NET INCOME PER COMMON UNIT- Determination of Net Income (Loss) per Common Unit (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018
Net income per common unit
Net income attributable to controlling interests	$ 56	$ 62	$ 204	$ 231
Net income attributable to the Class B units	(1)	(4)	(1)	(4)
Net income attributable to the General Partner and common units	55	58	203	227
Net income attributable to the General Partner	(1)	(1)	(4)	(5)
Class B Units
Net income per common unit
Net income attributable to the Class B units	(1)	(4)	(1)	(4)
Common Units
Net income per common unit
Net income attributable to common units	$ 54	$ 57	$ 199	$ 222
Weighted average common units outstanding - basic and diluted (in units)	71.3	71.3	71.3	71.3
Net income (loss) per common unit - basic and diluted (in dollars per unit)	$ 0.76	$ 0.79	$ 2.79	$ 3.11
GTN | Class B Units | TC Energy | 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%
Threshold of GTN's distributions for payment to Class B units			$ 20		$ 20	$ 20
Percentage applied to GTN's distributable cash flow			30.00%	30.00%
30% of GTN's distributable cash flow			$ 25	$ 31
Net income attributable to controlling interests	$ 1	$ 1	$ 1	$ 1