Note 8 - Fair Value of Financial Instruments (Tables)

12 Months Ended

Sep. 30, 2024

Notes Tables

Fair Value, by Balance Sheet Grouping [Table Text Block]

					Classification of
					Estimated Fair Value
					Quoted
					Prices in		Significant
					Active		Observable
	Carrying		Fair		Markets		Inputs
	Amount		Value		(Level 1)		(Level 2)
Spire
As of September 30, 2024
Cash and cash equivalents	$	4.5	$	4.5	$	4.5	$	—
Notes payable		947.0		947.0		—		947.0
Long-term debt, including current portion		3,746.4		3,600.3		—		3,600.3
As of September 30, 2023
Cash and cash equivalents	$	5.6	$	5.6	$	5.6	$	—
Notes payable		955.5		955.5		—		955.5
Long-term debt, including current portion		3,710.6		3,270.2		—		3,270.2
Spire Missouri
As of September 30, 2024
Notes payable - associated companies	$	495.3	$	495.3	$	—	$	495.3
Long-term debt		1,803.4		1,736.9		—		1,736.9
As of September 30, 2023
Cash and cash equivalents	$	0.8	$	0.8	$	0.8	$	—
Notes payable - associated companies		540.6		540.6		—		540.6
Long-term debt		1,785.4		1,592.4		—		1,592.4
Spire Alabama
As of September 30, 2024
Cash and cash equivalents	$	1.5	$	1.5	$	1.5	$	—
Notes payable - associated companies		48.4		48.4		—		48.4
Long-term debt		746.3		711.8		—		711.8
As of September 30, 2023
Cash and cash equivalents	$	1.2	$	1.2	$	1.2	$	—
Notes payable - associated companies		124.1		124.1		—		124.1
Long-term debt		745.9		648.0		—		648.0