COMMITMENTS AND CONTINGENCIES - ENVIRONMENTAL (Details) CAD in Millions, $ in Millions		12 Months Ended			77 Months Ended
	Jun. 15, 2017 CAD	Dec. 31, 2017 CAD	Dec. 31, 2016 CAD	Dec. 31, 2015 CAD	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2015 USD ($)
CONTINGENCIES
Operating leases, rent expense | CAD		CAD 118	CAD 85	CAD 72
Line 6B Crude Oil Release
CONTINGENCIES
Estimated cost, net of tax						$ 195
Amount of insurance claim recognized, net of tax					$ 80
Aggregate limited amount for pollution liability under insurance program						650
Insurance coverage remaining						103
Amount receivable subject to lawsuit						85
Unfavorable binding arbitration							$ 85
Civil penalties paid | CAD	CAD 61
Line 6B Crude Oil Release | Enbridge Energy Partners, L.P.
CONTINGENCIES
Estimated cost						1,200
Amount of insurance claim recognized					$ 547
Estimated fine or penalty amount						69
Lakehead System Line 6A and 6B Crude Oil Release
CONTINGENCIES
Payments | CAD	68
Removal costs and interest paid | CAD	6
Lakehead System Line 6A and 6B Crude Oil Release | Enbridge Energy Partners, L.P.
CONTINGENCIES
Estimated liability						$ 62
Line 6A Crude Oil Release
CONTINGENCIES
Civil penalties paid | CAD	CAD 1