Fair Value of Financial Instruments (Tables)

3 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Summary of Financial Instruments Measured at Fair Value on Recurring Basis

					Classification of Estimated Fair Value
	Carrying Amount		Fair Value		Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)
Spire
As of December 31, 2018
Cash and cash equivalents	$	8.4	$	8.4	$	8.4	$	—
Short-term debt		626.1		626.1		—		626.1
Long-term debt, including current portion		2,167.0		2,133.9		—		2,133.9
As of September 30, 2018
Cash and cash equivalents	$	4.4	$	4.4	$	4.4	$	—
Short-term debt		553.6		553.6		—		553.6
Long-term debt, including current portion		2,075.6		2,074.0		—		2,074.0
As of December 31, 2017
Cash and cash equivalents	$	6.7	$	6.7	$	6.7	$	—
Short-term debt		583.6		583.6		—		583.6
Long-term debt, including current portion		2,135.5		2,280.1		—		2,280.1
Spire Missouri
As of December 31, 2018
Cash and cash equivalents	$	4.9	$	4.9	$	4.9	$	—
Short-term debt		308.0		308.0		—		308.0
Long-term debt, including current portion		974.5		997.3		—		997.3
As of September 30, 2018
Cash and cash equivalents	$	2.0	$	2.0	$	2.0	$	—
Short-term debt		345.3		345.3		—		345.3
Long-term debt, including current portion		874.4		906.6		—		906.6
As of December 31, 2017
Cash and cash equivalents	$	4.1	$	4.1	$	4.1	$	—
Short-term debt		275.6		275.6		—		275.6
Long-term debt, including current portion		974.1		1,068.6		—		1,068.6
Spire Alabama
As of December 31, 2018
Short-term debt	$	164.2	$	164.2	$	—	$	164.2
Long-term debt		322.6		311.3		—		311.3
As of September 30, 2018
Short-term debt	$	142.5	$	142.5	$	—	$	142.5
Long-term debt		322.6		321.7		—		321.7
As of December 31, 2017
Short-term debt	$	163.1	$	163.1	$	—	$	163.1
Long-term debt		277.8		303.5		—		303.5