CHANGE IN OPERATING WORKING CAPITAL - GTN's Carty Lateral Construction Accrual (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Non-cash items
Capital expenditures	$ 11	$ 3
GTN
Non-cash items
Accruals for capital expenditures			$ 10
Capital expenditures	$ 10