Amount of distribution to be paid to its non-controlling interest owners.

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The amount of interest in an investee's unrestricted cash as part of distribution.

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Amount of equity impact of cash distribution declared to unit-holder of limited partnership (LP).

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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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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Amount of incentive obligation paid in cash or stock during the period to a limited liability corporation managing member or limited partnership general partner.

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Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

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The number of limited partner units issued.

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SUBSEQUENT EVENTS - Distributions (Details) - USD ($) $ / shares in Units, $ in Millions								3 Months Ended
	May 13, 2019	May 01, 2019	Apr. 30, 2019	Apr. 24, 2019	Apr. 23, 2019	Apr. 16, 2019	Apr. 09, 2019	Mar. 31, 2019	Mar. 31, 2018
Distributions
Limited Partners, Distributions paid								$ 13	$ 15
Partnership's share of distributions								$ 56	$ 43
Northern Border
Distributions
Ownership interest (as a percent)								50.00%
Great Lakes
Distributions
Ownership interest (as a percent)								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		$ 23
Subsequent Events \| Iroquois
Distributions
Ownership interest (as a percent)		49.34%
Partnership's share of distributions		$ 14
Interest in unrestricted cash		$ 2
Subsequent Events \| Northern Border
Distributions
Limited partners, Distribution declared							$ 15
Subsequent Events \| Great Lakes
Distributions
Limited partners, Distribution declared						$ 49
Subsequent Events \| Iroquois
Distributions
Limited partners, Distribution declared				$ 28
Subsequent Events \| PNGTS
Distributions
Limited partners, Distribution declared							$ 19
Share of distributions to its non-controlling interest owner			$ 7
General Partner \| General Partner
Distributions
Ownership interest in the Partnership (as a percent)								2.00%	2.00%
Forecast \| Subsequent Events
Distributions
Limited Partners, Distributions paid	$ 47
Distribution to General Partner	1
Common units \| Subsequent Events
Distributions
Per Unit Distribution, declared (in dollars per unit)					$ 0.65
Common units \| Subsequent Events \| General Partner
Distributions
Ownership interest in the Partnership (as a percent)					2.00%
Common units \| General Partner \| Subsequent Events
Distributions
Number of units held by investor			5,797,106
Common units \| TC Energy \| Subsequent Events
Distributions
Number of units held by investor			11,287,725
Common units \| Forecast \| Subsequent Events
Distributions
Limited Partners, Distributions paid	46
Common units \| Forecast \| General Partner \| Subsequent Events
Distributions
Limited Partners, Distributions paid	4
Common units \| Forecast \| TC Energy \| Subsequent Events
Distributions
Limited Partners, Distributions paid	$ 7