Supplementary Information for Exploration and Production Activities - Proved Developed and Undeveloped Oil and Gas Reserve Quantities (Details) Bcf in Thousands		12 Months Ended
		Sep. 30, 2024 MBbls MMcf Bcf	Sep. 30, 2023 MMcf MBbls Bcf	Sep. 30, 2022 MBbls MMcf Bcf	Sep. 30, 2021 MMcf MBbls
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved undeveloped reserve volume | Bcf		1,267,000,000	985,000,000	858,000,000
Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period		4,535,084	4,170,662	3,723,433
Extensions and Discoveries		601,679	670,438	837,510
Revisions of Previous Estimates		7,046	32,379	2,953
Production		(392,047)	(372,271)	(342,911)
Sale of Minerals in Place				(50,323)
Purchases of Minerals in Place			33,876
Proved Developed and Undeveloped Reserves, End of Period		4,751,762	4,535,084	4,170,662
Proved developed reserves volume		3,484,852	3,550,034	3,312,568	3,091,463
Proved undeveloped reserve volume		1,266,910	985,050	858,094	631,970
Oil Mbbl
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period | MBbls		216	250	21,537
Extensions and Discoveries | MBbls				296
Revisions of Previous Estimates | MBbls		8	(4)	787
Production		(31)	(30)	(1,604)
Sale of Minerals in Place | MBbls				(20,766)
Proved Developed and Undeveloped Reserves, End of Period | MBbls		193	216	250
Proved developed reserves volume | MBbls		193	216	250	20,941
Proved undeveloped reserve volume | MBbls		0	0	0	596
Appalachian Region | Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period		4,535,084	4,170,662	3,693,148
Extensions and Discoveries	[1]	601,679	670,438	837,510
Revisions of Previous Estimates		7,046	32,379	2,882
Production	[2]	(392,047)	(372,271)	(341,700)
Sale of Minerals in Place				(21,178)
Purchases of Minerals in Place			33,876
Proved Developed and Undeveloped Reserves, End of Period		4,751,762	4,535,084	4,170,662
Proved developed reserves volume		3,484,852	3,550,034	3,312,568	3,061,178
Proved undeveloped reserve volume		1,266,910	985,050	858,094	631,970
Appalachian Region | Oil Mbbl
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period | MBbls		216	250	11
Extensions and Discoveries | MBbls				0
Revisions of Previous Estimates | MBbls		8	(4)	255
Production		(31)	(30)	(16)
Sale of Minerals in Place | MBbls				0
Proved Developed and Undeveloped Reserves, End of Period | MBbls		193	216	250
Proved developed reserves volume | MBbls		193	216	250	11
Proved undeveloped reserve volume | MBbls		0	0	0	0
West Coast Region | Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period		0	0	30,285
Extensions and Discoveries		0	0	0
Revisions of Previous Estimates		0	0	71
Production		0	0	(1,211)
Sale of Minerals in Place				(29,145)
Purchases of Minerals in Place			0
Proved Developed and Undeveloped Reserves, End of Period		0	0	0
Proved developed reserves volume		0	0	0	30,285
Proved undeveloped reserve volume		0	0	0	0
West Coast Region | Oil Mbbl
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period | MBbls		0	0	21,526
Extensions and Discoveries | MBbls				296
Revisions of Previous Estimates | MBbls		0	0	532
Production		0	0	(1,588)
Sale of Minerals in Place | MBbls				(20,766)
Proved Developed and Undeveloped Reserves, End of Period | MBbls		0	0	0
Proved developed reserves volume | MBbls		0	0	0	20,930
Proved undeveloped reserve volume | MBbls		0	0	0	596
Marcellus Shale Fields
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved undeveloped reserve volume | Bcf		342,000,000	112,000,000	355,000,000
Marcellus Shale Fields | Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Extensions and Discoveries | Bcf		230	163	301
Production		(235,955)	(190,290)	(209,463)
Percentage exceeding total reserve of production in proved developed and undeveloped reserves		15.00%
Utica Shale
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved undeveloped reserve volume | Bcf		925,000,000	873,000,000	503,000,000
Utica Shale | Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Extensions and Discoveries | Bcf		372	507	537
Production		(154,701)	(180,750)	(130,240)
Percentage exceeding total reserve of production in proved developed and undeveloped reserves		15.00%

[1] Extensions and discoveries include 301 Bcf (during 2022), 163 Bcf (during 2023) and 230 Bcf (during 2024), of Marcellus Shale gas (which exceed 15% of total reserves) in the Appalachian region. Extensions and discoveries include 537 Bcf (during 2022), 507 Bcf (during 2023) and 372 Bcf (during 2024), of Utica Shale gas (which exceed 15% of total reserves) in the Appalachian region.

[2] Production includes 209,463 MMcf (during 2022), 190,290 MMcf (during 2023) and 235,955 MMcf (during 2024), from Marcellus Shale fields. Production includes 130,240 MMcf (during 2022), 180,750 MMcf (during 2023) and 154,701 MMcf (during 2024), from Utica Shale fields.