NONCONTROLLING INTERESTS (Consolidated statements of financial position) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Comprehensive income (loss) attributable to noncontrolling interests	$ 102.9	$ (191.9)	$ 261.8	$ (52.8)
Eastern Access Interests [Member]
Comprehensive income (loss) attributable to noncontrolling interests	37.6	48.3	113.9	153.0
U.S. Mainline Expansion Interests [Member]
Comprehensive income (loss) attributable to noncontrolling interests	39.1	39.0	108.3	99.7
North Dakota Pipeline Company Interests [Member]
Comprehensive income (loss) attributable to noncontrolling interests	1.8	(269.6)	18.6	(269.6)
Line 3 Replacement Interests [Member]
Comprehensive income (loss) attributable to noncontrolling interests	8.1	0.0	18.7	0.0
Enbridge Holdings DakTex LLC Interests [Member]
Comprehensive income (loss) attributable to noncontrolling interests	16.3	0.0	21.1	0.0
Midcoast Energy Partners, L.P. - Discontinued Operations [Member]
Comprehensive income (loss) attributable to noncontrolling interests	$ 0.0	$ (9.6)	$ (18.8)	$ (35.9)