Risk Management and Hedging Activities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Accumulated other comprehensive loss	$ (8)	$ (8)
Common unitholders, units issued	114,742,948	114,740,148
Commodity Derivatives [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	$ (1)
Cash Flow Hedge [Member]
Derivative [Line Items]
Accumulated other comprehensive loss	(8)	$ (8)	$ (8)	$ (9)
Cash Flow Hedge [Member] | Commodity Derivatives [Member]
Derivative [Line Items]
Accumulated other comprehensive loss	(6)	(6)	(6)	(6)
Cash Flow Hedge [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Accumulated other comprehensive loss	$ (3)	$ (3)	$ (3)	$ (4)
Senior Notes, 4.95% Due 2022 [Member]
Derivative [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.95%