REGULATORY MATTERS Schedule of Regulatory Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Revenue Accruals and Deferrals
Current assets	$ 6,620	$ 7,489
Non-current assets — other	3,362
Current liabilities	(38,296)	(53,763)
Non-current liabilities	(74,223)	(28,613)
Ending balance	$ (102,537)	$ (72,168)

Net Regulatory Asset (Liability) Associated with Revenue Accruals and Deferrals

No definition available.

Name:	itc_NetRegulatoryAssetLiabilityAssociatedwithRevenueAccrualsandDeferrals
Namespace Prefix:	itc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of accrued revenue for our regulated operating subsidiaries when the actual net revenue requirement for the reporting period is higher than the amounts billed relating to that reporting period. The revenue accrual is expected to be recovered through transmission rates within two years.

+ References

No definition available.

+ Details

Name:	itc_RegulatoryAssetsRevenueAccrualNoncurrent
Namespace Prefix:	itc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

+ References

No definition available.

+ Details

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Namespace Prefix:	itc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of deferred revenue for our regulated operating subsidiaries when the actual net revenue requirement for the reporting period is lower than the amounts billed relating to that reporting period. The revenue deferral is expected to be refunded through a reduction in transmission rates within two years.

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No definition available.

+ Details

Name:	itc_RegulatoryLiabilityRevenueDeferralNoncurrent
Namespace Prefix:	itc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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No definition available.

+ Details

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Namespace Prefix:	itc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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