NET INCOME PER COMMON UNIT (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended										6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012 GTN	May 31, 2011 GTN	May 03, 2011 GTN	Jun. 30, 2012 Bison	May 31, 2011 Bison	May 03, 2011 Bison	Jun. 30, 2012 General Partner
Common units and interest in the partnership
Additional percentage investment held by General Partner															2.00%
Ownership interest at the end of the period (as a percent)									25.00%	25.00%	25.00%	25.00%	25.00%	25.00%
Net income	$ 33	[1]	$ 36	[1]	$ 72	[1]	$ 78	[1]
Net Income allocated to General Partner	(1)		(1)		(2)		(2)
Net Income allocable to common units	$ 32		$ 35		$ 70		$ 76
Weighted average common units outstanding	53.5		50.9		53.5		48.6
Net income per common unit (in dollars per unit)	$ 0.60		$ 0.69		$ 1.31		$ 1.58

[1] 25 percent interests in each of GTN and Bison were acquired in May 2011.