Fair Value Measurements (Tables)

12 Months Ended

Sep. 30, 2020

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, 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
As of September 30, 2019
ASSETS
Gas Utility:
U.S. stock/bond mutual funds	$	20.5	$	—	$	—	$	—		$	20.5
Gas Marketing:
NYMEX/ICE natural gas contracts		0.9		6.5		—		(6.9	)		0.5
Natural gas commodity contracts		—		16.8		—		(2.5	)		14.3
Other:
U.S. stock/bond mutual funds		15.5		—		—		—			15.5
Total	$	36.9	$	23.3	$	—	$	(9.4	)	$	50.8
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	12.3	$	—	$	—	$	(12.3	)	$	—
Gas Marketing:
NYMEX/ICE natural gas contracts		0.4		8.5		—		(8.9	)		—
Natural gas commodity contracts		—		13.8		0.1		(2.5	)		11.4
Other:
Interest rate swaps		—		43.4		—		—			43.4
Total	$	12.7	$	65.7	$	0.1	$	(23.7	)	$	54.8

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, 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	)		—
Total	$	28.5	$	—	$	—	$	(6.6	)	$	21.9
LIABILITIES
NYMEX/ICE natural gas contracts	$	0.9	$	—	$	—	$	(0.9	)	$	—
As of September 30, 2019
ASSETS
U.S. stock/bond mutual funds	$	20.5	$	—	$	—	$	—		$	20.5
LIABILITIES
NYMEX/ICE natural gas contracts	$	12.3	$	—	$	—	$	(12.3	)	$	—