Financial Instruments (Derivatives In Fair Value Hedging Relationships) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2011
Operating Revenues [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain or (Loss) Recognized in the Consolidated Statement of Income	$ (625,482)
Purchased Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain or (Loss) Recognized in the Consolidated Statement of Income	1,076,443
Energy Marketing [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain or (Loss) Recognized in the Consolidated Statement of Income	451
Fixed Price Sales Commitments Of Natural Gas [Member] | Energy Marketing [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain or (Loss) Recognized in the Consolidated Statement of Income	(625)
Fixed Price Purchase Commitments Of Natural Gas [Member] | Energy Marketing [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain or (Loss) Recognized in the Consolidated Statement of Income	$ 1,076