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Amount of cash distribution paid to unit-holder of limited partnership (LP).

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Per unit of ownership amount of cash distributions declared to unit-holder of a limited partnership (LP).

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Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities.

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SUBSEQUENT EVENTS - Distributions (Details) - USD ($) $ / shares in Units, $ in Millions							3 Months Ended		9 Months Ended
	Nov. 14, 2019	Nov. 01, 2019	Oct. 22, 2019	Oct. 18, 2019	Oct. 15, 2019	Oct. 09, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Distributions
Cash distribution	$ 47								$ 13	$ 15
Partnership's share of distributions									$ 168	$ 142
Two Percent interest
Distributions
Cash distribution	$ 1
Northern Border
Distributions
Ownership interest (as a percent)							50.00%		50.00%
Great Lakes
Distributions
Ownership interest (as a percent)							46.45%		46.45%
Subsequent Events \| Northern Border
Distributions
Ownership interest (as a percent)				50.00%
Partnership's share of distributions				$ 7
Subsequent Events \| Great Lakes
Distributions
Ownership interest (as a percent)				46.45%
Partnership's share of distributions				$ 11
Subsequent Events \| Iroquois
Distributions
Ownership interest (as a percent)		49.34%
Partnership's share of distributions		$ 14
Subsequent Events \| Northern Border
Distributions
Limited partners, Distribution declared						$ 15
Subsequent Events \| Great Lakes
Distributions
Limited partners, Distribution declared					$ 23
Subsequent Events \| Iroquois
Distributions
Limited partners, Distribution declared		$ 28
Subsequent Events \| PNGTS
Distributions
Limited partners, Distribution declared						10
Share of distributions to its non-controlling interest owner						$ 4
General Partner \| General Partner \| TC Pipelines, LP
Distributions
Ownership interest in the Partnership (as a percent)							2.00%	2.00%	2.00%	2.00%
Common Units
Distributions
Per Unit Distribution, declared (in dollars per unit)	$ 0.65
Cash distribution	$ 46
Common Units \| General Partner \| TC Pipelines, LP
Distributions
Ownership interest in the Partnership (as a percent)			2.00%
Common Units \| General Partner
Distributions
Cash distribution	$ 4
Number of units held by investor	5,797,106
Common Units \| TC Energy
Distributions
Cash distribution	$ 7
Number of units held by investor	11,287,725