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Decommissioning and Other Asset Retirement Obligations (Details) (USD $)
In Millions, unless otherwise specified
1 Months Ended 3 Months Ended 6 Months Ended
Aug. 31, 2011
Jun. 30, 2011
Jun. 30, 2011
Notes (Details)      
Asset retirement obligations associated with properties sold during the period $ 3.3 $ 72.7 $ 118.7