COMPONENTS OF ACCUMULATED OTHER COMPREHENSIVE LOSS (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Changes in AOCI
Balance at the beginning of the period	$ 63,368
Other comprehensive income/(loss) retained in AOCI	(175)	$ (203)
Total before tax impact	(104)	(131)
Income tax on amounts retained in AOCI	(92)	(128)
Income tax on amounts reclassified to earnings	(16)	(15)
Tax impact	(108)	(143)
Balance at the end of the period	64,273	65,988
Interest rate contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	76	63
Commodity contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	0	1
Foreign exchange contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	(4)	1
Other contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	2
Total
Changes in AOCI
Balance at the beginning of the period	(1,096)	(1,401)
Balance at the end of the period	(1,308)	(1,675)
Cash Flow Hedges
Changes in AOCI
Balance at the beginning of the period	(897)	(1,326)
Other comprehensive income/(loss) retained in AOCI	384	493
Other		17
Total before tax impact	458	575
Income tax on amounts retained in AOCI	(92)	(120)
Income tax on amounts reclassified to earnings	(17)	(13)
Tax impact	(109)	(133)
Balance at the end of the period	(548)	(884)
Cash Flow Hedges | Interest rate contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	76	63
Cash Flow Hedges | Commodity contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	0	1
Cash Flow Hedges | Foreign exchange contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	(4)	1
Cash Flow Hedges | Other contracts
Changes in AOCI
Other comprehensive loss/(income) reclassified to earnings	2
Excluded Components of Fair Value Hedges
Changes in AOCI
Balance at the beginning of the period	0	5
Other comprehensive income/(loss) retained in AOCI	(1)	(1)
Total before tax impact	(1)	(1)
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	(1)	4
Net Investment Hedges
Changes in AOCI
Balance at the beginning of the period	(166)	(215)
Other comprehensive income/(loss) retained in AOCI	133	105
Total before tax impact	133	105
Income tax on amounts retained in AOCI	0	(12)
Income tax on amounts reclassified to earnings	0	0
Tax impact	0	(12)
Balance at the end of the period	(33)	(122)
Cumulative Translation Adjustment
Changes in AOCI
Balance at the beginning of the period	56	568
Other comprehensive income/(loss) retained in AOCI	(691)	(774)
Other		(20)
Total before tax impact	(691)	(794)
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	(635)	(226)
Equity Investees
Changes in AOCI
Balance at the beginning of the period	(5)	66
Other comprehensive income/(loss) retained in AOCI	0	(26)
Other		3
Total before tax impact	0	(23)
Income tax on amounts retained in AOCI	0	4
Income tax on amounts reclassified to earnings	0	0
Tax impact	0	4
Balance at the end of the period	(5)	47
Pension and OPEB Adjustment
Changes in AOCI
Balance at the beginning of the period	(84)	(499)
Other comprehensive loss/(income) reclassified to earnings	(3)	7
Total before tax impact	(3)	7
Income tax on amounts retained in AOCI	0	0
Income tax on amounts reclassified to earnings	1	(2)
Tax impact	1	(2)
Balance at the end of the period	$ (86)	$ (494)