RELATED PARTY TRANSACTIONS (Schedule of Net Income Attributable to Noncontrolling Interests) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Related Party Transaction [Line Items]
Net income	$ 10.0	$ 42.4	$ 61.3	$ 78.7
Alberta Clipper Interests [Member]
Related Party Transaction [Line Items]
Net income		11.6	(0.8)	21.7
Eastern Access Interests [Member]
Related Party Transaction [Line Items]
Net income	$ 45.1	27.2	89.9	48.8
U.S. Mainline Expansion Interests [Member]
Related Party Transaction [Line Items]
Net income	27.9	5.7	44.4	10.1
Midcoast Energy Partners, L.P. [Member]
Related Party Transaction [Line Items]
Net income	$ (63.0)	$ (2.1)	$ (72.2)	$ (1.9)