ACQUISITION - Acquisition of Ownership Interest in PNGTS (Details) - Portland Natural Gas Transmission System - USD ($) $ in Millions		6 Months Ended
Jan. 01, 2016	Jun. 30, 2016	Jul. 18, 2016
Acquisition
Interest acquired (as a percent)	49.90%	49.90%	49.90%
Net purchase price		$ 193
TransCanada \| Transaction between entities under common control
Acquisition
Total purchase price	$ 228
Net purchase price	193
Purchase price adjustments	5
Assumption of proportional debt	35
Additional contingent payment, minimum	5
Additional contingent payment, maximum	$ 50
Period following closing date during which additional payments may be required	15 years

This item represents the entity's ownership percentage in the investee multiplied by the investee's total debt.

No definition available.

Name:	tcp_EquityMethodInvestmentUnderlyingEquityInDebt
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For contingent consideration arrangements associated with the purchase of an equity method investment, this element represents the period during which additional payments may be required.

+ References

No definition available.

+ Details

Name:	tcp_PaymentsToAcquireEquityMethodInvestmentsContingentConsiderationArrangementsMeasurementPeriod
Namespace Prefix:	tcp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

For contingent consideration arrangements associated with the purchase of an equity method investment, this element represents an estimate of the high-end of the potential range (undiscounted) of the consideration which may be paid.

+ References

No definition available.

+ Details

Name:	tcp_PaymentsToAcquireEquityMethodInvestmentsContingentConsiderationArrangementsRangeOfOutcomesValueHigh
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For contingent consideration arrangements associated with the purchase of an equity method investment, this element represents an estimate of the low-end of the potential range (undiscounted) of the consideration which may be paid.

+ References

No definition available.

+ Details

Name:	tcp_PaymentsToAcquireEquityMethodInvestmentsContingentConsiderationArrangementsRangeOfOutcomesValueLow
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the amount of any measurement period adjustment (as defined) realized during the reporting period to items of consideration associated with the purchase of an equity method investment for which the initial accounting was incomplete.

+ References

No definition available.

+ Details

Name:	tcp_PaymentsToAcquireEquityMethodInvestmentsProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_BusinessCombinationConsiderationTransferredAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the aggregate cost of investments accounted for under the equity method of accounting.

+ 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 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3213-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=tcp_TransCanadaCorporationAndSubsidiariesExcludingGeneralPartnerSubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=tcp_TransactionBetweenEntitiesUnderCommonControlMember
Namespace Prefix:
Data Type:	na
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Period Type: