COMMITMENTS AND CONTINGENT LIABILITIES (Details)			3 Months Ended																12 Months Ended
		May. 01, 2002	Dec. 31, 2015 USD ($)		Sep. 30, 2015 USD ($)	[1],[2]	Jun. 30, 2015 USD ($)	[1],[2]	Mar. 31, 2015 USD ($)	[1],[2]	Dec. 31, 2014 USD ($)		Sep. 30, 2014 USD ($)	[2]	Jun. 30, 2014 USD ($)	[2]	Mar. 31, 2014 USD ($)	[2]	Dec. 31, 2015 USD ($)		Dec. 31, 2014 USD ($)		Dec. 31, 2013 USD ($)	Oct. 20, 2015	Apr. 06, 2015	Jan. 31, 2015	Jan. 05, 2015
Commitments and Contingent Liabilities
FERC approved capital structure, equity percentage			60.00%																60.00%
Non-current regulatory liabilities			$ 254,788,000								$ 160,070,000								$ 254,788,000		$ 160,070,000
Operating revenues			224,034,000	[1],[2]	$ 273,189,000		$ 275,058,000		$ 272,487,000		231,097,000	[2]	$ 270,134,000		$ 263,214,000		$ 258,603,000		1,044,768,000	[1],[2]	1,023,048,000	[2]	$ 941,272,000
Interest expense																			203,779,000		186,636,000		168,319,000
NET INCOME			37,365,000	[1],[2]	$ 65,573,000		$ 72,336,000		$ 67,132,000		46,738,000	[2],[3]	$ 73,873,000	[3]	$ 54,336,000	[3]	$ 69,136,000	[3]	242,406,000	[1],[2]	244,083,000	[2],[3]	233,506,000
Purchase obligations			61,400,000																61,400,000
Rent expense																			1,100,000		1,000,000		$ 800,000
Future Minimum Lease Payments
2016			932,000																932,000
2017			824,000																824,000
2018			700,000																700,000
2019			545,000																545,000
2020 and thereafter			1,971,000																1,971,000
Total minimum lease payments			4,972,000																4,972,000
Customer Concentration Risk | DTE Electric
Other Commitments
Major customer revenue																			232,600,000
Customer Concentration Risk | Consumers Energy
Other Commitments
Major customer revenue																			244,600,000
Customer Concentration Risk | IP&L
Other Commitments
Major customer revenue																			$ 299,900,000
Customer Concentration Risk | Billed Revenues | DTE Electric
Other Commitments
Concentration percentage																			20.80%
Customer Concentration Risk | Billed Revenues | Consumers Energy
Other Commitments
Concentration percentage																			21.90%
Customer Concentration Risk | Billed Revenues | IP&L
Other Commitments
Concentration percentage																			26.80%
Estimated Potential Refund Related to Return on Equity Complaint
Commitments and Contingent Liabilities
Non-current regulatory liabilities	[4]		167,977,000								47,780,000								$ 167,977,000		47,780,000
Rate of Return on Equity and Capital Structure Complaint
Commitments and Contingent Liabilities
Estimated potential refund, minimum			168,000,000																168,000,000
Estimated potential refund, maximum			212,400,000																212,400,000
Operating revenues																					46,900,000
Additional potential estimated refund, pre-tax			44,400,000																44,400,000
Additional potential estimated decrease to net income			$ 27,300,000																27,300,000
Rate of Return on Equity and Capital Structure Complaint | Impact from Recognition of Liability
Commitments and Contingent Liabilities
Operating revenues																			115,100,000		46,900,000
Interest expense																			5,100,000		900,000
NET INCOME																			73,200,000		28,900,000
Rate of Return on Equity and Capital Structure Complaint | Impact from Recognition of Liability | 2014 and 2013
Commitments and Contingent Liabilities
NET INCOME																			$ 28,400,000
Rate of Return on Equity and Capital Structure Complaint | Impact from Recognition of Liability | 2013
Commitments and Contingent Liabilities
NET INCOME																					2,900,000
Rate of Return on Equity and Capital Structure Complaint | Complaint One | Expert Witness Testimony
Commitments and Contingent Liabilities
Recommended rate of return on equity in the event FERC elects to change base return on equity																									11.39%
Presiding administrative law judges recommended base ROE on initial decision on initial complain																									10.32%
Presiding administrative law judges recommended maximum ROE on initial decision on initial complain																									11.35%
Rate of Return on Equity and Capital Structure Complaint | Complaint Two | Expert Witness Testimony
Commitments and Contingent Liabilities
Recommended rate of return on equity in the event FERC elects to change base return on equity																								10.75%
ITCTransmission
Commitments and Contingent Liabilities
Rate of return on equity			12.38%																12.38%
ITCTransmission | Rate of Return on Equity and Capital Structure Complaint | Complaint One
Commitments and Contingent Liabilities
Reduced rate of return on equity			9.15%																9.15%
Complaint capital structure, equity percentage			50.00%																50.00%
FERC approved capital structure, equity percentage			60.00%																60.00%
ITCTransmission | Rate of Return on Equity and Capital Structure Complaint | Complaint Two
Commitments and Contingent Liabilities
Reduced rate of return on equity			8.67%																8.67%
ITCTransmission | Sales and Use Tax Audit
Commitments and Contingent Liabilities
Potential liability			$ 18,000,000																$ 18,000,000
Recorded contingent liability			5,900,000.0																5,900,000.0
ITCTransmission | Sales and Use Tax Audit | Audit Period
Commitments and Contingent Liabilities
Potential liability			10,400,000																10,400,000
MISO Operating Subsidiaries
Commitments and Contingent Liabilities
Equity in capital structure for ratemaking purposes			$ 2,900,000,000																$ 2,900,000,000
Effect on net income from 10 basis point reduction in the authorized base return on equity											$ 2,900,000										$ 2,900,000
ITC Midwest
Commitments and Contingent Liabilities
Rate of return on equity			12.38%																12.38%
Approved Return on Equity Rate Incentive Adder for Participation in Regional Transmission Organization																											0.50%
ROE rate incentive adder for independent transmission ownership																										1.00%
ITC Midwest | Rate of Return on Equity and Capital Structure Complaint | Complaint One
Commitments and Contingent Liabilities
Reduced rate of return on equity			9.15%																9.15%
Complaint capital structure, equity percentage			50.00%																50.00%
FERC approved capital structure, equity percentage			60.00%																60.00%
ITC Midwest | Rate of Return on Equity and Capital Structure Complaint | Complaint Two
Commitments and Contingent Liabilities
Reduced rate of return on equity			8.67%																8.67%
METC
Commitments and Contingent Liabilities
Rate of return on equity			12.38%																12.38%
Approved Return on Equity Rate Incentive Adder for Participation in Regional Transmission Organization																											0.50%
METC | Purchase and Sale Agreement for Ancillary Services | Consumers Energy
Other Commitments
Original term		1 year
Automatic renewal term																			1 year
METC | Easement Agreement | Consumers Energy
Other Commitments
Automatic renewal term																			50 years
Annual cost																			$ 10,000,000
Number of automatic renewals																			10
METC | Rate of Return on Equity and Capital Structure Complaint | Complaint One
Commitments and Contingent Liabilities
Reduced rate of return on equity			9.15%																9.15%
Complaint capital structure, equity percentage			50.00%																50.00%
FERC approved capital structure, equity percentage			60.00%																60.00%
METC | Rate of Return on Equity and Capital Structure Complaint | Complaint Two
Commitments and Contingent Liabilities
Reduced rate of return on equity			8.67%																8.67%
METC | Sales and Use Tax Audit
Commitments and Contingent Liabilities
Potential liability			$ 10,500,000																$ 10,500,000
Recorded contingent liability			$ 0																$ 0
ITC Great Plains | Maintenance Agreement | Mid-Kansas Electric Company LLC
Other Commitments
Original term																			10 years
Automatic renewal term																			10 years

[1] During the third and fourth quarters of 2015, we recognized an aggregate regulatory liability for the refund relating to the formula rate template modifications filing as described in Note 4, which resulted in a reduction in operating revenues and operating income of $9.5 million and an estimated $6.2 million reduction to net income for the year ended December 31, 2015.

[2] During the year ended December 31, 2015 and the fourth quarter of 2014, we recognized an aggregate estimated regulatory liability for the potential refunds relating to the ROE complaints as described in Note 16, which resulted in a reduction in operating revenues and operating income of $115.1 million and $46.9 million and an estimated $73.2 million and $28.9 million reduction to net income for the years ended December 31, 2015 and 2014, respectively.

[3] During the second quarter of 2014, we incurred a loss on extinguishment of debt of $29.2 million related to the tender of ITC Holdings Senior Notes as described in Note 8, which resulted in an estimated reduction to net income of $18.2 million.

[4] Refer to discussion of the estimated potential refund in Note 16 under “Rate of Return on Equity and Capital Structure Complaints.”