Note 5 - Shareholders' Equity (Tables)

12 Months Ended

Sep. 30, 2022

Notes Tables

Stock Purchase Contract Obligation, Number of Shares to be Purchased [Table Text Block]

If the applicable market value* per share	Number of shares to be purchased per
of Spire common stock is:	stock purchase contract is:
Equal to or greater than $78.6906 (“threshold appreciation price”)	0.6354 (“minimum settlement rate”)
Less than $78.6906, but greater than $64.24	$50.00 ÷ applicable market value*
Less than or equal to $64.24 (“reference price”)	0.7783 (“maximum settlement rate”)

Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]

	Net			Defined Benefit			Net Unrealized
	Unrealized			Pension and			Gain (Loss) on
	Gain (Loss)			Other			Available-for-
	on Cash Flow			Postretirement			Sale Debt
	Hedges			Benefit Plans			Securities			Total
Spire
Balance at September 30, 2020	$	(38.4	)	$	(2.9	)	$	0.1		$	(41.2	)
Other comprehensive income (loss)		46.3			(1.3	)		(0.2	)		44.8
Balance at September 30, 2021		7.9			(4.2	)		(0.1	)		3.6
Other comprehensive income (loss)		42.5			1.5			(0.4	)		43.6
Balance at September 30, 2022	$	50.4		$	(2.7	)	$	(0.5	)	$	47.2
Spire Missouri
Balance at September 30, 2020	$	—		$	(2.9	)	$	—		$	(2.9	)
Other comprehensive loss		—			(1.3	)		—			(1.3	)
Balance at September 30, 2021		—			(4.2	)		—			(4.2	)
Other comprehensive income		—			1.5			—			1.5
Balance at September 30, 2022	$	—		$	(2.7	)	$	—		$	(2.7	)