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Inventories (Details Textual) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2011
Year
bcf
Sep. 30, 2010
Year
bcf
Inventories (Textual) [Abstract]  
Volume of gas storage inventories released under SCAAs with non-affiliates (In Cubic Feet)3,900,000,0008,000,000,000
Carrying value of gas storage inventories released under SCAAs with non-affiliates$ 19.0$ 41.9