Oil and Gas Assets (Tables)
9 Months Ended
Sep. 30, 2011
Oil and Gas Assets (Tables) [Abstract] 
Capitalized Costs relating to Oil and Gas Producing Activities Disclosure
            
       September 30, 2011 December 31, 2010
          
            
        (In millions)
  Oil and gas properties:      
   Subject to amortization $ 11,874 $ 10,627
   Not subject to amortization   2,346   1,658
   Gross oil and gas properties   14,220   12,285
   Accumulated depreciation, depletion and amortization   (6,293)   (5,730)
    Net oil and gas properties   7,927   6,555
  Other property and equipment   137   114
   Accumulated depreciation and amortization   (70)   (61)
    Net other property and equipment   67   53
     Total property and equipment, net $ 7,994 $ 6,608
            
Costs incurred by year for oil and gas properties not subject to amortization
                  
    Costs Incurred In   
    2011 2010 2009 2008 and prior  Total
    (In millions)
Acquisition costs $ 370 $ 357 $ 143 $ 464 $ 1,334
Exploration costs   450   78   61   67   656
Development costs   42   32   16   48   138
Fee mineral interests   —   —   —   23   23
Capitalized interest   61   58   51   25   195
 Total oil and gas properties not               
  subject to amortization $ 923 $ 525 $ 271 $ 627 $ 2,346