Financial Risk Management Activities - Credit Risk - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Outstanding letters of credit	$ 188	$ 113
Integrated Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	37.00%
Independent E&P Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	19.00%
National Oil Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	16.00%
Storage and Transportation Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	10.00%
Refining and Marketing Companies
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	7.00%
Others [Member]
Fair Value Concentration Of Risk Financial Statement Captions [Line Items]
Accounts receivable - Trade	11.00%