Summary of Significant Accounting Policies (Tables)

6 Months Ended

Mar. 31, 2021

Accounting Policies [Abstract]

Schedule of Inter-Company Transactions

Spire Missouri’s and Spire Alabama’s other transactions with affiliates are presented below

	Three Months Ended March 31,				Six Months Ended March 31,
	2021		2020		2021		2020
Spire Missouri
Purchases of natural gas from Spire Marketing Inc.	$	57.6	$	13.3	$	68.3	$	32.8
Transportation services received from Spire STL Pipeline LLC		7.9		7.9		16.0		11.8
Sales of natural gas to Spire Marketing Inc.		—		—		1.1		—
Transportation services received from Spire NGL Inc.		0.2		0.2		0.5		0.5
Spire Alabama
Purchases of natural gas from Spire Marketing Inc.	$	5.8	$	1.0	$	10.6	$	4.3
Sales of natural gas to Spire Marketing Inc.		0.1		—		0.1		—

Schedule of Capital Expenditures Excluded from Statement of Cash Flow

Accrued capital expenditures, shown in the following table, are excluded from capital expenditures in the statements of cash flows until paid.

	March 31,		September 30,		March 31,
	2021		2020		2020
Spire	$	36.1	$	67.6	$	51.4
Spire Missouri		21.8		34.3		21.5
Spire Alabama		4.7		17.0		17.6

Schedule of Allowance for Credit Losses

	Three Months Ended March 31, 2021									Six Months Ended March 31, 2021
				Spire			Spire						Spire			Spire
	Spire			Missouri			Alabama			Spire			Missouri			Alabama
Allowance at beginning of period	$	28.9		$	21.4		$	6.2		$	24.9		$	18.1		$	5.5
Provision for expected credit losses		6.6			5.7			0.6			10.7			9.0			1.3
Write-offs, net of recoveries		(1.1	)		(0.5	)		(0.3	)		(1.2	)		(0.5	)		(0.3	)
Allowance at end of period	$	34.4		$	26.6		$	6.5		$	34.4		$	26.6		$	6.5