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Suspended Wells - Summary of Net Changes in Suspended Exploratory Well Costs (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]      
Beginning balance $ 1,013 $ 908 $ 660
Additions pending the determination of proved reserves 96 216 342
Reclassifications to proved properties (72) (106) (39)
Sales of suspended well investment   (4) (21)
Charged to dry hole expense   (1) (34)
Ending balance $ 1,037 $ 1,013 $ 908