NET INCOME PER COMMON UNIT- Terms of Class B Unit Distributions and Determination of Net Income (Loss) per Common Unit (Details) - USD ($) $ / shares in Units, shares in Millions					3 Months Ended								9 Months Ended	12 Months Ended
		Feb. 14, 2017	Feb. 12, 2016	Apr. 01, 2015	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Net income (loss) per common unit
Net income attributable to controlling interests														$ 252,000,000	$ 248,000,000	[1]	$ 37,000,000	[1]
Net income attributable to PNGTS' former parent														(2,000,000)	(4,000,000)		(24,000,000)
Net income allocable to General Partner and Limited Partners														250,000,000	244,000,000		13,000,000
Incentive distributions attributable to the General Partner														(12,000,000)	(7,000,000)		(3,000,000)
Net income (loss) allocable to the General Partner and common units														223,000,000	215,000,000		(2,000,000)
Net income allocable to the General Partner's two percent interest														(4,000,000)	(4,000,000)
Net income (loss) per common unit - basic (in dollars per unit)					$ 0.77	$ 0.61	$ 0.73	$ 1.05	$ 0.70	$ 0.65	$ 0.76	$ 1.10
Class B Units
Net income (loss) per common unit
Net income (loss) attributable to common units														15,000,000	22,000,000		12,000,000
Common Units
Net income (loss) per common unit
Net income (loss) attributable to common units														$ 219,000,000	$ 211,000,000	[1]	$ (2,000,000)	[1]
Weighted average common units outstanding - basic (in units)														69.2	65.7	[1]	63.9	[1]
Weighted average common units outstanding - diluted (in units)														69.2	65.7		63.9
Net income (loss) per common unit - basic (in dollars per unit)	[2]													$ 3.16	$ 3.21	[1]	$ (0.03)	[1]
Net income (loss) per common unit - diluted (in dollars per unit)														$ 3.16	$ 3.21		$ (0.03)
GTN | Class B Units | TransCanada | Distributions
Net income (loss) per common unit
Net income attributable to controlling interests														$ (15,000,000)	$ (22,000,000)		$ (12,000,000)
Distributions
Percentage applied to GTN's distributable cash flow			30.00%										30.00%	30.00%
Threshold of GTN's distributions for payment to Class B units		$ 20,000,000	$ 15,000,000										$ 15,000,000	$ 20,000,000	$ 20,000,000		$ 15,000,000
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%										30.00%
30% of GTN's distributable cash flow														$ 35,000,000

[1] Recast to consolidate PNGTS (Refer to Notes 2 and 7).

[2] Net income per common unit prior to recast (Refer to Note 2).