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

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Represents, for rights of the holder of capital units to receive partners capital account distributions, the threshold of subsidiary distributions for payment to the holder, prorated in the year of issuance.

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Represents the combined amount of cash distributions paid to the general partner interest and unit-holder of limited partnership (LP), excluding any distribution made to limited partner based on distributable cash flow of subsidiary.

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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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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 outstanding.

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

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SUBSEQUENT EVENTS - Distributions (Details) - USD ($) $ / shares in Units, $ in Millions																					1 Months Ended	12 Months Ended
	Mar. 31, 2020	Feb. 28, 2020	Feb. 18, 2020	Feb. 14, 2020	Jan. 31, 2020	Jan. 21, 2020	Jan. 15, 2020	Jan. 10, 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	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 01, 2017
Distributions
Partnership's share of distributions																						$ 200.0	$ 188.0	$ 140.0
Return on investment distribution classified as investing activities																						$ 58.0	$ 10.0	$ 5.0
Northern Border
Distributions
Ownership interest (as a percent)																						50.00%
Return on investment distribution classified as investing activities																						$ 50.0
Great Lakes
Distributions
Ownership interest (as a percent)																						46.45%
Northern Border
Distributions
Cash distribution																					$ 100.0
Ownership interest (as a percent)																									50.00%
Subsequent Events
Distributions
Total cash distribution				$ 47.0
Subsequent Events \| Northern Border
Distributions
Ownership interest (as a percent)		50.00%			50.00%
Partnership's share of distributions		$ 9.0			$ 9.0
Subsequent Events \| Great Lakes
Distributions
Ownership interest (as a percent)					46.45%
Partnership's share of distributions					$ 16.0
Subsequent Events \| Iroquois
Distributions
Ownership interest (as a percent)			49.34%
Partnership's share of distributions	$ 13.0
Return on investment distribution classified as investing activities	$ 2.6
Subsequent Events \| Northern Border
Distributions
Cash distribution								$ 18.0
Limited partners, Distribution declared				19.0
Subsequent Events \| Great Lakes
Distributions
Limited partners, Distribution declared								$ 34.0
Subsequent Events \| Iroquois
Distributions
Limited partners, Distribution declared			$ 27.0
Subsequent Events \| PNGTS
Distributions
Limited partners, Distribution declared							$ 18.0
Share of distributions to its non-controlling interest owner							$ 7.0
TC Pipelines, LP \| Subsequent Events \| Two Percent interest
Distributions
Cash distribution				1.0
Common Units
Distributions
Cash distribution									$ 46.0	$ 46.0	$ 46.0	$ 46.0	$ 46.0	$ 46.0	$ 46.0	$ 71.0	$ 70.0	$ 69.0	$ 65.0	$ 64.0
Number of units																						71,300,000	71,300,000	70,600,000
Common Units \| General Partner \| TC Pipelines, LP
Distributions
Ownership interest in the Partnership (as a percent)																						2.00%	2.00%	2.00%
Common Units \| Subsequent Events
Distributions
Per Unit Distribution, declared (in dollars per unit)						$ 0.65
Cash distribution				46.0
Common Units \| Limited Partners
Distributions
Number of units																						71,306,396
Common Units \| TC Pipelines, LP \| Subsequent Events
Distributions
Cash distribution				$ 4.0
Common Units \| TC Pipelines, LP \| Limited Partners
Distributions
Number of units																						5,797,106
Common Units \| TC Pipelines, LP \| Limited Partners \| Subsequent Events
Distributions
Number of units				5,797,106
Common Units \| TC Energy \| Subsequent Events
Distributions
Cash distribution				$ 7.0
Common Units \| TC Energy \| Limited Partners
Distributions
Number of units																						11,287,725
Common Units \| TC Energy \| Limited Partners \| Subsequent Events
Distributions
Number of units				11,287,725
Class B Units
Distributions
Cash distribution												$ 13.0				$ 15.0				$ 22.0		$ 13.0	$ 15.0	$ 22.0
Class B Units \| Subsequent Events
Distributions
Cash distribution				$ 8.0
Limited partners, Distribution declared						$ 13.0
Class B Units \| TC Energy \| GTN
Distributions
Threshold of GTN's distributions for payment to Class B units																						$ 20.0