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Disclosures About Fair Value Measurements (Narrative) (Detail)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2017
Mar. 31, 2016
USD ($)
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     54.62   51.58
Management Estimate of Future Natural Gas Price | $ / Mcf     3.04 2.82 3.32
Annual discount rate 10.00%        
Carrying Amount   $ 3,438      
Impairment Expense   $ 1,525