Fair Value Measurements (Tables)

6 Months Ended

Mar. 31, 2025

Fair Value Disclosures [Abstract]

Schedule of Derivative Assets and Liabilities, Including Receivables and Payables

	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Effects of Netting and Cash Margin Receivables /Payables			Total
As of March 31, 2025
ASSETS
Gas Utility:
U.S. stock/bond mutual funds	$	24.6	$	—	$	—		$	24.6
NYMEX/ICE natural gas contracts		17.5		—		(17.5	)		—
Gas Marketing:
NYMEX/ICE natural gas contracts		16.6		—		(16.6	)		—
Natural gas commodity contracts		—		48.5		(3.6	)		44.9
Other:
U.S. stock/bond mutual funds		22.0		—		—			22.0
U.S. bonds		15.6		—		—			15.6
Global bonds		4.5		—		—			4.5
Interest rate swaps		—		10.7		—			10.7
Total	$	100.8	$	59.2	$	(37.7	)	$	122.3
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	4.0	$	—	$	(4.0	)	$	—
Gas Marketing:
NYMEX/ICE natural gas contracts		19.4		—		(19.3	)		0.1
Natural gas commodity contracts		—		42.7		(3.6	)		39.1
Total	$	23.4	$	42.7	$	(26.9	)	$	39.2

	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Effects of Netting and Cash Margin Receivables /Payables			Total
As of September 30, 2024
ASSETS
Gas Utility:
U.S. stock/bond mutual funds	$	24.3	$	—	$	—		$	24.3
NYMEX/ICE natural gas contracts		3.4		—		(3.4	)		—
Gas Marketing:
NYMEX/ICE natural gas contracts		7.0		—		(7.0	)		—
Natural gas commodity contracts		—		46.0		(3.5	)		42.5
Other:
U.S. stock/bond mutual funds		17.9		—		—			17.9
U.S. bonds		21.9		—		—			21.9
Global bonds		5.9		—		—			5.9
Interest rate swaps		—		0.8		—			0.8
Total	$	80.4	$	46.8	$	(13.9	)	$	113.3
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	13.6	$	—	$	(3.8	)	$	9.8
Gas Marketing:
NYMEX/ICE natural gas contracts		17.7		—		(17.7	)		—
Natural gas commodity contracts		—		24.5		(3.5	)		21.0
Other:
Interest rate swaps		—		1.5		—			1.5
Total	$	31.3	$	26.0	$	(25.0	)	$	32.3
As of March 31, 2024
ASSETS
Gas Utility:
U.S. stock/bond mutual funds	$	22.6	$	—	$	—		$	22.6
NYMEX/ICE natural gas contracts		3.7		—		(3.7	)		—
Gasoline and heating oil contracts		—		0.1		(0.1	)		—
Gas Marketing:
NYMEX/ICE natural gas contracts		8.6		—		(8.6	)		—
Natural gas commodity contracts		-		62.2		(2.6	)		59.6
Other:
U.S. stock/bond mutual funds		16.6		—		—			16.6
U.S. bonds		17.1		—		—			17.1
Global bonds		1.4		—		—			1.4
Interest rate swaps		—		29.0		—			29.0
Total	$	70.0	$	91.3	$	(15.0	)	$	146.3
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	35.7	$	—	$	(35.7	)	$	—
Gas Marketing:
NYMEX/ICE natural gas contracts		30.7		—		(30.7	)		—
Natural gas commodity contracts		—		25.3		(2.6	)		22.7
Total	$	66.4	$	25.3	$	(69.0	)	$	22.7

	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Effects of Netting and Cash Margin Receivables /Payables			Total
As of March 31, 2025
ASSETS
U.S. stock/bond mutual funds	$	24.6	$	—	$	—		$	24.6
NYMEX/ICE natural gas contracts		17.5		—		(17.5	)		—
Total	$	42.1	$	—	$	(17.5	)	$	24.6
LIABILITIES
NYMEX/ICE natural gas contracts	$	4.0	$	—	$	(4.0	)	$	—
As of September 30, 2024
ASSETS
U.S. stock/bond mutual funds	$	24.3	$	—	$	—		$	24.3
NYMEX/ICE natural gas contracts		3.4		—		(3.4	)		—
Total	$	27.7	$	—	$	(3.4	)	$	24.3
LIABILITIES
NYMEX/ICE natural gas contracts	$	13.6	$	—	$	(3.8	)	$	9.8
As of March 31, 2024
ASSETS
U.S. stock/bond mutual funds	$	22.6	$	—	$	—		$	22.6
NYMEX/ICE natural gas contracts		3.7		—		(3.7	)		—
Gasoline and heating oil contracts		—		0.1		(0.1	)		—
Total	$	26.3	$	0.1	$	(3.8	)	$	22.6
LIABILITIES
NYMEX/ICE natural gas contracts	$	35.7	$	—	$	(35.7	)	$	—