SUBSEQUENT EVENTS (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended
	Apr. 29, 2016	Apr. 28, 2016	Mar. 31, 2016	Mar. 31, 2015
Subsequent Event [Line Items]
Amount of Distribution			$ 201.7	$ 193.5
Subsequent Event [Member]
Subsequent Event [Line Items]
Cash distributions paid per limited partner unit outstanding (in dollars per share)	$ 0.5830
Cash available for distribution	$ 261.2
Distribution Payment Date	May 13, 2016
Record Date	May 06, 2016
Distribution Declaration Date	Apr. 29, 2016
Total amount of distribution paid	$ 216.0
Subsequent Event [Member] | I Units [Member]
Subsequent Event [Line Items]
Amount of Distribution	44.3
Amount Paid To Parent	$ 0.9
Master Limited Partnership Ownership Interest (in percentage)	2.00%
Series EA Interests [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Amount Paid To Parent	$ 79.0
Distribution Declaration Date	Apr. 29, 2016
Series ME Interests [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Amount Paid To Parent	$ 43.2
Distribution Declaration Date	Apr. 29, 2016
Midcoast Energy Partners [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Amount of Distribution		$ 7.6
Amount Paid To Parent		$ 8.9
Cash distributions paid per limited partner unit outstanding (in dollars per share)		$ 0.3575
Cash available for distribution		$ 16.5
Distribution Payment Date		May 13, 2016
Record Date		May 06, 2016
Distribution Declaration Date		Apr. 28, 2016
Midcoast Operating [Member]
Subsequent Event [Line Items]
Reduction of distribution			$ 0.8
Maximum Quarterly Distribution Per Share			$ 0.005
Midcoast Operating [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Amount Paid To Parent		$ 26.0
Amount paid to the noncontrolling interest		$ 22.9
Record Date		May 06, 2016
Distribution Declaration Date		Apr. 28, 2016