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Derivatives (Details)
Jun. 30, 2012
billioncubicfeet
Dec. 31, 2011
billioncubicfeet
Dec. 31, 2011
Crude Oil - Collars 2011 (in barrels)
bbl
Mar. 30, 2012
Natural Gas - Swaps January 2012- March 2012 (in million cubic feet)
millionscubicfeet
Cash-Flow Hedges        
Daily volume     12,000 50
Average Floor (in dollars per barrel)     32.92  
Average Cap (in dollars per barrel)     46.35  
Average Price (in dollars per thousands of cubic feet)       6.07
Natural gas held in storage (in billion cubic feet) 17 25    
Forecast sale of natural gas from storage designated as cash-flow hedges (in billion cubic feet) 23 35