VARIABLE INTEREST ENTITIES - Schedule of Assets and Liabilities of Consolidated VIEs (Details) - CAD CAD in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Cash and cash equivalents	CAD 480	CAD 1,494	CAD 654	CAD 799
Accounts receivable and other	7,053	4,978
Accounts receivable from affiliates	47	14
Inventory	1,528	1,233
Total Current assets	9,215	7,787
Property, plant and equipment, net	90,711	64,284
Long-term investments	16,644	6,836
Restricted long-term investments	267	90
Deferred amounts and other assets	6,442	3,391
Intangible assets, net	3,267	1,573
Goodwill	34,457	78
Deferred income taxes	1,090	1,170
Total assets	162,093	85,209
Liabilities
Short-term borrowings	1,444	351
Accounts payable and other	9,478	7,295
Accounts payable to affiliates	157	122
Interest payable	634	333
Environmental liabilities	40	142
Current portion of long-term debt	2,871	4,100
Total Current liabilities	14,624	12,343
Long-term debt	60,865	36,494
Other long-term liabilities	7,510	4,981
Deferred income taxes	8,205	4,866
Total Liabilities	92,294	59,854
Variable Interest Entity, Primary Beneficiary
Assets
Cash and cash equivalents	368	314
Accounts receivable and other	2,132	781
Accounts receivable from affiliates	3	3
Inventory	220	53
Total Current assets	2,723	1,151
Property, plant and equipment, net	68,685	45,720
Long-term investments	6,258	954
Restricted long-term investments	206	83
Deferred amounts and other assets	2,921	2,227
Intangible assets, net	296	488
Goodwill	29	29
Deferred income taxes	145	231
Total assets	81,263	50,883
Liabilities
Short-term borrowings	485	0
Accounts payable and other	2,859	1,446
Accounts payable to affiliates	131	105
Interest payable	312	204
Environmental liabilities	35	140
Current portion of long-term debt	2,129	342
Total Current liabilities	5,951	2,237
Long-term debt	31,469	20,176
Other long-term liabilities	4,301	1,207
Deferred income taxes	3,010	1,753
Total Liabilities	44,731	25,373
Net assets before noncontrolling interests	CAD 36,532	CAD 25,510