Note 1 - Summary of Significant Accounting Policies (Tables)

12 Months Ended

Sep. 30, 2022

Notes Tables

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

September 30	2022		2021		2020
Spire	$	77.8	$	59.5	$	67.6
Spire Missouri		45.6		37.1		34.3
Spire Alabama		19.2		13.6		17.0

Schedule of Asset Retirement Obligations [Table Text Block]

	Spire						Spire Missouri						Spire Alabama
	2022			2021			2022			2021			2022			2021
Asset retirement obligations, beginning of year	$	519.6		$	540.1		$	143.4		$	153.4		$	362.8		$	374.3
Liabilities incurred during the period		3.2			11.1			1.2			1.4			0.5			7.4
Liabilities settled during the period		(9.2	)		(21.9	)		(4.1	)		(9.7	)		(2.0	)		(10.7	)
Accretion		21.1			21.8			5.9			6.2			14.7			15.0
Revisions in estimated cash flows		(13.8	)		(31.5	)		(35.8	)		(7.9	)		22.7			(23.2	)
Asset retirement obligations, end of year	$	520.9		$	519.6		$	110.6		$	143.4		$	398.7		$	362.8

Schedule of Related Party Transactions [Table Text Block]

	Spire Missouri						Spire Alabama
	2022		2021		2020		2022		2021		2020
Natural gas purchases from Spire Marketing	$	86.3	$	92.5	$	56.9	$	3.2	$	10.4	$	6.3
Natural gas sales to Spire Marketing		—		1.1		0.1		0.5		0.1		0.3
Transportation services from Spire STL Pipeline LLC		32.0		32.0		27.9		—		—		—
Transportation services from Spire NGL Inc.		—		0.5		1.0		—		—		—

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

	Spire									Spire Missouri									Spire Alabama
	2022			2021			2020			2022			2021			2020			2022			2021			2020
Allowance at beginning of year	$	30.3		$	24.9		$	23.0		$	22.6		$	18.1		$	14.9		$	6.6		$	5.5		$	6.3
Provision for expected credit losses		11.6			14.7			14.0			11.2			11.1			12.7			0.3			3.1			0.9
Write-offs, net of recoveries		(10.0	)		(9.3	)		(12.1	)		(8.9	)		(6.6	)		(9.5	)		(0.6	)		(2.0	)		(1.7	)
Allowance at end of year	$	31.9		$	30.3		$	24.9		$	24.9		$	22.6		$	18.1		$	6.3		$	6.6		$	5.5