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CASH DISTRIBUTIONS - General Partner Distribution Incentives (Details) - $ / shares
12 Months Ended
Apr. 01, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Common units        
Schedule of Capitalization, Equity [Line Items]        
Number of units   67,400,000 64,300,000 63,600,000
Limited Partners | Common units        
Schedule of Capitalization, Equity [Line Items]        
Number of units   67,454,831    
Limited Partners | Common units | TC PipeLines GP, Inc.        
Schedule of Capitalization, Equity [Line Items]        
Number of units   5,797,106    
General Partner | TC PipeLines GP, Inc.        
Schedule of Capitalization, Equity [Line Items]        
General partner interest (as a percent) 2.00% 2.00% 2.00% 2.00%
Minimum Quarterly Distribution        
Schedule of Capitalization, Equity [Line Items]        
Total Quarterly Distribution Per Unit Target Amount (in dollars per unit)   $ 0.45    
Minimum Quarterly Distribution | Limited Partners | Common units        
Schedule of Capitalization, Equity [Line Items]        
Marginal Percentage Interest in Distribution, Common Unitholders (as a percent)   98.00%    
Minimum Quarterly Distribution | General Partner        
Schedule of Capitalization, Equity [Line Items]        
Marginal Percentage Interest in Distribution, General Partner (includes IDRs)   2.00%    
First Target Distribution | Minimum        
Schedule of Capitalization, Equity [Line Items]        
Total Quarterly Distribution Per Unit Target Amount (in dollars per unit)   $ 0.45    
First Target Distribution | Maximum        
Schedule of Capitalization, Equity [Line Items]        
Total Quarterly Distribution Per Unit Target Amount (in dollars per unit)   $ 0.81    
First Target Distribution | Limited Partners | Common units        
Schedule of Capitalization, Equity [Line Items]        
Marginal Percentage Interest in Distribution, Common Unitholders (as a percent)   98.00%    
First Target Distribution | General Partner        
Schedule of Capitalization, Equity [Line Items]        
Marginal Percentage Interest in Distribution, General Partner (includes IDRs)   2.00%    
Second Target Distribution | Minimum        
Schedule of Capitalization, Equity [Line Items]        
Total Quarterly Distribution Per Unit Target Amount (in dollars per unit)   $ 0.81    
Second Target Distribution | Maximum        
Schedule of Capitalization, Equity [Line Items]        
Total Quarterly Distribution Per Unit Target Amount (in dollars per unit)   $ 0.88    
Second Target Distribution | Limited Partners | Common units        
Schedule of Capitalization, Equity [Line Items]        
Marginal Percentage Interest in Distribution, Common Unitholders (as a percent)   85.00%    
Second Target Distribution | General Partner        
Schedule of Capitalization, Equity [Line Items]        
Marginal Percentage Interest in Distribution, General Partner (includes IDRs)   15.00%    
Thereafter | Minimum        
Schedule of Capitalization, Equity [Line Items]        
Total Quarterly Distribution Per Unit Target Amount (in dollars per unit)   $ 0.88    
Thereafter | Limited Partners | Common units        
Schedule of Capitalization, Equity [Line Items]        
Marginal Percentage Interest in Distribution, Common Unitholders (as a percent)   75.00%    
Thereafter | General Partner        
Schedule of Capitalization, Equity [Line Items]        
Marginal Percentage Interest in Distribution, General Partner (includes IDRs)   25.00%