Amount received from termination of customer contract.

No definition available.

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

- Definition

Represents the combined amount of cash distributions paid to the general partner interest and unit-holder of limited partnership (LP). Includes any incentive distributions paid to the general partner.

+ References

No definition available.

+ Details

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

- Definition

Sum of the carrying values as of the balance sheet date of obligations incurred through that date and due within one year of provision for revenue sharing during the period.

+ References

No definition available.

+ Details

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

- Definition

The amount of a public utility entity agreed with regulatory agency to refund to customers.

+ References

No definition available.

+ Details

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

- Definition

Amount, before tax, of income (loss) attributable to parent. Includes, but is not limited to, income (loss) from continuing operations, discontinued operations and equity method investments.

+ References

+ Details

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

- Definition

Amount of income (loss) for proportionate share of equity method investee's income (loss).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(12))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(10))
-URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(13)(f))
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

+ Details

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

- Definition

Amount, before tax, of income (loss) including portion attributable to noncontrolling interest. Includes, but is not limited to, income (loss) from continuing operations, discontinued operations and equity method investments.

+ References

+ Details

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

- Definition

Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

+ Details

Name:	us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of net income or loss for the period per each limited partnership and general partnership unit in instances when basic and diluted earnings per unit are the same amount and aggregated on the face of the financial statements. Basic earnings per unit is the amount of net income or loss for the period per unit outstanding during the reporting period. Diluted earnings per unit includes the amount of net income or loss for the period available to each limited and general partnership unit outstanding during the reporting period and to each unit that would have been outstanding assuming the issuance of units for all dilutive potential units outstanding during the reporting period.

+ References

No definition available.

+ Details

Name:	us-gaap_NetIncomeLossPerOutstandingLimitedPartnershipAndGeneralPartnershipUnitBasicAndDiluted
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of regulated pipeline operating revenues recognized during the period.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Details

Name:	us-gaap_LimitedPartnersCapitalAccountByClassAxis=tcp_LimitedPartnerCommonUnitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LimitedPartnersCapitalAccountByClassAxis=tcp_LimitedPartnerClassBUnitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=tcp_TCPipelinesGPInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=tcp_TCPipelinesLpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=tcp_GasTransmissionNorthwestLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAgencyAxis=tcp_FederalEnergyRegulatoryCommissionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=tcp_BisonPipelineLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

QUARTERLY FINANCIAL DATA (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions													3 Months Ended								12 Months Ended
	Nov. 14, 2019	Aug. 14, 2019	May 13, 2019	Feb. 11, 2019	Nov. 14, 2018	Aug. 15, 2018	May 15, 2018	Feb. 13, 2018	Nov. 14, 2017	Aug. 11, 2017	May 15, 2017	Feb. 14, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Nov. 30, 2018	Oct. 16, 2018
Quarterly financial data (unaudited)
Transmission revenues													$ 104	$ 93	$ 93	$ 113	$ 220	$ 103	$ 111	$ 115	$ 403	$ 549	$ 422
Equity earnings													45	31	30	54	44	34	36	59	160	173	124
Net income (loss)													82	59	57	100	(406)	65	75	102
Net income (loss) attributable to controlling interests													$ 76	$ 56	$ 55	$ 93	$ (413)	$ 62	$ 73	$ 96
Net income (loss) per common unit (in dollars per unit)													$ 0.95	$ 0.76	$ 0.75	$ 1.28	$ (5.80)	$ 0.79	$ 1.00	$ 1.32
Cash distribution paid	$ 47	$ 47	$ 47	$ 60	$ 47	$ 47	$ 47	$ 91	$ 74	$ 74	$ 68	$ 90									$ 189	218	$ 284
Provision for revenue sharing																						$ 10
Common Units
Quarterly financial data (unaudited)
Net income (loss) per common unit (in dollars per unit)																					$ 3.74	$ (2.68)	$ 3.16
Cash distribution paid													$ 47	$ 47	$ 47	$ 47	$ 47	$ 47	$ 47	$ 76
Class B Units
Quarterly financial data (unaudited)
Cash distribution paid																$ 13				$ 15
General Partner \| TC Pipelines, LP \| Common Units
Quarterly financial data (unaudited)
General partner interest (as a percent)																					2.00%	2.00%	2.00%
GTN \| FERC
Quarterly financial data (unaudited)
Provision for revenue sharing																	$ 1	$ 9
Amount agreed to issue as refund to customers from January 1 to October 31, 2018																								$ 10	$ 10
Bison
Quarterly financial data (unaudited)
Contract Termination Proceeds																						$ 97