FAIR VALUE MEASUREMENTS (Tables)

6 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of Fair Value Measurements, Measured on Recurring Basis

	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 March 31, 2018
ASSETS
US stock/bond mutual funds	$	19.1	$	4.1	$	—	$	—		$	23.2
NYMEX/ICE natural gas contracts	0.1		—		—		(0.1		)	—
Total	$	19.2	$	4.1	$	—	$	(0.1	)	$	23.2
LIABILITIES
NYMEX/ICE natural gas contracts	$	0.2	$	—	$	—	$	(0.2	)	$	—
Total	$	0.2	$	—	$	—	$	(0.2	)	$	—

As of September 30, 2017
ASSETS
US stock/bond mutual funds	$	18.3	$	4.1	$	—	$	—		$	22.4
NYMEX/ICE natural gas contracts	3.4		—		—		(3.4		)	—
NYMEX gasoline and heating oil contracts	0.1		—		—		—			0.1
Total	$	21.8	$	4.1	$	—	$	(3.4	)	$	22.5
LIABILITIES
NYMEX/ICE natural gas contracts	$	1.9	$	—	$	—	$	(1.9	)	$	—
Total	$	1.9	$	—	$	—	$	(1.9	)	$	—

As of March 31, 2017
ASSETS
US stock/bond mutual funds	$	17.7	$	4.1	$	—	$	—		$	21.8
NYMEX/ICE natural gas contracts	4.5		—		—		(1.8		)	2.7
NYMEX gasoline and heating oil contracts	0.2		—		—		—			0.2
Total	$	22.4	$	4.1	$	—	$	(1.8	)	$	24.7
LIABILITIES
NYMEX/ICE natural gas contracts	$	0.5	$	—	$	—	$	(0.5	)	$	—
Total	$	0.5	$	—	$	—	$	(0.5	)	$	—

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 March 31, 2018
ASSETS
Gas Utility:
US stock/bond mutual funds	$	19.1	$	4.1	$	—	$	—		$	23.2
NYMEX/ICE natural gas contracts	0.1		—		—		(0.1		)	—
Gas Marketing:
NYMEX/ICE natural gas contracts	0.2		3.3		—		(3.5		)	—
Natural gas commodity contracts	—		7.4		0.1		(2.1		)	5.4
Other:
Interest rate swaps	—		1.0		—		—			1.0
Total	$	19.4	$	15.8	$	0.1	$	(5.7	)	$	29.6
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	0.2	$	—	$	—	$	(0.2	)	$	—
Gas Marketing:
NYMEX/ICE natural gas contracts	0.6		9.8		—		(10.4		)	—
Natural gas commodity contracts	—		14.3		—		(2.1		)	12.2
Total	$	0.8	$	24.1	$	—	$	(12.7	)	$	12.2

	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, 2017
ASSETS
Gas Utility:
US stock/bond mutual funds	$	18.3	$	4.1	$	—	$	—		$	22.4
NYMEX/ICE natural gas contracts	3.4		—		—		(3.4		)	—
NYMEX gasoline and heating oil contracts	0.1		—		—		—			0.1
Gas Marketing:
NYMEX/ICE natural gas contracts	1.3		1.3		—		(2.1		)	0.5
Natural gas commodity contracts	—		6.8		0.1		(1.2		)	5.7
Total	$	23.1	$	12.2	$	0.1	$	(6.7	)	$	28.7
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	1.9	$	—	$	—	$	(1.9	)	$	—
Gas Marketing:
NYMEX/ICE natural gas contracts	1.8		0.3		—		(2.1		)	—
Natural gas commodity contracts	—		8.4		—		(1.2		)	7.2
Other:
Interest rate swaps	—		0.9		—		—			0.9
Total	$	3.7	$	9.6	$	—	$	(5.2	)	$	8.1
As of March 31, 2017
ASSETS
Gas Utility:
US stock/bond mutual funds	$	17.7	$	4.1	$	—	$	—		$	21.8
NYMEX/ICE natural gas contracts	4.5		—		—		(1.8		)	2.7
NYMEX gasoline and heating oil contracts	0.2		—		—		—			0.2
Gas Marketing:
NYMEX/ICE natural gas contracts	1.0		3.6		—		(4.4		)	0.2
Natural gas commodity contracts	—		6.2		0.2		(0.5		)	5.9
Other:
Interest rate swaps	—		0.2		—		—			0.2
Total	$	23.4	$	14.1	$	0.2	$	(6.7	)	$	31.0
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	0.5	$	—	$	—	$	(0.5	)	$	—
Gas Marketing:
NYMEX/ICE natural gas contracts	2.1		3.9		—		(6.0		)	—
Natural gas commodity contracts	—		6.5		—		(0.5		)	6.0
Total	$	2.6	$	10.4	$	—	$	(7.0	)	$	6.0