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GOODWILL AND REGULATORY (Details)
$ in Millions
3 Months Ended 12 Months Ended
Jan. 06, 2017
item
Aug. 01, 2016
Jun. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Mar. 31, 2017
USD ($)
Dec. 31, 2015
USD ($)
Goodwill and Regulatory Matters            
Goodwill [1]       $ 130 $ 130 $ 130
GTN | FERC            
Goodwill and Regulatory Matters            
Decrease of system-wide unit rate (as a percent)       10.00%    
Additional decrease of unit rate (as a percent)       8.00%    
North Baja Pipeline, LLC | FERC            
Goodwill and Regulatory Matters            
Number of compression units | item 2          
Tuscarora Gas Transmission Company            
Goodwill and Regulatory Matters            
Goodwill       $ 82   $ 82
Tuscarora Gas Transmission Company | Tuscarora Settlement | FERC            
Goodwill and Regulatory Matters            
Decrease of system-wide unit rate (as a percent)   17.00%        
Additional decrease of unit rate (as a percent)   7.00%        
Goodwill     $ 82      
Tuscarora Gas Transmission Company | Tuscarora Settlement | FERC | Maximum            
Goodwill and Regulatory Matters            
Estimated Fair value over carrying value (as a percent)     10.00%      
[1] Recast to consolidate PNGTS for all periods presented (Refer to Note 2).