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ORGANIZATION - Ownership Interests in Natural Gas Pipeline Systems of Subsidiaries and Equity Method Investments (Details) - mi
12 Months Ended
Jan. 01, 2016
Dec. 31, 2015
Mar. 31, 2015
Sep. 30, 2014
Jun. 30, 2013
Feb. 28, 2007
GTN            
Organization            
Ownership interest (as a percent)   100.00%        
Northern Border            
Organization            
Ownership interest (as a percent)   50.00%        
Bison            
Organization            
Ownership interest (as a percent)   100.00%        
Great Lakes            
Organization            
Ownership interest (as a percent)   46.45% 46.45%     46.45%
North Baja Pipeline, LLC            
Organization            
Ownership interest (as a percent)   100.00%        
Tuscarora Gas Transmission Company            
Organization            
Ownership interest (as a percent)   100.00%        
TransCanada | GTN            
Organization            
Remaining noncontrolling ownership interest (as a percent)     30.00%      
TransCanada | Bison            
Organization            
Remaining noncontrolling ownership interest (as a percent)       30.00%    
GTN            
Organization            
Length of pipeline owned (in miles)   1,377        
Northern Border            
Organization            
Length of pipeline owned (in miles)   1,408        
Bison            
Organization            
Length of pipeline owned (in miles)   303        
Great Lakes            
Organization            
Length of pipeline owned (in miles)   2,115        
North Baja Pipeline, LLC            
Organization            
Length of pipeline owned (in miles)   86        
Tuscarora Gas Transmission Company            
Organization            
Length of pipeline owned (in miles)   305        
Portland Natural Gas Transmission System            
Organization            
Length of pipeline owned (in miles)   295        
TransCanada | Bison            
Organization            
Remaining ownership interest (as a percent)         75.00%  
TransCanada | Great Lakes            
Organization            
Remaining ownership interest (as a percent)   53.55%        
ONEOK Partners, L.P. | Northern Border            
Organization            
Remaining ownership interest (as a percent)   50.00%        
Subsequent event | Portland Natural Gas Transmission System            
Organization            
Ownership interest (as a percent) 49.90%          
Subsequent event | TransCanada | Portland Natural Gas Transmission System            
Organization            
Remaining noncontrolling ownership interest (as a percent) 11.81%          
Subsequent event | North New England Investment | Portland Natural Gas Transmission System            
Organization            
Remaining noncontrolling ownership interest (as a percent) 38.29%