RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - FAIR VALUE OF DERIVATIVES (Details) - CAD CAD in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value of Derivatives
Current derivative liabilities	CAD (1,130)	CAD (1,941)
Fair Value	(2,192)	(4,150)
Forward currency contracts
Fair Value of Derivatives
Fair Value	(1,383)	(2,842)
Interest rate contracts
Fair Value of Derivatives
Fair Value	(348)	(1,045)
Commodity contracts
Fair Value of Derivatives
Fair Value	(457)	(261)
Other contracts
Fair Value of Derivatives
Fair Value	(4)	(2)
Fair Value
Fair Value of Derivatives
Current derivative assets	296	353
Long-term derivative assets	181	151
Current derivative liabilities	(1,130)	(1,941)
Long-term derivative liabilities	(1,539)	(2,713)
Fair Value	(2,192)	(4,150)
Fair Value \| Forward currency contracts
Fair Value of Derivatives
Current derivative assets	143	109
Long-term derivative assets	145	73
Current derivative liabilities	(359)	(995)
Long-term derivative liabilities	(1,312)
Fair Value	(1,383)	(2,842)
Fair Value \| Interest rate contracts
Fair Value of Derivatives
Current derivative assets	8	3
Long-term derivative assets	13	8
Current derivative liabilities	(329)	(583)
Long-term derivative liabilities	(40)	(2,029)
Fair Value	(348)	(1,045)
Fair Value \| Commodity contracts
Fair Value of Derivatives
Current derivative assets	145	241
Long-term derivative assets	23	68
Current derivative liabilities	(439)	(359)
Long-term derivative liabilities	(186)	(473)
Fair Value	(457)	(261)
Fair Value \| Other contracts
Fair Value of Derivatives
Long-term derivative assets		2
Current derivative liabilities	(3)	(4)
Long-term derivative liabilities	(1)	(211)
Fair Value		(2)
Level 1 \| Fair Value
Fair Value of Derivatives
Current derivative assets	1	2
Current derivative liabilities	(13)	(12)
Fair Value	(12)	(10)
Level 1 \| Fair Value \| Commodity contracts
Fair Value of Derivatives
Current derivative assets	1	2
Current derivative liabilities	(13)	(12)
Fair Value	(12)	(10)
Level 2 \| Fair Value
Fair Value of Derivatives
Current derivative assets	181	198
Long-term derivative assets	160	126
Current derivative liabilities	(778)	(1,657)
Long-term derivative liabilities	(1,356)	(2,512)
Fair Value	(1,793)	(3,845)
Level 2 \| Fair Value \| Forward currency contracts
Fair Value of Derivatives
Current derivative assets	143	109
Long-term derivative assets	145	73
Current derivative liabilities	(359)	(995)
Long-term derivative liabilities	(1,312)
Fair Value	(1,383)	(2,842)
Level 2 \| Fair Value \| Interest rate contracts
Fair Value of Derivatives
Current derivative assets	8	3
Long-term derivative assets	13	8
Current derivative liabilities	(329)	(583)
Long-term derivative liabilities	(40)	(2,029)
Fair Value	(348)	(1,045)
Level 2 \| Fair Value \| Commodity contracts
Fair Value of Derivatives
Current derivative assets	30	86
Long-term derivative assets	2	43
Current derivative liabilities	(87)	(75)
Long-term derivative liabilities	(3)	(473)
Fair Value	(58)	44
Level 2 \| Fair Value \| Other contracts
Fair Value of Derivatives
Long-term derivative assets		2
Current derivative liabilities	(3)	(4)
Long-term derivative liabilities	(1)	(10)
Fair Value	(4)	(2)
Level 3 \| Fair Value
Fair Value of Derivatives
Current derivative assets	114	153
Long-term derivative assets	21	25
Current derivative liabilities	(339)	(272)
Long-term derivative liabilities	(183)	(201)
Fair Value	(387)	(295)
Level 3 \| Fair Value \| Commodity contracts
Fair Value of Derivatives
Current derivative assets	114	153
Long-term derivative assets	21
Current derivative liabilities	(339)	(272)
Long-term derivative liabilities	(183)	0
Fair Value	CAD (387)	(295)
Level 3 \| Fair Value \| Other contracts
Fair Value of Derivatives
Long-term derivative assets		0
Long-term derivative liabilities		CAD (201)

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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