Note 1 - Summary of Significant Accounting Policies (Tables)

6 Months Ended

Mar. 31, 2023

Notes Tables

Schedule of Related Party Transactions [Table Text Block]

	Three Months Ended March 31,				Six Months Ended March 31,
	2023		2022		2023		2022
Spire Missouri
Purchases of natural gas from Spire Marketing	$	13.8	$	17.9	$	42.3	$	36.1
Transportation services received from Spire STL Pipeline		7.8		7.8		15.9		15.9
Sales of natural gas to Spire Marketing		0.1		—		0.1		—
Spire Alabama
Purchases of natural gas from Spire Marketing	$	—	$	—	$	1.1	$	—

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

	March 31,		September 30,		March 31,
	2023		2022		2022
Spire	$	66.3	$	77.8	$	38.8
Spire Missouri		35.4		45.6		28.7
Spire Alabama		5.2		19.2		5.0

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

	Spire						Spire Missouri						Spire Alabama
Three Months Ended March 31,	2023			2022			2023			2022			2023			2022
Allowance at beginning of period	$	34.5		$	31.4		$	28.2		$	23.8		$	5.5		$	6.7
Provision for expected credit losses		8.2			5.2			7.3			4.7			0.5			0.5
Write-offs, net of recoveries		(2.1	)		(1.5	)		(1.0	)		(1.5	)		(0.7	)		(0.1	)
Allowance at end of period	$	40.6		$	35.1		$	34.5		$	27.0		$	5.3		$	7.1

Six Months Ended March 31,	2023			2022			2023			2022			2023			2022
Allowance at beginning of period	$	31.9		$	30.3		$	24.9		$	22.6		$	6.3		$	6.6
Provision for expected credit losses		12.3			6.7			11.1			6.8			0.7			—
Write-offs, net of recoveries		(3.6	)		(1.9	)		(1.5	)		(2.4	)		(1.7	)		0.5
Allowance at end of period	$	40.6		$	35.1		$	34.5		$	27.0		$	5.3		$	7.1