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PARTNERS' EQUITY - Class B Units (Details) - Class B Units - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
[1]
PARTNERS' EQUITY    
Limited Partners, Distributions paid $ 15 $ 22
Distributions    
PARTNERS' EQUITY    
Limited Partners, Distributions paid $ 15  
GTN | TransCanada | Distributions    
PARTNERS' EQUITY    
Portion of GTN's annual distributions to which the Class B units are entitled to receive a percentage share of the distributions above threshold (as a percent) 30.00%  
Percentage applied to 30 percent of GTN's distributions above threshold through March 31, 2020 100.00%  
Threshold of GTN's total distributable cash flows for payment to Class B units $ 20  
Percentage applied to 30 percent of GTN's distributions above threshold after March 31, 2020 25.00%  
[1] Recast to consolidate PNGTS (Refer to Note 2).