CHANGE IN OPERATING WORKING CAPITAL - GTN's Carty Lateral Construction Accrual (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended		12 Months Ended
	Mar. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Non-cash items
Capital expenditures		$ 21	$ 45
GTN
Non-cash items
Accruals for capital expenditures				$ 10
Capital expenditures	$ 10