Summary of Significant Accounting Policies (Tables)

6 Months Ended

Mar. 31, 2025

Accounting Policies [Abstract]

Schedule of Related Party Transactions

	Three Months Ended March 31,				Six Months Ended  March 31,
	2025		2024		2025		2024
Spire Missouri
Purchases of natural gas from Spire Marketing	$	6.0	$	5.6	$	8.2	$	10.6
Transportation services received from Spire STL Pipeline		7.8		8.3		15.9		16.5
Transportation services received from Spire MoGas Pipeline		1.9		1.4		3.7		1.4
Sales of natural gas to Spire Marketing		0.1		0.3		0.1		0.3
Natural gas storage services from Spire Storage Salt Plains LLC		—		0.4		—		0.7
Spire Alabama
Purchases of natural gas from Spire Marketing	$	9.0	$	—	$	13.9	$	3.4

Schedule Of Capital Expenditure Excluded From Statement Of Cash Flow

	March 31,		September 30,		March 31,
	2025		2024		2024
Spire	$	66.8	$	116.5	$	80.4
Spire Missouri		45.6		67.4		47.2
Spire Alabama		8.5		14.1		2.7

Accounts Receivable, Allowance for Credit Loss

	Spire						Spire Missouri						Spire Alabama
Three Months Ended March 31,	2025			2024			2025			2024			2025			2024
Allowance at beginning of period	$	34.7		$	35.4		$	27.9		$	28.9		$	6.0		$	5.7
Provision for expected credit losses		8.9			7.9			6.6			6.2			2.0			1.4
Write-offs, net of recoveries		(6.8	)		(4.2	)		(4.9	)		(3.1	)		(1.9	)		(0.9	)
Allowance at end of period	$	36.8		$	39.1		$	29.6		$	32.0		$	6.1		$	6.2
Six Months Ended March 31,	2025			2024			2025			2024			2025			2024
Allowance at beginning of period	$	31.4		$	32.5		$	24.9		$	26.2		$	5.7		$	5.7
Provision for expected credit losses		14.0			12.0			10.7			9.8			2.8			1.7
Write-offs, net of recoveries		(8.6	)		(5.4	)		(6.0	)		(4.0	)		(2.4	)		(1.2	)
Allowance at end of period	$	36.8		$	39.1		$	29.6		$	32.0		$	6.1		$	6.2