Supplementary Information for Oil and Gas Producing Activities - Narrative (Details) $ in Millions, Bcf in Billions	12 Months Ended
	Sep. 30, 2023 USD ($) pUDLocation Bcf	Sep. 30, 2022 USD ($) pUDLocation Bcf	Sep. 30, 2021 USD ($) Bcf	Sep. 30, 2020	Sep. 30, 2019
Reserve Quantities [Line Items]
Amount spent for developing proved undeveloped reserves | $	$ 342.0	$ 154.3	$ 81.2
Proved undeveloped reserve volume (in Bcfe)	985	858	636
Percentage of PUD reserves to the total proved reserves	21.70%	20.60%	16.50%
Increase in PUD reserves (in Bcfe)	127	222
New PUD reserve additions (in Bcfe)	554	502
PUD reserves added back (in Bcfe)	14
Number of PUD wells added back | pUDLocation	1
PUD upward revisions (in Bcfe)	23	23
PUD conversions to developed reserves (in Bcfe)	402	287
Proved undeveloped reserves removed (in Bcfe)	62	13
Number of PUD well locations removed | pUDLocation	7	1
Investment made to convert proved undeveloped reserves to developed reserves | $	$ 342.0	$ 154.0
Conversion of undeveloped proved reserves to developed proved reserves after revisions (in Bcfe)	440	333
Conversion of PUD to developed to PUD reserves booked at end of prior year (as a percent)	47.00%	45.00%	34.00%	36.00%	39.00%
Arbitrary discount rate (as a percent)	10.00%
Total PUD Reserve Additions Estimated in the Next Fiscal Year
Reserve Quantities [Line Items]
Amount to be spent on developing proved undeveloped reserves | $	$ 315.0
Utica Shale
Reserve Quantities [Line Items]
Proved undeveloped reserve volume (in Bcfe)	873	503	411
PUD conversions to developed reserves (in Bcfe)	127	231
Marcellus Shale Fields
Reserve Quantities [Line Items]
Proved undeveloped reserve volume (in Bcfe)	112	355	220
PUD conversions to developed reserves (in Bcfe)	275	55
West Coast Region
Reserve Quantities [Line Items]
Proved undeveloped reserve volume (in Bcfe)		0	5
PUD conversions to developed reserves (in Bcfe)		1
Proved undeveloped reserves removed (in Bcfe)		3
Number of well locations developed with net PUD reserves | pUDLocation		6
Number of well locations to be developed with net PUD reserves | pUDLocation		17
Appalachian Region
Reserve Quantities [Line Items]
Number of well locations developed with net PUD reserves | pUDLocation	39	31
Number of well locations to be developed with net PUD reserves | pUDLocation	77	65