Financial Risk Management Activities - Gross Notional Volumes of Derivative Contracts Outstanding (Detail) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Foreign Exchange
Derivative [Line Items]
Outstanding gross notional amount	$ 837,000,000	$ 967,000,000
Interest Rate Swaps
Derivative [Line Items]
Outstanding gross notional amount	$ 1,300,000,000	$ 1,300,000,000