Capitalization (Narrative) (Details) (USD $)	3 Months Ended			3 Months Ended		0 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2011	Sep. 30, 2011 6.70% Medium-Term Notes November 2011 [Member]	Dec. 31, 2011 6.70% Medium-Term Notes November 2011 [Member]	Dec. 01, 2011 4.9% Notes Due In December 2021 [Member]
Schedule of Capitalization [Line Items]
Common stock shares issued due to stock option exercises	272,292
Issue shares of common stock for the Direct Stock Purchase and Dividend Reinvestment Plan	31,474
Shares issued for restricted stock	41,525
Common stock issued	4,050
Shares tendered	123,533
Current Portion of Long-Term Debt	$ 0		$ 150,000,000		$ 150,000,000
Percentage of principal amount						101.00%
Carrying Amount	1,399,000,000		1,049,000,000
Long-term debt, face value						500,000,000
Long-term debt maturity date				Nov. 01, 2011		Dec. 01, 2021
Long-term debt, interest rate					6.70%	4.90%
Net Proceeds from Issuance of Long-Term Debt	$ 496,085,000	$ 0				$ 496,100,000