NET INCOME PER COMMON UNIT (Details 2) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Net income per common unit
Net income attributable to controlling interests	$ 47	$ 31	$ 37	$ 57	$ 41	$ 37	$ 34	$ 43	$ 172	$ 155	[1]	$ 192	[1]
Net income allocated to controlling interests									172	129	[1]	137	[1]
Net income allocated to General Partner, including incentive distribution rights (IDRs)									4	3	[1]	3	[1]
Net income allocable to common units									168	126	[1]	134	[1]
Weighted average common units outstanding (millions) - basic (in units)									62.7	58.9		53.5
Weighted average common units outstanding (millions) - diluted (in units)									62.7	58.9		53.5
Net income per common unit - basic (in dollars per unit)	$ 0.71	$ 0.48	$ 0.58	$ 0.90	$ 0.63	$ 0.58	$ 0.40	$ 0.52	$ 2.67	$ 2.13		$ 2.51
Net income per common unit - diluted (in dollars per unit)									$ 2.67	$ 2.13		$ 2.51
Former parent, TransCanada subsidiaries | Equity of former parent | GTN and Bison
Net income per common unit
Net income attributed to GTN and Bison's former parent										$ (26)	[1]	$ (55)	[1]

[1] Recast as discussed in Note 2 and Note 6.