Supplementary Information For Oil And Gas Producing Activities (Proved Developed And Undeveloped Oil And Gas Reserve Quantities) (Details) ft³ in Billions		12 Months Ended
		Sep. 30, 2021 MMcf MBbls ft³	Sep. 30, 2020 Bcf MBbls MMcf ft³	Sep. 30, 2019 MBbls MMcf ft³	Sep. 30, 2018 MBbls MMcf
Reserve Quantities [Line Items]
Purchases of Minerals in Place | Bcf			684,141
Proved Undeveloped Reserve (Volume) | ft³		636	551	1,018
Natural Gas (Mmcf) [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves		3,325,085	2,949,519	2,357,342
Extensions and Discoveries		689,395	7,246	686,549
Revisions of Previous Estimates		22,973	(88,419)	103,508
Production Volume		(314,020)	(227,402)	(197,880)
Purchases of Minerals in Place			684,141
Proved Developed and Undeveloped Reserves		3,723,433	3,325,085	2,949,519
Proved Developed Reserves (Volume)		3,091,463	2,773,823	1,934,795	1,606,532
Proved Undeveloped Reserve (Volume)		631,970	551,262	1,014,724	750,810
Oil Mbbl [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves | MBbls		22,100	24,873	27,663
Extensions and Discoveries | MBbls		1,041	288	787
Revisions of Previous Estimates | MBbls		631	(713)	(1,254)
Production Volume		(2,235)	(2,348)	(2,323)
Proved Developed and Undeveloped Reserves | MBbls		21,537	22,100	24,873
Proved Developed Reserves (Volume) | MBbls		20,941	22,100	24,259	26,703
Proved Undeveloped Reserve (Volume) | MBbls		596	0	614	960
West Coast Region [Member] | Natural Gas (Mmcf) [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves		28,972	33,633	36,840
Extensions and Discoveries		0	0	0
Revisions of Previous Estimates		3,033	(2,772)	(1,233)
Production Volume		(1,720)	(1,889)	(1,974)
Purchases of Minerals in Place			0
Proved Developed and Undeveloped Reserves		30,285	28,972	33,633
Proved Developed Reserves (Volume)		30,285	28,972	33,633	36,840
Proved Undeveloped Reserve (Volume)		0	0	0	0
West Coast Region [Member] | Oil Mbbl [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves | MBbls		22,088	24,860	27,649
Extensions and Discoveries | MBbls		1,041	288	787
Revisions of Previous Estimates | MBbls		630	(715)	(1,256)
Production Volume		(2,233)	(2,345)	(2,320)
Proved Developed and Undeveloped Reserves | MBbls		21,526	22,088	24,860
Proved Developed Reserves (Volume) | MBbls		20,930	22,088	24,246	26,689
Proved Undeveloped Reserve (Volume) | MBbls		596	0	614	960
Appalachian Region [Member] | Natural Gas (Mmcf) [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves		3,296,113	2,915,886	2,320,502
Extensions and Discoveries	[1]	689,395	7,246	686,549
Revisions of Previous Estimates		19,940	(85,647)	104,741
Production Volume	[2]	(312,300)	(225,513)	(195,906)
Purchases of Minerals in Place			684,141
Proved Developed and Undeveloped Reserves		3,693,148	3,296,113	2,915,886
Proved Developed Reserves (Volume)		3,061,178	2,744,851	1,901,162	1,569,692
Proved Undeveloped Reserve (Volume)		631,970	551,262	1,014,724	750,810
Appalachian Region [Member] | Oil Mbbl [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves | MBbls		12	13	14
Extensions and Discoveries | MBbls		0	0	0
Revisions of Previous Estimates | MBbls		1	2	2
Production Volume		(2)	(3)	(3)
Proved Developed and Undeveloped Reserves | MBbls		11	12	13
Proved Developed Reserves (Volume) | MBbls		11	12	13	14
Proved Undeveloped Reserve (Volume) | MBbls		0	0	0	0
Marcellus Shale Fields [Member]
Reserve Quantities [Line Items]
Proved Undeveloped Reserve (Volume) | ft³		220	287	383
Marcellus Shale Fields [Member] | Natural Gas (Mmcf) [Member]
Reserve Quantities [Line Items]
Extensions and Discoveries		180,000	7,000	175,000
Production Volume		(218,016)	(169,453)	(163,015)
Percentage exceeding total reserve of production in proved developed and undeveloped reserves		15.00%
Utica Shale [Member]
Reserve Quantities [Line Items]
Proved Undeveloped Reserve (Volume) | ft³		411	265	632
Utica Shale [Member] | Natural Gas (Mmcf) [Member]
Reserve Quantities [Line Items]
Extensions and Discoveries		497,000	0	512,000
Production Volume		(93,253)	(55,392)	(32,095)
Percentage exceeding total reserve of production in proved developed and undeveloped reserves		15.00%

[1] Extensions and discoveries include 175 Bcf (during 2019), 7 Bcf (during 2020) and 180 Bcf (during 2021), of Marcellus Shale gas (which exceed 15% of total reserves) in the Appalachian region. Extensions and discoveries include 512 Bcf (during 2019), 0 Bcf (during 2020) and 497 Bcf (during 2021), of Utica Shale gas (which exceed 15% of total reserves) in the Appalachian region.

[2] Production includes 163,015 MMcf (during 2019), 169,453 MMcf (during 2020) and 218,016 MMcf (during 2021), from Marcellus Shale fields. Production includes 32,095 MMcf (during 2019), 55,392 MMcf (during 2020) and 93,253 MMcf (during 2021), from Utica Shale fields.