REVENUE - Narrative (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018 CAD ($)	Jun. 30, 2018 CAD ($)
Revenue from Contract with Customer [Abstract]
Revenue recognized	$ 29	$ 124
Increase (decrease) in contract with customers, liability	103	198
Remaining performance obligation	65,700	65,700
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-07-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	3,500	$ 3,500
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, period		1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-07-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	$ 6,000	$ 6,000