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ORGANIZATION - Capitalization (Details 2) - shares
12 Months Ended
Apr. 01, 2015
May. 22, 2013
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Common units          
Partners' Equity          
Number of units     64,300,000 63,600,000 62,300,000 [1]
General Partner | TC PipeLines GP, Inc.          
Partners' Equity          
IDRs ownership (as a percent)     100.00%    
Ownership interest in the Partnership (as a percent) 2.00% 2.00% 2.00% 2.00% 2.00%
Limited Partners | Common units          
Partners' Equity          
Number of units     64,317,449    
Limited Partners | Common units | TC PipeLines GP, Inc.          
Partners' Equity          
Number of units     5,797,106    
Limited Partners | Common units | TransCanada          
Partners' Equity          
Number of units     11,287,725    
Limited partner interest (as a percent)     26.60%    
Limited Partners | Class B units | TransCanada          
Partners' Equity          
Number of units     1,900,000    
Limited partner interest (as a percent)     100.00%    
[1] Recast as discussed in Note 2 and Note 6.