GOODWILL AND INTANGIBLE ASSETS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Goodwill and Intangible Assets
Goodwill	$ 950		$ 950		$ 950
Intangible assets	40		40		43
Accumulated amortization	35		35		32
Amortization expense	1	$ 1	3	$ 3
Expected amortization expense, year one	3		3
Expected amortization expense, year two	3		3
Expected amortization expense, year three	3		3
Expected amortization expense, year four	3		3
Expected amortization expense, year five	3		3
ITCTransmission
Goodwill and Intangible Assets
Goodwill	173		173		173
METC
Goodwill and Intangible Assets
Goodwill	454		454		454
Intangible assets	26		26		28
Accumulated amortization	33		33		31
ITC Midwest
Goodwill and Intangible Assets
Goodwill	323		323		323
ITC Great Plains
Goodwill and Intangible Assets
Intangible assets	14		14		15
Accumulated amortization	$ 2		$ 2		$ 1