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Impairments - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Asset Impairment Charges [Abstract]    
Impairment of oil and natural gas properties $ 853 $ 4,976
Effects of Cash Flow Hedges Considered in Calculation Ceiling Limitation, Amount $ 166 $ 195