DEBT Additional Information (Details) - USD ($)		Sep. 30, 2016	Mar. 31, 2017	Mar. 23, 2017	Mar. 15, 2017
Debt Instrument [Line Items]
Commercial paper program, maximum authorized amount outstanding			$ 400,000,000
Commercial paper			$ 135,000,000
Commercial paper, weighted average interest rate			1.30%
Commercial paper, weighted average days to maturity		26 days
ITC Holdings
Debt Instrument [Line Items]
Weighted average interest rate	[1]		2.10%
ITC Midwest
Debt Instrument [Line Items]
Weighted average interest rate	[2]		1.90%
ITCTransmission
Debt Instrument [Line Items]
Weighted average interest rate	[2]		1.90%
Unsecured Debt | Term Loan Credit Agreement, Due March 24, 2018 [Member] | ITC Holdings
Debt Instrument [Line Items]
Term loan				$ 200,000,000
Weighted average interest rate			1.90%
Unsecured Debt | Term Loan Credit Agreement, Due March 23, 2019 [Member] | ITCTransmission
Debt Instrument [Line Items]
Term loan				$ 50,000,000
Weighted average interest rate			1.60%
Secured Debt | First Mortgage Bonds, Series H, due April 18, 2047 [Member] | ITC Midwest
Debt Instrument [Line Items]
Principal amount					$ 200,000,000
Interest rate					4.16%

[1] 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.

[2] 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.