Note 1 - Summary of Significant Accounting Policies (Tables)

9 Months Ended

Jun. 30, 2023

Notes Tables

Schedule of Related Party Transactions [Table Text Block]

	Three Months Ended June 30,				Nine Months Ended June 30,
	2023		2022		2023		2022
Spire Missouri
Purchases of natural gas from Spire Marketing	$	6.5	$	26.2	$	48.8	$	62.3
Transportation services received from Spire STL Pipeline		8.0		8.0		23.9		23.9
Sales of natural gas to Spire Marketing		0.3		—		0.4		—
Spire Alabama
Purchases of natural gas from Spire Marketing	$	1.7	$	3.2	$	2.8	$	3.2

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

	June 30,		September 30,		June 30,
	2023		2022		2022
Spire	$	62.2	$	77.8	$	52.6
Spire Missouri		33.4		45.6		39.2
Spire Alabama		4.5		19.2		7.7

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

	Spire						Spire Missouri						Spire Alabama
Three Months Ended June 30,	2023			2022			2023			2022			2023			2022
Allowance at beginning of period	$	40.6		$	35.1		$	34.5		$	27.0		$	5.3		$	7.1
Provision for expected credit losses		1.2			1.9			0.3			1.8			0.8			—
Write-offs, net of recoveries		(7.1	)		(4.4	)		(6.1	)		(3.7	)		(0.8	)		(0.5	)
Allowance at end of period	$	34.7		$	32.6		$	28.7		$	25.1		$	5.3		$	6.6

Nine Months Ended June 30,	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		13.5			8.6			11.4			8.6			1.5			—
Write-offs, net of recoveries		(10.7	)		(6.3	)		(7.6	)		(6.1	)		(2.5	)		—
Allowance at end of period	$	34.7		$	32.6		$	28.7		$	25.1		$	5.3		$	6.6