Note 17 - Leases (Tables)

12 Months Ended

Sep. 30, 2023

Notes Tables

Schedule of Operating Lease Cost, Cash Flow and Non Cash Information [Table Text Block]

	Spire						Spire Missouri						Spire Alabama
	2023		2022		2021		2023		2022		2021		2023		2022		2021
Operating lease cost, including amounts capitalized	$	7.3	$	7.4	$	7.2	$	0.5	$	0.5	$	0.4	$	2.0	$	2.1	$	2.1
Cash flow and noncash information about operating leases:
Operating cash flows representing cash paid for amounts included in the measurement of lease liabilities		7.3		7.3		7.2		0.5		0.5		0.4		2.1		2.1		2.1
Right-of-use assets obtained in exchange for lease liabilities		0.8		24.6		—		0.8		1.1		—		—		23.5		—

Schedule of Balance Sheet and Weighted Average Information About Operating Leases [Table Text Block]

	Spire						Spire Missouri						Spire Alabama
	2023			2022			2023			2022			2023			2022
Right-of-use assets	$	70.6		$	73.7		$	2.1		$	1.7		$	19.2		$	20.2
Lease liabilities, current		6.8			6.5			0.5			0.4			1.9			1.9
Lease liabilities, noncurrent		70.2			73.7			1.8			1.5			23.5			24.6
Weighted-average remaining lease term (in years)		14.1			15.0			5.6			5.1			13.3			14.3
Weighted-average discount rate		4.2	%		4.1	%		3.3	%		2.2	%		3.7	%		3.7	%

Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block]

	Spire			Spire Missouri			Spire Alabama
2024	$	6.9		$	0.5		$	1.9
2025		7.5			0.6			2.2
2026		7.5			0.4			2.2
2027		7.4			0.3			2.3
2028		7.4			0.3			2.3
Thereafter		65.9			0.5			21.7
Total undiscounted lease payments		102.6			2.6			32.6
Less present value discount		(25.6	)		(0.3	)		(7.2	)
Total current and noncurrent lease liabilities	$	77.0		$	2.3		$	25.4