PARTNERS' EQUITY - ATM Equity Issuance Program (Details)		4 Months Ended		6 Months Ended	9 Months Ended
	Aug. 05, 2016 USD ($) item Institution	Jun. 30, 2016 USD ($) $ / shares	Jun. 30, 2016	Jun. 30, 2016 shares	Sep. 30, 2016 USD ($) shares	Sep. 30, 2015
Partners' Equity
Net proceeds from public offering of common units					$ 83,000,000
Common units issuance subject to rescission net					83,000,000
General Partner
Partners' Equity
Net proceeds from public offering of common units					2,000,000
Common units issuance subject to rescission net					$ 2,000,000
TC PipeLines GP, Inc. | General Partner
Partners' Equity
Ownership interest in the Partnership (as a percent)					2.00%	2.00%
ATM Equity Issuance Program | Common units
Partners' Equity
Units sold | shares				1,619,631	2,270,150
Net proceeds from public offering of common units					$ 116,000,000
Sales agent commissions					1,200,000
Common units issuance subject to rescission net		$ 82,334,015			83,000,000
ATM Equity Issuance Program | TC PipeLines GP, Inc. | General Partner
Partners' Equity
Equity contribution					$ 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 | Institution	6
Amended shelf registration with SEC	$ 400,000,000
Equity Distribution Agreement (EDA) | Minimum | Common units
Partners' Equity
Number of managers to agree with equity sale method | item	1
Equity Distribution Agreement (EDA) | Maximum | Common units
Partners' Equity
Aggregate offering price of units	$ 400,000,000