Supplementary Information For Oil And Gas Producing Activities (Narrative) (Details) $ in Millions, ft³ in Billions	12 Months Ended
	Sep. 30, 2022 USD ($) ft³	Sep. 30, 2021 USD ($) ft³	Sep. 30, 2020 USD ($) ft³	Sep. 30, 2019	Sep. 30, 2018
Reserve Quantities [Line Items]
Amount spent for developing proved undeveloped reserves | $	$ 154.3	$ 81.2	$ 219.9
Proved Undeveloped Reserve (Volume)	858	636	551
Percentage of PUD reserves to the total proved reserves	20.60%	16.50%	16.00%
New PUD reserve additions	502	344
PUD Upward Revisions	23	9
PUD conversions to developed reserves	287	188
Proved Undeveloped Reserves, Removed		80
PUD Well Locations Removed	1	8
Increase in Proved undeveloped (PUD) reserves	222	85
Investment made to convert proved undeveloped reserves to developed reserves | $	$ 154.0	$ 81.0
Conversion Of Undeveloped Proved Reserves To Developed Proved Reserves After Revisions	333	198
Conversion of PUD to Developed as a Percentage of PUD Reserves Booked at End of Prior Year	45.00%	34.00%	36.00%	39.00%	51.00%
Arbitrary discount rate	10.00%
Appalachian Region [Member]
Reserve Quantities [Line Items]
Well Locations Developed With Net PUD Reserves	31	18
Well Locations To Be Developed With Net PUD Reserves	65	53
Marcellus Shale Fields [Member]
Reserve Quantities [Line Items]
Proved Undeveloped Reserve (Volume)	355	220	287
PUD conversions to developed reserves	55	82
Proved Undeveloped Reserves, Removed		54
PUD Well Locations Removed		6
Utica Shale [Member]
Reserve Quantities [Line Items]
Proved Undeveloped Reserve (Volume)	503	411	265
PUD conversions to developed reserves	231	106
Proved Undeveloped Reserves, Removed	13	26
PUD Well Locations Removed		2
West Coast Region [Member]
Reserve Quantities [Line Items]
Proved Undeveloped Reserve (Volume)	0	5
PUD conversions to developed reserves	1
Proved Undeveloped Reserves, Removed	3
Well Locations Developed With Net PUD Reserves	6
Well Locations To Be Developed With Net PUD Reserves	17
Total PUD Reserve Additions Estimated In The Next Fiscal Year [Member]
Reserve Quantities [Line Items]
Amount to be spent on developing proved undeveloped reserves | $	$ 308.0