CONSOLIDATED STATEMENT OF CHANGES IN PARTNERS' EQUITY (Parenthetical)	Dec. 31, 2016	Jan. 01, 2016	Dec. 31, 2015
Transaction between entities under common control \| Former parent, TransCanada subsidiaries \| Portland Natural Gas Transmission System
Interest acquired (as a percent)	49.90%	49.90%	49.90%

Percentage of voting equity interests acquired at the acquisition date in the business combination.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463

Name:	us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant