GOODWILL AND INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2007	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill and Intangible Assets
Goodwill		$ 950,163	$ 950,163	$ 950,163
Intangible assets		45,602	48,794
Accumulated amortization		28,242	24,917
Amortization expense		3,300	3,300	$ 3,200
ITCTransmission
Goodwill and Intangible Assets
Goodwill		173,400	173,400
METC
Goodwill and Intangible Assets
Goodwill		453,800	453,800
METC | Regulatory Deferrals
Goodwill and Intangible Assets
Intangible assets		21,800	23,700
Intangible assets, useful Life	20 years
METC | ADIT Deferral
Goodwill and Intangible Assets
Accumulated amortization		9,400	10,500
Intangible assets, useful Life	18 years
ITC Midwest
Goodwill and Intangible Assets
Goodwill		323,000	323,000
ITC Great Plains
Goodwill and Intangible Assets
Intangible assets		14,400	14,600
Accumulated amortization		$ 1,000	$ 700
Intangible assets, useful Life		50 years