Consolidated Statements Of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Statement of Comprehensive Income [Abstract]
Net Income Available for Common Stock	$ 92,620	$ 108,158	$ 403,189	$ 407,879
Other Comprehensive Income (Loss), Before Tax:
Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	65,244	(200,084)	673,381	(678,558)
Reclassification Adjustment for Realized (Gains) Losses on Derivative Financial Instruments in Net Income	(57,692)	298,371	120,590	591,180
Other Post-Retirement Adjustment for Regulatory Proceeding	0	0	0	(7,351)
Other Comprehensive Income (Loss), Before Tax	7,552	98,287	793,971	(94,729)
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	17,885	(54,762)	184,655	(185,717)
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Derivative Financial Instruments in Net Income	(15,813)	81,663	32,967	161,803
Income Tax Expense (Benefit) Related to Other Post-Retirement Adjustment for Regulatory Proceeding	0	0	0	(1,544)
Income Taxes – Net	2,072	26,901	217,622	(25,458)
Other Comprehensive Income (Loss)	5,480	71,386	576,349	(69,271)
Comprehensive Income	$ 98,100	$ 179,544	$ 979,538	$ 338,608