NET INCOME (LOSS) PER COMMON UNIT - General Partner Effective Interest and Allocated Incentive Distributions (Details)			12 Months Ended
Apr. 01, 2015	May. 22, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
TC PipeLines GP, Inc. \| General Partner
Partners' Equity
General partner interest (as a percent)	2.00%	2.00%	2.00%	2.00%	2.00%

Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

Name:	us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration