Financial Risk Management Activities - Credit Risk - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Letters of credit – Issued	$ 246	$ 188
Integrated Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	50.00%
Independent E&P Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	14.00%
National Oil Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	2.00%
Storage and Transportation Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	7.00%
Refining and Marketing Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	17.00%
Others
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	10.00%