Fair Value of Financial Instruments (Tables)

12 Months Ended

Sep. 30, 2020

Fair Value Disclosures [Abstract]

Summary of Financial Instruments Measured at Fair Value on Recurring Basis

The carrying amounts and estimated fair values of financial instruments not measured at fair value on a recurring basis were as follows:

					Classification of Estimated Fair Value
	Carrying Amount		Fair Value		Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)
Spire
As of September 30, 2020
Cash and cash equivalents	$	4.1	$	4.1	$	4.1	$	—
Notes payable		648.0		648.0		—		648.0
Long-term debt, including current portion		2,484.1		2,908.6		—		2,908.6
As of September 30, 2019
Cash and cash equivalents	$	5.8	$	5.8	$	5.8	$	—
Notes payable		743.2		743.2		—		743.2
Long-term debt, including current portion		2,122.6		2,373.4		—		2,373.4
Spire Missouri
As of September 30, 2020
Notes payable - associated companies	$	301.2	$	301.2	$	—	$	301.2
Long-term debt		1,092.0		1,313.5		—		1,313.5
As of September 30, 2019
Cash and cash equivalents	$	2.6	$	2.6	$	2.6	$	—
Notes payable - associated companies		386.4		386.4		—		386.4
Long-term debt		925.0		1,065.2		—		1,065.2
Spire Alabama
As of September 30, 2020
Notes payable - associated companies	$	121.3	$	121.3	$	—	$	121.3
Long-term debt, including current portion		471.8		576.9		—		576.9
As of September 30, 2019
Notes payable - associated companies	$	128.7	$	128.7	$	—	$	128.7
Long-term debt, including current portion		412.2		474.8		—		474.8