DEBT Revolving Credit Agreements (Details)	12 Months Ended
	Dec. 31, 2015 USD ($)
Line of Credit Facility
Total available capacity	$ 1,000,000,000
Outstanding balance	319,900,000	[1]
Unused capacity	680,100,000
ITC Holdings Corp.
Line of Credit Facility
Total available capacity	400,000,000
Outstanding balance	137,700,000	[1]
Unused capacity	$ 262,300,000	[2]
Weighted average interest rate	1.60%	[3]
Commitment fee rate	0.175%	[4]
Unused capacity, adjusted for commercial paper outstanding	$ 167,300,000
Interest rate description	Loan bears interest at a rate equal to LIBOR plus an applicable margin of 1.25% or at a base rate, which is defined as the higher of the prime rate, 0.50% above the federal funds rate or 1.00% above the one month LIBOR, plus an applicable margin of 0.25%, subject to adjustments based on ITC Holdings’ credit rating.
ITCTransmission
Line of Credit Facility
Total available capacity	$ 100,000,000
Outstanding balance	48,300,000	[1]
Unused capacity	$ 51,700,000
Weighted average interest rate	1.40%	[5]
Commitment fee rate	0.10%	[4]
Interest rate description	Loans bear interest at a rate equal to LIBOR plus an applicable margin of 1.00% or at a base rate, which is defined as the higher of the prime rate, 0.50% above the federal funds rate or 1.00% above the one month LIBOR, subject to adjustments based on the borrower’s credit rating.
METC
Line of Credit Facility
Total available capacity	$ 100,000,000
Outstanding balance	2,500,000	[1]
Unused capacity	$ 97,500,000
Weighted average interest rate	1.40%	[5]
Commitment fee rate	0.10%	[4]
ITC Midwest
Line of Credit Facility
Total available capacity	$ 250,000,000
Outstanding balance	72,300,000	[1]
Unused capacity	$ 177,700,000
Weighted average interest rate	1.40%	[5]
Commitment fee rate	0.10%	[4]
ITC Great Plains
Line of Credit Facility
Total available capacity	$ 150,000,000
Outstanding balance	59,100,000	[1]
Unused capacity	$ 90,900,000
Weighted average interest rate	1.40%	[5]
Commitment fee rate	0.10%	[4]

[1] Included within long-term debt.

[2] ITC Holdings’ revolving credit agreement may be used for general corporate purposes, including to repay commercial paper issued pursuant to the commercial paper program described above, if necessary. While outstanding commercial paper does not reduce available capacity under ITC Holdings’ revolving credit agreement, the unused capacity under this agreement adjusted for the commercial paper outstanding was $167.3 million as of December 31, 2015.

[3] Loan bears interest at a rate equal to LIBOR plus an applicable margin of 1.25% or at a base rate, which is defined as the higher of the prime rate, 0.50% above the federal funds rate or 1.00% above the one month LIBOR, plus an applicable margin of 0.25%, subject to adjustments based on ITC Holdings’ credit rating.

[4] Calculation based on the average daily unused commitments, subject to adjustment based on the borrower’s credit rating.

[5] Loans bear interest at a rate equal to LIBOR plus an applicable margin of 1.00% or at a base rate, which is defined as the higher of the prime rate, 0.50% above the federal funds rate or 1.00% above the one month LIBOR, subject to adjustments based on the borrower’s credit rating.