Summary of Significant Accounting Policies (Tables)

3 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Schedule of Inter-Company Transactions

In addition, Spire Missouri’s other transactions with affiliates are presented in the table below

	Three Months Ended December 31,
	2020		2019
Purchases of natural gas from Spire Marketing Inc.	$	10.7	$	19.5
Transportation services received from Spire STL Pipeline LLC		8.1		3.9
Sales of natural gas to Spire Marketing Inc.		1.1		—
Transportation services received from Spire NGL Inc.		0.3		0.3

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,
	2020		2020		2019
Spire	$	40.9	$	67.6	$	45.8
Spire Missouri		23.1		34.3		20.2
Spire Alabama		4.2		17.0		9.8

Schedule of Allowance for Credit Losses

				Spire		Spire
	Spire			Missouri		Alabama
Allowance at beginning of period	$	24.9		$	18.1	$	5.5
Provision for expected credit losses		4.1			3.3		0.7
Write-offs, net of recoveries		(0.1	)		—		—
Allowance at end of period	$	28.9		$	21.4	$	6.2