REGULATORY MATTERS - Schedule of Regulatory Assets and Liabilities (Details) - CAD CAD in Millions	Dec. 31, 2017	Dec. 31, 2016
Liquids Pipelines | Tolling deferrals
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	CAD (34)	CAD (37)
Liquids Pipelines | Pipeline future abandonment costs
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	(141)	(88)
Liquids Pipelines | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory assets	1,492	1,270
Liquids Pipelines | Recoverable income taxes
Regulatory Assets [Line Items]
Regulatory assets	46	51
Gas Transmission and Midstream | Regulatory liability related to income taxes2
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	(1,078)	0
Gas Transmission and Midstream | Other
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	(16)	0
Gas Transmission and Midstream | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory assets	717	0
Gas Distribution | Future removal and site restoration reserves
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	(1,066)	(606)
Gas Distribution | Site restoration clearance adjustment
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	(31)	(109)
Gas Distribution | Other
Regulatory Liabilities [Line Items]
Regulatory (liabilities)		(4)
Gas Distribution | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory assets	1,000	385
Gas Distribution | Purchased gas variance
Regulatory Assets [Line Items]
Regulatory assets	51	5
Gas Distribution | Pension plans and OPEB
Regulatory Assets [Line Items]
Regulatory assets	102	116
Gas Distribution | Constant dollar net salvage adjustment
Regulatory Assets [Line Items]
Regulatory assets	38	CAD 38
Gas Distribution | Other
Regulatory Assets [Line Items]
Regulatory assets	CAD 31