REGULATORY MATTERS Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Schedule of Regulatory Assets and Liabilities
Current regulatory assets	$ 35	$ 53
Non-current regulatory assets	278	247
Current regulatory liabilities	(165)	(129)
Non-current regulatory liabilities	(109)	$ (249)
Revenue Deferrals, Including Accrued Interest
Schedule of Regulatory Assets and Liabilities
Current regulatory liabilities	(22)
Non-current regulatory liabilities	(30)
Revenue Accruals, Including Accrued Interest
Schedule of Regulatory Assets and Liabilities
Current regulatory assets	20
Non-current regulatory assets	$ 38

[Line Items] for Schedule of Regulatory Assets and Liabilities [Table]

No definition available.

Name:	itc_ScheduleofRegulatoryAssetsandLiabilitiesLineItems
Namespace Prefix:	itc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

+ Details

Name:	us-gaap_RegulatoryAssetsCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ References

+ Details

Name:	us-gaap_RegulatoryAssetsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 405
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

+ Details

Name:	us-gaap_RegulatoryLiabilityCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_RegulatoryLiabilityNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=itc_RevenueDeferralsIncludingAccruedInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=itc_RevenueAccrualsIncludingAccruedInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: