NET INCOME PER COMMON UNIT (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Common units and interest in the partnership
Net income	$ 29	$ 39
Net income allocated to General Partner	(1)	(1)
Net income allocable to common units	$ 28	$ 38
Weighted average common units outstanding (millions) - basic (in units)	53.5	53.5
Weighted average common units outstanding (millions) - diluted (in units)	53.5	53.5
Net income per common unit - basic (in dollars per unit)	$ 0.52	$ 0.71
Net income per common unit - diluted (in dollars per unit)	$ 0.52	$ 0.71
General Partner
Common units and interest in the partnership
Additional percentage investment held by General Partner	2.00%