COMMITMENTS AND CONTINGENT LIABILITIES (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Sep. 28, 2016	Jun. 30, 2016	Oct. 20, 2015	Apr. 06, 2015	Mar. 31, 2015	Feb. 12, 2015	Jan. 30, 2015	Jan. 05, 2015	Nov. 30, 2014	Nov. 12, 2013
Commitments and Contingent Liabilities
Current regulatory liability	$ 157		$ 129
Regulatory assets	46		53
Non-current regulatory liability	109		249
Interest expense	53	$ 50
Operating revenues	298	280
NET INCOME	80	65
Estimated Potential Refund Related to Return on Equity Complaints
Commitments and Contingent Liabilities
Current regulatory liability	140
Non-current regulatory liability			258
Rate of Return on Equity and Capital Structure Initial Complaint
Commitments and Contingent Liabilities
Current regulatory liability			$ 118
Payments for Other Operating Activities	121
Rate of Return on Equity and Capital Structure Initial Complaint | Expert Witness Testimony
Commitments and Contingent Liabilities
Recommended rate of return on equity							12.38%
Rate of Return on Equity and Capital Structure Initial Complaint | FERC Order | Minimum
Commitments and Contingent Liabilities
Revised rate of return on equity				10.32%
Rate of Return on Equity and Capital Structure Initial Complaint | FERC Order | Maximum
Commitments and Contingent Liabilities
Revised rate of return on equity				11.35%
Rate of Return on Equity and Capital Structure Initial Complaint True-up
Commitments and Contingent Liabilities
Regulatory assets	3
Rate of Return on Equity and Capital Structure Second Complaint | Expert Witness Testimony
Commitments and Contingent Liabilities
Rate of return on equity						12.38%
Rate of Return on Equity and Capital Structure Second Complaint | Presiding Administrative Law Judge Initial Decision | Minimum
Commitments and Contingent Liabilities
Recommended rate of return on equity					9.70%
Rate of Return on Equity and Capital Structure Second Complaint | Presiding Administrative Law Judge Initial Decision | Maximum
Commitments and Contingent Liabilities
Recommended rate of return on equity					10.68%
Rate of Return on Equity and Capital Structure Complaints | Impact from Recognition of Liability
Commitments and Contingent Liabilities
Interest expense	1	1
Operating revenues		(18)
NET INCOME	(1)	$ (12)
Rate of Return on Equity and Capital Structure Complaints | Minimum
Commitments and Contingent Liabilities
Estimated potential refund	103
Rate of Return on Equity and Capital Structure Complaints | Maximum
Commitments and Contingent Liabilities
Estimated potential refund	140
ITCTransmission
Commitments and Contingent Liabilities
Rate of return on equity													12.38%
FERC approved capital structure, equity percentage													60.00%
Revised rate of return on equity				11.35%
ITCTransmission | Rate of Return on Equity and Capital Structure Initial Complaint
Commitments and Contingent Liabilities
Reduced rate of return on equity													9.15%
Complaint capital structure, equity percentage													50.00%
ITCTransmission | Rate of Return on Equity and Capital Structure Second Complaint
Commitments and Contingent Liabilities
Reduced rate of return on equity									8.67%
METC
Commitments and Contingent Liabilities
Rate of return on equity													12.38%
FERC approved capital structure, equity percentage													60.00%
Revised rate of return on equity				11.35%
Approved incentive adder for RTO participation											0.50%
Requested incentive adder for RTO participation												0.50%
METC | Maximum
Commitments and Contingent Liabilities
Revised rate of return on equity				11.35%
METC | Rate of Return on Equity and Capital Structure Initial Complaint
Commitments and Contingent Liabilities
Reduced rate of return on equity													9.15%
Complaint capital structure, equity percentage													50.00%
METC | Rate of Return on Equity and Capital Structure Second Complaint
Commitments and Contingent Liabilities
Reduced rate of return on equity									8.67%
METC | Sales and Use Tax Audit
Commitments and Contingent Liabilities
Potential liability	11
ITC Midwest
Commitments and Contingent Liabilities
Rate of return on equity													12.38%
FERC approved capital structure, equity percentage													60.00%
Revised rate of return on equity				11.32%
Approved incentive adder for RTO participation											0.50%
Requested incentive adder for RTO participation												0.50%
Requested incentive adder for independence										1.00%
Approved incentive adder for independence								0.50%
ITC Midwest | Rate of Return on Equity and Capital Structure Initial Complaint
Commitments and Contingent Liabilities
Reduced rate of return on equity													9.15%
Complaint capital structure, equity percentage													50.00%
ITC Midwest | Rate of Return on Equity and Capital Structure Second Complaint
Commitments and Contingent Liabilities
Reduced rate of return on equity									8.67%
MISO Operating Subsidiaries
Commitments and Contingent Liabilities
Equity in capital structure for ratemaking purposes	3,000
Effect on net income from 10 basis point reduction in the authorized base return on equity	$ 3