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Disclosures About Fair Value Measurements (Narrative) (Detail)
$ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Mar. 31, 2016
USD ($)
Jun. 30, 2017
Dec. 31, 2024
$ / bbl
$ / Mcf
Dec. 31, 2020
$ / Mcf
Dec. 31, 2017
$ / bbl
$ / Mcf
Disclosure Fair Value Narrative [Abstract]          
Management Estimate of Future Oil Price | $ / bbl     53.68   45.26
Management Estimate of Future Natural Gas Price | $ / Mcf     3.03 2.83 3.16
Annual discount rate   10.00%      
Carrying Amount $ 3,438        
Impairment Expense $ 1,525