Summary of Significant Accounting Policies (Tables)

3 Months Ended

Dec. 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 December 31,
	2021		2020
Spire Missouri
Purchases of natural gas from Spire Marketing Inc.	$	18.2	$	10.7
Transportation services received from Spire STL Pipeline LLC		8.1		8.1
Sales of natural gas to Spire Marketing Inc.		—		1.1
Transportation services received from Spire NGL Inc.		—		0.3
Spire Alabama
Purchases of natural gas from Spire Marketing Inc.	$	—	$	4.8

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.

	December 31,		September 30,		December 31,
	2021		2021		2020
Spire	$	33.5	$	59.5	$	40.9
Spire Missouri		27.2		37.1		23.1
Spire Alabama		1.2		13.6		4.2

Schedule of Allowance for Credit Losses

	Spire						Spire Missouri					Spire Alabama
Three Months Ended December 31,	2021			2020			2021			2020		2021			2020
Allowance at beginning of period	$	30.3		$	24.9		$	22.6		$	18.1	$	6.6		$	5.5
Provision for expected credit losses		1.5			4.1			2.1			3.3		(0.5	)		0.7
Write-offs, net of recoveries		(0.4	)		(0.1	)		(0.9	)		—		0.6			—
Allowance at end of period	$	31.4		$	28.9		$	23.8		$	21.4	$	6.7		$	6.2