Note 1 - Summary of Significant Accounting Policies (Tables)

6 Months Ended

Mar. 31, 2024

Notes Tables

Schedule of Related Party Transactions [Table Text Block]

	Three Months Ended March 31,				Six Months Ended March 31,
	2024		2023		2024		2023
Spire Missouri
Purchases of natural gas from Spire Marketing	$	5.6	$	13.8	$	10.6	$	42.3
Transportation services received from Spire STL Pipeline		8.3		7.8		16.5		15.9
Transportation services received from Spire MoGas Pipeline		1.4		—		1.4		—
Sales of natural gas to Spire Marketing		0.3		0.1		0.3		0.1
Natural gas storage services from Spire Storage Salt Plains LLC		0.4		—		0.7		—
Spire Alabama
Purchases of natural gas from Spire Marketing	$	—	$	—	$	3.4	$	1.1

Schedule Of Capital Expenditure Excluded From Statement Of Cash Flow [Table Text Block]

	March 31,		September 30,		March 31,
	2024		2023		2023
Spire	$	80.4	$	104.3	$	66.3
Spire Missouri		47.2		56.5		35.4
Spire Alabama		2.7		4.6		5.2

Accounts Receivable, Allowance for Credit Loss [Table Text Block]

	Spire						Spire Missouri						Spire Alabama
Three Months Ended March 31,	2024			2023			2024			2023			2024			2023
Allowance at beginning of period	$	35.4		$	34.5		$	28.9		$	28.2		$	5.7		$	5.5
Provision for expected credit losses		7.9			8.2			6.2			7.3			1.4			0.5
Write-offs, net of recoveries		(4.2	)		(2.1	)		(3.1	)		(1.0	)		(0.9	)		(0.7	)
Allowance at end of period	$	39.1		$	40.6		$	32.0		$	34.5		$	6.2		$	5.3
Six Months Ended March 31,	2024			2023			2024			2023			2024			2023
Allowance at beginning of period	$	32.5		$	31.9		$	26.2		$	24.9		$	5.7		$	6.3
Provision for expected credit losses		12.0			12.3			9.8			11.1			1.7			0.7
Write-offs, net of recoveries		(5.4	)		(3.6	)		(4.0	)		(1.5	)		(1.2	)		(1.7	)
Allowance at end of period	$	39.1		$	40.6		$	32.0		$	34.5		$	6.2		$	5.3