INCOME TAXES - COMPONENTS (Details) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings/(loss) before income taxes and discontinued operations
Earnings before income taxes	CAD 569	CAD 2,451	CAD 11
Current income taxes
Total current income taxes	180	99	163
Deferred income taxes
Total deferred income taxes	(2,877)	43	7
Income taxes on earnings before discontinued operations	(2,697)	142	170
Canada
Income Taxes
Operating Loss Carryforwards	3,800	2,500
Earnings/(loss) before income taxes and discontinued operations
Domestic	2,200	2,034	(1,365)
Current income taxes
Domestic	129	74	157
Deferred income taxes
Domestic	299	188	(558)
United States
Income Taxes
Operating Loss Carryforwards	2,100	1,300
Earnings/(loss) before income taxes and discontinued operations
Foreign	(2,431)	(333)	808
Current income taxes
Foreign	46	21	3
Deferred income taxes
Foreign	(3,160)	(151)	565
Other
Earnings/(loss) before income taxes and discontinued operations
Foreign	800	750	568
Current income taxes
Foreign	5	4	3
Deferred income taxes
Foreign	CAD (16)	CAD 6	CAD 0