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REVENUES - Additional Information - Narrative (Details)
$ in Billions
12 Months Ended
Dec. 31, 2019
CAD ($)
Long-term pipeline capacity arrangements and transportation contracts  
Disaggregation of Revenue [Line Items]  
Future revenues, remaining performance obligation $ 26.6
Rate-regulated firm capacity contracts  
Disaggregation of Revenue [Line Items]  
Future revenues, expected timing of satisfaction, explanation one to three years
Natural gas storage and other  
Disaggregation of Revenue [Line Items]  
Future revenues, remaining performance obligation $ 0.8