Financial Risk Management Activities - Credit Risk - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Outstanding amount of letters of credit	$ 269	$ 272
Integrated Companies
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Accounts receivable - Trade	39.00%
Independent E&P Companies
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Accounts receivable - Trade	39.00%
Refining and Marketing Companies
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Accounts receivable - Trade	8.00%
National Oil Companies
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Accounts receivable - Trade	5.00%
Storage and Transportation Companies
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Accounts receivable - Trade	5.00%
Others
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Accounts receivable - Trade	4.00%