Summary Of Significant Accounting Policies (Average Depreciation Depletion And Amortization Rates) (Details) - USD ($)		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Depreciation depletion and amortization rate per Mcfe	[1]	$ 0.65	$ 0.87	$ 1.52
Utility [Member]
Segment Reporting Information [Line Items]
Average depreciation, depletion and amortization rates		2.80%	2.70%	2.60%
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Average depreciation, depletion and amortization rates		2.20%	2.40%	2.40%
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Average depreciation, depletion and amortization rates		7.90%	7.90%	6.10%
Gathering [Member]
Segment Reporting Information [Line Items]
Average depreciation, depletion and amortization rates		3.40%	4.00%	4.00%
All Other And Corporate [Member]
Segment Reporting Information [Line Items]
Average depreciation, depletion and amortization rates		1.30%	1.80%	1.40%
Oil And Gas Producing Properties [Member]
Segment Reporting Information [Line Items]
Depreciation depletion and amortization rate per Mcfe		$ 0.63	$ 0.85	$ 1.49

[1] Amounts include depletion of oil and gas producing properties as well as depreciation of fixed assets. As disclosed in Note M — Supplementary Information for Oil and Gas Producing Activities, depletion of oil and gas producing properties amounted to $0.63, $0.85 and $1.49 per Mcfe of production in 2017, 2016 and 2015, respectively.