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Basis of Presentation and Significant Accounting Policies Basis of Presentation and Significant Accounting Policies - Capitalized Costs of Unproved Properties Table (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Accounting Policies [Abstract]        
Acquisition Costs, Period Cost $ 109 $ 99 $ 507 $ 2,956
Acquisition Costs, Cumulative 3,671      
Exploration Costs, Period Cost 24 36 13 34
Exploration Costs, Cumulative 107      
Capitalized Interest of Unproved Properties Excluded from Amortization, Period Cost 194 201 184 445
Capitalized Interest Of Unproved Properties Excluded From Amortization Cumulative 1,024      
Capitalized Costs of Unproved Properties Excluded from Amortization, Period Cost 327 336 $ 704 $ 3,435
Unproved properties $ 4,802 $ 6,798