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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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SUBSEQUENT EVENTS - Distributions (Details) - USD ($) $ / shares in Units, $ in Millions									1 Months Ended	3 Months Ended		6 Months Ended
	Aug. 01, 2029	Aug. 14, 2019	Aug. 01, 2019	Jul. 31, 2019	Jul. 23, 2019	Jul. 16, 2019	Jul. 12, 2019	Jul. 08, 2019	Aug. 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2029	Jun. 30, 2019	Jun. 30, 2018
Distributions
Limited Partners, Distributions paid													$ 13.0	$ 15.0
Partnership's share of distributions													$ 112.0	$ 96.0
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				$ 7.0
Subsequent Events \| Great Lakes
Distributions
Ownership interest (as a percent)			46.45%
Partnership's share of distributions			$ 9.0
Subsequent Events \| Iroquois
Distributions
Ownership interest (as a percent)									49.34%
Partnership's share of distributions	$ 14.0
Interest in unrestricted cash									$ 2.6
Subsequent Events \| Northern Border
Distributions
Limited partners, Distribution declared								$ 15.0
Subsequent Events \| Great Lakes
Distributions
Limited partners, Distribution declared						$ 20.0
Subsequent Events \| Iroquois
Distributions
Limited partners, Distribution declared				$ 28.0
Subsequent Events \| PNGTS
Distributions
Limited partners, Distribution declared							$ 7.0
Share of distributions to its non-controlling interest owner			$ 3.0
General Partner \| General Partner
Distributions
Ownership interest in the Partnership (as a percent)										2.00%	2.00%	2.00%	2.00%	2.00%
Incentive distribution paid to the General Partner														$ 3.0
Forecast \| Subsequent Events
Distributions
Limited Partners, Distributions paid		$ 47.0
Distribution to General Partner		$ 1.0
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		$ 46.0
Common Units \| Forecast \| General Partner \| Subsequent Events
Distributions
Limited Partners, Distributions paid		4.0
Common Units \| Forecast \| TC Energy \| Subsequent Events
Distributions
Limited Partners, Distributions paid		$ 7.0