INCOME TAXES - UNITED STATES TAX REFROM (Details) CAD in Millions, $ in Billions	12 Months Ended
	Dec. 31, 2017 CAD	Dec. 31, 2017 USD ($)	Dec. 31, 2016 CAD	Dec. 31, 2015 CAD
Income Tax Disclosure [Abstract]
Provisional tax expense	CAD 34
Deferred income tax provision	3,100
Deferred income tax asset benefit	1,100
Impact of United States tax reform	CAD 2,045		CAD 0	CAD 0
Reduction in tax amount | $		$ 0.2