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SUPPLEMENTARY OIL AND GAS INFORMATION (UNAUDITED) SUPPLEMENTARY OIL AND GAS INFORMATION (UNAUDITED) (Schedule of Changes in the Standardized Measure) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]      
Balance at beginning of year $ 1,392 $ 6,421 $ 9,417
Sales, net of production expenses (831) (928) (3,062)
Net changes in sales and transfer prices, net of production expenses (341) (7,766) (2,875)
Extensions, discoveries and improved recoveries 0 45 194
Changes in estimated future development costs, including timing and other 146 1,287 (498)
Previously estimated development costs incurred during the year 295 985 982
Sales of reserves in-place (1,049) 0 (1,323)
Other purchases of reserves in-place 0 0 487
Revisions of quantity estimates 12 (1,170) 399
Accretion of discount 139 797 1,195
Net change in income taxes 0 1,721 1,505
Total changes (1,629) (5,029) (2,996)
Balance at end of year $ (237) $ 1,392 $ 6,421