NET INCOME PER COMMON UNIT (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013		Jun. 30, 2014	Jun. 30, 2013
Ownership interests in the Partnership
Net income	$ 45	$ 42	[1]	$ 112	$ 95	[1]
Net income attributed to GTN and Bison's former parent		(11)			(26)
Net income attributable to non-controlling interests	(8)	(8)	[1]	(18)	(17)	[1]
Net income attributable to controlling interests	37	23	[1]	94	52	[1]
Net income allocated to General Partner	1			2	1	[1]
Net income allocable to common units	36	23	[1]	92	51	[1]
Weighted average common units outstanding (millions) - basic (in units)	62.3	57.4	[1]	62.3	55.4	[1]
Weighted average common units outstanding (millions) - diluted (in units)	62.3	57.4	[1]	62.3	55.4	[1]
Net income per common unit - basic (in dollars per unit)	$ 0.58	$ 0.40	[1]	$ 1.48	$ 0.92	[1]
Net income per common unit - diluted (in dollars per unit)	$ 0.58	$ 0.40	[1]	$ 1.48	$ 0.92	[1]
General Partner
Ownership interests in the Partnership
Net income				$ 2
TC PipeLines GP, Inc. | General Partner
Ownership interests in the Partnership
Additional percentage investment held by General Partner				2.00%

[1] (a) Recast as discussed in Note 2.