Leases (Tables)

12 Months Ended

Sep. 30, 2025

Leases [Abstract]

Schedule of Operating Lease Cost, Cash Flow and Non Cash Information

Operating lease cost, cash flow and noncash information are shown in the following table.

	Spire						Spire Missouri						Spire Alabama
	2025		2024		2023		2025		2024		2023		2025		2024		2023
Operating lease cost, including amounts    capitalized	$	7.1	$	7.3	$	7.3	$	0.5	$	0.5	$	0.5	$	2.0	$	2.0	$	2.0
Operating cash flows representing cash    paid for amounts included in the    measurement of lease liabilities		7.3		7.4		7.3		0.5		0.5		0.5		2.2		2.1		2.1
Right-of-use assets obtained in exchange    for lease liabilities		—		—		0.8		—		—		0.8		—		—		—

Schedule of Balance Sheet and Weighted Average Information About Operating Leases

The following table shows year-end balance sheet and weighted-average information about operating leases.

	Spire						Spire Missouri						Spire Alabama
	2025			2024			2025			2024			2025			2024
Right-of-use assets	$	59.2		$	63.1		$	1.6		$	1.7		$	17.0		$	18.1
Lease liabilities, current		6.1			6.6			0.5			0.5			2.0			1.9
Lease liabilities, noncurrent		59.1			62.7			1.2			1.3			20.9			22.3
Weighted-average remaining lease term (in years)		12.6			13.5			4.8			5.1			11.3			12.3
Weighted-average discount rate		4.2	%		4.2	%		3.8	%		3.4	%		3.7	%		3.7	%

Lessee, Operating Lease, Liability, to be Paid, Maturity

Following is a maturity analysis by fiscal year for operating lease liabilities as of September 30, 2025.

	Spire			Spire Missouri			Spire Alabama
2026	$	6.3		$	0.5		$	2.0
2027		6.7			0.4			2.3
2028		6.8			0.3			2.3
2029		6.7			0.3			2.4
2030		6.7			0.2			2.4
Thereafter		51.3			0.2			16.9
Total undiscounted lease payments		84.5			1.9			28.3
Less present value discount		(19.3	)		(0.2	)		(5.4	)
Total current and noncurrent lease liabilities	$	65.2		$	1.7		$	22.9