Financial Risk Management Activities - Credit Risk - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Letters of credit – Issued	$ 284	$ 246
Financial Institutions
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	34.00%
Integrated Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	24.00%
Independent E&P Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	22.00%
National Oil Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	7.00%
Storage and Transportation Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	3.00%
Refining and Marketing 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	5.00%