Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Net Income Available for Common Stock	$ 518,504	$ 77,513	$ 476,866
Other Comprehensive Income (Loss), Before Tax:
Increase (Decrease) in the Funded Status of the Pension and Other Post-Retirement Benefit Plans	(14,593)	(17,511)	(9,660)
Reclassification Adjustment for Amortization of Prior Year Funded Status of the Pension and Other Post-Retirement Benefit Plans	4,252	2,507	1,674
Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	(3,166)	286,894	708,206
Reclassification Adjustment for Realized (Gains) Losses on Derivative Financial Instruments in Net Income	(45,891)	(216,655)	88,656
Other Comprehensive Income (Loss), Before Tax	(59,398)	55,235	788,876
Income Tax Expense (Benefit) Related to the Increase (Decrease) in the Funded Status of the Pension and Other Post-Retirement Benefit Plans	(3,445)	(3,996)	(2,284)
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	1,001	584	411
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	(858)	81,197	214,270
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Derivative Financial Instruments in Net Income	(12,350)	(62,134)	5,806
Income Taxes — Net	(15,652)	15,651	218,203
Other Comprehensive Income (Loss)	(43,746)	39,584	570,673
Comprehensive Income	$ 474,758	$ 117,097	$ 1,047,539