DISPOSITIONS AND DISCONTINUED OPERATIONS (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended
	Jun. 28, 2017	Mar. 31, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	[1]	Jun. 30, 2016
Gain (Loss) on Disposition of Assets			$ 51.5	$ 0.0	$ 62.1		$ 0.0
Proceeds from Sale of Property, Plant, and Equipment		$ 219.6	97.6
Increase (Decrease) in Partners' Capital	$ (2,130.0)
General Partners [Member]
Proceeds from Divestiture of Businesses	$ 2,260.0
Midcoast Operating L.P. [Member]
Equity Method Investment, Ownership Percentage	48.40%
Midcoast Holding LLC [Member]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
Midcoast Energy Partners L.P. [Member]
Business Combination, Consideration Transferred	$ 1,310.0
Aggregate Indebtedness	$ 953.0
Equity Method Investment, Ownership Percentage	51.90%
Asset Held For Sale At Carrying Value	$ 4,290.0
Noncontrolling Interest in Limited Partnerships	$ 296.6
General and Administrative Expense [Member]
Gain (Loss) on Disposition of Assets		$ 10.6	$ 51.5

[1] Certain costs that are not allocated to individual segments, including Other, interest expense, allowance for equity used during construction, and income taxes are included in the consolidated total.