Capitalization and Short-Term Borrowings (Summary of Changes in Common Stock Equity) (Details) - USD ($) $ in Thousands		3 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)		85,956,814
Beginning balance		$ 820,223
Balance at Beginning of Period		1,098,900	$ 851,669
Balance at Beginning of Period		(67,750)	(30,123)
Net Income Available for Common Stock		102,660	198,654
Dividends Declared on Common Stock		(36,663)	(35,590)
Other Comprehensive Income (Loss), Net of Tax		$ 39,060	(10,796)
Ending balance (shares)		86,270,957
Ending balance		$ 817,076
Balance at December 31		1,172,334	1,014,733
Balance at End of Period		(28,690)	(40,919)
Paid-in Capital [Member]
Schedule of Capitalization, Equity [Line Items]
Beginning balance		820,223	796,646
Share-Based Payment Expense	[1]	4,917	3,511
Common Stock Issued (Repurchased) Under Stock and Benefit Plans (Value)		(8,064)	191
Ending balance		817,076	800,348
Earnings Reinvested in The Business [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		1,098,900	851,669
Net Income Available for Common Stock		102,660	198,654
Dividends Declared on Common Stock		(36,663)	(35,590)
Cumulative Effect of Adoption of Authoritative Guidance for Financial Assets and Liabilities		7,437
Balance at December 31		1,172,334	1,014,733
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		(67,750)	(30,123)
Other Comprehensive Income (Loss), Net of Tax		39,060	(10,796)
Balance at End of Period		$ (28,690)	$ (40,919)
Common Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)		85,957,000	85,543,000
Beginning balance (value)		$ 85,957	$ 85,543
Common Stock Issued (Repurchased) Under Stock and Benefit Plans (Shares)		314,000	218,000
Common Stock Issued (Repurchased) Under Stock and Benefit Plans (Value)		$ 314	$ 218
Ending balance (shares)		86,271,000	85,761,000
Ending balance (value)		$ 86,271	$ 85,761

[1] Paid in Capital includes compensation costs associated with performance shares and/or restricted stock awards. The expense is included within Net Income Available For Common Stock, net of tax benefits.