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, 2025 Bcf MBbls MMcf	Sep. 30, 2024 Bcf MBbls MMcf	Sep. 30, 2023 MMcf MBbls Bcf	Sep. 30, 2022 MBbls MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved undeveloped reserve volume | Bcf		1,316,000,000	1,267,000,000	985,000,000
Marcellus Shale Fields
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved undeveloped reserve volume | Bcf		197,000,000	342,000,000	112,000,000
Marcellus Shale Fields | Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Extensions and Discoveries | Bcf		0	230	163
Production		(209,379)	(235,955)	(190,290)
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		1,119,000,000	925,000,000	873,000,000
Utica Shale | Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Extensions and Discoveries | Bcf		633	372	507
Production		(215,681)	(154,701)	(180,750)
Percentage exceeding total reserve of production in proved developed and undeveloped reserves		15.00%
Appalachian Region | Gas MMcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period		4,751,762	4,535,084	4,170,662
Extensions and Discoveries	[1]	632,536	601,679	670,438
Revisions of Previous Estimates		22,469	7,046	32,379
Production	[2]	(426,357)	(392,047)	(372,271)
Purchases of Minerals in Place				33,876
Proved Developed and Undeveloped Reserves, End of Period		4,980,410	4,751,762	4,535,084
Proved developed reserves volume		3,664,381	3,484,852	3,550,034	3,312,568
Proved undeveloped reserve volume		1,316,029	1,266,910	985,050	858,094
Appalachian Region | Oil Mbbl
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved Developed and Undeveloped Reserves, Beginning of Period | MBbls		193	216	250
Extensions and Discoveries | MBbls		0	0	0
Revisions of Previous Estimates | MBbls		15	8	(4)
Production | MBbls		(28)	(31)	(30)
Purchases of Minerals in Place | MBbls				0
Proved Developed and Undeveloped Reserves, End of Period | MBbls		180	193	216
Proved developed reserves volume | MBbls		180	193	216	250
Proved undeveloped reserve volume | MBbls		0	0	0	0

[1] Extensions and discoveries include 163 Bcf (during 2023), 230 Bcf (during 2024) and 0 Bcf (during 2025), of Marcellus Shale gas (which exceed 15% of total reserves) in the Appalachian region. Extensions and discoveries include 507 Bcf (during 2023), 372 Bcf (during 2024) and 633 Bcf (during 2025), of Utica Shale gas (which exceed 15% of total reserves) in the Appalachian region.

[2] Production includes 190,290 MMcf (during 2023), 235,955 MMcf (during 2024) and 209,379 MMcf (during 2025), from Marcellus Shale fields. Production includes 180,750 MMcf (during 2023), 154,701 MMcf (during 2024) and 215,681 MMcf (during 2025), from Utica Shale fields.