Details of Selected Consolidated Balance Sheet Captions - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Sep. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Storage plant	$ 589,210	$ 539,972
Transmission plant	4,325,540	3,725,347
Distribution plant	13,511,409	12,085,654
General plant	937,500	868,962
Intangible plant	38,612	38,612
Property, plant and equipment	19,402,271	17,258,547
Construction in progress	835,868	626,551
Total property, plant and equipment and construction in progress	20,238,139	17,885,098
Less: accumulated depreciation and amortization	(2,997,900)	(2,821,128)
Net property, plant and equipment	17,240,239	15,063,970
Plant acquisition adjustments	$ (26,600)	$ (28,500)