Summary of Significant Accounting Policies - Average Depreciation, Depletion and Amortization Rates (Details) - USD ($)		12 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Exploration and Production
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization rate (in dollars per Mcfe of production)	[1]	$ 0.65	$ 0.59	$ 0.56
Pipeline and Storage
Segment Reporting Information [Line Items]
Average depreciation, depletion and amortization rates		2.60%	2.70%	2.60%
Gathering
Segment Reporting Information [Line Items]
Average depreciation, depletion and amortization rates		3.60%	3.60%	3.60%
Utility
Segment Reporting Information [Line Items]
Average depreciation, depletion and amortization rates		2.70%	2.70%	2.70%
All Other and Corporate
Segment Reporting Information [Line Items]
Average depreciation, depletion and amortization rates		2.90%	1.40%	3.40%
Oil and Gas Producing Properties
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization rate (in dollars per Mcfe of production)		$ 0.63	$ 0.57	$ 0.54

[1] Amounts include depletion of oil and gas producing properties as well as depreciation of fixed assets. As disclosed in Note N — Supplementary Information for Oil and Gas Producing Activities, depletion of oil and gas producing properties amounted to $0.63, $0.57 and $0.54 per Mcfe of production in 2023, 2022 and 2021, respectively.