Fair Value Measurements (Tables)

3 Months Ended

Dec. 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 December 31, 2025
ASSETS
Gas Utility:
U.S. stock/bond mutual funds	$	27.2	$	—	$	—		$	27.2
NYMEX/ICE natural gas contracts		1.6		—		(1.6	)		—
Gas Marketing:
NYMEX/ICE natural gas contracts		8.7		—		(8.7	)		—
Natural gas commodity contracts		—		39.5		(1.8	)		37.7
Other:
U.S. stock/bond mutual funds		23.6		—		—			23.6
U.S. bonds		22.9		—		—			22.9
Global bonds		2.5		—		—			2.5
Interest rate swaps		—		14.0		—			14.0
Total	$	86.5	$	53.5	$	(12.1	)	$	127.9
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	17.8	$	—	$	(3.0	)	$	14.8
Gas Marketing:
NYMEX/ICE natural gas contracts		17.5		—		(17.5	)		—
Natural gas commodity contracts		—		19.9		(1.8	)		18.1
Total	$	35.3	$	19.9	$	(22.3	)	$	32.9

	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, 2025
ASSETS
Gas Utility:
U.S. stock/bond mutual funds	$	27.5	$	—	$	—		$	27.5
NYMEX/ICE natural gas contracts		2.9		—		(2.9	)		—
Gas Marketing:
NYMEX/ICE natural gas contracts		11.4		—		(11.4	)		—
Natural gas commodity contracts		—		44.8		(2.7	)		42.1
Other:
U.S. stock/bond mutual funds		27.0		—		—			27.0
U.S. bonds		23.5		—		—			23.5
Global bonds		1.5		—		—			1.5
Interest rate swaps		—		10.0		—			10.0
Total	$	93.8	$	54.8	$	(17.0	)	$	131.6
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	25.9	$	—	$	(1.3	)	$	24.6
Gas Marketing:
NYMEX/ICE natural gas contracts		19.0		—		(19.0	)		—
Natural gas commodity contracts		—		16.7		(2.7	)		14.0
Total	$	44.9	$	16.7	$	(23.0	)	$	38.6
As of December 31, 2024
ASSETS
Gas Utility:
U.S. stock/bond mutual funds	$	24.7	$	—	$	—		$	24.7
NYMEX/ICE natural gas contracts		5.9		—		(5.9	)		—
Gas Marketing:
NYMEX/ICE natural gas contracts		8.8		—		(8.8	)		—
Natural gas commodity contracts		—		44.1		(1.2	)		42.9
Other:
U.S. stock/bond mutual funds		20.8		—		—			20.8
U.S. bonds		15.6		—		—			15.6
Global bonds		6.0		—		—			6.0
Interest rate swaps		—		16.1		—			16.1
Total	$	81.8	$	60.2	$	(15.9	)	$	126.1
LIABILITIES
Gas Utility:
NYMEX/ICE natural gas contracts	$	6.8	$	—	$	(6.8	)	$	—
Gas Marketing:
NYMEX/ICE natural gas contracts		15.1		—		(15.1	)		—
Natural gas commodity contracts		—		29.1		(1.2	)		27.9
Total	$	21.9	$	29.1	$	(23.1	)	$	27.9

	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Effects of Netting and Cash Margin Receivables /Payables			Total
As of December 31, 2025
ASSETS
U.S. stock/bond mutual funds	$	27.2	$	—	$	—		$	27.2
NYMEX/ICE natural gas contracts		1.6		—		(1.6	)		—
Total	$	28.8	$	—	$	(1.6	)	$	27.2
LIABILITIES
NYMEX/ICE natural gas contracts	$	17.8	$	—	$	(3.0	)	$	14.8
As of September 30, 2025
ASSETS
U.S. stock/bond mutual funds	$	27.5	$	—	$	—		$	27.5
NYMEX/ICE natural gas contracts		2.9		—		(2.9	)		—
Total	$	30.4	$	—	$	(2.9	)	$	27.5
LIABILITIES
NYMEX/ICE natural gas contracts	$	25.9	$	—	$	(1.3	)	$	24.6
As of December 31, 2024
ASSETS
U.S. stock/bond mutual funds	$	24.7	$	—	$	—		$	24.7
NYMEX/ICE natural gas contracts		5.9		—		(5.9	)		—
Total	$	30.6	$	—	$	(5.9	)	$	24.7
LIABILITIES
NYMEX/ICE natural gas contracts	$	6.8	$	—	$	(6.8	)	$	—