CASH DISTRIBUTIONS - Distributions by Payment Date (Details 3) - USD ($)																												9 Months Ended	12 Months Ended
	Feb. 12, 2016	Jan. 21, 2016	Nov. 13, 2015	Oct. 22, 2015	Aug. 14, 2015	Jul. 23, 2015	May. 15, 2015	Apr. 23, 2015	Apr. 01, 2015	Feb. 13, 2015	Jan. 22, 2015	Nov. 14, 2014	Oct. 23, 2014	Aug. 14, 2014	Jul. 23, 2014	May. 15, 2014	Apr. 25, 2014	Feb. 14, 2014	Jan. 16, 2014	Nov. 14, 2013	Oct. 24, 2013	Aug. 14, 2013	Jul. 23, 2013	May. 15, 2013	Apr. 23, 2013	Feb. 14, 2013	Jan. 17, 2013	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Distributions
General Partner 2% paid			$ 1,000,000		$ 2,000,000		$ 1,000,000			$ 1,000,000		$ 1,000,000		$ 1,000,000		$ 1,000,000		$ 1,000,000		$ 1,000,000		$ 1,000,000		$ 1,000,000		$ 1,000,000
General Partner IDRs paid			1,000,000		1,000,000							1,000,000																	$ 2,000,000	$ 1,000,000	$ 0
Total Cash Distribution			$ 59,000,000		$ 59,000,000		$ 55,000,000			$ 55,000,000		$ 55,000,000		$ 54,000,000		$ 52,000,000		$ 51,000,000		$ 51,000,000		$ 51,000,000		$ 43,000,000		$ 43,000,000			$ 228,000,000	$ 212,000,000	$ 188,000,000	[1]
Common units
Distributions
Per Unit Distribution, declared (in dollars per unit)				$ 0.89		$ 0.89		$ 0.84			$ 0.84		$ 0.84		$ 0.84		$ 0.81		$ 0.81		$ 0.81		$ 0.81		$ 0.78		$ 0.78
Per Unit Distribution, paid (in dollars per unit)			$ 0.89		$ 0.89		$ 0.84			$ 0.84		$ 0.84		$ 0.84		$ 0.81		$ 0.81		$ 0.81		$ 0.81		$ 0.78		$ 0.78
Limited Partners, Distribution declared				$ 57,000,000		$ 56,000,000		$ 54,000,000			$ 54,000,000		$ 53,000,000		$ 53,000,000		$ 51,000,000		$ 50,000,000		$ 50,000,000		$ 50,000,000		$ 42,000,000		$ 42,000,000
Limited Partners, Distributions paid			$ 57,000,000		$ 56,000,000		$ 54,000,000			$ 54,000,000		$ 53,000,000		$ 53,000,000		$ 51,000,000		$ 50,000,000		$ 50,000,000		$ 50,000,000		$ 42,000,000		$ 42,000,000
GTN | Class B units | TransCanada | Distributions
Distributions
Portion of GTN's annual distributions to which the Class B units are entitled to receive a percentage share of the distributions above threshold (as a percent)									30.00%
Percentage applied to GTN's distributable cash flow for the nine month ended December 31, 2015																												30.00%
Prorated threshold of GTN's distributions for payment to Class B units																												$ 15,000,000
Subsequent event
Distributions
General Partner 2% paid	$ 1,000,000
General Partner IDRs paid	1,000,000
Total Cash Distribution	$ 71,000,000
Subsequent event | Common units
Distributions
Per Unit Distribution, declared (in dollars per unit)		$ 0.89
Per Unit Distribution, paid (in dollars per unit)	$ 0.89
Limited Partners, Distribution declared		$ 57,000,000
Limited Partners, Distributions paid	$ 57,000,000
Subsequent event | Class B units
Distributions
Limited Partners, Distribution declared		$ 12,000,000
Limited Partners, Distributions paid	$ 12,000,000

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