CASH DISTRIBUTIONS - Distributions by Payment Date (Details) - USD ($) $ / shares in Units, $ in Millions																3 Months Ended								12 Months Ended
	Feb. 14, 2020	Jan. 21, 2020	Nov. 14, 2019	Aug. 14, 2019	May 13, 2019	Feb. 11, 2019	Nov. 14, 2018	Aug. 15, 2018	May 15, 2018	Feb. 13, 2018	Nov. 14, 2017	Aug. 11, 2017	May 15, 2017	Feb. 14, 2017	Apr. 01, 2015	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Partners' Equity
Per Unit Distribution, paid (in dollars per unit)			$ 0.65	$ 0.65	$ 0.65	$ 0.65	$ 0.65	$ 0.65	$ 0.65	$ 1.00	$ 1.00	$ 1.00	$ 0.94	$ 0.94
General Partner 2% paid			$ 1	$ 1	$ 1	$ 1	$ 1	$ 1	$ 1	$ 2	$ 1	$ 2	$ 1	$ 2
General Partner IDRs paid										3	3	3	2	2										$ 0	$ 3	$ 10
Total cash distributions			47	47	47	60	47	47	47	91	74	74	68	90										189	218	284
Common Units
Partners' Equity
Per Unit Distribution, paid (in dollars per unit)	$ 0.65
Cash distribution			$ 46	$ 46	$ 46	46	$ 46	$ 46	$ 46	71	$ 70	$ 69	$ 65	64
Total cash distributions																$ 47	$ 47	$ 47	$ 47	$ 47	$ 47	$ 47	$ 76
Class B Units
Partners' Equity
Cash distribution						$ 13				$ 15				$ 22										$ 13	$ 15	$ 22
Total cash distributions																			$ 13				$ 15
GTN | Class B Units | TC Energy | Distributions
Partners' Equity
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%
Subsequent Events
Partners' Equity
Per Unit Distribution, paid (in dollars per unit)	$ 0.65
General Partner 2% paid	$ 1
Total cash distributions	55
Total Cash Distribution	47
Subsequent Events | Common Units
Partners' Equity
Per Unit Distribution, declared (in dollars per unit)		$ 0.65
Cash distribution	46
Subsequent Events | Class B Units
Partners' Equity
Cash distribution	$ 8