Supplementary Information for Exploration and Production Activities - Narrative (Details) $ in Millions, Bcf in Billions	12 Months Ended
	Sep. 30, 2025 USD ($) pUDLocation Bcf	Sep. 30, 2024 USD ($) pUDLocation Bcf	Sep. 30, 2023 USD ($) Bcf	Sep. 30, 2022	Sep. 30, 2021
Reserve Quantities [Line Items]
Amount spent for developing proved undeveloped reserves | $	$ 246.3	$ 305.6	$ 342.0
Proved undeveloped reserve volume (in Bcfe)	1,316	1,267	985
Percentage of PUD reserves to the total proved reserves	26.40%	26.70%	21.70%
Increase in PUD reserves (in Bcfe)	49	282
New PUD reserve additions (in Bcfe)	473	602
PUD upward revisions (in Bcfe)		76
PUD conversions to developed reserves (in Bcfe)	399	291
Proved undeveloped reserves removed (in Bcfe)	18	105
Number of PUD well locations removed | pUDLocation	1	9
Adjustments to remaining PUD reserves (in Bcfe)	7
Investment made to convert proved undeveloped reserves to developed reserves | $	$ 246.0	$ 306.0
Conversion of undeveloped proved reserves to developed proved reserves after revisions (in Bcfe)	415	374
Conversion of PUD to developed to PUD reserves booked at end of prior year (as a percent)	31.00%	30.00%	47.00%	45.00%	34.00%
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 | $	$ 295.0
Utica Shale
Reserve Quantities [Line Items]
Proved undeveloped reserve volume (in Bcfe)	1,119	925	873
PUD conversions to developed reserves (in Bcfe)	254
Marcellus Shale Fields
Reserve Quantities [Line Items]
Proved undeveloped reserve volume (in Bcfe)	197	342	112
PUD conversions to developed reserves (in Bcfe)	145
Appalachian Region
Reserve Quantities [Line Items]
Number of well locations developed with net PUD reserves | pUDLocation	27	20
Number of well locations to be developed with net PUD reserves | pUDLocation	73	73