Asset Impairments and Dispositions (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	3 Months Ended				9 Months Ended
	Sep. 30, 2011 Impaired Assets Held And Used [Member]	Sep. 30, 2010 Impaired Assets To Be Disposed Of By Sale [Member]	Jun. 30, 2010 Impaired Assets To Be Disposed Of By Sale [Member]	Sep. 30, 2011 Dispositions [Member]	Sep. 30, 2010 Dispositions [Member]	Sep. 30, 2011 Dispositions [Member]	Sep. 30, 2010 Dispositions [Member]
Schedule Of Impaired Assets [Line Items]
Estimated fair value of assets	$ 6.4	$ 8.2
Book value of materials and supplies after impairment	26.2
Book Value Before Impairment		11.5
Amount of Impairment Loss	28.6	3.3	2.2
Volume of gas sold (in Bcf)				3.1	3.3	4.5
Book value of additional gas available for sale				6.9	7.5	10.3
Gains Losses On Sale Of Other Assets				$ 6.0	$ 12.1	$ 9.2	$ 12.1