NET INCOME PER COMMON UNIT - Terms of Class B Unit Distributions and Determination of Net Income per Common Unit (Details) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended			6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015
Net income (loss) per common unit
Net income attributable to controlling interests	$ 58,000,000		$ 49,000,000		$ 185,000,000	$ 150,000,000
Net income attributable to the General Partner	(2,000,000)		(1,000,000)		(4,000,000)	(3,000,000)
Incentive distributions attributable to the General Partner	(2,000,000)		(1,000,000)		(5,000,000)	(2,000,000)
Class B units
Net income (loss) per common unit
Net income allocated to limited partners	11,000,000	$ 1,000,000	2,000,000		12,000,000	2,000,000
Common units
Net income (loss) per common unit
Net income allocated to limited partners	$ 43,000,000		$ 45,000,000		$ 164,000,000	$ 143,000,000
Weighted average common units outstanding - basic (in units)	66.1		64.0		65.3	63.8
Weighted average common units outstanding - diluted (in units)	66.1		64.0		65.3	63.8
Net income per common unit - basic (in dollars per unit)	$ 0.65		$ 0.70		$ 2.51	$ 2.23
Net income per common unit - diluted (in dollars per unit)	$ 0.65		$ 0.70		$ 2.51	$ 2.23
GTN
Distributions
30% of GTN's distributable cash flow					$ 32,000,000
GTN | Class B units | TransCanada | Distributions
Distributions
Percentage applied to GTN's distributable cash flow for the twelve month period ending December 31, 2016					30.00%
Threshold of GTN's total distributable cash flows for payment to Class B units					$ 20,000,000
Prorated threshold of GTN's distributions for payment to Class B units							$ 20,000,000	$ 15,000,000
30% of GTN's distributable cash flow				$ 17,000,000	$ 32,000,000