Summary of Significant Accounting Policies (Tables)

3 Months Ended

Dec. 31, 2024

Accounting Policies [Abstract]

Schedule of Related Party Transactions

	Three Months Ended December 31,
	2024		2023
Spire Missouri
Purchases of natural gas from Spire Marketing	$	2.2	$	5.0
Transportation services received from Spire STL Pipeline		8.1		8.2
Transportation services received from Spire MoGas Pipeline		1.8		—
Natural gas storage services from Spire Storage Salt Plains LLC		—		0.3
Spire Alabama
Purchases of natural gas from Spire Marketing	$	4.9	$	3.4

Schedule Of Capital Expenditure Excluded From Statement Of Cash Flow

	December 31,		September 30,		December 31,
	2024		2024		2023
Spire	$	73.7	$	116.5	$	90.5
Spire Missouri		38.1		67.4		38.1
Spire Alabama		10.5		14.1		2.4

Accounts Receivable, Allowance for Credit Loss

	Spire						Spire Missouri						Spire Alabama
Three Months Ended December 31,	2024			2023			2024			2023			2024			2023
Allowance at beginning of period	$	31.4		$	32.5		$	24.9		$	26.2		$	5.7		$	5.7
Provision for expected credit losses		5.1			4.1			4.1			3.6			0.8			0.3
Write-offs, net of recoveries		(1.8	)		(1.2	)		(1.1	)		(0.9	)		(0.5	)		(0.3	)
Allowance at end of period	$	34.7		$	35.4		$	27.9		$	28.9		$	6.0		$	5.7