Pension Plans and Other Postretirement Benefits - Additional Information (Details)	3 Months Ended
	Dec. 31, 2024 USD ($)
Spire Missouri [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined benefit plan, plan assets, contributions by employer	$ 22,300,000
Anticipated contributions to pension plans qualified trusts	13,200,000
Spire Missouri [Member] | Pension Plan [Member] | Nonqualified Plan [Member]
Defined benefit plan, plan assets, contributions by employer	0
Spire Missouri [Member] | Other Postretirement Benefits Plan [Member]
Defined benefit plan, plan assets, contributions by employer	0
Anticipated contributions to pension plans qualified trusts	0
Spire Alabama Inc [Member] | Pension Plan [Member]
Defined benefit plan, plan assets, contributions by employer	2,600,000
Anticipated contributions to pension plans qualified trusts	11,900,000
Spire Alabama Inc [Member] | Other Postretirement Benefits Plan [Member]
Defined benefit plan, plan assets, contributions by employer	0
Anticipated contributions to pension plans qualified trusts	$ 0