Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net Income (Loss) Available for Common Stock	$ 283,482	$ (290,958)	$ (379,427)
Other Comprehensive Income (Loss), Before Tax:
Increase (Decrease) in the Funded Status of the Pension and Other Post-Retirement Benefit Plans	15,661	(21,378)	(31,538)
Reclassification Adjustment for Amortization of Prior Year Funded Status of the Pension and Other Post-Retirement Benefit Plans	13,433	10,068	9,217
Unrealized Gain (Loss) on Securities Available for Sale Arising During the Period	4,008	1,524	(3,234)
Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	5,347	60,493	381,018
Reclassification Adjustment for Realized (Gains) Losses on Securities Available for Sale in Net Income	(1,575)	(1,374)	(591)
Reclassification Adjustment for Realized (Gains) Losses on Derivative Financial Instruments in Net Income	(81,605)	(220,919)	(184,953)
Other Comprehensive Income (Loss), Before Tax	(44,731)	(171,586)	169,919
Income Tax Expense (Benefit) Related to the Increase (Decrease) in the Funded Status of the Pension and Other Post-Retirement Benefit Plans	6,175	(8,351)	(11,922)
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	4,929	3,723	3,375
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Securities Available for Sale Arising During the Period	1,505	592	(1,195)
Income Tax Expense (Benefit) Related to Unrealized Gain (Loss) on Derivative Financial Instruments Arising During the Period	2,009	18,648	160,872
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Securities Available for Sale in Net Income	(580)	(527)	(217)
Reclassification Adjustment for Income Tax Benefit (Expense) on Realized Losses (Gains) from Derivative Financial Instruments in Net Income	(34,286)	(86,659)	(78,345)
Income Taxes - Net	(20,248)	(72,574)	72,568
Other Comprehensive Income (Loss)	(24,483)	(99,012)	97,351
Comprehensive Income (Loss)	$ 258,999	$ (389,970)	$ (282,076)