Capitalization and Short-Term Borrowings (Summary of Changes in Common Stock Equity) (Details) - USD ($) $ in Thousands		3 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)		86,315,287
Beginning balance		$ 832,264
Balance at Beginning of Period		1,272,601	$ 1,098,900
Balance at Beginning of Period		(52,155)	(67,750)
Net Income Available for Common Stock		86,591	102,660
Dividends Declared on Common Stock		(37,650)	(36,663)
Other Comprehensive Income (Loss), Net of Tax		$ (3,995)	39,060
Ending balance (shares)		86,551,528
Ending balance		$ 831,146
Balance at December 31		1,320,592	1,172,334
Balance at End of Period		(56,150)	(28,690)
Paid-in Capital [Member]
Schedule of Capitalization, Equity [Line Items]
Beginning balance		832,264	820,223
Share-Based Payment Expense	[1]	2,828	4,917
Common Stock Repurchased under Stock and Benefit Plans		(3,946)	(8,064)
Ending balance		831,146	817,076
Earnings Reinvested in The Business [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		1,272,601	1,098,900
Net Income Available for Common Stock		86,591	102,660
Dividends Declared on Common Stock		(37,650)	(36,663)
Balance at December 31		1,320,592	1,172,334
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		(52,155)	(67,750)
Other Comprehensive Income (Loss), Net of Tax		(3,995)	39,060
Balance at End of Period		$ (56,150)	$ (28,690)
Common Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)		86,315,000	85,957,000
Beginning balance (value)		$ 86,315	$ 85,957
Common Stock Issued Under Stock and Benefit Plans (Shares)		237,000	314,000
Common Stock Issued Under Stock and Benefit Plans (Value)		$ 237	$ 314
Ending balance (shares)		86,552,000	86,271,000
Ending balance (value)		$ 86,552	$ 86,271
Guidance for Hedging [Member]
Schedule of Capitalization, Equity [Line Items]
Cumulative Effect of Adoption of Authoritative Guidance		(1,000)
Guidance for Hedging [Member] | Earnings Reinvested in The Business [Member]
Schedule of Capitalization, Equity [Line Items]
Cumulative Effect of Adoption of Authoritative Guidance		$ (950)
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member]
Schedule of Capitalization, Equity [Line Items]
Cumulative Effect of Adoption of Authoritative Guidance			7,400
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member] | Earnings Reinvested in The Business [Member]
Schedule of Capitalization, Equity [Line Items]
Cumulative Effect of Adoption of Authoritative Guidance			$ 7,437

[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.