Financing (Tables)

6 Months Ended

Mar. 31, 2025

Debt Disclosure [Abstract]

Schedule of Short-Term Debt

	Spire (Parent Only)			Spire Missouri						Spire Alabama			Spire
	CP			Term			Spire			Spire			Consol-
	Program			Loan			Note			Note			idated
Six Months Ended March 31, 2025
Highest borrowings outstanding	$	1,223.0		$	—		$	615.0		$	73.2		$	1,223.0
Lowest borrowings outstanding		943.5			—			461.3			1.2			943.5
Weighted average borrowings		1,103.1			—			544.1			47.0			1,103.1
Weighted average interest rate		4.5	%		0.0	%		4.8	%		4.8	%		4.5	%
As of March 31, 2025
Borrowings outstanding	$	1,015.0		$	—		$	461.3		$	41.8		$	1,015.0
Weighted average interest rate		4.3	%		0.0	%		4.7	%		4.7	%		4.3	%
As of September 30, 2024
Borrowings outstanding	$	947.0		$	—		$	495.3		$	48.4		$	947.0
Weighted average interest rate		5.2	%		0.0	%		5.2	%		5.2	%		5.2	%
As of March 31, 2024
Borrowings outstanding	$	586.0		$	200.0		$	243.9		$	37.4		$	786.0
Weighted average interest rate		5.6	%		6.3	%		5.6	%		5.6	%		5.8	%

Summary of Capitalized Interest

	Three Months Ended March 31,				Six Months Ended  March 31,
	2025		2024		2025		2024
Spire	$	6.3	$	4.0	$	12.6	$	7.8
Spire Missouri		1.2		1.1		2.4		2.3
Spire Alabama		1.0		0.4		1.8		0.8