COMPONENTS OF ACCUMULATED OTHER COMPREHENSIVE LOSS (Details) - CAD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Changes in AOCI
Balance at the beginning of the period	$ 64,363,000
Other comprehensive income/(loss) retained in AOCI	(74,000)	$ 851,000
Total before tax impact	166,000	1,044,000
Income tax on amounts retained in AOCI	(69,000)	172,000
Income tax on amounts reclassified to earnings	(56,000)	(45,000)
Tax impact	(125,000)	127,000
Balance at the end of the period	64,662,000	68,435,000
Interest rate contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	218,000	179,000
Commodity contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	(4,000)	(1,000)
Foreign exchange contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	4,000	3,000
Other contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	1,000	(1,000)
Total
Changes in AOCI
Balance at the beginning of the period	(1,401,000)	(272,000)
Balance at the end of the period	(1,360,000)	899,000
Cash Flow  Hedges
Changes in AOCI
Balance at the beginning of the period	(1,326,000)	(1,073,000)
Other comprehensive income/(loss) retained in AOCI	284,000	(696,000)
Other comprehensive loss/(income) reclassified to earnings	17,000
Total before tax impact	520,000	(516,000)
Income tax on amounts retained in AOCI	(72,000)	167,000
Income tax on amounts reclassified to earnings	(51,000)	(42,000)
Tax impact	(123,000)	125,000
Balance at the end of the period	(929,000)	(1,464,000)
Cash Flow  Hedges | Interest rate contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	218,000	179,000
Cash Flow  Hedges | Commodity contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	(4,000)	(1,000)
Cash Flow  Hedges | Foreign exchange contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	4,000	3,000
Cash Flow  Hedges | Other contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	1,000	(1,000)
Excluded Components of Fair Value Hedges
Changes in AOCI
Balance at the beginning of the period	5,000	0
Other comprehensive income/(loss) retained in AOCI	(3,000)	7,000
Total before tax impact	(3,000)	7,000
Income tax on amounts retained in AOCI	0	0
Income tax on amounts reclassified to earnings	0	0
Tax impact	0	0
Balance at the end of the period	2,000	7,000
Net Investment Hedges
Changes in AOCI
Balance at the beginning of the period	(215,000)	(317,000)
Other comprehensive income/(loss) retained in AOCI	18,000	(228,000)
Total before tax impact	18,000	(228,000)
Income tax on amounts retained in AOCI	(2,000)	7,000
Income tax on amounts reclassified to earnings	0	0
Tax impact	(2,000)	7,000
Balance at the end of the period	(199,000)	(538,000)
Cumulative Translation Adjustment
Changes in AOCI
Balance at the beginning of the period	568,000	1,396,000
Other comprehensive income/(loss) retained in AOCI	(340,000)	1,760,000
Other comprehensive loss/(income) reclassified to earnings	(20,000)
Total before tax impact	(360,000)	1,760,000
Income tax on amounts retained in AOCI	0	0
Income tax on amounts reclassified to earnings	0	0
Tax impact	0	0
Balance at the end of the period	208,000	3,156,000
Equity Investees
Changes in AOCI
Balance at the beginning of the period	66,000	67,000
Other comprehensive income/(loss) retained in AOCI	(33,000)	8,000
Other comprehensive loss/(income) reclassified to earnings	3,000
Total before tax impact	(30,000)	8,000
Income tax on amounts retained in AOCI	5,000	(2,000)
Income tax on amounts reclassified to earnings	0	0
Tax impact	5,000	(2,000)
Balance at the end of the period	41,000	73,000
Pension and OPEB Adjustment
Changes in AOCI
Balance at the beginning of the period	(499,000)	(345,000)
Other comprehensive loss/(income) reclassified to earnings	21,000	13,000
Total before tax impact	21,000	13,000
Income tax on amounts retained in AOCI	0	0
Income tax on amounts reclassified to earnings	(5,000)	(3,000)
Tax impact	(5,000)	(3,000)
Balance at the end of the period	$ (483,000)	$ (335,000)