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SUBSEQUENT EVENTS (Details) - USD ($) $ / shares in Units, $ in Millions						3 Months Ended
	Jun. 29, 2020	May 01, 2020	Apr. 30, 2020	Apr. 15, 2020	Apr. 07, 2020	Mar. 31, 2020	Mar. 31, 2019
Distributions
Cash distribution						$ 8	$ 13
Partnership's share of distributions						$ 65	$ 56
Northern Border
Distributions
Ownership interest						50.00%
Great Lakes
Distributions
Ownership interest						46.45%
Subsequent Events
Distributions
Cash distribution		$ 47
Subsequent Events \| Two Percent interest
Distributions
Cash distribution, general partner		1
Subsequent Events \| Northern Border
Distributions
Ownership interest			50.00%
Partnership's share of distributions			$ 8
Subsequent Events \| Great Lakes
Distributions
Ownership interest			46.45%
Partnership's share of distributions			$ 21
Subsequent Events \| Northern Border
Distributions
Limited partners, distribution declared					$ 16
Subsequent Events \| Great Lakes
Distributions
Limited partners, distribution declared				$ 46
Subsequent Events \| Iroquois
Distributions
Limited partners, distribution declared		$ 21
Subsequent Events \| PNGTS
Distributions
Limited partners, distribution declared					$ 16
Share of distributions to its non-controlling interest owner			$ 6
Common Units \| Subsequent Events
Distributions
Distribution declared (in dollars per unit)		$ 0.65
Cash distribution		$ 46
Common Units \| General Partner \| Subsequent Events
Distributions
Cash distribution		$ 4
Number of units held by investor		5,797,106
Common Units \| TC Energy \| Subsequent Events
Distributions
Cash distribution		$ 7
Number of units held by investor		11,287,725
Forecast \| Iroquois
Distributions
Ownership interest	49.34%
Partnership's share of distributions	$ 11