SUBSEQUENT EVENTS - Distributions (Details) - USD ($)																																	9 Months Ended	12 Months Ended
	Feb. 28, 2017	Feb. 15, 2017	Feb. 14, 2017	Feb. 01, 2017	Jan. 31, 2017	Jan. 23, 2017	Jan. 09, 2017	Nov. 14, 2016	Oct. 20, 2016	Aug. 12, 2016	Jul. 21, 2016	May 13, 2016	Apr. 21, 2016	Feb. 12, 2016	Jan. 21, 2016	Nov. 13, 2015	Oct. 22, 2015	Aug. 14, 2015	Jul. 23, 2015	May 15, 2015	Apr. 23, 2015	Apr. 01, 2015	Feb. 13, 2015	Jan. 22, 2015	Nov. 14, 2014	Oct. 23, 2014	Aug. 14, 2014	Jul. 23, 2014	May 15, 2014	Apr. 25, 2014	Feb. 14, 2014	Jan. 16, 2014	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2015
Distributions
General Partner IDRs paid			$ 2,000,000					$ 2,000,000		$ 2,000,000		$ 1,000,000		$ 1,000,000		$ 1,000,000		$ 1,000,000							$ 1,000,000									$ 6,000,000	$ 2,000,000	$ 1,000,000
Partnership distribution																																		$ 262,000,000	237,000,000	262,000,000
Equity contribution																																			$ 2,000,000
Northern Border
Distributions
Ownership interest (as a percent)																																		50.00%
Great Lakes
Distributions
Ownership interest (as a percent)																																	46.45%	46.45%	46.45%		46.45%
Subsequent Events
Distributions
Total cash distribution			68,000,000
Subsequent Events | Distribution declared | Northern Border
Distributions
Partnership distribution							$ 16,000,000
Subsequent Events | Distribution declared | Great Lakes
Distributions
Distribution declared							14,000,000
Subsequent Events | Cash Distribution Paid | Northern Border
Distributions
Distribution declared		$ 18,000,000					$ 16,000,000
Partnership's share of distributions	$ 9,000,000				$ 8,000,000
Subsequent Events | Cash Distribution Paid | Great Lakes
Distributions
Partnership's share of distributions				$ 7,000,000
General Partner
Distributions
Partnership distribution																																		$ 10,000,000	$ 7,000,000	$ 5,000,000
Equity contribution																						$ 2,000,000													$ 2,000,000
TC PipeLines GP, Inc. | Subsequent Events
Distributions
General partner cash distributions			4,000,000
General Partner IDRs paid			2,000,000
TC PipeLines GP, Inc. | General Partner
Distributions
Ownership interest in the Partnership (as a percent)																						2.00%												2.00%	2.00%	2.00%
TC PipeLines GP, Inc. | General Partner | Subsequent Events
Distributions
General partner cash distributions			2,000,000
Common units
Distributions
Per Unit Distribution, declared (in dollars per unit)						$ 0.94			$ 0.94		$ 0.94		$ 0.89		$ 0.89		$ 0.89		$ 0.89		$ 0.84			$ 0.84		$ 0.84		$ 0.84		$ 0.81		$ 0.81
Distribution declared						$ 64,000,000			$ 63,000,000		$ 62,000,000		$ 58,000,000		$ 57,000,000		$ 57,000,000		$ 56,000,000		$ 54,000,000			$ 54,000,000		$ 53,000,000		$ 53,000,000		$ 51,000,000		$ 50,000,000
Limited Partners, Distributions paid			64,000,000					$ 63,000,000		$ 62,000,000		$ 58,000,000		57,000,000		$ 57,000,000		$ 56,000,000		$ 54,000,000			$ 54,000,000		$ 53,000,000		$ 53,000,000		$ 51,000,000		$ 50,000,000
Number of units																																	64,300,000	67,400,000	64,300,000	63,600,000
Common units | Subsequent Events
Distributions
Per Unit Distribution, declared (in dollars per unit)						$ 0.94
Distribution declared			64,000,000
Common units | Limited Partners
Distributions
Partnership distribution																																		$ 240,000,000	$ 221,000,000	$ 207,000,000
Number of units																																		67,454,831
Common units | TC PipeLines GP, Inc. | Subsequent Events
Distributions
Limited Partners, Distributions paid			5,000,000
Common units | TC PipeLines GP, Inc. | Limited Partners
Distributions
Number of units																																		5,797,106
Common units | TransCanada | Subsequent Events
Distributions
Limited Partners, Distributions paid			11,000,000
Common units | TransCanada | Limited Partners
Distributions
Number of units																																		11,287,725
Class B units
Distributions
Distribution declared						$ 22,000,000									$ 12,000,000
Limited Partners, Distributions paid			22,000,000											$ 12,000,000																				$ 12,000,000
Class B units | Subsequent Events
Distributions
Distribution declared						$ 22,000,000
Limited Partners, Distributions paid			22,000,000
Class B units | Limited Partners
Distributions
Partnership distribution																																		$ 12,000,000
Class B units | TransCanada | Limited Partners
Distributions
Number of units																																		1,900,000
Class B units | TransCanada | Distributions | GTN
Distributions
Percentage applied to GTN's distributable cash flow for the twelve month period ending December 31, 2016																																	30.00%	30.00%
Threshold of GTN's distributions for payment to Class B units			$ 20,000,000																														$ 15,000,000	$ 20,000,000	$ 15,000,000