REGULATORY MATTERS - Liquids Pipelines (Narrative) (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory assets	$ 5,865	$ 5,629
Canadian Mainline
Public Utilities, General Disclosures [Line Items]
Term of CTS establishing a Canadian Local Toll	10 years
Regulatory assets	$ 2,100	$ 1,900
Southern Lights Pipeline
Public Utilities, General Disclosures [Line Items]
Pre-determined after-tax rate of return on equity (ROE) (as a percent)	10.00%