Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income (Loss) Available for Common Stock	$ 566,021	$ 363,647	$ (123,772)
Other Comprehensive Income (Loss), Before Tax:
Increase (Decrease) in the Funded Status of the Pension and Other Post-Retirement Benefit Plans	9,561	17,862	(19,214)
Reclassification Adjustment for Amortization of Prior Year Funded Status of the Pension and Other Post-Retirement Benefit Plans	11,054	16,229	15,361
Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	(1,050,831)	(665,371)	9,862
Reclassification Adjustment for Realized (Gains) Losses on Derivative Financial Instruments in Net Income	882,581	83,711	(93,295)
Cumulative Effect of Adoption of Authoritative Guidance for Hedging	0	0	1,313
Other Post-Retirement Adjustment for Regulatory Proceeding	(7,351)	0	0
Other Comprehensive Income (Loss), Before Tax	(154,986)	(547,569)	(85,973)
Income Tax Expense (Benefit) Related to the Increase (Decrease) in the Funded Status of the Pension and Other Post-Retirement Benefit Plans	2,169	4,072	(4,357)
Reclassification Adjustment for Income Tax Benefit Related to the Amortization of the Prior Year Funded Status of the Pension and Other Post-Retirement Benefit Plans	2,574	3,762	3,566
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	(287,608)	(179,028)	2,578
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Derivative Financial Instruments in Net Income	241,559	22,465	(25,521)
Income Tax Benefit (Expense) on Cumulative Effect of Adoption of Authoritative Guidance for Hedging	0	0	363
Income Tax Expense (Benefit) Related to Other Post-Retirement Adjustment for Regulatory Proceeding	(1,544)	0	0
Income Taxes - Net	(42,850)	(148,729)	(23,371)
Other Comprehensive Income (Loss)	(112,136)	(398,840)	(62,602)
Comprehensive Income (Loss)	$ 453,885	$ (35,193)	$ (186,374)