Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net Income (Loss) Available for Common Stock	$ 363,647	$ (123,772)	$ 304,290
Other Comprehensive Income (Loss), Before Tax:
Increase (Decrease) in the Funded Status of the Pension and Other Post-Retirement Benefit Plans	17,862	(19,214)	(44,089)
Reclassification Adjustment for Amortization of Prior Year Funded Status of the Pension and Other Post-Retirement Benefit Plans	16,229	15,361	7,332
Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	(665,371)	9,862
Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period			79,301
Reclassification Adjustment for Realized (Gains) Losses on Derivative Financial Instruments in Net Income	83,711	(93,295)
Reclassification Adjustment for Realized (Gains) Losses on Derivative Financial Instruments in Net Income			5,464
Cumulative Effect of Adoption of Authoritative Guidance for Hedging	0	1,313	0
Reclassification Adjustment for the Cumulative Effect of Adoption of Authoritative Guidance for Financial Assets and Liabilities to Earnings Reinvested in the Business	0	0	(11,738)
Other Comprehensive Income (Loss), Before Tax	(547,569)	(85,973)	36,270
Income Tax Expense (Benefit) Related to the Increase (Decrease) in the Funded Status of the Pension and Other Post-Retirement Benefit Plans	4,072	(4,357)	(10,473)
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	3,762	3,566	1,698
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	(179,028)	2,578
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period			20,619
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Derivative Financial Instruments in Net Income	22,465	(25,521)
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Derivative Financial Instruments in Net Income			2,726
Income Tax Benefit (Expense) on Cumulative Effect of Adoption of Authoritative Guidance for Hedging	0	363	0
Reclassification Adjustment for Income Tax Benefit (Expense) on the Cumulative Effect of Adoption of Authoritative Guidance for Financial Assets and Liabilities to Earnings Reinvested in the Business	0	0	(4,301)
Reclassification Adjustment for Stranded Tax Effects Related to the 2017 Tax Reform Act to Earnings Reinvested in the Business	0	0	10,406
Income Taxes - Net	(148,729)	(23,371)	20,675
Other Comprehensive Income (Loss)	(398,840)	(62,602)	15,595
Comprehensive Income (Loss)	$ (35,193)	$ (186,374)	$ 319,885