VARIABLE INTEREST ENTITIES - Schedule of Assets and Liabilities of Consolidated VIEs (Details) - CAD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets
Cash and cash equivalents	$ 452	$ 648
Restricted cash	38	28
Accounts receivable and other	5,258	6,669
Inventory	1,536	1,299
Current assets	7,350	8,713
Property, plant and equipment, net	94,571	93,723	$ 94,540
Long-term investments	13,818	16,528
Restricted long-term investments	553	434
Deferred amounts and other assets	8,446	7,433
Intangible assets, net	2,080	2,173
Total assets	160,276	163,157
Liabilities
Accounts payable and other	9,228	9,951
Current liabilities	13,979	15,898
Other long-term liabilities	8,783	8,324
Deferred income taxes	10,332	9,867
Liabilities	95,913	93,750
Variable Interest Entity, Primary Beneficiary
Assets
Cash and cash equivalents	215	208
Restricted cash	1	1
Accounts receivable and other	65	76
Inventory	7	4
Current assets	288	289
Property, plant and equipment, net	3,201	3,392
Long-term investments	14	15
Restricted long-term investments	84	69
Deferred amounts and other assets	3	4
Intangible assets, net	115	124
Total assets	3,705	3,893
Liabilities
Accounts payable and other	52	56
Current liabilities	52	56
Other long-term liabilities	175	130
Deferred income taxes	5	5
Liabilities	232	191
Net assets before noncontrolling interests	$ 3,473	$ 3,702