Fair Value Measurements (Tables)

12 Months Ended

Sep. 30, 2021

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis

Spire

	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Effects of Netting and Cash Margin Receivables /Payables			Total
As of September 30, 2021
ASSETS
Gas Utility:
U.S. stock/bond mutual funds	$	23.8	$	—	$	—	$	—		$	23.8
NYMEX/ICE natural gas contracts		104.0		—		—		(104.0	)		—
Gas Marketing:
NYMEX/ICE natural gas contracts		—		114.7		—		(93.7	)		21.0
Natural gas commodity contracts		—		35.2		—		(5.5	)		29.7
Other:
U.S. stock/bond mutual funds		26.2		—		—		—			26.2
Interest rate swaps		12.6		—		—		(5.2	)		7.4
Total	$	166.6	$	149.9	$	—	$	(208.4	)	$	108.1
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	0.3	$	—	$	—	$	(0.3	)	$	—
Gas Marketing:
NYMEX/ICE natural gas contracts		—		62.0		—		(62.0	)		—
Natural gas commodity contracts		—		96.7		—		(5.5	)		91.2
Other:
Interest rate swaps		5.7		—		—		(5.2	)		0.5
Total	$	6.0	$	158.7	$	—	$	(73.0	)	$	91.7
As of September 30, 2020
ASSETS
Gas Utility:
U.S. stock/bond mutual funds	$	21.9	$	—	$	—	$	—		$	21.9
Gasoline and heating oil contracts		0.3		—		—		(0.3	)		—
NYMEX/ICE natural gas contracts		6.3		—		—		(6.3	)		—
Gas Marketing:
NYMEX/ICE natural gas contracts		—		27.7		—		(25.4	)		2.3
Natural gas commodity contracts		—		14.5		0.4		—			14.9
Other:
U.S. stock/bond mutual funds		18.6		—		—		—			18.6
Total	$	47.1	$	42.2	$	0.4	$	(32.0	)	$	57.7
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	0.9	$	—	$	—	$	(0.9	)	$	—
Gas Marketing:
NYMEX/ICE natural gas contracts		0.7		21.4		—		(22.1	)		—
Natural gas commodity contracts		—		22.3		—		—			22.3
Other:
Interest rate swaps		—		54.2		—		—			54.2
Total	$	1.6	$	97.9	$	—	$	(23.0	)	$	76.5

Spire Missouri

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis

Spire Missouri

	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Effects of Netting and Cash Margin Receivables /Payables			Total
As of September 30, 2021
ASSETS
U.S. stock/bond mutual funds	$	23.8	$	—	$	—	$	—		$	23.8
NYMEX/ICE natural gas contracts		104.0		—		—		(104.0	)		—
Total	$	127.8	$	—	$	—	$	(104.0	)	$	23.8
LIABILITIES
NYMEX/ICE natural gas contracts	$	0.3	$	—	$	—	$	(0.3	)	$	—
As of September 30, 2020
ASSETS
U.S. stock/bond mutual funds	$	21.9	$	—	$	—	$	—		$	21.9
Gasoline and heating oil contracts		0.3		—		—		(0.3	)		—
NYMEX/ICE natural gas contracts		6.3		—		—		(6.3	)		—
U.S. stock/bond mutual funds	$	28.5	$	—	$	—	$	(6.6	)	$	21.9
LIABILITIES
NYMEX/ICE natural gas contracts	$	0.9	$	—	$	—	$	(0.9	)	$	—