribution	5
Spire Alabama | Current Ownership
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)	4
Number of former manufactured gas distribution	1