RELATED PARTY TRANSACTIONS (Distributions by Affiliates) (Details) - USD ($) $ in Millions	1 Months Ended		6 Months Ended
	May. 15, 2015	Feb. 13, 2015	Jun. 30, 2015
First Quarter Distribution [Member]
Distribution Declaration Date			Jan. 29, 2015
Distribution Payment Date			Feb. 13, 2015
Total amount of distribution paid		$ 194.2
Second Quarter Distribution [Member]
Distribution Declaration Date			Apr. 30, 2015
Distribution Payment Date			May 15, 2015
Total amount of distribution paid	$ 209.6
Midcoast Energy Partners [Member]
Amount Paid To Parent			$ 17.1
Amount paid to the noncontrolling interest			14.7
Total amount of distribution paid			$ 31.8
Midcoast Energy Partners [Member] | First Quarter Distribution [Member]
Distribution Declaration Date			Jan. 28, 2015
Distribution Payment Date			Feb. 13, 2015
Amount Paid To Parent		8.5
Amount paid to the noncontrolling interest		7.3
Total amount of distribution paid		15.8
Midcoast Energy Partners [Member] | Second Quarter Distribution [Member]
Distribution Declaration Date			Apr. 29, 2015
Distribution Payment Date			May 15, 2015
Amount Paid To Parent	8.6
Amount paid to the noncontrolling interest	7.4
Total amount of distribution paid	16.0
Alberta Clipper Pipeline [Member] | First Quarter Distribution [Member]
Distribution Declaration Date			Jan. 29, 2015
Distribution Payment Date			Feb. 13, 2015
Amount Paid To Parent		13.7
Amount paid to the noncontrolling interest		27.5
Total amount of distribution paid		41.2
Series EA [Member]
Amount Paid To Parent			$ 39.8
Amount paid to the noncontrolling interest			119.3
Total amount of distribution paid			$ 159.1
Series EA [Member] | First Quarter Distribution [Member]
Distribution Declaration Date			Jan. 29, 2015
Distribution Payment Date			Feb. 13, 2015
Amount Paid To Parent		22.3
Amount paid to the noncontrolling interest		67.0
Total amount of distribution paid		89.3
Series EA [Member] | Second Quarter Distribution [Member]
Distribution Declaration Date			Apr. 30, 2015
Distribution Payment Date			May 15, 2015
Amount Paid To Parent	17.5
Amount paid to the noncontrolling interest	52.3
Total amount of distribution paid	69.8
Series ME Interests [Member]
Amount Paid To Parent			$ 3.3
Amount paid to the noncontrolling interest			9.7
Total amount of distribution paid			$ 13.0
Series ME Interests [Member] | First Quarter Distribution [Member]
Distribution Declaration Date			Jan. 29, 2015
Distribution Payment Date			Feb. 13, 2015
Amount Paid To Parent		1.8
Amount paid to the noncontrolling interest		5.2
Total amount of distribution paid		$ 7.0
Series ME Interests [Member] | Second Quarter Distribution [Member]
Distribution Declaration Date			Apr. 30, 2015
Distribution Payment Date			May 15, 2015
Amount Paid To Parent	1.5
Amount paid to the noncontrolling interest	4.5
Total amount of distribution paid	$ 6.0