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

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Future cash outflow to pay for construction in progress expenditures that have occurred.

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Amount of expense (income) related to the increase (decrease) in reserve for business combination costs. Includes, but is not limited to, legal, accounting, and other costs incurred to consummate the merger.

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CHANGE IN OPERATING WORKING CAPITAL - Certain Non-Cash Items Excluded from Change in Operating Working Capital (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2013	Jan. 01, 2016
Non-cash items
Accruals for capital expenditures	$ 10
Accruals for costs related to acquisition	2
GTN
Non-cash items
Accruals for capital expenditures		$ 10
Portland Natural Gas Transmission System \| Former parent, TransCanada subsidiaries \| Transaction between entities under common control
Non-cash items
Accruals for costs related to acquisition	$ 2
Subsequent event \| Portland Natural Gas Transmission System \| Former parent, TransCanada subsidiaries \| Transaction between entities under common control
Non-cash items
Interest acquired (as a percent)			49.90%