PARTNERS' EQUITY - ATM Equity Issuance Program (Details)				2 Months Ended	3 Months Ended	12 Months Ended
		Aug. 05, 2016 USD ($) item	Apr. 01, 2015 USD ($)	May 19, 2016 USD ($) item $ / shares	May 19, 2016 shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares	Aug. 31, 2014 USD ($)
Partners' Equity
Net proceeds from public offering of common units	[1]					$ 83,000,000
Equity contribution							$ 2,000,000
Common units issuance subject to rescission net						83,000,000
Common units subject to rescission						83,000,000
General Partner
Partners' Equity
Net proceeds from public offering of common units	[1]					$ 2,000,000
Equity contribution			$ 2,000,000				$ 2,000,000
TC PipeLines GP, Inc. | General Partner
Partners' Equity
Ownership interest in the Partnership (as a percent)			2.00%			2.00%	2.00%	2.00%
ATM Equity Issuance Program | Common units
Partners' Equity
Aggregate offering price of units									$ 200,000,000
Units sold | shares					1,619,631	3,100,000	700,000	1,300,000
Net proceeds from issuance of common units						$ 164,000,000	$ 43,000,000	$ 71,000,000
Sales agent commissions						2,000,000	400,000	1,000,000
Common units issuance subject to rescission net				$ 82,334,015
Number of unitholders that have claimed or exercised any rescission rights to date | item				0
ATM Equity Issuance Program | TC PipeLines GP, Inc. | General Partner
Partners' Equity
Equity contribution						$ 3,000,000	$ 1,000,000	$ 2,000,000
ATM Equity Issuance Program | Minimum | Common units
Partners' Equity
Common units (price per unit) | $ / shares				$ 47.00
ATM Equity Issuance Program | Maximum | Common units
Partners' Equity
Common units (price per unit) | $ / shares				$ 54.95
Period of time for Section 5 Securities violations to be filed within				1 year
Equity Distribution Agreement (EDA) | Common units
Partners' Equity
Number of financial institutions | item		5
Amended shelf registration with SEC		$ 400,000,000

[1] These units are treated as outstanding for financial reporting purposes.