Capitalization (Narrative) (Details) (USD $)	9 Months Ended						0 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Direct Stock Purchase And Dividend Reinvestment Plan [Member]	Jun. 30, 2012 5.25% Notes Due in March 2013	Jun. 30, 2012 6.70% Medium-Term Notes November 2011 [Member]	Sep. 30, 2011 6.70% Medium-Term Notes November 2011 [Member]	Dec. 01, 2011 4.9% Notes Due In December 2021 [Member]
Debt Instrument [Line Items]
Common stock shares issued due to stock option exercises	442,894
Issue shares of common stock for the Direct Stock Purchase and Dividend Reinvestment Plan			118,523
Shares issued for restricted stock	41,525
Common stock issued	11,705
Shares tendered	156,961
Current portion of long-term debt				$ 250,000,000	$ 150,000,000	$ 150,000,000
Percentage of principal amount							101.00%
Long-term debt, face value							500,000,000
Long-term debt, interest rate				5.25%	6.70%	6.70%	4.90%
Net proceeds from issuance of long-term debt	$ 496,085,000	$ 0					$ 496,100,000