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FAIR VALUE MEASUREMENTS - Interest Rate Swaps (Details) - Interest rate swaps - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Term loan \| TC PipeLines, LP 2013 Term Loan Facility due July 2018
Interest rate derivatives
Weighted average fixed interest rate (as a percent)	2.31%
Hedges of cash flows
Interest rate derivatives
Change in fair value of interest rate derivative instruments recognized in other comprehensive income (loss)	$ 1	$ (2)
Hedges of cash flows \| Financial charges and other.
Interest rate derivatives
Net realized loss related to the interest rate swaps	0	$ 0
Hedges of cash flows \| Recurring fair value measurement \| Level 2
Interest rate derivatives
Fair value of derivatives, net	2
Designated as hedge \| Recurring fair value measurement \| Level 2
Interest rate derivatives
Fair value of derivative asset, gross	$ 2
Fair value of derivative liability, gross			$ 0
Designated as hedge \| Hedges of cash flows \| Level 2
Interest rate derivatives
Fair value of derivative asset, gross			1
Fair value of derivative liability, gross			$ 1