DEBT Schedule of Revolving Credit Agreements (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($)
Line of Credit Facility [Line Items]
Total available capacity	$ 900
Outstanding Balance	301	[1]
Unused Capacity	599
ITC Holdings Corp. [Member]
Line of Credit Facility [Line Items]
Total available capacity	400
Outstanding Balance	0	[1]
Unused Capacity	$ 400
Debt, Weighted Average Interest Rate	0.00%	[2]
Commitment Fee Rate	0.175%	[3]
ITCTransmission [Member]
Line of Credit Facility [Line Items]
Total available capacity	$ 100
Outstanding Balance	57	[1]
Unused Capacity	$ 43
Debt, Weighted Average Interest Rate	1.10%	[2]
Commitment Fee Rate	0.10%	[3]
METC LLC [Member]
Line of Credit Facility [Line Items]
Total available capacity	$ 100
Outstanding Balance	45	[1]
Unused Capacity	$ 55
Debt, Weighted Average Interest Rate	1.10%	[2]
Commitment Fee Rate	0.10%	[3]
ITC Midwest LLC [Member]
Line of Credit Facility [Line Items]
Total available capacity	$ 225
Outstanding Balance	169	[1]
Unused Capacity	$ 56
Debt, Weighted Average Interest Rate	1.10%	[2]
Commitment Fee Rate	0.10%	[3]
ITC Great Plains LLC [Member]
Line of Credit Facility [Line Items]
Total available capacity	$ 75
Outstanding Balance	30	[1]
Unused Capacity	$ 45
Debt, Weighted Average Interest Rate	1.10%	[2]
Commitment Fee Rate	0.10%	[3]

[1] Included within long-term debt in the condensed consolidated statements of financial position.

[2] Interest charged on borrowings depends on the variable rate structure we elected at the time of each borrowing.

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