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COMMON SHARES - TC Energy Corporation At-the-Market Equity Issuance Program (Details) - At-the-Market Equity Issuance Program - CAD ($)
 1 Months Ended 12 Months Ended
Dec. 31, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2019
Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]          
Stock issuance program, period in effect (in months)     25 months    
Authorized amount   $ 2,000,000,000.0 $ 1,000,000,000.0    
Additional authorized amount   $ 1,000,000,000.0      
Treasury stock reissued during period (in shares) 3,500,000     0 20,000,000
Price per share (in Canadian dollars per share) $ 63.03       $ 56.13
Consideration received on transaction $ 216,000,000       $ 1,100,000,000
Payments of stock issuance costs $ 2,000,000       $ 10,000,000