RELATED PARTY TRANSACTIONS (Distributions by Affiliates) (Details) - First Quarter Distribution [Member] - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Feb. 12, 2016	Mar. 31, 2016
Distribution Declaration Date		Jan. 29, 2016
Distribution Payment Date		Feb. 12, 2016
Midcoast Energy Partners [Member]
Distribution Declaration Date		Jan. 28, 2016
Distribution Payment Date		Feb. 12, 2016
Amount Paid To Parent	$ 8.9
Amount paid to the noncontrolling interest	7.6
Total amount of distribution paid	16.5
Series EA [Member]
Distribution Declaration Date		Jan. 29, 2016
Distribution Payment Date		Feb. 12, 2016
Amount Paid To Parent	79.2
Amount paid to the noncontrolling interest	0.0
Total amount of distribution paid	79.2
U.S. Mainline Expansion Interests [Member]
Distribution Declaration Date		Jan. 29, 2016
Distribution Payment Date		Feb. 12, 2016
Amount Paid To Parent	40.8
Amount paid to the noncontrolling interest	0.0
Total amount of distribution paid	$ 40.8