Financial Instruments (Derivatives In Fair Value Hedging Relationships) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2012
Operating Revenues [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain or (Loss) Recognized in the Consolidated Statement of Income	$ 8,021,910
Purchased Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain or (Loss) Recognized in the Consolidated Statement of Income	(1,235,817)
Energy Marketing [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain or (Loss) Recognized in the Consolidated Statement of Income	6,786
Fixed Price Sales Commitments Of Natural Gas [Member] | Energy Marketing [Member] | Operating Revenues [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain or (Loss) Recognized in the Consolidated Statement of Income	8,022
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	(1,261)
Natural Gas Held In Storage [Member] | Energy Marketing [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain or (Loss) Recognized in the Consolidated Statement of Income	$ 25