CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - Transaction between entities under common control - Former parent, TransCanada subsidiaries	Dec. 31, 2016	Jan. 01, 2016	Dec. 31, 2015	Apr. 01, 2015	Oct. 01, 2014
Portland Natural Gas Transmission System
Acquisitions
Interest acquired (as a percent)	49.90%	49.90%	49.90%
GTN
Acquisitions
Interest acquired (as a percent)				30.00%
Bison
Acquisitions
Interest acquired (as a percent)	30.00%			30.00%	30.00%