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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 ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Goodwill and Regulatory Matters          
Goodwill       $ 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%      
Terms of the settlement   Unless superseded by a subsequent rate case or settlement, this rate will remain in effect until July 31, 2019, after which time the unit rate will decrease an additional seven percent from August 1, 2019 through July 31, 2022.      
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%