Represents the amount of carrying value of additional interest acquired in acquiree.

No definition available.

Name:	tcp_BusinessCombinationCarryingValueOfAdditionalInterestAcquired
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the amount of carrying value of pre-existing investment in acquiree.

+ References

No definition available.

+ Details

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

- Definition

Amount of preliminary purchase price adjustments under acquisitions.

+ References

No definition available.

+ Details

Name:	tcp_BusinessCombinationConsiderationTransferredPreliminaryPurchasePriceAdjustments
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Excess purchase price over net assets acquired under business combination.

+ References

No definition available.

+ Details

Name:	tcp_BusinessCombinationExcessPurchasePrice
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Purchase price before assumption of debt under business combination.

+ References

No definition available.

+ Details

Name:	tcp_BusinessCombinationPurchasePriceBeforeAssumptionOfDebt
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of long-term debt including current portion, assumed at the acquisition date.

+ References

No definition available.

+ Details

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

- Definition

Reduction in partner's capital due to excess purchase price under business combination.

+ References

No definition available.

+ Details

Name:	tcp_BusinessCombinationReductionInPartnerSEquityDueToExcessPurchasePrice
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Excess purchase price under equity method investment.

+ References

No definition available.

+ Details

Name:	tcp_EquityMethodInvestmentExcessPurchasePrice
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cash outflow associated with the option to acquire under equity method investment.

+ References

No definition available.

+ Details

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

- Definition

Option to acquire the percentage of voting equity interests in the business combination.

+ References

No definition available.

+ Details

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Namespace Prefix:	tcp_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of debt reported by an equity method investment of the entity.

+ References

No definition available.

+ Details

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

- Definition

Carrying value under equity method investments.

+ References

No definition available.

+ Details

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

- Definition

Purchase price before assumption of debt under equity method investments.

+ References

No definition available.

+ Details

Name:	tcp_EquityMethodInvestmentsPurchasePriceBeforeAssumptionOfDebt
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Net purchase price under equity method investments.

+ References

No definition available.

+ Details

Name:	tcp_EquityMethodInvestmentsPurchasePriceNet
Namespace Prefix:	tcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Reduction in partner's equity due to excess purchase price under equity method investments.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of quarters over which surplus cash will be distributed under equity method investment.

+ References

No definition available.

+ Details

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Namespace Prefix:	tcp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Percentage of voting equity interests acquired at the acquisition date in the business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the fair value of the noncontrolling interest in the acquiree at the acquisition date.

+ References

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	instant

- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer, acquired at the acquisition date.

+ References

+ Details

Name:	us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of liabilities due within one year or within the normal operating cycle, if longer, assumed at the acquisition date.

+ References

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of deferred tax liability attributable to taxable temporary difference assumed at the acquisition date that are classified as noncurrent.

+ References

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Period Type:	instant

- Definition

Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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-Name Accounting Standards Codification
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of property, plant, and equipment recognized as of the acquisition date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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- Definition

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

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-SubTopic 10
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-Paragraph 3
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- References

No definition available.

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- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3213-108585

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- 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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Paragraph 13
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- Definition

Cash dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporations that are returns of capital. Excludes dividends or distributions from equity method investments classified as operating activities.

+ References

No definition available.

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ACQUISITION - 2017 Acquisition (Details)			6 Months Ended
ACQUISITION - 2017 Acquisition (Details)	Aug. 01, 2017 USD ($) item	Jun. 01, 2017 USD ($)	Jun. 30, 2017 USD ($)
Iroquois
ACQUISITION
Interest acquired (as a percent)		49.34%	49.34%
Option to acquire (as a percent)		0.66
Preliminary purchase price adjustments		$ 6,000,000
Net purchase price	$ 28,000,000	710,000,000
Outstanding debt		164,000,000
Payment for option to acquire		1,000
Iroquois net purchase price
Net Purchase Price		581,000,000
Less: TransCanada's carrying value of Iroquois at June 1, 2017		223,000,000
Excess purchase price		358,000,000
Purchase price before assumption of debt		710,000,000
Reduction in partner's equity under equity method investments		$ 358,000,000
Iroquois \| Accounts payable to affiliates
ACQUISITION
Net purchase price			$ 28,000,000
Portland Natural Gas Transmission System
ACQUISITION
Interest acquired (as a percent)		11.81%
Interest acquired by Partnership (as a percent)		61.71%
Preliminary purchase price adjustments		$ 3,000,000
Net purchase price		55,000,000
Outstanding debt		5,000,000
PNGTS purchase price
Current assets		25,000,000
Property, plant and equipment, net		294,000,000
Current liabilities		(4,000,000)
Deferred state income taxes		(10,000,000)
Long-term debt, including current portion		(41,000,000)
Net Purchase Price		264,000,000
Non-controlling interest		(100,000,000)
Carrying value of pre-existing Investment in PNGTS		(132,000,000)
TransCanada's carrying value of the acquired 11.81 percent interest at June 1, 2017		32,000,000
Excess purchase price over net assets acquired		21,000,000
Total cash consideration		53,000,000
Purchase price before assumption of debt		58,000,000
Reduction in partner's equity due to excess purchase price		21,000,000
Portland Natural Gas Transmission System \| Iroquois
ACQUISITION
Purchase price		765,000,000
Preliminary purchase price adjustments		$ 9,000,000
Subsequent Events \| Iroquois \| Investing Activities
ACQUISITION
Return on investment distribution classified as investing activities	$ 28,000,000
Number of quarters for distribution of surplus cash \| item	11