RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - FAIR VALUE OF DERIVATIVES (Details) - CAD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Fair Value of Derivatives
Current derivative assets	$ 529	$ 323
Current derivative liabilities	(717)	(896)
Total net derivative asset/(liability)	(359)	(1,069)
Foreign exchange contracts
Fair Value of Derivatives
Total net derivative asset/(liability)	(227)	(299)
Interest rate contracts
Fair Value of Derivatives
Total net derivative asset/(liability)	(22)	(610)
Commodity contracts
Fair Value of Derivatives
Total net derivative asset/(liability)	(115)	(156)
Other contracts
Fair Value of Derivatives
Total net derivative asset/(liability)	5	(4)
Fair Value
Fair Value of Derivatives
Current derivative assets	529	323
Long-term derivative assets	360	561
Current derivative liabilities	(717)	(894)
Long-term derivative liabilities	(531)	(1,059)
Total net derivative asset/(liability)		(1,069)
Fair Value | Foreign exchange contracts
Fair Value of Derivatives
Current derivative assets	259	180
Long-term derivative assets	240	466
Current derivative liabilities	(303)	(185)
Long-term derivative liabilities	(423)	(760)
Total net derivative asset/(liability)	(227)	(299)
Fair Value | Interest rate contracts
Fair Value of Derivatives
Current derivative assets	64	0
Long-term derivative assets	88	56
Current derivative liabilities	(150)	(425)
Long-term derivative liabilities	(24)	(241)
Total net derivative asset/(liability)	(22)	(610)
Fair Value | Commodity contracts
Fair Value of Derivatives
Current derivative assets	204	143
Long-term derivative assets	29	39
Current derivative liabilities	(264)	(280)
Long-term derivative liabilities	(84)	(58)
Total net derivative asset/(liability)	(115)	(156)
Fair Value | Other contracts
Fair Value of Derivatives
Current derivative assets	2	0
Long-term derivative assets	3	0
Current derivative liabilities	0	(4)
Long-term derivative liabilities	0	0
Total net derivative asset/(liability)		(4)
Level 1 | Fair Value
Fair Value of Derivatives
Current derivative assets	38	43
Long-term derivative assets	0	1
Current derivative liabilities	(52)	(39)
Long-term derivative liabilities	0	(1)
Total net derivative asset/(liability)	(14)	4
Level 1 | Fair Value | Foreign exchange contracts
Fair Value of Derivatives
Current derivative assets	0	0
Long-term derivative assets	0	0
Current derivative liabilities	0	0
Long-term derivative liabilities	0	0
Total net derivative asset/(liability)	0	0
Level 1 | Fair Value | Interest rate contracts
Fair Value of Derivatives
Current derivative assets	0	0
Long-term derivative assets	0	0
Current derivative liabilities	0	0
Long-term derivative liabilities	0	0
Total net derivative asset/(liability)	0	0
Level 1 | Fair Value | Commodity contracts
Fair Value of Derivatives
Current derivative assets	38	43
Long-term derivative assets	0	1
Current derivative liabilities	(52)	(39)
Long-term derivative liabilities	0	(1)
Total net derivative asset/(liability)	(14)	4
Level 1 | Fair Value | Other contracts
Fair Value of Derivatives
Current derivative assets	0	0
Long-term derivative assets	0	0
Current derivative liabilities	0	0
Long-term derivative liabilities	0	0
Total net derivative asset/(liability)	0	0
Level 2 | Fair Value
Fair Value of Derivatives
Current derivative assets	396	213
Long-term derivative assets	352	546
Current derivative liabilities	(519)	(632)
Long-term derivative liabilities	(466)	(1,009)
Total net derivative asset/(liability)	(237)	(882)
Level 2 | Fair Value | Foreign exchange contracts
Fair Value of Derivatives
Current derivative assets	259	180
Long-term derivative assets	240	466
Current derivative liabilities	(303)	(185)
Long-term derivative liabilities	(423)	(760)
Total net derivative asset/(liability)	(227)	(299)
Level 2 | Fair Value | Interest rate contracts
Fair Value of Derivatives
Current derivative assets	64	0
Long-term derivative assets	88	56
Current derivative liabilities	(150)	(425)
Long-term derivative liabilities	(24)	(241)
Total net derivative asset/(liability)	(22)	(610)
Level 2 | Fair Value | Commodity contracts
Fair Value of Derivatives
Current derivative assets	71	33
Long-term derivative assets	21	24
Current derivative liabilities	(66)	(18)
Long-term derivative liabilities	(19)	(8)
Total net derivative asset/(liability)	7	31
Level 2 | Fair Value | Other contracts
Fair Value of Derivatives
Current derivative assets	2	0
Long-term derivative assets	3	0
Current derivative liabilities	0	(4)
Long-term derivative liabilities	0	0
Total net derivative asset/(liability)	5	(4)
Level 3 | Fair Value
Fair Value of Derivatives
Current derivative assets	95	67
Long-term derivative assets	8	14
Current derivative liabilities	(146)	(223)
Long-term derivative liabilities	(65)	(49)
Total net derivative asset/(liability)	(108)	(191)
Level 3 | Fair Value | Foreign exchange contracts
Fair Value of Derivatives
Current derivative assets	0	0
Long-term derivative assets	0	0
Current derivative liabilities	0	0
Long-term derivative liabilities	0	0
Total net derivative asset/(liability)	0	0
Level 3 | Fair Value | Interest rate contracts
Fair Value of Derivatives
Current derivative assets	0	0
Long-term derivative assets	0	0
Current derivative liabilities	0	0
Long-term derivative liabilities	0	0
Total net derivative asset/(liability)	0	0
Level 3 | Fair Value | Commodity contracts
Fair Value of Derivatives
Current derivative assets	95	67
Long-term derivative assets	8	14
Current derivative liabilities	(146)	(223)
Long-term derivative liabilities	(65)	(49)
Total net derivative asset/(liability)	(108)	(191)
Level 3 | Fair Value | Other contracts
Fair Value of Derivatives
Current derivative assets	0	0
Long-term derivative assets	0	0
Current derivative liabilities	0	0
Long-term derivative liabilities	0	0
Total net derivative asset/(liability)	$ 0	$ 0