REGULATORY MATTERS - Schedule of Regulatory Assets and Liabilities (Details) - CAD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Liquids Pipelines | Tolling deferrals
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	$ (25)	$ (28)
Liquids Pipelines | Pipeline future abandonment costs
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	(293)	(201)
Liquids Pipelines | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory assets	1,767	1,673
Liquids Pipelines | Recoverable income taxes
Regulatory Assets [Line Items]
Regulatory assets	24	27
Liquids Pipelines | Other
Regulatory Assets [Line Items]
Regulatory assets	32	0
Gas Transmission and Midstream | Pipeline future abandonment costs
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	(159)	(111)
Gas Transmission and Midstream | Regulatory liability related to income taxes3
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	(866)	(912)
Gas Transmission and Midstream | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory assets	511	826
Gas Transmission and Midstream | Long-term debt
Regulatory Assets [Line Items]
Regulatory assets	108	124
Gas Transmission and Midstream | Other
Regulatory Assets [Line Items]
Regulatory assets	215	205
Gas Distribution and Storage
Regulatory Assets [Line Items]
Regulatory assets	145	0
Gas Distribution and Storage | Purchased gas variance
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	(19)
Gas Distribution and Storage | Future removal and site restoration reserves5
Regulatory Liabilities [Line Items]
Regulatory (liabilities)	(1,424)	(1,107)
Gas Distribution and Storage | Other
Regulatory Liabilities [Line Items]
Regulatory (liabilities)		(4)
Gas Distribution and Storage | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory assets	1,273	1,132
Gas Distribution and Storage | Long-term debt
Regulatory Assets [Line Items]
Regulatory assets	362	387
Gas Distribution and Storage | Purchased gas variance
Regulatory Assets [Line Items]
Regulatory assets		197
Gas Distribution and Storage | Pension plans and OPEB
Regulatory Assets [Line Items]
Regulatory assets	275	118
Gas Distribution and Storage | Constant dollar net salvage adjustment
Regulatory Assets [Line Items]
Regulatory assets	0	$ 6
Gas Distribution and Storage | Other
Regulatory Assets [Line Items]
Regulatory assets	$ 88