Consolidated Statements Of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Statement of Comprehensive Income [Abstract]
Net Income Available for Common Stock	$ 140,880	$ 167,328	$ 310,570	$ 299,720
Other Comprehensive Income (Loss), Before Tax:
Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	310,544	(641,606)	608,137	(478,474)
Reclassification Adjustment for Realized (Gains) Losses on Derivative Financial Instruments in Net Income	18,940	130,221	178,281	292,809
Other Post-Retirement Adjustment for Regulatory Proceeding	0	(7,351)	0	(7,351)
Other Comprehensive Income (Loss), Before Tax	329,484	(518,736)	786,418	(193,016)
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	85,394	(175,605)	166,770	(130,956)
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Derivative Financial Instruments in Net Income	5,208	35,641	48,779	80,141
Income Tax Expense (Benefit) Related to Other Post-Retirement Adjustment for Regulatory Proceeding	0	(1,544)	0	(1,544)
Income Taxes – Net	90,602	(141,508)	215,549	(52,359)
Other Comprehensive Income (Loss)	238,882	(377,228)	570,869	(140,657)
Comprehensive Income (Loss)	$ 379,762	$ (209,900)	$ 881,439	$ 159,063