Annual report pursuant to Section 13 and 15(d)

Supplemental Oil and Natural Gas Reserve Data (unaudited) (Proved Undeveloped Reserves) (Details)

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Supplemental Oil and Natural Gas Reserve Data (unaudited) (Proved Undeveloped Reserves) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Boe
Dec. 31, 2012
Boe
Dec. 31, 2011
Boe
Dec. 31, 2010
Boe
Reserve Quantities [Line Items]        
Proved Developed and Proved Undeveloped Reserves (BOE), Net 14,857,000 14,072,000    
Proved Developed and Proved Undeveloped Reserves (BOE), Percentage Change Between Periods 6.00%      
Proved Undeveloped Reserves (BOE), Percentage Change Between Periods 1.00% 18.00%    
Proved Undeveloped Reserves (Energy) 7,387,000 7,337,000 8,925,000 7,019,000
Proved Developed And Proved Undeveloped Reserves Extensions Discoveries And Additions 5,168,000 2,344,000    
Proved Developed And Proved Undeveloped Reserves Transfers of Proved Developed Production Reserves from Development Program (3,724,000) 557,000    
Proved Developed And Proved Undeveloped Reserves Sales Of Minerals In Place (1,297,000) (1,148,000)    
Proved Developed And Proved Undeveloped Reserves Sales Of Minerals In Place, Percentage 18.00%      
Proved Developed And Proved Undeveloped Reserves Revisions Of Previous Estimates Increase (Decrease)   2,227,000    
Proved Undeveloped Reserves Conversion to Proved Developed Reserves, Percentage Transferred 51.00% 6.00%    
Proved Undeveloped Reserves Conversion to Proved Developed Reserves Total Cost   $ 19    
Permian Basin [Member]
       
Reserve Quantities [Line Items]        
Exploratory Wells Drilled, Net Productive 26      
Medusa fields in the Gulf of Mexico [Member]
       
Reserve Quantities [Line Items]        
Proved Undeveloped Reserves (Energy)   1,297,000