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, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018
Net income per common unit
Net income attributable to controlling interests	$ 55	$ 73	$ 148	$ 169
Net income attributable to the General Partner	(1)	(1)	(3)	(3)
Class B Units
Net income per common unit
Net income attributable to common units	0	0	0	0
Common Units
Net income per common unit
Net income attributable to common units	$ 54	$ 72	$ 145	$ 166
Weighted average common units outstanding - basic and diluted (in units)	71.3	71.3	71.3	71.2
Net income (loss) per common unit - basic and diluted (in dollars per unit)	$ 0.75	$ 1.00	$ 2.03	$ 2.33
GTN | Class B Units | TC Energy | Distributions
Distributions
Percentage applied to GTN's distributable cash flow			30.00%
GTN's distributions for payment to Class B units			$ 20		$ 20	$ 20